1

Digitally Signed by: Content manager’s Name

DN : CN = Webmaster’s name

O = University of Nigeria, Nsukka

OU = Innovation Centre

Ugwoke Oluchi C.

Faculty of Biological Sciences

Department of Biochemistry

CHARACTERIZATION OF COCONUT OIL AND ITS

TRANS STERIFICATION REACTION RATE WITH ETHANOL

OTAMIRI, FAITH OLUCHI

PG/M.Sc/11/ 58646

2

TITLE PAGE

CHARACTERIZATION OF COCONUT OIL AND ITS TRANS-ESTERIFICATION

REACTION RATE WITH ETHANOL

A DISSERTATION SUBMITTED IN PARTIAL FULFILMENT OF THE

REQUIREMENT FOR THE AWARD OF DEGREE OF MASTER OF SCIENCE

(M.Sc) IN INDUSTRIAL BIOCHEMISTRY AND BIOTECHNOLOGY

UNIVERSITY OF NIGERIA

NSUKKA

BY

OTAMIRI, FAITH OLUCHI

PG/M.Sc/11/ 58646

DEPARTMENT OF BIOCHEMISTRY

UNIVERSITY OF NIGERIA

NSUKKA

SUPERVISOR: DR. V. N. OGUGUA

SEPTEMBER, 2013.

3

CERTIFICATION

This is to certify that Otamiri, Faith Oluchi, a postgraduate student with Registration

Number PG/M.Sc/11/58646 in the Department of Biochemistry has satisfactorily completed

the requirement for the course work and research for the degree of Master of Science (M.Sc)

in Industrial Biochemistry and Biotechnology. The work embodied in this report is original

and has not been submitted in part or full for any other diploma or degree of this or any

other University.

----------------------- ---------------------------

Dr. V. N. Ogugua Prof. O. F. C. Nwodo (Supervisor) (Head of Department)

-------------------------

External Examiner

4

DEDICATION

This work is dedicated to God Almighty who in his infinite mercy led to the success of this

work.

5

ABSTRACT

Biodiesel is a renewable alternate fuel that could partially/fully replace or reduce the use of

petroleum diesel fuel. This research project evaluates the viability of coconut oil for

biodiesel production and the effect of varied oil-to-ethanol ratios on its transesterification

reaction rate with ethanol. Thus, the moisture content of the coconut kernel was determined

and coconut oil was extracted from coconut copra using cold extraction. The percentage

moisture content of the kernel and the yield of the coconut oil extracted were 14.99% and

44.13% respectively. The physicochemical properties of the coconut oil were determined

and the result revealed that the oil is pale yellow, with a specific gravity of 0.88, viscosity of

35.04 mm2/s at 40

oC, flash point of 220

oC, cloud point of 24

oC, pour point of 23

oC, volatile

matter of 99.72%, refractive index of 1.46, heat of combustion of 35.60 MJ/kg, acid value of

2.24 mgKOH/g, saponification value of 273.38 mgKOH/g, peroxide value of 3.02 meq/kg,

iodine value of 9.11 mI2/g and free fatty acid content of 5.64%. The transesterification of the

coconut oil (50ml) with ethanol (150 ml) using sodium hydroxide (0.1g) as catalyst gave

93.90% yield of ethyl ester. The physicochemical properties of the ethyl ester produced were

also determined and the result obtained were as follows: colour (colourless), specific gravity

(0.86), viscosity (6.00mm2/s at 40

oC), cetane number (71), flash point (132

oC), cloud point

(-5oC), pour point (-10

oC), ash content (0.02%), refractive index (1.43), conductivity (0.00

µS/cm), heat of combustion (36.786 MJ/kg), acid value (0.25 mgKOH/g), saponification

value (218.076 mgKOH/g), peroxide value (0.15 meq/kg) and iodine value (1.91 mI2/g). The

transesterification rate constant at varied oil to ethanol ratio of 1:6, 1:3, 1:2, 1:1.5 and 1:1

were 0.4150, 0.3616, 0.2135, 0.1833 and 0.1006 respectively. The result showed that as the

oil to ethanol ratios increased from 1:1 to 1:6, the reaction rate constant increased with the

highest reaction rate constant of 0.4150 at 1:6 oil to ethanol ratio.

6

ACKNOWLEDGEMENT

Above all, I thank the Almighty God for His blessings, protection and assistance throughout

my project research. Also, my heartfelt gratitude goes to my parents, Mr. and Mrs. Otamiri

Alexander, for their parental guidance and financial support throughout this research.

This research would not have been a reality without the assistance, encouragement and

support of numerous individual to whom I owe my gratitude. First and foremore, I want to

appreciate my supervisors, Prof. I. N. E. Onwurah and Dr. V. N. Ogugua for their time and

effort put into this work. My profound gratitude goes to Prof. O. F. C. Nwodo, the Head, and

the entire staffs of the Department of Biochemistry among whom are Prof. L. U. S.

Ezeanyika, the immediate past Head, Prof. F. C. Chilaka, Prof. O. U. Njoku, Prof. P. N.

Uzoegwu, Prof. E. A. Alumanah, Prof. M. O. Eze, Prof. O. Obidoa, Dr. H. A. Onwubiko,

Dr. B. C. Nwanguma, Dr. S. O. O. Eze, Dr. Parker. E. Joshua, Dr. (Mrs). C. A. Anosike,

Dr. (Mrs). C. I. Ezekwe, Dr. O. C. Enechi, Dr. C. S. Ubani, Mr. P. A. C. Egbuna, Mr. O. E.

Ikwuagwu, Mrs M. N. Awachie, Mr. V. E. O. Ozougwu, Mrs. U. O. Njoku and a host of

others, for their assistance and the knowledge they imparted to me.

I also thank Mr. Obinna Ojeh, Obiora, Atamah Jane, Akudo, Rex, Emeka, Darlington,

Joseph, Ejike, Blessing, Chibueze, Onyinyechi, Chinenye, chioma Eze, Ozioma Nwabor,

Dickson I. Dickson, Nsikak and all my colleagues I worked with in the laboratory for their

friendly relationship and support.

7

TABLE OF CONTENTS

Title Page - - - - - - - - - - i

Certification - - - - - - - - - - ii

Dedication - - - - - - - - - - iii

Abstract - - - - - - - - - - iv

Acknowledgement - - - - - - - - - v

Table of Content - - - - - - - - - vi

List of Figures - - - - - - - - - - xi

List of Tables - - - - - - - - - - xii

List of Abbreviations - - - - - - - - -

xiii

CHAPTER ONE: INTRODUCTION

1.1 Background of study - - - - - - - - 1

1.2 History of biodiesel - - - - - - - - 2

1.3 Sources of biodiesel - - - - - - - - 4

1.3.1 The coconut - - - - - - - - - 4

1.3.1.1 Botanical description of coconut - - - - - - 6

1.3.1.2 Scientific classification of coconut - - - - - - 7

1.3.1.3 Geographical distribution and propagation - - - - - 7

1.3.1.4 Coconut oil - - - - - - - - - 8

1.3.1.5 Uses of coconut oil - - - - - - - - 9

1.4 Methods of modification of vegetable oils to fuel - - - - 9

1.4.1 Dilution - - - - - - - - - - 10

1.4.2 Microemulsion - - - - - - - - - 10

1.4.3 Pyrolysis - - - - - - - - - - 10

1.4.4 Catalytic cracking - - - - - - - - 10

1.4.5 Transesterification - - - - - - - - 11

1.5 Methods of transesterification - - - - - - - 12

1.5.1 Non-Catalytic transesterification - - - - - - 12

8

1.5.2 Catalytic transesterification - - - - - - - 12

1.5.2.1 Heterogenous catalytic transesterification - - - - - 12

1.5.2.2 Homogenous catalytic transesterification - - - - - 13

1.5.2.2.1 Acid catalyzed transesterification - - - - - - 13

1.5.2.2.2 Base catalyzed transesterification - - - - - - 15

1.5.2.2.3 Enzyme catalyzed transesterification - - - - - 17

1.6 Factors effecting transesterification reaction - - - - - 18

1.6.1 Effect of molar ratio of oil to alcohol - - - - - 18

1.6.2 Type and amount of catalyst - - - - - - - 18

1.6.3 Effect of water and free fatty acid content - - - - - 19

1.6.4 Effect of temperature - - - - - - - - 20

1.6.5 Effect of stirring intensity - - - - - - - 20

1.6.6 Effect of reaction time - - - - - - - 21

1.7 Influence of biodiesel composition on fuel properties - - - - 21

1.7.1 Viscosity - - - - - - - - - 21

1.7.2 Low temperature operability - - - - - - - 22

1.7.3 Oxidative stability - - - - - - - - 23

1.7.4 Heat of combustion - - - - - - - - 23

1.7.5 Cetane number - - - - - - - - - 24

1.7.6 Exhaust emissions - - - - - - - - 25

1.7.7 Lubricity - - - - - - - - - - 26

1.7.8 Contaminants - - - - - - - - - 26

1.7.9 Biodiesel standard specifications and test methods - - - - 27

1.8 Advantages of biodiesel - - - - - - - - 29

1.9 Disadvantages of biodiesel - - - - - - - 30

1.10 Uses of biodiesel - - - - - - - - - 30

1.11 Aim and objectives - - - - - - - - 31

1.11.1 Aim of the study - - - - - - - - 31

1.11.2 Specific objectives of the study - - - - - - 31

CHAPTER TWO: MATERIALS AND METHODS

2.1 Materials - - - - - - - - - - 32

9

2.1.1 Plant material - - - - - - - - - 32

2.1.2 Instruments / Equipment - - - - - - - 32

2.1.3 Reagents/Chemicals - - - - - - - - 32

2.2 Methods - - - - - - - - - - 33

2.2.1 Preparation of reagents - - - - - - - - 33

2.2.2 Moisture content determination of the kernel - - - - - 36

2.2.3 Extraction of coconut oil - - - - - - - 36

2.2.4 Purification of crude coconut oil - - - - - - 37

2.2.4.1 Water degumming - - - - - - - - 37

2.2.4.2 Acid pretreatment - - - - - - - - 38

2.2.5 Physicochemical characterization of coconut oil - - - - 38

2.2.5.1 Physical characterization of coconut oil - - - - - 38

2.2.5.1.1 Determination of the colour of the oil - - - - - 38

2.2.5.1.2 Determination of the specific gravity of the oil - - - - 38

2.2.5.1.3 Determination of the viscosity of the oil - - - - - 38

2.2.5.1.4 Determination of the flash point of the oil - - - - - 39

2.2.5.1.5 Determination of the cloud point of the oil - - - - - 39

2.2.5.1.6 Determination of the pour point of the oil - - - - - 40

2.2.5.1.7 Determination of the volatile matter of the oil - - - - 40

2.2.5.1.8 Determination of the refractive index of the oil - - - - 40

2.2.5.1.9 Determination of heat of combustion of the oil - - - - 41

2.2.5.2 Chemical characterization of coconut oil - - - - - 41

2.2.5.2.1 Determination of acid value of the oil - - - - - 41

2.2.5.2.2 Determination of saponification value of the oil - - - - 42

2.2.5.2.3 Determination of peroxide value of the oil - - - - - 42

2.2.5.2.4 Determination of iodine value of the oil - - - - - 43

2.2.5.2.5 Determination of percentage free fatty acids of the oil - - - 43

2.2.6 Transesterification of coconut oil with ethanol using NaOH as catalyst - 44

10

2.2.7 Physicochemical characterization of the ethyl esters produced - - - 45

2.2.7.1 Physical characterization of ethyl ester produced - - - - 45

2.2.7.1.1 Determination of the colour of the ethyl ester - - - - 45

2.2.7.1.2 Determination of the specific gravity of the ethyl ester - - - 45

2.2.7.1.3 Determination of the viscosity of the ethyl ester - - - - 45

2.2.7.1.4 Determination of the cetane number of the ethyl ester - - - 46

2.2.7.1.5 Determination of the flash point of the ethyl ester - - - - 46

2.2.7.1.6 Determination of the cloud point of the ethyl ester - - - - 46

2.2.7.1.7 Determination of the pour point of the ethyl ester - - - - 47

2.2.7.1.8 Determination of the ash content of the ethyl ester - - - - 47

2.2.7.1.9 Determination of the refractive index of the ethyl ester - - - 47

2.2.7.1.10 Determination of conductivity of the ethyl ester - - - - 48

2.2.7.1.11 Determination of heat of combustion of the ethyl ester - - - 48

2.2.7.2 Chemical characterization of coconut oil - - - - - 49

2.2.7.2.1 Determination of acid value of the ethyl ester - - - - 49

2.2.7.2.2 Determination of saponification value of the ethyl ester - - - 49

2.2.7.2.3 Determination of peroxide value of the ethyl ester - - - - 50

2.2.7.2.4 Determination of iodine value of the ethyl ester - - - - 50

2.2.8 Investigation of the transesterification reaction rate - - - - 51

2.2.8.1 Experimental design - - - - - - - - 51

2.2.8.2 Analysis of ethyl esters using UV-visible spectrophotometer - - 51

CHAPTER THREE: RESULTS

3.1 Result of Percentage moisture content, oil yield and ethyl ester yield - - 53

3.2 Physicochemical properties of the coconut oil - - - - - 54

3.2.1 Physical properties of the coconut oil - - - - - - 54

3.2.2 Chemical properties of the coconut oil - - - - - - 55

3.3 Physicochemical properties of the coconut oil ethyl ester - - - 56

3.3.1 Physical properties of the coconut oil ethyl ester - - - - 56

3.3.2 Chemical properties of the coconut oil ethyl ester - - - - 57

3.4 Investigation of the transesterification reaction rate - - - - 58

11

3.4.1 Progress curve for 1:6 oil/ethanol volumetric ratio transesterification - - 59

3.4.2 Progress curve for 1:3 oil/ethanol volumetric ratio transesterification - - 60

3.4.3 Progress curve for 1:2 oil/ethanol volumetric ratio transesterification - - 61

3.4.4 Progress curve for 1:1.5 oil/ethanol volumetric ratio transesterification - 62

3.4.5 Progress curve for 1:1 oil/ethanol volumetric ratio transesterification - - 63

3.5 Reaction rate constant against oil to ethanol volumetric ratio - - - 64

3.6 Determination of kinetic parameters (Km and Vmax) of the transesterification

Reaction - - - - - - - - - - 65

CHAPTER FOUR: DISCUSSION

4.1 Discussion - - - - - - - - - - 66

4.2 Conclusion - - - - - - - - - 75

4.3 Suggestions for Further Studies - - - - - - - 75

References - - - - - - - - - - 76

Appendices - - - - - - - - - - 89

12

LIST OF FIGURES

Fig. 1: Bunch of coconuts on a coconut tree - - - - - - 5

Fig. 2: The transesterification reaction - - - - - - 11

Fig. 3: Mechanism of acid catalyzed transesterification - - - - 14

Fig. 4: Mechanism of base catalyzed transesterification - - - - 16

Fig. 5: Saponification reaction of free fatty acids during base catalyzed transesterification 20

Fig. 6: Dehusked coconuts and extracted coconut oil- - - - - 36

Fig. 7: Pictures of coconut oil after degumming and standing in a separating funnel to form

two distinct layers; the upper layer (of oil) and the lower layer (of phosphatides and

other impurities) - - - - - - - - 37

Fig. 8: Experimental set-up during transesterification and separation of the mixture

into biodiesel (upper layer) and glycerol (lower layer) in a separating funnel 44

Fig. 9: Appearance of the yellow colour in the standard and test samples - - 52

Fig. 10: Progress curve for 1:6 oil/ethanol volumetric ratio transesterification - 59

Fig. 11: Progress curve for 1:3 oil/ethanol volumetric ratio transesterification - 60

Fig. 12: Progress curve for 1:2 oil/ethanol volumetric ratio transesterification - 61

Fig. 13: Progress curve for 1:1.5 oil/ethanol volumetric ratio transesterification - 62

Fig. 14: Progress curve for 1:1 oil/ethanol volumetric ratio transesterification - 63

Fig. 15: Reaction rate constant against oil to ethanol volumetric ratio - - 64

Fig.16: Lineweaver-Burk plot of NaOH-catalysed transesterification reaction - 65

13

LIST OF TABLES

Table 1: World production of coconuts, area and productivity in 2005 - - 6

Table 2: Scientific classification of coconut - - - - - - 7

Table 3: The chemical composition of coconut oil - - - - - 8

Table 4: Specifications and test methods of ASTM d6751 and EN 14214 standards for

Biodiesel - - - - - - - - - 28

Table 5: Glycerol standard preparation and absorbance results - - - 52

Table 6: Result of percentage moisture content, oil yield and ethyl ester - - 53

Table 7: Physical properties of the coconut oil - - - - - 54

Table 8: Chemical properties of the coconut oil - - - - - 55

Table 9: Physical properties of the coconut oil ethyl ester - - - - 56

Table 10: Chemical properties of the coconut oil ethyl ester - - - - 67

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LIST OF ABBREVIATIONS

AOAC Association of Official Analytical Chemists

APCC Asian and Pacific Coconut Community

ASTM American Society for Testing Material

CFPP Cold Filter Plugging Point

CN Cetane Number

CO Carbon Monoxide

CP Cloud Point

EN European Standards

EPA Environmental Protection Agency

FAAE Fatty Acids Alkyl Esters

FFA Free Fatty Acid

NMCE National Multi-Commodity Exchange

NOx Nitrogen Oxide Species

PM Particulate Matter

PP Pour Point

SME Soyabean Methyl Ester

15

CHAPTER ONE

INTRODUCTION

1.1 Background of the Study

The search for environmentally-friendly materials that have potential to substitute mineral

oil in various industrial applications is currently being considered a top priority research area

in the fuel and energy sector (Jha et al., 2007). With, the scarcity of conventional fossil

fuels, growing emissions of combustion-generated pollutants, and their increasing costs will

make biomass or renewable sources more attractive (Sensoz et al., 2000). An alternative fuel

to petrodiesel must be technically feasible, economically competitive, environmentally-

friendly, and easily available. Biodiesel is the best alternative for diesel fuels in diesel

engine (Demirbas, 2009).

Biodiesel is defined as the mono alkyl esters of long fatty acids derived from renewable lipid

feedstock such as vegetable oils or animal fats, for use in compression ignition (diesel)

engines (National Biodiesel Board, 1996). The advantages of biodiesel are availability,

lower exhaust emissions, renewability, biodegradability, higher lubricity and higher

combustion efficiency (Demirbas, 2009). It can be used in its pure state or blended with

petroleum-based diesel fuel (B20 is assigned for 20 vol. % biodiesel and 80 vol. %

petroleum-based fuel blend) (Issariyakul et al., 2007). Biodiesel can offer other benefits,

including reduction of greenhouse gas emissions, regional development and social structure,

especially to developing countries (Dermirbas and Dermirbas, 2007). On the other hand, the

major disadvantages of biodiesel are its high viscosity, low energy content, high cloud point

and pour point, high nitrogen oxide (NOx) emissions, low engine speed and power, injector

coking, engine compatibility, and high price (Demirbas, 2008a). Nevertheless, the

advantages of biodiesel supersede the disadvantages generally on the environmental aspects,

making it a very popular alternative to petroleum derived-diesel oil (Dermirbas, 2009).

Biodiesel can be processed from any type of vegetable oil, animal fats (Vicente et al., 2004)

and algal oil (Hossain et al., 2008). Alamu et al. (2010) investigated the biodiesel

production potential of coconut oil and the biodiesel produced was subsequently blended

16

with petroleum diesel and characterized as alternative diesel fuel through the American

Society for Testing and Materials standard fuel tests (Alamu et al., 2010).

The conventional method for vegetable oil conversion into biodiesel is called

transesterification (Srivastava and Prasad, 2000). Transesterification is a chemical reaction

involving oil or fat, and an alcohol to yield fatty acid alkyl esters and glycerol

(Thiruvengadaravi et al., 2009). In the reaction, each mole of triglyceride reacts

stoichiometrically with 3 moles of a primary alcohol and yields 3 moles of alkyl esters and 1

mole of glycerol (Singh et al., 2006). The actual mechanism of the reaction consists of a

sequence of three consecutive and reversible reactions (Darnoko and Cheryan, 2000), in

which di- and monoglycerides are formed as intermediates (Knothe et al., 2005).

Furthermore, this process can be performed with or without catalyst (Gerpen, 2005), with

the catalytic process being mostly used due to its simpler operation and shorter reaction

period to produce biodiesel (Marchetti et al., 2007). Under catalytic process,

transesterification is carried out using homogeneous or heterogeneous catalysts which may

be bases, acids or enzymes (Krishnan and Dass, 2012). Homogeneous alkaline catalysts are

widely used due to the fact that the reaction is completed in a short time under mild

temperature and pressure conditions (Pilar et al., 2004). Usually uses catalysts such as

sodium hydroxide (NaOH), potassium hydroxide (KOH) (Meher et al., 2006b).

There are number of factors which could affect the transesterification process, these factors

include moisture content, free fatty acid contents, molar ratio of oil to alcohol, type and

amount of catalyst, reaction time, reaction temperature, mixing intensity, and co-solvent

(Sharma and Singh, 2009). Evidentally, for optimization of the transesterification reaction

the effect of these factors should be examined (Thiruvengadaravi et al., 2009).

1.2 History of Biodiesel

The term “biodiesel” was first coined in 1988, but the history of using vegetable oil in place

of diesel as a fuel dates back to 1900 (Songstad et al., 2009). The roots of what eventually

became known as “biodiesel” extend back to the discovery of the diesel engine by Rudolf

Diesel. When first demonstrating the engine bearing his name, Rudolf Diesel ran it on

17

peanut oil at the World’s Fair in Paris in1900. The diesel engine was built by the French

Otto Company and it was tested at this event using peanut oil (Knothe, 2001). Knothe

(2001) also relates that the French Government was interested in vegetable oil fuels for

diesel engines because of its availability in their colonies in Africa, thereby eliminating the

need to import liquid fuels or coal. Knowledge that vegetable oils could be used to fuel the

diesel engine gave a sense of energy self-sufficiency to those countries producing oil crops,

especially for those countries in Africa in the 1940s (Songstad et al., 2009). In China, tung

oil and other vegetable oils were used to produce a version of gasoline and kerosene

(Songstad et al., 2009).

Furthermore, prompted by fuel shortages during World War II, India conducted research on

conversion of a variety of vegetable oils to diesel. This interest in biodiesel was also evident

in the USA where research was performed to evaluate cottonseed oil as a diesel fuel

(Songstad et al., 2009). However, related to this are the efforts of automobile entrepreneur

Henry Ford and the development of the “soybean car” in 1941. Mr. Ford was a true

visionary and was motivated by combining the strength of the automobile industry with

agriculture (Songstad et al., 2009). According to the Benson Ford Research Center, there

was a single experimental soybean car built, made in part with soybean and propelled by

ethanol derived from corn (Young, 2003).

Since the 1950s, interest in converting vegetable oils into biodiesel has been driven more by

geographical and economic factors than by fuel shortages. For instance, the USA is a top

producer of soybean oil, whereas Europe produces large amounts of canola oil, and this

essentially determines which oil is used for biodiesel within these geographies (Songstad et

al., 2009). Also, for those remote geographic locations to which fossil fuel refining and

distribution are problematic, vegetable oil-based biodiesel is a sustainable and practical

means to meet the fuel energy demands. Furthermore, sources for biodiesel have been

expanded to include spent vegetable oil from the food service industry as well as animal fats

from slaughterhouses (Knothe, 2001). However, additional research is required to identify

new oil crops to meet the increasing demand for biodiesel. A variety of tools including plant

breeding, molecular breeding, and biotechnology are needed to increase oil production from

18

conventional crops such as soybean and to develop new oil crops for specific regions

(Songstad et al., 2009).

1.3 Sources of Biodiesel

A variety of biolipids can be used to produce biodiesel. These are (a) virgin vegetable oil

feedstock; rapeseed and soybean oils are most commonly used; though other crops such as

mustard, palm oil, sunflower, hemp, (Dermirbas, 2006) and even algae can also be used; (b)

waste vegetable oil; (c) animal fats including tallow, lard, and yellow grease (Ramadhas et

al., 2004); and (d) non-edible oils such as jatropha, neem oil, castor oil, and tall oil

(Dermirbas, 2008a).

Various oils have been in use in different countries as raw materials for biodiesel production

owing to their availability. Soybean oil is commonly used in United States and rapeseed oil

is used in many European countries for biodiesel production, whereas, coconut oil and palm

oils are used in Malaysia and Indonesia for biodiesel production (Dermirbas, 2009). In India

and Southeast Asia, the Jatropha tree (Jatropha curcas) (Tiwari et al., 2007), Karanja

(Pongamia pinnata) (Srivastava and Verma, 2008; Sharma and Singh, 2008) and Mahua (M.

indica) (Ghadge and Raheman, 2005) is used as a significant fuel source. Commonly

accepted biodiesel raw materials include the oils from soy, canola, corn, rapeseed, and palm.

New plant oils that are under consideration include mustard seed, peanut, coconut,

sunflower, and cotton seed (Dermirbas, 2009). The most commonly considered animal fats

include those derived from poultry, beef and pork (Usta et al., 2005). Also, it may be

possible to produce enough oil by farming microbes, such as algae, whose oil yields per unit

land area could be two orders of magnitude higher than with conventional oil crops (Hossain

et al., 2008).

1.3.1 The Coconut

The coconut (Cocos nucifera L.) (Fig. 1) is an important fruit tree in the world, providing

food for millions of people, especially in the trophical and subtropical regions and with its

many use it is called the tree of life (Chan and Elevitch, 2006). India is the third largest

coconut-producing country, after Indonesia and the Philippines, having an area of about 1.94

19

million hectares under the crop. Annual production is about 7562 million nuts with an

average of 5295 nuts/hectare (APCC Coconut Statistical Yearbook 2005) (Table 1).

.

Fig. 1: Bunch of coconuts on a coconut tree

Source: (Chan and Elevitch, 2006).

20

Table 1: World production of coconuts, area and productivity in 2005

COUNTRY Production

Nut

Equivalent

(billion nuts

Production

Copra

Equivalent

(million

tones)

% of Total

World

Production

Area

under

Coconuts

(million

ha)

Productivity

(tonnes

copra

equiv /ha)

Indonesia 16.49 3.30 27.7% 3.89 0.85

Philippines 14.06 2.81 23.6% 3.24 0.87

India 12.83 2.57 21.5% 1.94 1.33

Brazil 3.79 0.76 6.4% 0.28 2.70

Sri Lanka 2.22 0.44 3.7% 0.40 1.12

Thailand 1.20 0.24 2.0% 0.34 0.70

Mexico 1.19 0.24 2.0% 0.15 1.58

Papua New Guinea 0.81 0.16 1.4% 0.26 0.63

Vietnam 0.68 0.14 1.1% 0.13 1.03

Malaysia 0.39 0.08 0.7% 0.13 0.60

80 Other Countries 5.91 1.18 9.9% 1.40 0.84

TOTAL / AVERAGE 59.57 11.91 100% 12.17 0.98

Source: (APCC Coconut Statistical Yearbook 2005).

1.3.1.1 Botanical Description of Coconut

Coconut (Cocos nucifera L.) is a monocotyledon belonging to the Arecaceae family (Order

Arecales). There are mainly two distinct varieties of coconut i.e. tall and the dwarf; the tall

varieties grow slow and bear fruits 6 to 10 years after planting (NMCE, 2007). Its copra, oil

and fiber are of good quality and this type is comparatively hardy, and lives up to a ripe age

of 80 to 120 years (Ohler, 1999). As the male flowers mature earlier than the female flowers,

this type is highly cross- pollinated. The nuts mature within a period of 12 months after

pollination (Mandal and Mandal, 2011).

The dwarf varieties are fast-growing and bear early i.e. takes 4 to 5 years (NMCE, 2007).

Due to overlapping of the male and female phases, the dwarf varieties are self pollinated; the

nuts are yellow, red, green and orange coloured (Ohler, 1999). These are less hardy and

require favourable climatic conditions and soil type for better yield (Mandal and Mandal,

2011).

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1.3.1.2 Scientific Classification of Coconut

Table 2: Scientific classification of coconut

Kingdom Plantae – Plants

Subkingdom Tracheobionta – Vascular plants

Superdivision Spermatophyta – Seed plants

Division Magnoliophyta – Flowering plants

Class Liliopsida – Monocotyledons

Subclass Arecidae

Order Arecales

Family Arecaceae – Palm family

Genus Cocos L. – coconut palm P

Species Cocos nucifera L. – coconut palm

Source: (Chan and Elevitch, 2006).

1.3.1.2 Geographical Distribution and Propagation

Within 20 North and South latitudes, the coconut palm is productive, especially along

coastal areas. Palms grown beyond the limits of the Torrid Zone are generally non-

productive (Mandal and Mandal, 2011). The major coconut-growing areas are located in

Asia, islands of the Pacific Ocean, Africa, and Central and South America. In 1991 the

world coconut hectarage was 10.9 million (Arranza, 1994).

Cultivation of coconut depends on type, slope of land, and rainfall distribution. It grows well

on well-drained loamy and clay soil. A year-round warm and humid climate favours the

growth of coconut (Ohler, 1999). A mean annual temperature of 27oC, an evenly distributed

rainfall of 1500-2500 mm per annum and relative humidity of above 60% provide the ideal

climatic conditions for the vigorous growth and yield of the palm (Chan and Elevitch, 2006).

For cultivation of coconut, usually 7-8 month old seedlings, raised from fully mature fruits

are used for transplants (Ohler, 1999). Nuts are planted in nursery after about 16 weeks,

usually 70-150 trees/ hectare; with triangular spacing of 10 meters (Mandal and Mandal,

2011). It is desirable to transplant in rainy season. During first three years seedlings are

watered during drought, with an application of 16 L/tree of water, twice a week (Ohler,

22

1999). Female flowers set in 12 months and fruits set to mature with a yield 60-100 nuts /

tree. A coconut tree in its life time can produce up 10,000 nuts (Mandal and Mandal, 2011).

1.3.1.3 Coconut Oil

The kernel is the origin of the products which are mainly coconut oil and desiccated coconut

or dried kernel (copra). The copra which is mainly used for oil extraction contains about 65

to 75% oil (Mandal and Mandal, 2011). The different fatty acids present in coconut oil

(Table 3) range from C6 to C18 (Russell and Williams, 1995) and approximately 50% of the

fatty acid is lauric acid (Mandal and Mandal, 2011).

Table 3: Chemical composition of coconut oil

Component Fraction

%

Chemical Formula Systematic name Acronym

Lauric acid 51.0 CH3(CH2)10COOH Dodecanoic acid 12:0

Myristic acid 18.5 CH3(CH2)12COOH Tetradecanoic

acid

14:0

Caprilic acid 9.5 CH3(CH2)6COOH Octanoic acid 8:0

Palmitic acid 7.5 CH3(CH2)14COOH Hexadecanoic

acid

16:0

Oleic acid 5.0 CH3(CH2)7CH=CH

3(CH2)7COOH 9Z‐Octadecenoic

acid

18:1

Capric acid 4.5 CH3(CH2)8COOH Decanoic acid 10:0

Stearic acid 3.0 CH3(CH2)16COOH Octadecanoic

acid

18:0

Linoleic acid 1.0 CH3(CH2)4CH=CH

CH2CH=CH(CH2)7

COOH

9Z,12Z‐

Octadecadienoic

acid

18:2

Source: (Mandal and Mandal, 2011). Note: ( a) Z denotes cis configuration; (b) The numbers

denote the number of carbon atoms and double bonds in one molecule.

1.3.1.4 Uses of Coconut Oil

The Spectrum of Coconut Products states that in food preparation and in diet, coconut oil

performs the following functions (Enig, 1998).

• It serves as an important source of energy in the diet.

• It supplies specific nutritional requirements.

• It provides a lubricating action in dressings or leavening effect in baked items.

23

• It acts as carrier and protective agent for fat-soluble vitamins.

• It enhances the flavour of food.

One of the major non-edible applications of coconut oil is in the soap industries. Coconut oil

has many other industrial uses in the pharmaceuticals, cosmetics, plastics, synthetic resins

(Krishna et al., 2010). In Thailand, coconut oil is mixed with 10 to 20% kerosene, settle to

remove free fats, filtered and used as a diesel fuel substitute. In Vanuatu and other Pacific

Islands, coconut oil is used directly as a substitute for diesel (Bawalan, 2005). The

Philippines has discovered that coconut methyl ester (CME) or coco-biodiesel derived from

coconut oil is better than conventional diesel fuel (Mandal and Mandal, 2011). The higher

cetane number of CME (70) relative to diesel (56) implies that CME burns more completely,

resulting in more mileage and lower emissions (Robeerto, 2001). Methyl esters of coconut

oil fatty acids are also being used as lubricants and biodiesel in aviation industry (Krishna et

al., 2010).

1.4 Methods of Modification of Vegetable Oils to Fuel

Vegetable oils can be used as fuels for diesel engines, but their viscosities are much higher

than that of common diesel fuel and so require modifications of the engines (Kerschbaum

and Rinke, 2004). To overcome this problem, different methods have been considered to

reduce the viscosity of vegetable oils such as dilution, micro-emulsification, pyrolysis,

catalytic cracking and trans-esterification (Dermirbas, 2009). Among these, trans-

esterification has been considered as the most suitable modification because technical

properties of esters are nearly similar to diesel.

1.4.1 Dilution

Dilution of vegetable oils with solvents lowers their viscosities. For instance, the viscosity of

oil can be lowered by blending with pure ethanol or diesel (Bilgin et al., 2002). When

twenty-five parts of sunflower oil and seventy-five parts of diesel were blended as diesel

fuel; the viscosity obtained was 4.88 centistoke at 313 K (Dermirbas, 2009).

24

1.4.2 Microemulsion

A microemulsion is defined as a colloidal equilibrium dispersion of optically isotropic fluid

microstructure with dimensions generally into 1–150 range formed spontaneously from two

normally immiscible liquids and one and more ionic or more ionic amphiphiles (Singh and

Singh, 2010). Short-chain alcohols such as ethanol or methanol are used for microemulsions,

to reduce of the high viscosity of vegetable oils, microemulsions with immiscible liquids

such as methanol and ethanol and ionic or non-ionic amphiphiles have been studied (Billaud

et al., 1995).

1.4.3 Pyrolysis

Pyrolysis or thermal cracking is the conversion of one substance into another by means of

heating; it involves heating in the absence of air or oxygen and cleavage of chemical bonds

to yield small molecules (Mohan et al., 2006). Pyrolysis of oils and fats result in production

of alkanes, alkenes, alkadienes, cycloalkanes, alkylbenzenes, carboxylic acids, aromatics

and small amounts of gaseous products (Dermirbas, 2008b). The pyrolyzed material can be

vegetable oils, animal fats, natural fatty acids and methyl esters of fatty acids (Dermirbas,

2009).

1.4.4 Catalytic Cracking

This refers to pyrolytic treatment in the presence of a catalyst, which directs the process

mainly towards lower molecular weight aliphatic and aromatic hydrocarbons with lower

oxygen content (Sang et al., 2003).

1.4.5 Trans-esterification

The conventional method for vegetable oil conversion into biodiesel is trans-esterification

(Srivastava and Prasad, 2000). Trans-esterification refers to a chemical reaction involving

oil or fat, and an alcohol to yield fatty acid alkyl esters and glycerol (Thiruvengadaravi et

al., 2009).

25

Fig. 2: The trans-esterification reaction

Source: (Schuchardta et al., 1998)

The overall process consists of a sequence of three consecutive reversible reactions where

triglycerides are converted to diglycerides and then diglycerides are converted to

monoglycerides followed by the conversion of monoglycerides to glycerol (Dermirbas,

2009). In each step an ester is produced and thus three ester molecules are produced from

one molecule of triglycerides; these esters are commonly referred to as biodiesel (Sharma

and Singh, 2008).

The alcohols that can be used in the trans-esterification reaction are methanol, ethanol,

propanol, butanol and amyl alcohol; with methanol and ethanol being most frequently used

(Dermirbas, 2009). Ethanol is a preferred alcohol in the trans-esterification process

compared to methanol because it is derived from agricultural products and is renewable and

biologically less objectionable in the environment (Dermirbas, 2005). However methanol

has the merit of low cost as well as physical and chemical advantages (polar and shortest

chain alcohol) which make the trans-esterification process faster (Dermirbas, 2009).

1.5 Methods of Trans-esterification

The trans-esterification process can be performed with or without a catalyst (Gerpen, 2005;

Meher et al., 2006b). However, conventional trans-esterification process has been using

catalytic process to produce biodiesel due to its simpler operation and shorter reaction period

(Marchetti et al., 2007).

26

1.5.1 Non-Catalytic Trans-esterification

Non-catalytic trans-esterification process requires no catalyst. However, it is also less

favorable due to its high energy demand as non-catalytic process usually operates at

supercritical temperature and pressure of the alcohol (Marchetti et al., 2007). This process

usually uses supercritical alcohol such as supercritical methanol and supercritical ethanol to

produce fatty acid alkyl esters (biodiesel) (Dermirbas, 2005). Furthermore, at supercritical

conditions, non-catalytic trans-esterification process tends to become very difficult to

handle. Due to these factors, alternative methods, which have lower operational costs and

simpler operational processes, have been considered (Marchetti et al., 2007).

1.5.2 Catalytic Trans-esterification

Under catalytic process, trans-esterification of vegetable oils can be carried out using

homogeneous or heterogeneous catalysts that are base, acid or enzymes (Krishnan and Dass,

2012).

1.5.2.1 Heterogenous Catalytic Trans-esterification

Heterogeneous trans-esterification process uses solid catalyst such as metal oxides (Liu et

al., 2008), active metals supported on various medium, zeolites, resins, membranes and

enzymes (Miertus et al., 2009) to catalyze the trans-esterification process (Serio et al.,

2008). The benefits of heterogeneous trans-esterification process include easier and simpler

separation process (as the catalyst is in a different phase from the products/reactants),

elimination of soap formation and corrosion problems associated with their use (Miertus et

al., 2009). One of the main problems with heterogeneous catalysts is their deactivation with

time owing to many possible phenomena, such as poisoning, coking, sintering, and leaching

(Miertus et al., 2009). However, the performance of heterogeneous catalysts is generally

lower than that of the commonly used homogeneous catalysts. Notably, diffusional

limitations might sometimes drastically reduce the surface of the solid that is available for

promoting the trans-esterification reaction. Therefore, a careful design of the pore structure

of these materials is important. In this respect, zeolites are ideal systems (Miertus et al.,

2009).

27

1.5.2.2 Homogenous Catalytic Trans-esterification

Homogenous trans-esterification process usually uses catalysts which are in the same phase

the reactant such as sodium hydroxide, potassium hydroxide, sulfuric acid and hydrochloric

acid to catalyze the trans-esterification process (Dermirbas, 2009). Homogeneous trans-

esterification method has been long regarded as the easiest method to produce biodiesel

(Miertus et al., 2009). Unfortunately, the problems associated with the homogeneous

catalysts are high consumption of energy, formation of unwanted soap byproduct by reaction

of the free fatty acids (FFA), high cost of separation of the homogeneous catalyst from the

reaction mixture, and generation of large amount of wastewater during separation and

cleaning of the catalyst and the products. These could contribute to the loss of triglycerides.

All these downsides eventually lead to a very high production cost (Vyas et al., 2010).

1.5.2.2.1 Acid-Catalyzed Trans-esterification

Acid catalyzed trans-esterification process is catalyzed by Bronsted acids, preferably

sulfonic, sulfuric and hydrochloric acids, these catalysts are dissolved in alcohol by vigorous

stirring in a small reactor (Issariyakul et al., 2007). The oil is transferred into the biodiesel

reactor and then the catalyst/alcohol mixture is pumped into the oil (Dermirbas, 2009). Acid-

catalyzed trans-esterification can be used in a two-stage process, in which the first stage

involves the esterification of FFAs into biodiesel in the presence of the acid catalyst

followed by base-catalyzed trans-esterification (Miertus et al., 2009). Acid catalysts give

very high yields of alkyl esters and are insensitive to free fatty acids and moisture resulting

in the absence of soap formation, but there are a number of serious problems associated with

acid catalyzed trans-esterification such as requirement of high operating temperature and

pressure conditions (Miertus et al., 2009), slow reaction rate, requirement of an anti-

corrosion reactor and high alcohol-to-oil molar ratio (Dermirbas, 2009).

Zhang et al. (2003a) showed that, in a large excess of methanol, the acid-catalyzed trans-

esterification reaction of waste cooking oils is essentially a pseudo-first-order reaction. The

oil/methanol, acid molar ratio and temperature are the most significant factors affecting the

yield of fatty acid methyl esters (FAMEs) (Zhang et al., 2003a). Zullaikah et al. (2005)

28

investigated the acid-catalyzed methanolysis of dewaxed/degummed rice bran oil with

varying FFA contents at atmospheric pressure and 60oC using 1:10 molar ratio of oil:

methanol and 2 wt% sulfuric acid as catalyst. The initial FFA content appreciably influences

the rate of methanolysis and the final methyl ester content in the product. A methyl ester

content of about 96% in the product could be obtained in 8 h for rice bran oil with an initial

FFA content of 76 % (Miertus et al., 2009).

In the mechanism of acid-catalyzed trans-esterification of fatty acids (Fig. 3), the initial step

is protonation of the acid to give an oxonium ion, which can undergo an exchange reaction

with an alcohol to give the intermediate, and this in turn can lose a proton to become an

ester. Each step in the process is reversible, but in the presence of a large excess of the

alcohol, the equilibrium point of the reaction is displaced so that esterification proceeds

virtually to completion (Dermirbas, 2009).

Fig. 3: Mechanism of acid catalyzed trans-esterification

Source: (Schuchardta et al., 1998)

1.5.2.2.2 Base-Catalyzed Trans-esterification

The base-catalyzed trans-esterification of vegetable oils proceeds faster than the acid-

catalyzed reaction (Dermirbas, 2009). Due to this reason, and the fact that the alkaline

catalysts are less corrosive than acidic compounds, industrial processes usually favour base

catalysts, such as alkaline metal alkoxides and hydroxides as well as sodium or potassium

carbonates (Miertus et al., 2009). In the base-catalyzed trans-esterification method, the

29

catalyst (KOH or NaOH) is dissolved into alcohol by vigorous stirring in a small reactor.

The oil is transferred into a biodiesel reactor and then the catalyst/alcohol mixture is pumped

into the oil (Dermirbas, 2009).

Base-catalyzed trans-esterification is most often used industrially today (Meher et al.,

2006b). The most commonly-used alkaline catalysts in the biodiesel industry are potassium

hydroxide (KOH) and sodium hydroxide (NaOH) flakes which are inexpensive, easy to

handle in transportation and storage, and are preferred by small producers (Singh et al.,

2006). However, where the raw material has a high water or free fatty acid (FFA) content

pretreatment with an acidic catalyst is needed in order to esterify FFA (Zhang et al., 2003a).

Pretreatment is necessary to reduce soap formation during the reaction and ease the

extensive handling for separation of biodiesel and glycerol together with removal of catalyst

and alkaline wastewater (Meher et al., 2006b). On the other hand, the water problem can be

avoided if sodium and potassium methoxide (NaOMe and KOMe) solutions, which can be

prepared water-free, are applied (Issariyakul et al., 2007). Additionally, although the use of

methoxides cannot avoid soap formation if the feedstock contains free fatty acids, which is

also true for use of KOH or NaOH, very little saponification of esters or triglycerides occurs

because methoxides behave as weak Lewis bases (Singh et al., 2006).

Singh et al. (2006) studied the reaction of methanol with canola oil at different

concentrations of alkaline catalyst (NaOH, KOH, NaOMe, and KOMe), reaction

temperatures, and methanol-to-oil molar ratios. The result showed that potassium- based

catalysts gave better yields than the sodium-based catalysts, and methoxide catalysts gave

higher yields than the corresponding hydroxide catalysts. On the other hand, potassium-

based catalysts resulted in a larger extent of soap formation than the corresponding sodium-

based catalysts. Potassium and sodium hydroxides and methoxides were also investigated as

catalysts by Vicente et al. (2004) in the trans-esterification of sunflower oil using a

methanol-to-oil molar ratio of 6:1 and 1% catalyst. The yields of esters were reported to be

higher than 98% for the methoxide catalysts, and 85.9 and 91.67 wt% for the sodium and

potassium hydroxides, respectively, because the saponification resulted in more substantial

decreases in yield (Miertus et al., 2009).

30

The mechanism of alkali-catalyzed trans-esterification reaction (Fig. 4) shows that the first

step is the reaction of the base with the alcohol, producing an alkoxide and a protonated

catalyst. The nucleophilic attack of the alkoxide at the carbonyl group of the triglyceride

generates a tetrahedral intermediate, from which the alkyl ester and the corresponding anion

of the diglyceride are formed. Diglycerides and monoglycerides are converted by the same

mechanism into a mixture of alkyl esters and glycerol (Dermirbas, 2009).

Fig. 4: Mechanism of base catalyzed trans-esterification

Source: (Schuchardta et al., 1998)

1.5.2.3 Enzyme-Catalyzed Trans-esterification

Biodiesel can be obtained from enzyme or biocatalytic trans-esterification methods (Hama et

al., 2004). However, with the problems associated with conventional homogeneous catalytic

processes, such as removal of glycerol and the catalyst, high energy requirements, and the

need to pretreat feedstocks containing FFAs or to post-treat large amounts of waste water

enzyme-catalysed trans-esterification is preferred to other methods (Vyas et al., 2010).

31

These problems can be overcome by using enzymes catalysts (such as lipases) which are

able to effectively catalyze the trans-esterification of triglycerides with high selectivity to

yield FAMEs either in aqueous or in non-aqueous systems (Fukuda et al., 2001). Several

examples of the lipase-catalyzed production of biodiesel have been reported using different

feedstocks namely soybean oil, sunflower oil, palm oil, coconut oil, rice bran oil, mixtures

of vegetable oils, grease, and tallow (Dermirbas, 2006). It has been shown that the

enzymatic production of biodiesel is possible by using either extracellular or intracellular

lipases. The choice of the method is based on the balance between simplified upstream

operations (intracellular) and high conversions (extracellular). Both types can be

immobilized for use without a need for downstream operations (Fukuda et al., 2001).

However, some disadvantages of enzyme catalysis include the ease of inactivation of

enzymes in these systems, generally low reaction rates, and low conversions. For example,

the immobilized enzymes are easily inactivated in the absence of polar compounds such as

water and methanol. Moreover, immobilized enzymes are generally more expensive than

chemical catalysts (Miertus et al., 2009).

Noureddini et al. (2005) studied the enzymatic trans-esterification of soybean oil with

methanol and ethanol. Among nine lipases tested, lipase PS from Pseudomonas cepacia

resulted in the highest yield of alkyl esters.

1.6 Factors Effecting Trans-esterification Reactions

There are a number of factors which could affect the trans-esterification process. These

factors include moisture content, free fatty acid contents, molar ratio of oil-to-alcohol, type

and amount of catalyst, reaction time, reaction temperature and mixing intensity (Demirbas

and Dermirbas, 2007).

1.6.1 Effect of Molar Ratio of Oil-to-Alcohol

Based on the stoichiometry of trans-esterification reaction, every mole of triglyceride

requires three moles of alcohol to produce three moles of fatty acid alkyl esters and one

mole of glycerol (Dermirbas, 2009). However, trans-esterification is an equilibrium-

32

controlled reaction in which excess of alcohol is required to drive the reaction in the forward

direction, to achieve maximum conversions (Meher et al., 2006b). A molar ratio of 1:6 9 (oil

to alcohol) is considered the standard ratio (Fukuda et al., 2001; Gerpen, 2005). Ramadhas

et al. (2004) and Sahoo et al. (2007) have reported a molar ratio of 6:1 during acid

esterification and a molar ratio of 9:1 vegetable oil-alcohol during alkaline esterification, as

the optimum values for biodiesel production from high FFA rubber seed oil and polanga

seed oil. Veljkovic et al. (2006) used 18:1 molar ratio during acid esterification and 6:1

molar ratio during alkaline esterification. Meher et al. (2006a) used 6:1 molar ratio during

acid esterification and 12:1 molar ratio during alkaline esterification. Tiwari et al. (2007)

and Ghadge and Raheman (2005) used volume as a measure of ratio instead of taking molar

ratio. However, in all, higher molar ratios resulted in greater ester conversions in a shorter

time (Dermirbas, 2009).

1.6.2 Type and Amount of Catalyst

The type and amount of catalyst required in the trans-esterification process usually depend

on the quality of the feedstock and method applied for the trans-esterification process

(Miertus et al., 2009). However, for feedstock with high moisture and free fatty acid

contents, homogenous trans-esterification process is unsuitable due to high possibility of

occurrence of saponification process instead of trans-esterification process to occur, rather,

an acid catalyzed trans-esterification is suitable (Gerpen, 2005). For a purified feedstock,

any type of catalyst could be used for the trans-esterification process (Edger et al., 2005). In

addition, biodiesel formation is also affected by the amount or concentration of catalyst:

with increasing concentration of catalyst and oil, the conversion of triglycerides into

biodiesel also increases. On the other hand insufficient amount of catalyst leads to the

incomplete conversion of triglycerides to fatty acid esters (Guo, 2005; Leung and Guo,

2006). However, optimal product yield (biodiesel) has been achieved when the

concentration of NaOH reaches 1.5 wt. % at the same time further increase of catalyst

concentration proved to have negative impact on end product yield, but addition of excess

amount of alkali catalyst react with triglycerides to form more soap (Leung and Guo, 2006).

33

1.6.3 Effect of Water and Free Fatty Acid Content

The water and free fatty acid (FFA) contents are critical factors for trans-esterification

reaction. Generally, in the conventional trans-esterification of fats and vegetable oils for

biodiesel production, free fatty acids and water always produce negative effects since the

presence of free fatty acids and water causes soap formation, consumes catalyst, and reduces

catalyst effectiveness (Demirbas, 2009). Water content is an important factor in the

conventional catalytic trans-esterification of vegetable oil as the base-catalyzed trans-

esterification reaction requires water-free and low acid value (< 1) raw materials for

biodiesel production (Demirbas, 2009). Also, if the oil samples have high FFA content

(more than 1%) then the reaction requires more alkali catalyst to neutralize the FFA or

pretreatment with an acid catalyst (Zhang et al., 2003a).

Kusdiana and Saka (2004) are of the opinion that water can pose a greater negative effect

than the presence of free fatty acids and hence the feedstock should be water-free. Canakci

and Gerpen (1999) insist that even a small amount of water (0.1%) in the trans-esterification

reaction will decrease the ester conversion from vegetable oil.

Fig. 5: Saponification reaction of free fatty acids during base catalyzed trans-esterification

source: (Moser, 2009).

1.6.4 Effect of Temperature

The reaction temperature influences the reaction in a positive manner (Ojolo et al., 2011).

The trans-esterification reaction temperature should be below the boiling point of alcohol in

order to prevent evaporation of the alcohol (Dermirbas, 2009). The range of optimal reaction

temperature may vary from 50°C to 70°C depending on the type of oils or fats used (Leung

and Guo, 2006). It has been observed that increasing the reaction temperature, especially to

supercritical conditions, has a favourable influence on the yield of ester (Dermirbas, 2009).

For example higher reaction temperature increases the reaction rate and shortens the reaction

time due to the reduction in viscosity of oils (Mathiyazhagan and Ganapathi, 2011).

34

However, Leung and Guo (2006) and Eevera et al. (2009) found that increase in reaction

temperature beyond the optimal level leads to decrease of biodiesel yield, because higher

reaction temperature accelerates the saponification of triglycerides.

1.6.5 Effect of Stirring Intensity

Agitation speed plays an important role in the formation of end-product (biodiesel)

(Mathiyazhagan and Ganapathi, 2011). Generally, low reaction rates are observed in trans-

esterification as a result of a poor dispersion of the alcohol and oil phases, and an induction

period can be often seen on the kinetic curves (slow initial reaction before steady-state

concentrations are reached) (Miertus et al., 2009). On the other hand higher stirring speed

favors formation of soap. This is due to the reverse behavior of trans-esterification reaction

(Eevera et al., 2009). Therefore, intense mixing is very important for the trans-esterification

process with the optimum stirring rates in the range of 1000 rpm using both motionless and

high-shear mixers (Miertus et al., 2009).

1.6.6 Effect of Reaction Time

The reaction time of trans-esterification depends on the choice of method or catalyst,

notably further increase in reaction time does not increase the product yield (i.e.

biodiesel/mono alkyl ester) (Leung and Guo, 2006; Alamu et al., 2007). Besides, longer

reaction time leads to the reduction of end product (biodiesel) due to the reversibility of the

trans-esterification reaction, thus resulting in loss of esters as well as soap formation (Eevera

et al., 2009). The effect of reaction time has been studied from 45 minutes to 120 minutes on

methyl ester (biodiesel) yield (Ojolo et al., 2011). It was found that ester yield increased as

the reaction time increased. However, if the reaction time is increased beyond 1 hour, the

increase in the yield of ester is small (Krishnakumar et al., 2008).

1.7 Influence of Biodiesel Composition on Fuel Properties

The fatty ester composition, along with the presence of contaminants and minor components

dictate the fuel properties of biodiesel fuel; these properties include low-temperature

35

operability, oxidative and storage stability, viscosity, exhaust emissions, cetane number, and

energy content (Moser, 2009).

1.7.1 Viscosity

Viscosity is defined as the resistance to shear or flow; it is highly dependent on temperature

and it describes the behavior of a liquid in motion near a solid boundary like the walls of a

pipe (Sanford et al., 2009). Viscosity is the primary reason why biodiesel is used as an

alternative fuel instead of the pure vegetable oils or animal fats (Moser, 2009). The high

kinematic viscosities of vegetable oils and animal fats ultimately lead to operational

problems such as deposits in engines when used directly as fuels (Knothe and Steidley,

2005a): this is as a result of poorer atomization of the fuel spray and less accurate operation

of the fuel injectors (Dermirbas, 2009). The lower the viscosity of the biodiesel, the easier it

is to pump, atomize and achieve finer droplets (Islam and Beg, 2004). The conversion of

triglycerides to methyl or ethyl esters through the trans-esterification process reduces the

molecular weight of the triglyceride to one-third of its value, and reduces the viscosity by a

factor of about eight (Dermirbas, 2009).

Several structural features influence the kinematic viscosities of fatty acids alkyl esters

(FAAE), such as chain length, degree of unsaturation, double bond orientation, and type of

ester head group (Moser, 2009). Factors such as longer chain length and larger ester head

group result in increase in the viscosity (Kulkarni et al., 2007). Viscosity increases with the

molecular weight and decreases with increasing level of unsaturation and high temperature

(Moser, 2009).

1.7.2 Low Temperature Operability

Low temperature operability of biodiesel fuel is an important aspect from the engine

performance standpoint in cold weather conditions (Knothe et al., 2005). Low temperature

operability of biodiesel is normally determined by three common parameters: cloud point

(CP), pour point (PP) and cold filter plugging point (CFPP) (Moser, 2009). The PP is the

temperature at which the amount of wax from a solution is sufficient to gel the fuel; thus it is

the lowest temperature at which the fuel can flow (Dermirbas, 2009). The cloud point is the

36

temperature at which crystals first appear in the fuel when cooled. Biodiesel has a higher CP

and PP compared to conventional diesel (Prakash, 1998). The CFPP is defined as the lowest

temperature at which a given volume of biodiesel completely flows under vacuum through a

wire mesh filter screen within 60s (Moser, 2009). The CFPP is generally considered to be a

more reliable indicator of low-temperature operability than CP or PP, since the fuel will

contain solids of sufficient size to render the engine inoperable due to fuel filter plugging

once the CFPP is reached (Park et al., 2008).

The low-temperature behaviour of chemical compounds is dictated by molecular structure

(Moser, 2009). Structural features such as chain length, degree of unsaturation, orientation

of double bonds and type of ester head group strongly influence the low temperature

operability of biodiesel (Moser, 2009). The larger the ester head group, the lower the cloud

point (Foglia et al., 1997). A higher degree of unsaturation results in lower cloud point

(Moser, 2008).

1.7.3 Oxidative Stability

Oxidative stability is determined by parameters such as iodine value and peroxide value.

Iodine value is a measure of the unsaturation of fats and oil and high iodine value shows

high unsaturation of the oil (Belewu et al., 2010). The peroxide value measures the

miliequivalent of peroxide oxygen per kilogram weight. The higher the peroxide value of

biodiesel the greater the development of rancidity due do the products that are formed

through oxidation of lipids, such as aldehydes, shorter-chain fatty acids, other oxygenated

species (such as ketones), and polymers (Moser, 2009).

Stability of fatty compounds is influenced by factors such as presence of air, heat, traces of

metal, peroxides, light and structural features of the compounds themselves, mainly the

presence of double bonds (Bajpai and Tyagi, 2006). Oxidative stability decreases with the

increase of polyunsaturated fatty acid methyl esters content (McCormick et al., 2007; Park

et al., 2008). Autoxidation of unsaturated fatty compounds proceeds at different rates

depending on the number and position of double bonds. The bis-allylic positions in common

polyunsaturated fatty acids such as linoleic acid (one bis-allylic position at C-11) and

37

linolenic acid (two bisallylic positions at C-11 and C-14) are more susceptible to

autoxidation than allylic positions (Sokoto et al., 2011). Therefore, vegetable oils rich in

linoleic and linolenic acids, tend to impart poor oxidation stability to fuels (Sokoto et al.,

2011).

1.7.4 Heat of Combustion

Heat of combustion is the thermal energy that is liberated upon combustion, so it is

commonly referred to as energy content (Moser, 2009). The heat of combustion is an

important parameter for estimating fuel consumption, the greater the heat of combustion, the

lower the fuel consumption (Knothe, 2008). The heat of combustion or heating value is not

specified in the biodiesel standards ASTM D6751 and EN14214. However, a European

standard for using biodiesel as heating oil, EN 14213, specifies a minimum heating value of

35 MJ/kg (Sokoto et al., 2011).

Factors that influence the energy content of biodiesel include the oxygen content and

carbon-to-hydrogen ratio (Moser, 2009). Generally, lower carbon-to-hydrogen ratios (i.e.,

more hydrogen) exhibit greater energy content (Moser, 2009). The oxygen content of

biodiesel (contains 11% oxygen by weight and no sulfur) improves the combustion process

and decreases its oxidation potential, thus higher oxygen content of fatty acids alkyl esters

increase the energy content (Dermirbas, 2009). The structural oxygen content of a fuel

improves its combustion efficiency due to an increase in the homogeneity of oxygen with

the fuel during combustion due to this the combustion efficiency of biodiesel is higher than

that of petrodiesel (Dermirbas, 2009).

Heat of combustion increases with increasing chain length; thus, the energy content of

FAAE is directly proportional to chain length (Knothe, 2008). Therefore, energy content can

be predicted by saponification value, which is defined as the amount of potassium hydroxide

(KOH) in milligrams required to saponify one gram of fat or oil under the specified

conditions (AOAC, 1998). Based on the length of the fatty acids present in the

triacylglycerol molecule, the weight of the triacylglycerol molecule changes which in turn

affects the amount of KOH required to saponify the molecule (Sanford et al., 2009). Hence,

saponification value is a measure of the average molecular weight or the chain length of the

38

fatty acids present. As most of the mass of a triglyceride is due to the three fatty acid

moeities, it allows for comparison of the average fatty acid chain length (Sanford et al.,

2009). Saponification values is inversely related to the average molecular weight or chain

length of the fatty acids in the oil fractions. Thus, oil fractions with saponification values of

200 mg KOH/g and above possess low molecular weight fatty acids (Abayeh et al., 1998).

1.7.5 Cetane Number

Cetane number (CN) is widely used as diesel fuel quality parameter related to the ignition

delay time and combustion quality. An appropriate cetane number is required for good

engine performance (Dermirbas, 2009). The higher the cetane number, the better the ignition

property as it ensures good cold start properties and minimize the formation of white smoke

(Meher et al., 2006b). Cetane number (CN) is based on two compounds, hexadecane also

known as cetane (trivial name) as a high-quality reference standard with a short ignition

delay time and an arbitrarily assigned CN of 100; and 2,2,4,4,6,8,8-heptamethylnonane as

low-quality reference standard with a long ignition delay time and an arbitrarily-assigned

CN of 15 (Knothe et al., 1997). The CN of biodiesel is influenced by the fatty acid chain

length and degree of unsaturation, the longer the fatty acid chain length and the more

saturated the molecules, the higher the CN (Moser, 2009). The CN of biodiesel is generally

higher than that of conventional diesel, and the CN of biodiesel from animal fats is higher

than those of vegetable oils (Bala, 2005).

1.7.6 Exhaust Emissions

The combustion of biodiesel (B100) in diesel engines results in an average increase in NOx

exhaust emissions of 12% and decreases in PM and CO emissions of 48% and 48%,

respectively, in comparison to petrodiesel (Hess et al., 2007). For B20 blends of SME in

petrodiesel, NOx emissions are increased by 0–4% when neat petrodiesel is used, but PM,

THC, and CO emissions are reduced by 10%, 20%, and 11%, respectively (Hess et al.,

2007; EPA, 2002).

The increase in NOx emissions with combustion of biodiesel and in some cases of

biodiesel–petrodiesel blends is of concern in environmentally-sensitive areas such as

39

national parks and urban centers (Moser, 2009). Reduction of smog forming NOx exhaust

emissions to levels equal to or lower than those observed for petrodiesel is essential for

universal acceptance of biodiesel (Moser, 2009). NOx exhaust emissions of biodiesel and

blends with petrodiesel NOx emission may be reduced by several engine or after-treatment

technologies, such as exhaust gas re-circulation, selective catalytic reduction, diesel

oxidation catalysts, and NOx or particulate traps (McGeehan, 2004).

NOx emissions are influenced by the chemical nature of FAAE that constitute biodiesel.

Specifically, decreasing the chain length and/or increasing the number of double bonds (i.e.,

higher iodine value) of FAAE results in an increase in NOx emissions (Szybist et al. 2005;

Knothe et al., 2006). The chemical composition of biodiesel varies according to the

feedstock from which it is prepared. As a result, biodiesel obtained from feedstocks of

significantly different compositions will exhibit different NOx exhaust emission behavior

(Moser, 2009).

1.7.7 Lubricity

This is the property of the fuel that gives it the capacity to reduce friction. Biodiesel

possesses inherently good lubricity, especially when compared to petrodiesel (Knothe and

Steidley 2005b; Moser et al., 2008). Lubricity is determined at 60°C in accordance with

ASTM D6079 using a high-frequency reciprocating rig instrument. Lubricity is not

prescribed in ASTM D6751 or EN 14214. However, the petrodiesel standards, ASTM D975

and EN 590, contain maximum allowable wear scar limits of 520 and 460 µm respectively

(Moser, 2009).

Various structural features such as the presence of heteroatoms, chain length, and

unsaturation influence the lubricity of biodiesel (Moser, 2009). Biodiesel fuels possess at

least two oxygen atoms that in large part explain their enhanced lubricities over typical

hydrocarbon-containing petrodiesel fuels (Knothe and Steidley, 2005b). Generally,

increasing fatty acid chain length and increasing levels of unsaturation impart superior

lubricity to biodiesel (Moser, 2009).

40

1.7.8 Contaminants

Contaminants in biodiesel may include alcohol, water, FFA, soaps, metals, catalyst, glycerol

and its intermediates. Alcohol contamination in biodiesel is indirectly measured through

flash point determination following ASTM D93. If methanol, with its flash point of 12°C is

present in the biodiesel the flash point can be lowered considerably (Sanford et al., 2009).

The flash point is the lowest temperature at which fuel emits enough vapors to ignite

(ASTM, 2008). Biodiesel has a high flash point; usually more than 150°C, while

conventional diesel fuel has a flash point of 55-66°C (Knothe et al., 2005). However, the

flash point values of vegetable oil methyl esters are much lower than those of vegetable oils

(Dermirbas, 2009).

Water is a major source of fuel contamination. Its presence in biodiesel causes four serious

problems: corrosion of engine fuel system components, promotion of microbial growth,

hydrolysis of the biodiesel (Moser, 2009). Water also reduces the heat of combustion which

leads to more smoke, harder starting and less power (Dermirbas, 2009).

The acid value and conductivity test of the biodiesel can be used to determine the presence

of water; the acid value determination is an important test to assess the quality of a particular

biodiesel (Sanford et al., 2009). Acid value can indicate the extent or degree of hydrolysis of

the methyl ester, a particularly important aspect when considering storage and transportation

as large quantities of free fatty acids can cause corrosion in tanks (Wang et al., 2008). High

acid value and high conductivity of biodiesel indicate the presence of water (Moser, 2009).

Free fatty acids may be present in biodiesel that was prepared from a feedstock with high

FFA content or may be formed during hydrolysis of biodiesel in the presence of water and

catalyst (Moser, 2009). The presence of FFA in biodiesel may impact other important fuel

properties such as low temperature performance, oxidative stability, kinematic viscosity, and

lubricity (Moser, 2009). In addition to soap formation, FFAs are known to act as pro-

oxidants (Knothe and Steidley, 2005a), so the presence of FFA in biodiesel may have

negative impact to the oxidative stability. FFA increases the lubricity which is beneficial but

41

negatively increases the viscosity and low temperature operability properties of the biodiesel

(Moser, 2009).

Other contaminants such as soaps, metals, catalyst, glycerol and its intermediates may be

present in insufficiently purified biodiesel and their presence can be detected by simple

chemical test of the individual compounds (Moser, 2009). The primary problem associated

with metal contamination is elevated ash production during combustion (Knothe et al.,

2005). Thus, high percentage ash content is indicative of the presence of metals.

1.7.9 Biodiesel Standard Specifications and Test Methods

The standard specifications and test methods for biodiesel are summarized in Table 4.

42

Table 4: Specifications and test methods of ASTM D6751 and EN 14214 standards for

biodiesel

United States Standards

ASTM D6751

European Standards EN

14214

Property Units Test Methods Limits Test Methods limits

Density at 15 °C (Kg/m3) EN ISO 3675,

EN ISO 12185

860–900

Kinematic

viscosity, 40oc

mm2/s ASTM D445 1.9–6.0 EN ISO 3104,

ISO 3105

3.5–5.0

Cetane number ASTM D613 47 min EN ISO 5165 51 min.

Flash point oC ASTM D93 130.0 min EN ISO 3679 120 min.

Cloud point oC ASTM

D2500-05

–3 - +12 - -

Pour point ASTM D 97-

96a

–15- +10 -

Oxidation

stability

h EN 14112 3.0 min.

Cold filter

plugging point

ASTMD 6371 –4 to –9

Acid value

mg

KOH/g

ASTM D664 0.50 max EN 14104 0.50 max

Total glycerin % mass ASTM D6584 0.240 EN 14105 0.25 max %

(mol/mol)

Free glycerin % mass ASTM D6584

0.020 EN 14105 EN

14106

0.020 max %

(mol/mol)

Water content mg/kg ASTM D2709 500ppm EN ISO

12937

500 max

Iodine value I2/100 g EN 14111 120 max

Ash content % ASTM D 482 0.01 0.02

metals (group 1

&2)

mg/kg EN 14108,

14109

EN 14538

5 max

Carbon residue % mass ASTM D4530 0.050

max

EN ISO 10370 0.30 max %

(mol/mol)

Source: (Moser, 2009)

1.8 Advantages of Biodiesel

The biggest advantage of biodiesel is environmental friendliness that it has over gasoline

and petroleum diesel (Dermirbas, 2009). The advantages of biodiesel as a diesel fuel are its

portability, ready availability, renewability, higher combustion efficiency, lower sulfur and

43

aromatic content (Ma and Hanna 1999; Knothe et al., 2006), higher cetane number, and

higher biodegradability (Zhang et al., 2003b; Knothe et al., 2005).

A number of technical advantages of biodiesel fuel are (i) it prolongs engine life and reduces

the need for maintenance (biodiesel has better lubricating qualities than fossil diesel); (ii) it

is safer to handle, being less toxic, more biodegradable, and having a higher flash point; and

(iii) it reduces some exhaust emissions (Wardle, 2003). Among the many advantages of

biodiesel fuel, it is safe for use in all conventional diesel engines, offers the same

performance and engine durability as petroleum diesel fuel, it is non-flammable and non-

toxic, and reduces tailpipe emissions, visible smoke, and noxious fumes and odours (Chand,

2002). Biodiesel is better than diesel fuel in terms of sulfur content and aromatic content

(Martini and Schell, 1997).

The economic advantages of biodiesel are that it reduces greenhouse gas emissions, helps to

reduce reliance on crude oil imports, and supports agriculture by providing new labour and

market opportunities for domestic crops. In addition, it enhances lubrication and is widely

accepted by vehicle manufacturers (Palz et al., 2002; Clarke et al., 2003). Biodiesel is non-

toxic and degrades about four times faster than petrodiesel (Dermirbas, 2009). Biodiesel

provides significant lubricity improvement over petroleum diesel fuel; the lubricity

properties of fuel are important for reducing friction wear in engine components normally

lubricated by the fuel rather than crankcase oil (Ma and Hanna 1999; Dermirbas, 2003).

Even biodiesel levels below 1% can provide up to a 30% increase in lubricity (Dermirbas,

2008a). The sulfur content of petrodiesel is 20–50 times that of biodiesels (Dermirbas,

2009). Biodiesel has demonstrated a number of promising characteristics, including

reduction of exhaust emissions (Dunn, 2001). The risks of handling, transporting, and

storing biodiesel are much lower than those associated with petrodiesel (Dermirbas, 2009).

1.9 Disadvantages of Biodiesel

The major disadvantages of biodiesel are its higher viscosity, lower energy content, higher

cloud point and pour point, higher nitrogen oxide (NOx) emissions, lower engine speed/

power, injector coking and high price (Dermirbas, 2008a). Important operating

44

disadvantages of biodiesel in comparison with petrodiesel are cold start problems, the lower

energy content, higher copper strip corrosion and fuel pumping difficulty from higher

viscosity (Dermirbas, 2007).

1.10 Uses of Biodiesel

Apart from its use as an alternative fuel to petrodiesel in diesel engines, biodiesel may be

used as a replacement for petroleum as heating oil (Mushrush et al. 2001). As such, a

European standard (EN 14213) was established to cover the use of biodiesel for this

purpose. In the United States, blends of up to 5% biodiesel in heating oils (B5 Bioheat) have

recently been approved for inclusion in the ASTM heating oil standard, D396 (ASTM,

2008). The less harmful exhaust emissions from biodiesel to that of petrodiesel, have

encouraged the use of biodiesel to power underground mining equipment (Moser, 2009).

Another combustion-related application of biodiesel is as an aviation fuel, although the

relatively poor low-temperature properties of biodiesel restrict its use to low-altitude aircraft

(Dunn, 2001).

The use of biodiesel in diesel-fueled marine engines to reduce environmental impact is

another important application of this biodegradable and non-toxic fuel (Nine et al., 2000).

Biodiesel may also be used as a fuel for generators and turbines for the generation of

electricity (Hashimoto et al., 2008; Kalbande et al., 2008; Lin et al., 2008) or as a substitute

for hydrogen in fuel cells (Kram, 2008).

An important non-fuel application of FAAE is as an industrial environmentally friendly

solvent, since they are biodegradable, have high flash points, and have very low volatilities

(Wildes, 2002). The high solvent strength of biodiesel makes it attractive as a substitute for a

number of conventional and harmful organic solvents (Hu et al., 2004) in applications such

as industrial cleaning and degreasing, resin cleaning and removal (Wildes, 2002), as

plasticizers in the production of plastics (Wehlmann, 1999); in liquid–liquid extractions

(Spear et al., 2007); as polymerization solvent (Salehpour and Dube, 2008), and as a

medium in site bioremediation of crude petroleum spills (Pereira and Mudge, 2004;

Fernandezalvarez et al., 2006).

45

Fatty acid alkyl esters can also serve as valuable starting materials or intermediates in the

synthesis of fatty alcohols (Peters, 1996), lubricants (Moser et al., 2007; Sharma et al.,

2007; Dailey et al., 2008), cold flow improver additives (Moser et al., 2007; Dailey et al.,

2008), cetane improving additives (Poirier et al., 1995), and multifunctional lubricity and

combustion additives (Suppes et al., 2001; Suppes and Dasari, 2003). Moreover, biodiesel in

conjunction with certain surfactants can act as a contact herbicide to kill broadleaf weeds in

turfgrass (Vaughn and Holser, 2007).

1.11 Aim and Objectives

1.11.1 Aim of the Study

This study is aimed at characterizing coconut oil and evaluating its trans-esterification

reaction rate with ethanol.

1.11.2 Specific Objectives of the Study

This research is designed to achieve the following objectives:

• Extraction of oil from coconut copra (dry flesh) using cold extraction.

• Physicochemical characterization of the coconut oil.

• Trans-esterification of coconut oil with ethanol (ethanolysis) using NaOH as catalyst.

• Physicochemical characterization of the ethyl esters produced.

• Investigation of the trans-esterification reaction rate of the varied oil/ethanol

volumetric ratios of 1:6, 1:3, 1:2, 1:1.5 and 1:1.

46

CHAPTER TWO

MATERIALS AND METHODS

2.1 Materials

2.1.1 Plant Material

The coconut (Cocos nucifera) was obtained from Nnihi in Etche Local Government Area of

Rivers State, Nigeria. The nuts were dehusked and the shell split open in order to remove the

kernel (flesh). The kernel was ground into fine particles with a blender and sun-dried for 2

days.

2.1.2 Instruments/Equipment

The following instruments/equipment were used during the investigation:

Instruments/Equipments Manufacturers

Oswald viscometer B. Brain, made in England

Oxygen bomb calorimeter Model XRY-1A, Shanghai Changji, China

Blender Panasonic, made in Japan

Water bath Model SM801A, made by uniscope England

Oven Gellenkamp Hotbox, made in England

Abbe refractometer Model WYA-2S, Made by Searchtech Instruments

WTW conductivity meter Model LF. 90, made in Germany

UV/visible spectrophotometer: Jenway 6405, made in U.S.A.

Glass wares Pyrex, made in England

Heating magnetic stirrer Pyro-magnestir, made in USA, cat no.1266

Weighing balance: B2404-5 mettler Toledo, made in Switzerland.

Electric Muffle Furnace Model LF 3, made by Vecstar Limited.

2.1.3 Reagents/Chemicals

All chemicals used in this study were of analytical grade. Absolute ethanol, chloroform, n-

hexane and phenolphthalein were products of Riedel-de Haen, Germany. Iodine trichloride,

47

potassium chloride, sodium thiosulphate and starch powder were products of British Drug

House (BDH) Chemical, England. Potassium hydroxide (pellets), potassium iodide and

sodium hydroxide (pellets) were products of Avondale laboratories, England. Iodine crystals

and sodium sulphate were products of Burgoyne, India. Glacial acetic acid and sulphuric

acid were products of Cartivalues, India. Hydrochloric acid, diethylether, glycerol, acetyl

acetone, sodium carbonate and sodium periodate were products of Sigma Chemical

Company Limited (U.S.A.).

2.2 Methods

2.2.1 Preparation of reagents

Preparation of 0.5M Alcoholic Potassium Hydroxide (KOH) Solution

In preparing this, KOH pellets (28g) were transferred into a 1000ml conical flask, 300ml of

absolute ethanol was added to dissolve the pellets. Thereafter, the solution was made up to

1000ml mark using the same solvent.

Preparation of 0.1M Alcoholic Potassium Hydroxide (KOH) Solution

This was prepared by putting 5.6 g KOH into a 1000ml conical flask; 100ml of absolute

ethanol was added to dissolve the solute and then, the solution was made up to 1000ml mark

using the same solvent. The solution was filtered and stored in brown bottle for five days.

Preparation of Ethanol:Diethyl Ether Solution (1:1 v/v)

This solution was prepared by mixing 50ml of 95% ethanol and 50ml of diethyl ether in a

500ml conical flask.

Preparation of Phenolphthalein Indicator

Phenolphthalein indicator was prepared by putting 1g of phenolphthalein into a 100ml

conical flask, 66ml of ethanol was added to dissolve solute, after which the solution was

made up to 100 ml mark using distilled water.

48

Preparation of 20% Potassium Iodide (KI) Solution

This was prepared by putting 100g of KI into a 500ml conical flask and then 200ml of

distilled water was added to dissolve the KI. After that, the solution was made up to 500 ml

mark with distilled water.

Preparation of 0.1M Sodium Thiosulphate (Na2S2O3)

Sodium thiosulphate pentahydrate (24.8g) was put into a 1000ml conical flask, 300ml of

distilled was added to dissolve the solute, after which the solution was made up to 1000 ml

using distilled water.

Preparation of Starch Indicator

In preparing this, 1g of soluble starch powder was dissolved in little water and the

suspension was poured into 100ml of boiling water with constant stirring. The mixture was

boiled for one minute, allowed to cool and 3g of potassium iodide was added for

preservation.

Preparation of Wijs Reagent (Iodine monochloride) Solution

Wijs reagent was prepared by putting 2g of iodine trichloride into an amber bottle and 50ml

of glacial acetic acid was added. Iodine (2.25g) was dissolved in 100ml of glacial acetic acid

in another bottle and both solutions mixed together. The resulting mixture was then made up

to 250ml with glacial acetic, stored in the amber bottle at room temperature and kept out of

light its use.

Preparation of Glacial acetic acid:Chloroform Solution (3:2 v/v)

This solution was prepared by mixing 300ml of glacial acetic acid and 200ml of chloroform

in a 1000ml conical flask.

Preparation of 0.5M Hydrochloric acid (HCl) Solution

This was prepared with 37% HCl; 41.5 ml of HCl was pipetted into a 1000ml conical flask

containing 300ml of distilled water with thorough mixing, after which the solution was

made up to 1000ml with distilled water.

49

Preparation of 0.1M Sodium Hydroxide (NaOH) Solution

In preparing this solution, 4g of NaOH was put into a 1000ml conical flask, 100ml of

distilled water was added to dissolve the solute and then the solution was made up to 1000

ml with distilled water.

Preparation of 0.01M Potassium Chloride (KCl) Solution

Potassium chloride (0.75g) was put into a 1000ml conical flask, the solute was dissolved in

100ml of distilled water and then the solution was made up to 1000ml with distilled water.

Preparation of 0.2M Acetyl Acetone Solution

This was prepared by pipetting 21ml of acetyl acetone into a 1000ml conical flask, 300ml of

distilled water was added and the solution was thoroughly stirred. Then, the solution was

made up to 1000ml with distilled water.

Preparation of 10mM Sodium Periodate Solution

Sodium periodate (2.1g) was put into a 1000ml conical flask, 100ml of distilled was added

to dissolve the solute, after which the solution was made up to 1000ml with distilled water.

Preparation of 95% Ethanol:Deionized Water Solvent Solution (1:1)

This solution was prepared by mixing 500ml of 95% ethanol and 500ml of deionized water

in a 2000ml conical flask.

Preparation of 0.036mg/ml Glycerol Standard Solution

This was prepared with 98% glycerol; 29 µl of glycerol was pipetted into a 1000ml conical

flask, 200ml of 95% ethanol:deionized water was added with thorough mixing, after which

the solution was made up to 1000ml with the same solvent solution.

Preparation of 0.7M Sodium Carbonate Solution

In preparing this solution, 74.2g of sodium carbonate was put into a 1000ml conical flask,

100ml of distilled water was added to dissolve the solute and then the solution was made up

to 1000 ml with distilled water.

50

2.2.2 Determination of the Moisture Content of Kernel

The empty dish was weighed without and with the amount of kernel. This was placed in an

oven and dried at 105oC for 7 hr, weighing was repeated every 2 hr till a constant weight

was obtained and the weight was taken and compared with the initially recorded weight. The

percentage moisture content was calculated using the formula (Appendix 1);

% Moisture Content of the kernel =

Where W1 = Original weight of the sample before drying

W2 = Weight of the sample after drying.

2.2.3 Extraction of Coconut Oil

Extraction was done using cold extraction. Oil was extracted from the powdered sample

with n- hexane. The solvent mixture was poured into the powdered sample, covered, shaken

vigorously for 5 mins and left for 72 hrs. The mixture was filtered with Whatman no. 1 filter

paper and the solvent evaporated using a distillation apparatus and an oven. The liquid that

left after evaporation is the oil (Fig. 6B). The percentage yield was calculated using the

formula (Appendix 2):

% yield of oil =

Fig. 6: Dehusked coconuts (A) and extracted coconut oil (B)

A B

51

2.2.4 Purification of Crude Coconut Oil

2.2.4.1 Water De-gumming

The extracted crude coconut oil contains phosphatides, gums and other complex compounds

which can promote hydrolysis (increase in free fatty acid) of vegetable oil during storage.

During trans-esterification process, these compounds can also interfere. Therefore these

compounds are removed by water de-gumming process.

This was carried out by measuring 100ml of the extracted oil with a measuring cylinder into

a beaker. The oil and water was heated to 70oC on a water bath separately. As the oil was

stirred gently, the water was poured into the oil. Then, the mixture was stirred for 30 mins

and poured into a separating funnel. The mixture was allowed to stand for 60 mins, two

layers were formed. The lower layer (of phosphatides and other impurities) was run-off,

while the upper layer (of oil) was then run into a steel bowl and oven dried at 105oC for 5 hr

to remove moisture (Fig. 7).

Fig. 7: Coconut oil after degumming and standing in a separating funnel to form two distinct

layers; the upper layer of oil (A) and the lower layer of phosphatides and other impurities

(B)

A B

52

2.2.4.2 Acid Pretreatment

The oil (100ml) was introduced into a 500ml three-necked round-bottomed flask (reaction

flask) attached with a reflux condenser and thermometer; this was then placed in a beaker

containing water. The overall set-up was mounted on a heating magnetic stirrer and the oil

in the reaction flask was heated to 60oC. Concentrated sulfuric acid (0.1ml) was added to

40ml of ethanol in another flask; this was heated to 60°C and added to the reaction flask

containing the pre-heated oil (Zullaikah et al., 2005). This mixture was stirred on heating for

1 hr and without heating for 1 hr. The resulting mixture was then poured into a separating

funnel and allowed to settle for 2 hours. The top layer comprised unreacted methanol,

whereas the middle layer was oil and fatty acid ethyl ester (FAME) (small amount obtained

by conversion of free fatty acids to esters), and water at the bottom layer.

2.2.5 Physicochemical Characterization of the Coconut Oil

2.2.5.1 Physical Characterization of the Coconut Oil

2.2.5.1.1 Determination of the Colour of the Oil

This was determined visually.

2.2.5.1.2 Determination of the Specific Gravity of the Oil

A 4ml aliquot of the oil was weighed and its density calculated using the relationship

Then, the specific gravity of the oil was calculated using the formular (Appendix 3.1):

Specific Gravity =

2.2.5.1.3 Determination of the Viscosity of the Oil

Determination of the viscosity of the oil was done using the method of AOAC (1998). The

oil was gradually poured into the viscometer until its lobe was almost filled and then it was

placed in a water bath and allowed to heat up to an equilibrium temperature of 40oC. The oil

53

on the broad arm was sucked through the narrow arm until it reached the upper mark above

the lower lobe of this narrow arm. The oil was then allowed to flow back to the lower mark

just below the lower lobe. The time taken for the flow (flow time, t) was recorded. Then, the

viscosity was calculated using the formular (Appendix 3.2):

Where n = Viscosity of the oil, mm2/s

v = Viscosity of water, mm2/s

ρ1 = Density of the oil, kg/m3

ρ2 = Density of water, kg/m3

t1 = Time taken for the oil to flow back

t2 = Time taken for water to flow back

2.2.5.1.4 Determination of the Flash Point of the Oil

The flash point of the oil was determined according to the ASTM D 93 open cup method.

The cup was filled with a sample of the oil up to the mark (75ml) and the cup was heated

with a bunsen burner maintaining a small open flame from an external supply of natural gas.

Periodically, the flame was passed over the surface of the oil. When the flash temperature

was reached the surface of the oil caught fire. The temperature (at the moment) was noted

and recorded as the flash point temperature.

2.2.5.1.5 Determination of the Cloud Point of the Oil

The cloud point of the oil was determined according to the ASTM D 5773 method. The

cloud point is a measure of the temperature at which components in the oil begin to solidify

out of the solution.

A test tube with a thermometer inserted in it, was filled with a sample of the oil. The oil was

cooled at 2oC/min rate and continuously monitored until a white cloud appeared on the bulb

of thermometer. The temperature that corresponds to the first formation of a cloud in the oil

was recorded.

54

2.2.5.1.6 Determination of the Pour Point of the Oil

The pour point of the oil was determined according to the ASTM D 97-96a method. A

sample of the oil in a capillary tube was solidified; thereafter, it was attached to a

thermometer and inserted into a gradually heating beaker of water. The temperature at which

the sample started moving in the capillary tube was recorded.

2.2.5.1.7 Determination of the Volatile Matter of the Oil

Determination of the volatile matter of the oil was done using the method of AOAC (1998).

A porcelain crucible which was washed, dried in an oven at 100oC, cooled in a desiccators

and weighed. An aliquot of the oil was transferred into the porcelain crucible, weighed and

then placed in an oven at 105oC for 5 hr to evaporate water. The resulting dry oil was

weighed and heated in a muffle furnace at 600oC for 10 mins. The residue left after heating

was cooled in a dessicator and weighed. The percentage volatile matter was calculated using

the formular (Appendix 3.3):

Volatile Matter =

Where x = Weight of dried oil after oven drying at 105oc

y = Weight of residue after further heating at 600oC

w = Weight of sample (g)

2.2.5.1.8 Determination of the Refractive Index of the Oil

The refractive index of the oil was determined with a refractometer. The power switch was

turned on; the illuminating lamp came up and the display showed 0000. A drop of the oil

was introduced on the working surface of the lower refracting prism. The rotating arm and

the collecting lens cone of the light gathering illuminating units were rotated so as to make

the light-intake surface of the upper light-intake prism to be illuminated evenly. The field of

view was observed through the eye piece and the adjustable hand wheel was rotated so as to

make the line dividing the dark and light areas fall in the cross line. The dispersion

correction hand wheel was rotated so as to get a good contrast between the light and dark

area and minimum dispersion. The read button was pressed and the refractive index was

displayed on the screen.

55

2.2.5.1.9 Determination of the Heat of Combustion of the Oil

The heat of combustion was determined according to the method of AOAC (1998) using a

bomb calorimeter. Benzoic acid was used to standardize the calorimeter. A weighed amount

of a sample of the oil (1.11g) was put in the crucible of the calorimeter and the fuse wire

was attached between the electrodes. Thereafter, it was placed in the bomb, which was

pressurized to 18atm of oxygen. The bomb was placed in a vessel containing a measured

quantity of water (2000g). The ignition circuit was connected and the water temperature was

noted. After ignition, the temperature rise was monitored every minute till a constant

temperature was reached and recorded. The pressure was released, the length of unburned

fuse wire was measured and the residue titrated with 0.7M sodium carbonate solution using

phenolphthalein as indicator. The heat of combustion was calculated using the formular

(Appendix 3.4):

Heat of Combustion = g

VLTE −−∆ 3.2 (KJ/Kg)

Where E = Energy equivalent of the calorimeter using benzoic acid

∆T = Temperature rise

L = Length of burnt wire

V = Titration volume

g = Weight of sample

2.2.5.2 Chemical Characterization of Coconut Oil

2.2.5.2.1 Determination of Acid Value of the Oil

The acid value of the oil was determined according to the ASTM D 664 method. To

determine the acid value of the oil, a 2g aliquot of it was dissolved in 25 ml of 1:1 mixture

of ethanol and diethyl ether. The solution was titrated with 0.1M ethanolic KOH solution in

the presence of 5 drops of phenolphthalein as indicator until the end point (colourless to

pink) was recognized. The volume of 0.1M ethanolic KOH (V) for the sample titration was

noted. The total acidity (acid number) in mg KOH/g was calculated using the following

formular (Appendix 3.5):

56

Acid value =

Where V = Volume of 0.1N solution of ethanolic KOH in milliliter (ml)

m = Weight of the sample in gram

N = Normality of ethanolic KOH

2.2.5.2.2 Determination of Saponification Value of the Oil

The saponification value of the oil was determined using the method of AOAC (1998). The

oil (2.206g) was added to 25ml of 0.5N ethanolic potassium hydroxide solution in a flask to

which a reflux condenser was attached. The mixture was heated, and as soon as the ethanol

boiled, the flask was occasionally shaken using magnetic stirrer until the oil was completely

dissolved, and the solution was boiled for half an hour. After completely dissolving the oil, 5

drops of phenolphthalein indicator was added and the hot soap solution obtained was slowly

titrated with 0.5N hydrochloric acid and volume was recorded.

Then a blank determination was carried out upon the same quantity of potassium hydroxide

solution at the same time and under the same conditions and volume was recorded. The final

result was calculated using the formular (Appendix 3.6):

Saponification value =

Where W= Weight of oil taken in gram.

S = Sample titre value in ml

B = Blank titre value in ml

N = Normality of hydrochloric acid

2.2.5.2.3 Determination of Peroxide Value of the Oil

The Peroxide value of the oil was determined using the method of AOAC (1998). To

determine the peroxide value, 2.206g of the oil was dissolved in 30 ml of a mixture of

glacial acetic acid and chloroform (3:2, v/v). Then, 20% of potassium iodide (0.5 ml) was

added and the solution swirled in the dark for one minute after which 75ml of distilled water

was added. The mixture was titrated with 0.1M sodium thiosulphate with vigorous shaking

until the yellow colour of the iodine had disappeared. Starch indicator (0.5ml) was added

57

then to obtain a blue colour and titration continued until all the blue colour had disappeared.

The peroxide value was calculated from the formular (Appendix 3.7):

Peroxide value =

Where S = Sample titre value in ml

B = Blank titre value in ml

M = Molarity of sodium thiosulphate

2.2.5.2.4 Determination of Iodine Value of the Oil

The iodine value of the oil was determined using the method of AOAC (1998). An aliquot of

the oil (0.8825g) was weighed into a conical flask, tetrachloromethane (15ml) and 25 ml of

Wij’s solution was added. This mixture was placed in a stoppered conical flask, swirled

gently and placed in a dark cupboard for one hour after which 20 ml of 20% potassium

iodide solution and 100ml of distilled water were added. After gentle shaking, liberated

iodine was titrated with 0.1M sodium thiosulphate solution until the yellow colour of the

iodine had appeared. Starch indicator (1ml) was added then to obtain a blue colour and

titration continued until all the blue colour had disappeared. The iodine value was calculated

from the formular (Appendix 3.8):

Iodine value =

Where B = blank titre value in ml

S = sample titre value in ml

M = Molarity of sodium thiosulphate

2.2.5.2.5 Determination of Percentage Free Fatty Acid of the Oil

The percentage free fatty acid of the oil was determined using the method of AOAC (1998).

Two grams of the oil was weighed into a conical flask and 10 ml of 95% ethanol was added.

This was then titrated with 0.1 M sodium hydroxide using phenolphthalein as an indicator.

The conical flask was shaken constantly until a pink colour that persisted for 30 seconds was

obtained. The percentage free fatty acid was calculated from the formular (Appendix 3.9):

58

%Free Fatty Acid =

Where V=Volume of 0.1M sodium hydroxide used in ml

M=Molarity of sodium hydroxide

2.2.6 Trans-esterification of Coconut Oil with Ethanol Using NaOH as Catalyst

This was done using the methods of Ojolo et al. (2011) and Rahayu and Mindaryani (2009).

Ethanolysis reaction was carried out in a 500 ml three-necked round-bottomed flask attached

with a reflux condenser and thermometer and placed in a beaker containing water. The

overall set-up was mounted on a heating magnetic stirrer as shown in Fig. 8A.

Fig. 8: Experimental set-up during trans-esterification and separation of the mixture into

biodiesel (upper layer) (A) and glycerol (lower layer) in a separating funnel (B)

Initially, 50 ml of coconut oil was introduced into the three necked flask which was heated

to the temperature of 65oC. At the same time, but in another flask, 0.2g of NaOH was

dissolved in 150 ml of ethanol and the mixture was heated. When the selected oil

temperature was achieved, the mixture was added to the hot oil under stirring and heating.

The attainment of the selected temperature of the mixture determined the start of the

reaction time. The system was maintained under these conditions during the reaction. At the

end of the process, the mixture was poured into a separating funnel (Fig. 8B), allowing the

A B

59

glycerol and the catalyst to separate from the biodiesel. The glycerol layer and the biodiesel

layer were drained separately. The biodiesel was washed with hot distilled water and dried

with an oven prior to characterization. The percentage yield of the ethyl ester was calculated

from the formular (Appendix 4):

% yield of ethyl ester =

2.2.7 Physicochemical Characterization of the Ethyl Esters Produced

2.2.7.1 Physical Characterization of Ethyl Ester (Biodiesel) Produced

2.2.7.1.1 Determination of the Colour of the Ethyl Ester

This was determined visually.

2.2.7.1.2 Determination of the Specific Gravity of the Ethyl Ester

A 3ml aliquot of the ethyl ester was weighed and its density calculated using the relationship

Then, the specific gravity of the ethyl ester was calculated using the formular (Appendix

5.1):

Specific Gravity =

2.2.7.1.3 Determination of the Viscosity of the Ethyl Ester

Determination of the viscosity of the ethyl ester was done using the method of AOAC

(1998). The ethyl ester was gradually poured into the viscometer until its lobe was almost

filled and then it was placed in a water bath and allowed to heat up to an equilibrium

temperature of 40oC. The ethyl ester on the broad arm was sucked through the narrow arm

until it reached the upper mark above the lower lobe of this narrow arm. The ethyl ester was

then allowed to flow back to the lower mark just below the lower lobe. The time taken for

60

the flow (flow time, t) was recorded. Then, the viscosity was determined using the formular

(Appendix 5.2);

Where n = Viscosity of the ethyl ester, mm2/s

v = Viscosity of water, mm2/s

ρ1 = Density of the ethyl ester, kg/m3

ρ2 = Density of water, kg/m3

t1 = Time taken for the ethyl ester to flow back

t2 = Time taken for water to flow back

2.2.7.1.4 Determination of the Cetane Number of the Ethyl Ester

The cetane number of the ethyl ester was determined according to the ASTM D 613 method.

The cetane number of the ethyl ester was calculated from the empirical formula suggested

by Mohibbe et al. (2005), using the result of saponification value (SV) and the iodine value

(IV) of the ethyl ester (Appendix 5.3):

CN = 46.3+ (5458/SV) - 0.225(IV)

2.2.7.1.5 Determination of the Flash Point of the Ethyl Ester

The flash point of the ethyl ester was determined according to the ASTM D 93 open cup

method. The cup was filled with a sample of the ethyl ester up to the mark (75ml) and the

cup was heated with a bunsen burner maintaining a small open flame from an external

supply of natural gas. Periodically, the flame was passed over the surface of the ethyl ester.

When the flash temperature was reached the surface of the ethyl ester caught fire. The

temperature (at the moment) was noted and recorded as the flash point temperature.

2.2.5.6. Determination of the Cloud Point of the Ethyl Ester

The cloud point of the ethyl ester was determined according to the ASTM D 5773 method.

The cloud point is a measure of the temperature at which components in the ethyl ester

begin to solidify out of the solution.

61

A test tube with a thermometer inserted in it, was filled with a sample of the ethyl ester. The

ethyl ester was cooled at 2oC/min rate and continuously monitored until a white cloud

appeared on the bulb of thermometer. The temperature that corresponds to the first

formation of a cloud in the ethyl ester was recorded.

2.2.7.1.7 Determination of the Pour Point of the Ethyl Ester

The pour point of the ethyl ester was determined according to the ASTM D 97-96a method.

A sample of the ethyl ester in a capillary tube was solidified; thereafter, it was attached to a

thermometer and inserted into a gradually heating beaker of water. The temperature at which

the sample started moving in the capillary tube was recorded.

2.2.7.1.8 Determination of the Ash Content of the Ethyl Ester

Determination of the ash content of the ethyl ester was done using the method of AOAC

(1998). A porcelain crucible which was washed, dried in an oven at 100oC, cooled in a

desiccators and weighed. An aliquot of the ethyl ester was transferred into the porcelain

crucible, weighed and then heated in a muffle furnace at 600oC for 4 hr. The residue left

after heating was cooled in a dessicator and weighed. The percentage ash content was

calculated using the formular (Appendix 5.4):

% Ash Content =

x = Weight of ash

w = Weight of sample

2.2.7.1.9 Determination of Refractive Index of the Ethyl Ester

The refractive index of the ethyl ester was determined with a refractometer. The power

switch was turned on; the illuminating lamp came up and the display showed 0000. A drop

of the oil was introduced on the working surface of the lower refracting prism. The rotating

arm and the collecting lens cone of the light gathering illuminating units were rotated so as

to make the light-intake surface of the upper light-intake prism to be illuminated evenly. The

field of view was observed through the eye piece and the adjustable hand wheel was rotated

62

so as to make the line dividing the dark and light areas fall in the cross line. The dispersion

correction hand wheel was rotated so as to get a good contrast between the light and dark

area and minimum dispersion. The read button was pressed and the refractive index was

displayed on the screen.

2.2.7.1.10 Determination of Conductivity of the Ethyl Ester

The conductivity of the ethyl ester was determined using a conductivity meter. The

conductivity meter was standardized with 0.01M KCl solution. The electrode was rinsed

with deionized water, wiped and dipped into a sample of the ethyl ester and left for some

time to stabilize the reading. The reading was displayed on the screen and then recorded in

micro Siemens per centimeter (µS/cm).

2.2.7.1.11 Determination of Heat of Combustion of the Ethyl Ester

The heat of combustion was determined according to the method of AOAC (1998) using a

bomb calorimeter. Benzoic acid was used to standardize the calorimeter. A weighed amount

of a sample of the ethyl ester (1.058g) was put in the crucible of the calorimeter and the fuse

wire was attached between the electrodes. Thereafter, it was placed in the bomb, which was

pressurized to 18atm of oxygen. The bomb was placed in a vessel containing a measured

quantity of water (2000g). The ignition circuit was connected and the water temperature was

noted. After ignition, the temperature rise was monitored every minute till a constant

temperature was reached and recorded. The pressure was released, the length of unburned

fuse wire was measured and the residue titrated with 0.7M of sodium carbonate solution

using phenolphthalein as indicator. The heat of combustion was calculated using the

formular (Appendix 5.5):

.

Heat of Combustion = g

VLTE −−∆ 3.2 (KJ/Kg)

Where E = Energy equivalent of the calorimeter using benzoic acid

∆T = Temperature rise

L = Length of burnt wire

V = Titration volume

g = Weight of sample

63

2.2.7.2 Chemical Characterization of Coconut Oil

2.2.7.2.1 Determination of Acid Value of the Ethyl Ester

The acid value of the ethyl ester was determined according to the ASTM D 664 method. To

determine the acid value of the ethyl ester, a 3g aliquot of it was dissolved in 25 ml of 1:1

mixture of ethanol and diethyl ether. The solution was titrated with 0.1N ethanolic KOH

solution in the presence of 5 drops of phenolphthalein as indicator until the end point

(colourless to pink) was recognized. The volume of 0.1 N ethanolic KOH (V) for the sample

titration was noted. The total acidity (acid number) in mg KOH/g was calculated using the

following formular (Appendix 5.6):

Acid value =

Where V = Volume of 0.1N solution of ethanolic KOH in milliliter (ml)

m = Weight of the sample in gram

N = Normality of ethanolic KOH

2.2.7.2.2 Determination of Saponification Value of the Ethyl Ester

The saponification value of the ethyl ester was determined using the method of AOAC

(1998). The ethyl ester (2.054g) was added to 25ml of 0.5N ethanolic potassium hydroxide

solution in a flask to which a reflux condenser was attached. The mixture was heated, and as

soon as the ethanol boiled, the flask was occasionally shaken using magnetic stirrer until the

ethyl ester was completely dissolved, and the solution was boiled for half an hour. After

completely dissolving the ethyl ester, 5 drops of phenolphthalein indicator was added and

the hot soap solution obtained was slowly titrated with 0.5N hydrochloric acid and volume

was recorded.

Then a blank determination was carried out upon the same quantity of potassium hydroxide

solution at the same time and under the same conditions and volume was recorded. The final

result was calculated using the formular (Appendix 5.7):

Saponification value =

64

Where W = Weight of oil taken in gram.

S = Sample titre value in ml

B = Blank titre value in ml

N = Normality of hydrochloric acid

2.2.7.2.3 Determination of Peroxide Value of the Ethyl Ester

The Peroxide value of the ethyl ester was determined using the method of AOAC (1998). To

determine the peroxide value, 2.16g of the ethyl ester was dissolved in 30 ml of a mixture of

glacial acetic acid and chloroform (3:2, v/v). Then, 20% of potassium iodide (0.5 ml) was

added and the solution swirled in the dark for one minute after which 75ml of distilled water

was added. The mixture was titrated with 0.1M sodium thiosulphate with vigorous shaking

until the yellow colour of the iodine had disappeared. Starch indicator (0.5ml) was added

then to obtain a blue colour and titration continued until all the blue colour had disappeared.

The peroxide value (PV) was determined from the formular (Appendix 5.8):

Peroxide value =

Where S = Sample titre value in ml

B = Blank titre value in ml

M = Molarity of sodium thiosulphate

2.2.7.2.4 Determination of Iodine Value of the Ethyl Ester

The iodine value of the ethyl ester was determined using the method of AOAC (1998). An

aliquot of the ethyl ester (0.8633g) was weighed into a conical flask, tetrachloromethane

(15ml) and 25 ml of Wij’s solution was added. This mixture was placed in a stoppered

conical flask, swirled gently and placed in a dark cupboard for one hour after which 20 ml of

20% potassium iodide solution and 100ml of distilled water were added. After gentle

shaking, liberated iodine was titrated with 0.1M sodium thiosulphate solution until the

yellow colour of the iodine had appeared. Starch indicator (1ml) was added then to obtain a

blue colour and titration continued until all the blue colour had disappeared. The iodine

value was determined from the formular (Appendix 5.9):

65

Iodine value =

Where B = Blank titre value in ml.

S = Bample titre value in ml

M = Molarity of sodium thiosulphate

2.2.8 Investigation of the Trans-esterification Reaction Rate

2.2.8.1 Experimental Design

The experiment was designed to determine the reaction rate constants for the

transesterification of the following varied oil/ethanol volumetric ratio of 1:6, 1:3, 1:2, 1:1.5

and 1:1. The ethanolysis was conducted at fixed reaction temperature (65oC), catalyst

concentration (0.1g), stirring rate (maximum level of the equipment) and the reaction time of

90 minutes. These conditions were chosen based on the recommendation of Rahayu and

Mindaryani (2009). For each ethanolysis or transesterification, samples of 10mls were

withdrawn at 10, 20, 40, 60 and 90 mins reaction time. The reaction in the sample was

stopped by immersing it in cold water before the glycerol content was analyzed using UV-

visible spectrophotometer.

2.2.8.2 Analysis of Ethyl Ester Using UV-Visible Spectrophotometer

Principle

The amount of free glycerol in biodiesel can be measured with a UV-visible

spectrophotometer using a two-step reaction process according to the method of Bondioli

and Bella (2005). This results in the formation of a yellow complex proportional to the

amount of free glycerol in the sample. The sample is first treated with sodium periodate.

Sodium periodate reacts with free glycerol in the sample to generate formaldehyde. Reaction

between this formaldehyde and acetyl acetone produces the yellow complex, 3,5-diacetyl-

1,4-dihydrolutidine. This yellow compound exhibits a maximum absorbance at 410 nm,

where its concentration in the sample is measured.

66

Procedure

A solvent solution containing a 1:1 ratio of deionized water and 95% ethanol, and a

reference solution of 0.036 mg/ml glycerol in solvent was prepared. A series of six glycerol

reference standards was then prepared from these solutions as shown in Table 5, to obtain a

glycerol standard curve (Appendix 6). A pretreated biodiesel sample was mixed 1:4 with

solvent to get 2 ml of working sample solution.

Table 5: Glycerol standard preparation and absorbance results

standards Glycerol Reference Solution (ml) Solvent Solution (ml) Final Concentration

of Glycerol (mg/kg)

1 0.0 2.00 0.00

2 0.25 1.75 3.75

3 0.50 1.50 7.50

4 0.75 1.25 11.25

5 1.0 1.00 15.00

6 1.25 0.75 18.75

Each working standard and the sample were treated with 1.2 ml of a 10 mM sodium

periodate solution and shaken for 30 secs. Each solution was then treated with 1.2 ml of 0.2

M acetylacetone solution, placed in a water bath at 70 °C for 1 min and stirred manually.

The solutions turned yellow (Fig. 9) and were immediately placed in cold water to stop the

reaction. Absorbance of standards and samples were measured at 410 nm using a UV–

visible spectrophotometer. Standard 1 is a control sample and also used as the blank.

St Fig. 9: Appearance of the yellow colour in the standard and test samples

67

CHAPTER THREE

RESULTS

3.1 Result of Percentage Moisture Content, Oil Yield and Ethyl Ester Yield

Table 6 shows the percentage moisture content of the kernel, the percentage yield of the oil

after extraction and the percentage ethyl ester yield after transesterification of the coconut

oil with ethanol using sodium hydroxide as catalyst. The result revealed the moisture content

of 14.99% while the oil yield and ethyl ester yield were 14.13 and 89.55% respectively.

Table 6: Result of percentage moisture content, oil yield and ethyl ester

Parameter % value

Moisture content of kernel 14.99

Oil yield 44.13

Ethyl ester yield 93.90

68

3.2 Physicochemical Properties of the Coconut Oil

3.2.1 Physical Properties of the Coconut Oil

The physical characterization of the coconut oil extracted gave the physical properties as

summarized in Table 7. The result showed that the coconut oil has a specific gravity of

0.8825 and viscosity of 35.04 mm2/s at 40

oC. The flash point, cloud point and pour point of

oil are 220oC, 24

oC and 23

oC respectively.

Table 7: Physical properties of the coconut oil

Parameter Result

Colour

Specific gravity

Viscosity (mm2/s) at 40

oC

Flash point (oC)

Cloud point (oC)

Pour point (oC)

Volatile matter (%)

Refractive index

Heat of combustion (MJ/kg)

Pale yellow

0.88

35.04

220

24

23

99.72

1.46

35.60

69

3.2.2 Chemical Properties of the Coconut Oil

The chemical properties of the coconut oil in table 8 revealed an acid value of 2.24

mgKOH/g, saponification value of 273.38 mgKOH/g, peroxide value of 3.02 meq/kg, iodine

value of 9.11 mgI2/g and free fatty acid content of 5.64%.

Table 8: Chemical properties of the coconut oil

Parameter

Acid value (mgKOH/g)

Saponification value (mgKOH/g)

Peroxide value (meq/kg)

Iodine value (mgI2/g)

Free Fatty Acid (%)

value

2.24

273.38

3.02

9.11

5.64

70

3.3. Physicochemical Properties of the Coconut Oil Ethyl Ester

3.4.1 Physical Properties of the Coconut Oil Ethyl Ester

Table 9 shows the physical properties of the coconut oil ethyl ester, the result revealed a

specific gravity (0.86), viscosity (6.00 mm2/s), cetane number (71), flash point (132

oC),

cloud point (-5oC), pour point (-10

oC), ash content (0.02%), refractive index (1.43)

conductivity (0.00 µS/cm) and heat of combustion (36.79 MJ/kg).

Table 9: Physical properties of the coconut oil ethyl ester

Parameter Result

Colour

Specific Gravity

Viscosity (mm2/s) at 40

oc

Cetane Number

Flash Point (oC)

Cloud Point (oC)

Pour Point (oC)

Ash Content (%)

Refractive Index

Conductivity (µS/cm)

Heat of Combustion (MJ/kg)

colourless

0.86

6.00

71

132

-5

-10

0.02

1.43

0.00

36.79

71

3.3.2 Chemical Properties of the Coconut Oil Ethyl Ester

Table 10 shows the chemical properties of the coconut oil ethyl ester. The result revealed an

acid value of 0.25 mgKOH/g, saponification value of 218.08 mgKOH/g, peroxide value of

1.50 meq/kg and iodine value of 1.91 mgI2/g.

Table 10: Chemical properties of the coconut oil ethyl ester

Parameter

Acid value (mgKOH/g)

Saponification value (mgKOH/g)

Peroxide value (meq/kg)

Iodine value (mgI2/g)

value

0.25

218.08

1.50

1.91

72

3.4 Investigation of the Trans-esterification Reaction Rate

The progress curve for the trans-esterification of varied oil/ethanol volumetric ratio of 1:6,

1:3, 1:2, 1:1.5 and 1:1, showed that as the reaction time increased the concentration of

glycerol produced during the reaction increased (indicating progress of the reaction) until it

came to a point at which the curve became horizontal (indicating the end point/ completion

of the reaction or depletion of the oil) as presented in Fig.10 to 14. The determinations of the

rate constant are shown in Appendix 7.1 to 7.5.

The 1:6 oil/ethanol volumetric ratio trans-esterification showed that increase in the reaction

time was accompanied by increase in glycerol concentration at the rate of 0.415 mg/kg/min

for 40 mins, after which subsequent increase in the reaction time gave little or no increase in

the concentration of glycerol.

It was observed in the 1:3 oil/ethanol volumetric ratio trans-esterification that as the reaction

time increased, the concentration of glycerol increased at the rate of 0.3616 mg/kg/min for

60 mins. Thereafter, little increase was observed as the reaction time increased to 90 mins.

The progress curve for 1:2 oil/ethanol volumetric ratio trans-esterification showed that

increase in the reaction time gave increase in the concentration of glycerol at the rate of

0.2135 mg/kg/min for 60 mins reaction time, after which the glycerol concentration showed

no increase on further increase if the reaction time. A slight decrease was observed at 40

mins reaction time.

The 1:1.5 oil/ethanol volumetric ratio trans-esterification showed that increase in the

reaction time was accompanied by increased glycerol concentration at the rate of 0.1833

mg/kg/min 60 mins, after which subsequent increase in the reaction time gave little or no

increase in the concentration of glycerol.

It was observed that the 1:1 oil/ethanol volumetric ratio trans-esterification proceeded at the

rate of 0.1006 mg/kg/ min for 60 mins. Thereafter, the concentration of glycerol remained

fairly constant on further increase of the reaction time.

73

3.4.1. Progress Curves for the Trans-esterification of Varied Oil/Ethanol Volumetric

Ratio

Fig. 10: Progress curves for the trans-esterification of the varied oil/ethanol volumetric ratio

1:6

1:3

1:2

1:1.5

1:1

74

3.5 Reaction Rate Constant for varying Oil-to-Ethanol Volumetric Ratios

Fig. 15 shows the oil to ethanol ratio-dependent increase in the specific rate constant. The

highest reaction rate constant (0.415) was observed in 1:6 oil to ethanol volumetric ratio

while the lowest (0.1006) was observed in 1:1 oil to ethanol volumetric ratio.

Fig. 15: Reaction rate constant for varying oil-to-ethanol volumetric ratios

75

3.6 Determination of Kinetic Parameters (km and vmax) of the Trans-esterification

Reaction

The result obtained from the effect of varied oil to ethanol ratio on NaOH catalysed trans-

esterification was used for the Lineweaver-Burk plot. The kinetic parameter (km and vmax)

of the NaOH catalysed trans-esterification were calculated from the Lineweaver-Burk plot.

Fig. 16 revealed that the km and vmax of the reaction are 6.25 ml/ml ratio and 0.94

mg/kg/min respectively. [S] Represent ethanol volumetric ratio.

Fig. 16: Lineweaver-Burk plot of NaOH catalysed trans-esterification reaction

76

CHAPTER FOUR

DISCUSSION

The moisture content is an important parameter as it affects the percentage yield of the oil

during extraction. High moisture content could lead to reduction of oil yield (Mansor, et al.,

2012). The percentage moisture content of the coconut kernel was found to be 14.99%; the

high moisture content of the coconut kernel lead to the sun-drying of the kernel before

extraction in order to obtain optimum yield. Afolabi (2008) observed that the moisture

content of the coconut oil was found to be lower than that of fresh groundnut (37.002%) but

higher to those of almond nut (5.006%), castor seed (3.500%) and palm kernel seed

(4.870%). Oil was extracted from coconut (Cocos nucifera) copra using n-hexane. The yield

of the oil extracted from the coconut was 44.13%. The oil yield of the seeds as suggested by

the result, showed that coconut (Cocos nucifera) seeds have higher oil yield than fluted

pumpkin seed (33.732%), soybean (36%). This result is consistent with the findings of Eze

(2012) who observed that the value was almost the same to that of palm kernel (45.60 %)

and may be considered economical for commercial production of oil in Nigeria.

The physical characterization of the coconut oil showed a pale yellow colour. The colour

was the same with that reported by Akubugwo et al. (2008) and Eze (2012) for coconut oil.

The specific gravity of the oil was 0.88. This value was found to be slightly lower than that

reported by Alamu et al. (2010) for coconut oil (0.91), Lang, et al. (2001) for canola oil

(0.912) and sunflower oil (0.914); this could be due to location and variation in speices. The

result was almost the same with that of jatropha oil (0.8813) as reported by Belewu et al.

(2010). Viscosity of oil is the measure of the resistance of the oil to flow (Sanford et al.,

2009). The viscosity of the coconut oil at 40oC was found to be 35.04 mm

2/s; this high

viscosity of vegetable oils and animal fats ultimately lead to operational problems such as

engine deposits when used directly as fuels (Knothe and Steidley, 2005a). The viscosity of

the coconut oil was found to be lower to those of rapeseed oil (45.01 mm2/s) as reported by

Lang et al. (2001) and coconut oil at room temperature (43.30 mm2/s) as observed by Alamu

et al., (2010), but was higher than that reported by Kumar, et al., (2010) for coconut oil

(27.23mm2/s), Jatropha curcas oil (20.49 mm

2/s) and linseed oil (22.4 mm

2/s) as reported

by Belewu et al. (2010) and Lang, et al. (2001) respectively. The flash point is the lowest

77

temperature at which the oil emits enough vapour to ignite and it is a measure of the

volatility and flammability of the oil (Bello et al., 2011). The flash point of the oil was

220oC; the high flash point of the oil was as a result of its high viscosity. The flash point was

found to be low when compared to that reported by Kumar, et al. (2010) for coconut oil

(266oC) and sunflower oil (274

oC) as observed by Shereena and Thangaraj (2009), but was

higher than that of Babassu (150oC) as reported by Shereena and Thangaraj (2009). The

volatile matter is the measure of the true organic matter in the oil and gives information on

the volatility of the oil. This was found to be 99.72% for the coconut oil and implies that the

oil contains high amount of volatile organic matter which is an advantage for its use for

biodiesel production. The volatile matter of the coconut oil was found to be higher than that

observed by Ozioko (2012) for soya bean oil (72.27%) and Danish pine as reported by

Jahirul et al. (2012).

The cloud point is the temperature at which crystals first appear in the oil when cooled

(Dermirbas, 2009). This was found to be 24oC for the coconut oil and this implies that the

oil cannot be used in low temperature regions. The cloud point was high when compared to

that of peanut oil (12.8oC) and safflower oil (18.3

oC) as reported by Shereena and Thangaraj

(2009) but lower to that of palm (31oC) as observed by Shereena and Thangaraj (2009). The

pour point of oil is the lowest temperature at which the oil can flow (Dermirbas, 2009). This

was found to be 23oC for the coconut oil which also implies that the oil cannot be used

directly as fuel in regions where the temperature is below 23oC. The pour point was much

higher than that reported by Kumar, et al. (2010) for coconut (-6oC) soya bean (12.2

oC) by

the findings of Shereena and Thangaraj (2009) and most of other vegetable oils. The high

cloud and pour point of coconut oil indicates that the oil contains high proportion of

saturated fatty acids.

The heat of combustion measures the energy content in a fuel. It is an important property of

the biodiesel that determines the suitability of the fuel as an alternative diesel fuel (Sokoto et

al., 2011). The heat of combustion of the coconut oil was found to be 35.60MJ/kg. This

result is supported by the findings of Lang et al. (2001) which observed that this value was

found to be lower than those of canola oil (39.78 MJ/kg), sunflower oil (39.46 MJ/kg),

rapeseed oil (40.27 MJ/kg) and linseed oil (39.51 MJ/kg). The refractive index is the ratio

78

of the velocity of light in vacuum to the velocity of light in a medium which is an indication

of the level of saturation of the oil and also gives information on the purity of the oil

(Oderinde et al., 2009). The refractive index of the coconut oil found to be was 1.46, this

value was high when compared to that reported by opoku-Boahen et al. (2012) for coconut

oil (1.4450) and the recommended range for coconut oil by the Codex Standards (1.448-

1.450). The slight increase above the Codex Standard could be as a result of some impurities

and other components of the oil mixture.

This low value may be due to little or absence of water and low level of free fatty acids.

Thus, acid value is a measure of free fatty acid content due to hydrolytic activity and it

assesses the quality of the oil (Afolabi, 2008). The acid value was lower than that of coconut

oil (9.537 mgKOH/g) and groundnut oil (3.82 mgKOH/g) as reported by Opoku-Boahen et

al. (2012), but higher than those of castor seed oil (0.279 mgKOH/g), palm kernel seed oil

(0.834 mgKOH/g) and almond oil (0.770 mgKOH/g) as reported by Afolabi (2008).

Similarly, the value was almost the same to that reported by Kumar, et al. (2010) for

coconut oil (2.1 mgKOH/g). The percentage free fatty content was found to be 5.64%. The

value is higher than that reported by Akubugwo et al. (2008) for coconut oil (4.80%) and

other edible oils such as pumpkin (1.98%), breadfruit seed oil (4.22%) and oil bean seed oil

(1.40%), but was lower than that of Jatropha oil (14.8%) based on the search findings of

Mohammed-Dabo et al. (2012) and almost the same to that of avocado seed oil (5.77%) as

observed by Akubugwo et al. (2008). However, if the oil samples have high Free Fatty Acid

content (more than 1%) then the reaction requires more alkali catalyst to neutralize the Free

Fatty Acid or pretreatment with an acid catalyst (Zhang et al., 2003a). This suggests that

there should be acid pretreatment of the oil prior to base catalysed trans-esterification.

Saponification value is a measure of the average molecular weight or the chain length of the

fatty acids present in the oil (Sanford et al., 2009). It had been reported to be inversely

related to the average molecular weight of the fatty acids in the oil fractions (Abayeh et al.,

1998). The saponification of the coconut oil was found to be 273.38 mgKOH/g; this high

value implies a low average molecular weight. Akubugwo et al. (2008) had observed lower

saponification value (246 mgKOH/g) compared with value reported in this study. In the

same vien, similar trend was reported for jatropha seed oil (202.34 mgKOH/g) (Mohammed-

79

Dabo et al., 2012), palm kernel oil (191.97 mgKOH/g) (Afolabi, 2012) and bread fruit oil

(221.59mgKOH/g) (Eze, 2012).

Iodine value is a measure of the degree of unsaturation of the oil (Belewu et al., 2010). The

iodine value of the coconut oil was found to be 9.11 mgI2/g. This value was found to be

within the recommended range for coconut oil by the Codex Standards (6.3-10.6 mgI2/g)

and almost the same to that reported by Akubugwo et al. (2008) for coconut oil (9.60

mgI2/g) but lower than that of fluted pumpkin seed oil (49.4 mgI2/g) as observed by

Akubugwo et al. (2008). The low iodine value is indicative of low content of unsaturated

fatty acids. Peroxide value is an indicator of deterioration and oxidative stability/rancity

(Eze, 2012) of the oil. Fresh oils have peroxide values less than 10 meq/kg but peroxide

values between 20 and 40 result to rancid taste (having a disagreeable odour) (Akubugwo et

al., 2008). The peroxide value of the coconut oil was found to be 3.02 meq/kg; this low

value could have resulted from low content of unsaturated fatty acids in the oil, proper

storage and handling of the oil during and after extraction to avoid contaminants and factors

that enhance autoxidation of the oil. The peroxide value was lower when compared to that

reported for coconut seed oil (10.562 meq/kg), soya bean oil (16.32meq/kg), melon oil

(8.386 meq/kg) and palm kernel oil (7.96meq/kg) (Eze, 2012), but higher than those of

breadfruit (1.75meq/kg), oil bean (2.35meq/kg) (Akubugwo et al., 2008) and groundnut seed

oil (1.03meq/kg) (Eze, 2012).

Anastopoulos et al. (2009) revealed that the coconut oil ethyl ester yield was higher than

those of rapeseed ethyl esters yield (81.4%), olive oil ethyl esters (82.6%) while Alamu et

al. (2012) showed that coconut oil methyl esters yield was (10.4%). However, Rashid et al.

(2010) showed lower value compared to that of jatropha oil methyl esters (96.8%).

The physical characterization of the coconut oil ethyl esters showed a colourless colour. The

specific gravity of the coconut ethyl ester was 0.86; this value was lower than that of the oil.

The specific gravity obtained was found to be within the limits of EN 14214 (0.86 – 0.90)

biodiesel fuel standard. The specific gravity was found to be lower than those of palm kernel

oil ethyl esters (0.883), rapeseed oil ethyl esters (0.876) (Alamu et al., 2008), and sunflower

oil ethyl esters (0.876) (Lang et al., 2001), but was higher than that of petrol diesel (0.853)

80

(Alamu et al., 2008) and almost the same with that of canola oil ethyl esters (0.869) (Lang et

al., 2001). The viscosity of the coconut oil ethyl esters at 40 °C was 6.00 mm2/s; this value

is far lower than that of the oil, but was found to be within the limits of ASTM D6751 (1.9 –

6.0 mm2/s) biodiesel fuel standard. The viscosity of the coconut oil ethyl ester was found to

be higher than those of Jatropha oil biodiesel (4.80 mm2/s) as report by Rashid et al. (2012),

canola oil ethyl esters (4.892 mm2/s) (Alamu et al., 2008), olive oil ethyl esters (4.00

mm2/s), (Anastopoulos et al., 2009), but slightly higher than that of rapeseed ethyl esters

(6.170 mm2/s) (Alamu et al., 2008). The flash point of the coconut oil ethyl ester was 132

oC;

this value was lower than that of the oil due to the low viscosity of ethyl ester. The value

was also found to be above the minimum value (120 °C) of the EN 14214 and (130oc) of the

ASTM D6751 biodiesel fuel standard. The flash point of the coconut oil ethyl ester was

reported by Alamu et al. (2008) to be lower than that of palm kernel oil biodiesel (167°C)

but was higher than those of canola ethyl esters (177oC), sunflower ethyl esters (178

oC),

olive ethyl ester (182oC), and rapeseed ethyl ester (181

oC) as observed by Anastopoulos et

al. (2009). In the same vein, Alamu et al. (2008) found out that the flash point was

extremely higher than that of petrol diesel with a value of 74°C. These relatively higher

flash point values of coconut oil ethyl ester is indicative of the presence of little or no

residual alcohol and is of prime importance for prevention of fire outbreak in the compressor

engine when used as fuel, also important for storage and transportation of the fuel (Moser,

2009).

The cloud point of the coconut oil ethyl ester was -5oC and this was far lower than that of

the oil, but was within the limits of ASTM D6751 (-3 to 12oC) biodiesel fuel standard.

Alamu et al. (2008) reported that the cloud point was higher compared to that of canola

ethyl esters (-6oC), rapeseed ethyl esters (-10

oC) and extremely higher than that of petrol

diesel (-12oC) but lower to those of palm kernel oil biodiesel (6

oC), kumar et al. (2010)

reported -3oC for coconut methyl esters and Lang et al. (2001) reported -1

oC for sunflower

ethyl ester. The pour point of the coconut oil ethyl ester was found to be -10oC; this was also

far lower than that of the oil. The lowered pour point and cloud point implies that the

coconut oil ethyl ester can be used as fuel in regions where the temperature is within the

range of -5 to -10oC. The pour point of the coconut oil ethyl ester was found to be within the

81

limits of ASTM D 6751 (-15 to 10oC) biodiesel fuel standard. The value was lower

compared to those of sunflower ethyl esters (-6oC), rapeseed ethyl esters (-8

oC) and olive

ethyl esters (-5oC) as reported by Anastopoulos et al. (2009), but higher than that of petrol

diesel which is -12oC as shown by Alamu et al. (2008) and coconut methyl esters (12

oC)

being reported by Kumar et al. (2010).

Bello et al. (2011) pointed out that cetane number is one of the primary indicators of a good

diesel fuel quality and is related to the ignition delay time a fuel experiences once injected

into a diesel engine combustion chamber. The coconut oil biodiesel had empirically

calculated cetane number of 71 which is above the minimum value of the ASTM D6751 (40

minimum) and EN 14214 (51 minimum) international biodiesel fuel standards. The cetane

number of the coconut oil biodiesel (ethyl ester) was found to be higher than some

conventional biodiesels such as jatropha oil biodiesel (55) (Reddy and Ramesh, 2005), waste

cooking oil biodiesel (10.96) (Owolabi et al., 2011) and that reported for coconut biodiesel

(51) (Kumar, et al., 2001). Thus, the higher cetane number of coconut oil ethyl ester

indicates a shorter ignition delay time.

The ash content is a measure of the amount of residue left when the fuel is heated to 600oC

(Sanford et al., 2009); this was found to be 0.02% for the coconut oil ethyl ester. The ash

content of the coconut oil ethyl ester was found to be above the limit of ASTM D 6751

(0.01%), but was within the limit of EN 14214 (0.02%) biodiesel fuel standard. The ash

content of the coconut oil ethyl ester was also comparable to that of jatropha (0.016%) as

reported by Rashid et al. (2010). The slight increase of the ash content of the coconut oil

ethyl ester above the biodiesel fuel standard could be as a result of the presences of little

amount of metal contaminants. The heat of combustion of the coconut oil ethyl ester was

36.79 MJ/kg. Although, this value was lower than that of petrol diesel (45MJ/kg) as reported

by Lang et al. (2001), the heat of combustion of the coconut oil ethyl ester was comparable

to those of sunflower (38.6 MJ/kg), olive oil ethyl ester (39.2 MJ/kg) (Anastopoulos et al.,

2009) rapeseed oil ethyl ester (40.97 MJ/kg) and linseed oil ethyl ester (39.65 MJ/kg) as

reported by Lang et al. (2001).

82

This value was almost the same to that of palm oil methyl ester (1.430) and ghee methyl

ester (1.431) (Deshpande and Kulkarni, 2012), but lower than that of groundnut oil methyl

ester (1.463; Ibeto et al., 2011).The refractive index of petrodiesel was found to be 1.425

and from observations, biodiesel has refractive index of 1.430 to 1.431; these values indicate

that heavier molecules get converted into lighter one during transesterification process

(Deshpande and kulkarni, 2012). The slight increase above the normal range could be as a

result of the presence of some impurities. Conductivity is a measure of the ability of water to

pass an electrical current, it is indicative of the presence of water in the biodiesel (Sanford et

al., 2009). The conductivity of the ethyl ester was 0.00 µS/cm, this could be due to proper

drying and short storage time before the test was carried out.

The acid values of the coconut oil ethyl ester was found to be within the limits of the ASTM

D6751 (0.5 mgKOH/g maximum) and EN 14214 (0.5 mgKOH/g maximum) biodiesel fuel

standards and almost the same to that of canola oil ethyl ester (0.265 mgKOH/g) (Lang et

al., 2001). The acid value of the coconut oil ethyl ester was lower to those of sunflower oil

ethyl ester (0.610 mgKOH/g), linseed oil ethyl ester (0.324 mgKOH/g) as observed by Lang

et al. (2001) and rapeseed oil ethyl ester (1.02 mgKOH/g) as reported by Anastopoulos et al.

(2009). The acid value of the coconut oil ethyl ester was also lower to that of its oil but

higher than that reported for coconut oil methyl ester (0.18 mgKOH/g) as observed by

Kumar et al. (2010). The low acid value of the coconut oil ethyl ester indicates that the fuel

contains relatively little or no water which could hydrolyse the biodiesel to free fatty acids.

It could also indicate that the acid pretreatment done reduced the free fatty to the minimal.

This high value, though, lower than that of the coconut oil, indicates a low average

molecular weight. The saponification value of the coconut oil ethyl ester was found to be

higher than that of sunflower oil ethyl ester (192.1 mgKOH/g), rapeseed oil ethyl ester

(170.4 mgKOH/g), olive oil ethyl ester (196.2 mgKOH/g) and used frying oil ethyl ester

(193.2 mgKOH/g) (Anastopoulos et al., 2009).

The iodine value of the coconut oil ethyl ester was found to be 1.91 mgI2/g; this implies

lower degree of unsaturation and better oxidative stability of the coconut oil ethyl ester. The

iodine value of the coconut oil ethyl ester was found to be within the limits of EN 14214

83

(120 mgI2/g maximum) biodiesel fuel standard, but was lower than that of Jatropha methyl

ester (104 mgI2/g) (Singh and Padhi, 2009). The peroxide value of the coconut oil ethyl

ester was 1.50 meq/Kg. This value was lower when compared to that of the coconut oil and

groundnut oil methyl ester (3.23 meq/kg) as reported by Ibeto et al. (2011). The low

peroxide value of the coconut oil ethyl ester could be as a result of low level of unsaturated

fatty acids (as indicated by the iodine value of the ethyl ester). Also, proper storage and

handling of the coconut oil ethyl ester to avoid contaminants and factors that enhance

autoxidation could have contributed to the low peroxide value.

The investigation of the reaction rate constant of the trans-esterification of the varied oil to

ethanol volumetric ratio of 1:6, 1:3, 1:2, 1:1.5 and 1:1 showed that as the oil-to-ethanol

volumetric ratio increases from 1:1 to 1:6 the rate of trans-esterification increases with the

highest reaction rate constant of 0.415 at a ratio of 1:6 oil to ethanol. This could be due to

the fact that in a reversible reaction such as that of trans-esterification, at equilibrium, there

is a balance between the concentration of the reactants and products. If the volume of

ethanol is increased or more reactants are introduced into the equilibrium system, the

balance is disturbed. In order to relieve this restriction, the equilibrium position will shift to

the right, favouring the forward reaction or production of more esters as proposed product

(Dorado et al., 2004). This gives trans-esterification reaction an upper hand over

saponification (a side reaction of the process). However, a greater portion of the oil becomes

trans-esterified thereby resulting in higher concentration of glycerol/ high reaction rate

constant as seen as the oil to ethanol ratio increases from 1:1 to 1:6 (Figs 10 to 14). This

finding is in agreement with the work of Hossain and Al-saif (2010) where the effect of

volumetric ratio of oil to methanol and ethanol was investigated using percentage yield of

biodiesel. The results showed that the highest biodiesel yield was nearly 99.5% at 1:6

oil/methanol and 98.0% at 1:6 oil/ethanol. The work of Ehiri (2012) indicates that the yield

increases with increase in reactant ratio from 1:1 to 8:1 and decsreases thereafter from 9:1 to

10:1; with an optimal methyl ester yield of 95% occurred at 8:1 methanol: oil volume ratio.

The trans-esterification of coconut oil with ethanol using NaOH as catalyst also showed that

the reaction was almost completed after 1 hr, beyond this gave a small ethyl ester yield with

exception of the 1:6 volumetric ratio trans-esterification that was almost completed before 1

84

hr reaction time. This is in agreement with the work of Krishnakumar et al. (2008) where the

effect of reaction time was studied from 45 minutes to 120 minutes on the methyl ester

(biodiesel) yield. It was found that ester yield increased as the reaction time increases.

However if the reaction time is increased beyond 1 hour, the increase in the yield of ester is

small.

The catalysis of NaOH in the trans-esterification reaction was described using enzyme

kinetics (Lineweaver-Burk plot) owing to the fact that both are catalyst. Thus, it increases

the rate of a reaction without itself being consumed by the process. The kinetic parameters

from the Lineweaver-Burk plot were found to be 0.94 mg/kg/min and 6.25 ml/ml ratio (oil

to ethanol ratio) for Vmax and Km respectively. The Vmax (maximum velocity/rate) is the

maximum attainable rate of the reaction. The Vmax gives information on the rate at which

the product is formed (turnover number) (Anosike, 2001). It also gives information on how

efficient a catalyst is, in catalyzing a particular reaction. The Km or Michealis constant is the

substrate concentration at half the maximum velocity/rate (Vmax). It establishes the

relationship between the catalyst and its affinity for its substrate. A small Km value indicates

that the catalyst requires only a small amount of the substrate to become saturated; hence,

the maximum velocity is reached at relatively low substrate concentration while a large Km

indicates the need for high substrate concentration to achieve the maximum velocity

(Anosike, 2001).

4.2 Conclusion

The results obtained suggest that the coconut oil could be considered a viable raw material

for biodiesel production; this is due to the fact that its ethyl ester (biodiesel) meets the

standard specification of the American Society for Testing and Material (ASTM). The base

catalyzed transesterification reaction of coconut oil with ethanol gave higher yield of

biodiesel at higher oil to ethanol volume ratios. HoweverS, it is advised to increase the

concentration/volume of the alcohol than that of the oil because increase in the oil

concentration/volume favours saponification reaction which is a side reaction to the overall

process. This side reaction depletes the oil in the reaction; thereby, reducing the yield of

biodiesel.

85

4.3 Suggestions for Further Studies

Based on the findings of this work, the following suggestions are made for further studies:

• Process optimization study of ethanolysis of coconut oil using 1:6 oil/ethanol ratio,

such as the best amount of catalyst, temperature, reaction time, and/or agitation

intensity for the transesterification reaction.

• Further research on the use of variety of tools such as plant breeding, molecular

breeding, genetic modification and biotechnology as potential strategy for the

improvement of oil yield of coconut and fuel properties of coconut oil biodiesel, to

meet the increasing demand of biodiesel and food needs (since it an edible oil).

86

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APPENDICES

Appendix 1: Percentage Moisture Content of the Kernel

Original weight of the sample before drying (W1) = 10.2

Weight of the sample after drying (W2) = 8.87

% Moisture Content = = = 14. 994%

Appendix 2: Percentage Yield of Oil

% yield of oil =

= =44.125%

Appendix 3: Calculations for physicochemical characterization of oil

3.1 Specific Gravity of Oil

Density of oil =

= =0.8825g/ml

Specific Gravity of oil =

= = 0.8825

3.2 Viscosity of Oil

Viscosity of the oil at 40oc =

100

ν= viscosity of water = 1.005

ρ1=density of sample = 0.8825g/ml

ρ2= density of water = 1.00g/ml

t1=time taken for sample to flow back = 1987 sec

t2=time taken for water to flow back = 50.3 sec

=

= 35.04cst = 35.04mm2/s

3.3 Percentage Volatile Matter of Oil

Weight of empty crucible = 10.014g

Weight of empty crucible + sample = 13.204g

Weight of sample (w) = 3.190g

Weight of crucible + dry matter after oven drying for 5hrs at 105oc = 13.199

Weight of dried oil after oven drying at 105oc (x) = 3.185g

Weight of crucible + residue after drying in the furnace for 10mins at 600oc = 10.018

Weight of residue after further heating at 600oC (y) = 0.004

% volatile matter =

= = 99.72%

3.4 Heat of Combustion of Oil

Initial temperature = 30.218

Final temperature = 32.978

Energy equivalent of the calorimeter (E) = 13039.308

Temperature rise (∆T) = 32.978-30.218 = 2.760

101

Length of unburnt wire = 3.9+3.5 =7.4cm

Length of burnt wire (L) = 10-7.4 = 2.6cm

Titration volume (V) = 4.3

Weight of sample (g) = 1.011

Heat of Combustion = g

VLTE −−∆ 3.2 = =

35595.312kJ/kg

= 35.595MJ/kg

3.5 Acid Value of Oil

Volume of KOH 1st 2nd 3rd

Initial reading 32.00 33.00 40.00

Final reading 32.90 33.80 40.70

difference 0.90 0.80 0.70

Average titre = = 0.8

Acid Value = = = 2.244

3.6 Saponification Value of Oil

Volume of HCl (ml) Sample blank

1st 2nd 3rd 1st 2nd 3rd

Initial reading 22.50 23.40 24.10 17.50 10.00 16.50

Final reading 23.40 24.10 24.70 40.00 32.20 38.50

difference 0.90 0.70 0.60 22.50 22.20 22.00

Average titre for sample = = 0.7333ml

Average titre for sample = = 22.233ml

102

Saponification value = =

=273.38

3.7 Peroxide Value of Oil

Volume of sodium

thiosulfate (ml)

Sample blank

1st 2nd 3rd 1st 2nd 3rd

Initial reading 18.20 17.90 18.60 14.30 14.10 15.50

Final reading 18.60 18.20 18.80 14.70 14.30 15.60

difference 0.40 0.30 0.20 0.40 0.20 0.10

Average titre for sample = = 0.3ml

Average titre for blank = = 0.2333ml

Peroxide value = = = 3.024meq/kg

3.8 Iodine Value of the Oil

Volume of

sodium

thiosulfate (ml)

Sample blank

1st 2nd

3rd 1st 2nd 3rd

Initial reading 0.00 0.00 0.00 0.00 0.00 0.00

Final reading 39.50 40.10 40.90 45.00 48.20 46.30

difference 39.50 40.10 40.90 45.00 48.20 46.30

Average titre for sample = = 40.167ml

Average titre for blank = = 46.5ml

Iodine value = = = 9.107

103

3.9 Percentage Free Fatty Acid of Oil

Volume of KOH 1st 2nd 3rd

Initial reading 34.00 35.00 36.00

Final reading 34.50 35.40 36.30

difference 0.50 0.40 0.30

Average titre = = 0.4

% Free Fatty = = = 5.64%

Appendix 4: Percentage Yield of Ethyl Ester

% yield of ethyl ester =

= =93.90%

Appendix 5: Calculations for the physicochemical characterization of the Ethyl Ester

(biodiesel)

5.1 Specific Gravity of the Ethyl Ester

Density of ethyl ester =

= =0.8633g/ml

Specific Gravity Ethyl Ester =

= = 0.8633

104

5.2 Viscosity of the Ethyl Ester

Viscosity of the Ethyl Ester at 40oc =

=

ν= viscosity of water = 1.005

ρ1=density of sample = 0.8825g/ml

ρ2= density of water = 1.00g/ml

t1=time taken for sample to flow back = 1987 sec

t2=time taken for water to flow back = 50.3 sec

=

= 6.00cst = 6.00mm2/s

5.3 Cetane Number of the Ethyl Ester

CN = 46.3+ (5458/SV) - 0.225(IV)

= 46.3+ (5458/218.076) - 0.225(1.911)

= 71.7972-0.429975 = 70.897997 = approximately 71

5.4 Percentage Ash Content of Ethyl Ester

Weight of empty crucible = 9.535g

Weight of empty crucible + sample = 13.659g

Weight of sample (w) = 4.124g

Weight of crucible + ash after drying in the furnace for 5hrs at 600oc = 9.536

Weight of ash (x) = 0.001

% ash content =

= = 0.02%

105

5.5 Heat of Combustion of Ethyl Ester

Initial temperature = 30.865

Final temperature = 33.851

Energy equivalent of the calorimeter (E) = 13039.308

Temperature rise (∆T) = 2.986

Length of unburnt wire = 2.7+3.2 =5.9cm

Length of burnt wire (L) = 10-5.9 = 4.1cm

Titration volume (V) = 5.4

Weight of sample (g) = 1.058

Heat of Combustion = g

VLTE −−∆ 3.2 = = 36,786.90kJ/kg

= 36.786MJ/kg

5.6 Acid Value of Ethyl Ester

Volume of KOH 1st 2nd 3rd

Initial reading 20.00 21.00 22.00

Final reading 20.20 21.10 22.10

difference 0.20 0.10 0.10

Average titre = = 0.133

Acid Value = = = 0.25mgKOH/g

106

5.7 Saponification Value of Ethyl Ester

Volume of HCl (ml) Sample blank

1st 2nd 3rd 1st 2nd 3rd

Initial reading 17.9 24.40 30.6 17.50 10.00 16.50

Final reading 24.4 30.60 36.00 40.00 32.20 38.50

difference 6.50 6.20 6.00 22.50 22.20 22.00

Average titre for sample = = 6.2333ml

Average titre for sample = = 22.233ml

Saponification value = =

=218.076mgKOH/kg

5.8 Peroxide Value of Ethyl Ester

Volume of sodium

thiosulfate (ml)

Sample blank

1st 2nd 3rd 1st 2nd 3rd

Initial reading 18.20 17.90 18.60 14.30 14.10 15.50

Final reading 18.60 18.20 18.80 14.70 14.30 15.60

difference 0.30 0.30 0.20 0.40 0.20 0.10

Average titre for sample = = 0.2667ml

Average titre for blank = = 0.2333ml

Peroxide Value = = =1.5meq/kg

107

5.9 Iodine Value of the Ethyl Ester

Volume of sodium

thiosulfate (ml)

Sample blank

1st 2nd 3rd 1st 2nd 3rd

Initial reading 0.00 0.00 0.00 0.00 0.00 0.00

Final reading 44.70 45.40 45.50 45.00 48.20 46.30

difference 44.70 45.40 45.50 45.00 48.20 46.30

Average titre for sample = = 45.2ml

Average titre for blank = = 46.5ml

Iodine Value = = = 1.911mgI2/g

Appendix 6: Glycerol Standard Curve

108

Appendix 7: Determination of Rate of Constant of the Progress Curves

7.1 Determination of Rate Constant for 1:6 Oil/Ethanol Volumetric Ratio

Transesterification

7.2 Determination of Rate Constant for 1:3 Oil/Ethanol Volumetric Ratio

Transesterification

109

7.3 Determination of Rate Constant for 1:2 Oil/Ethanol Volumetric Ratio

Transesterification

7.4 Determination of Rate Constant for 1:1.5 Oil/Ethanol Volumetric Ratio

Transesterification

110

7.5 Determination of Rate Constant for 1:1 Oil/Ethanol Volumetric Ratio

Transesterification