advancements in development and characterization of biodiesel a review

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Fuel 87 (2008) 2355–2373

Review article

Advancements in development and characterizationof biodiesel: A review

Y.C. Sharma a,*, B. Singh a, S.N. Upadhyay b

a Environmental Engineering and Research Laboratories, Department of Applied Chemistry, Institute of Technology, Banaras Hindu University,

Varanasi, UP 221 005, Indiab Department of Chemical Engineering and Technology, Institute of Technology, Banaras Hindu University, Varanasi, UP 221 005, India

Received 7 November 2007; received in revised form 21 January 2008; accepted 22 January 2008Available online 20 February 2008

Abstract

An ever increasing demand of fuels has been a challenge for today’s scientific workers. The fossil fuel resources are dwindling day byday. Biodiesel seems to be a solution for future. Biodiesel is an environmentally viable fuel. Out of the four ways viz. direct use and blend-ing, micro-emulsions, thermal cracking and transesterification, most commonly used method is transesterification of vegetable oils, fats,waste oils, etc. Latest aspects of development of biodiesel have been discussed in this work. Yield of biodiesel is affected by molar ratio,moisture and water content, reaction temperature, stirring, specific gravity, etc. Biodegradability, kinetics involved in the process of bio-diesel production, and its stability have been critically reviewed. Emissions and performance of biodiesel has also been reported.� 2008 Elsevier Ltd. All rights reserved.

Keywords: Biodiesel; Transesterification; Catalyst; Stability; Biodegradation

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2356

0016-2

doi:10.

* CoE-m

1.1. Various raw materials used as feedstock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2357
2. Production of biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2360
2.1. Acid esterification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23602.2. Alkaline transesterification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2360

3. A special reference to karanja . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23624. Effect of different parameters on production of biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2363

4.1. Effect of molar ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23634.2. Effect of moisture and water content on the yield of biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23634.3. Effect of free fatty acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23644.4. Effect of temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23644.5. Effect of stirring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23644.6. Effect of specific gravity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2365

5. Biodegradability of biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23656. Stability of biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23657. Kinetics of the reaction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23668. Diesel engine emissions and performance of biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2366

361/$ - see front matter � 2008 Elsevier Ltd. All rights reserved.

1016/j.fuel.2008.01.014

rresponding author. Tel.: +91 542 2307025 (O), +91 9935616119 (M); fax: +91 542 2316428.ail address: [email protected] (Y.C. Sharma).

mailto:[email protected]

2356 Y.C. Sharma et al. / Fuel 87 (2008) 2355–2373

9. Indian scenario . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236810. Cost of biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236811. Instrumentation involved in biodiesel production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237012. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2370

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2370

1. Introduction

Whenever I think of fuel, a picture of villages of devel-oping nations eclipsed in darkness, full of poverty, noplanned mechanization, agriculture depending on rainGod for irrigation comes before my eyes. Be it lightingthe house, agriculture, or cooking, each process requiresenergy. Energy, most countries do not have energy evento light the cities! Superconductivity and hydrogen energyreflected some promise but these were completely short-lived. Biodiesel, yes, probably biodiesel is the FUEL offuture.

Biodiesel is derived from vegetable oils and hence is arenewable fuel. Gasoline and diesel come in the categoryof non-renewable fuel and will last for a limited period oftime. These non-renewable fuels also emit pollutants inthe form of oxides of nitrogen, oxides of sulphur, carbondioxide, carbon monoxide, lead, hydrocarbons, etc. duringtheir processing and use. A renewable fuel such as biodie-sel, with lesser exhaust emissions, is the need of the day.Hence, researchers and scientific community worldwidehave focused on development of biodiesel and the optimi-zation of the processes to meet the standards and specifica-tions needed for the fuel to be used commercially withoutcompromising on the durability of engine parts. The inter-est in the use of renewable fuel started with the direct use ofvegetable oils as a substitute for diesel. However, theirdirect use in compression ignition engines was restricteddue to high viscosity which resulted in poor fuel atomiza-tion, incomplete combustion and carbon deposition onthe injector and the valve seats causing serious engine foul-ing [1]. Other constraints of the direct application of vege-table oil were its low volatility and polyunsaturatedcharacter. To overcome these constraints, the processes likepyrolysis, micro-emulsification, transesterification, etc.were especially developed. Pyrolysis of the vegetable oilresulted in products with low viscosity, high cetane num-ber, accepted amounts of sulphur, water and sediments,accepted copper corrosion values but were unacceptablein the terms of their ash contents, carbon residues, andpour points. Similarly, micro-emulsion of vegetable oillowered the viscosity of the oil but resulted in irregularinjector needle sticking, heavy carbon deposits and incom-plete combustion during 200 h laboratory screening endur-ance test [2]. Transesterification is a chemical reactionbetween triglyceride and alcohol in the presence of a cata-lyst. It consists of a sequence of three consecutive reversiblereactions where triglycerides are converted to diglycerides,diglycerides are converted to monoglycerides followed by

the conversion of monoglycerides to glycerol. In each stepan ester is produced and thus three ester molecules are pro-duced from one molecule of triglyceride [3]. Out of thesethree methods, transesterification is the most viable processadopted known so far for the lowering of viscosity. It alsogives glycerol as a by-product which has a commercialvalue.

Stoichiometrically, three moles of alcohol are requiredfor each mole of triglyceride, but in general, a higher molarratio is often employed for maximum ester productiondepending upon the type of feedstock, amount of catalyst,temperature, etc. Commonly used alcohols include metha-nol, ethanol, propanol and butanol. However, the yield ofbiodiesel is independent of the type of the alcohol used andthe selection of one of these depends on cost and perfor-mance. Methanol is preferred over others due to its lowcost [1]. The conventional catalysts used are acid and alkalicatalysts depending upon the nature of the oil used for bio-diesel production. Another catalyst being studied is lipase.Lipase has advantage over acid and alkali catalysts but itscost is a limiting factor for its use in large scale productionof biodiesel. Choice of acid and alkali catalysts depends onthe free fatty acids (FFA) content in the raw oil. FFAshould not exceed a certain amount for transesterificationto occur by an alkali catalyst. Invariably, on all aspectsof development of biodiesel, Ma and Hanna [4] have donesignificant work. Canakci and Van Gerpan [5,6] reportedthat transesterification was not feasible if FFA content inthe oil was about 3%. Ramadhas et al. [1] and Veljkovicet al. [7] used rubber seed oil and tobacco seed oil, respec-tively, with higher free fatty acid content (17%). Theauthors reduced the FFA value to more than 2.0%, whichcorresponds to 4.0 mg KOH/g, by acid esterification usingH2SO4 as a catalyst. Sahoo et al. [8] used zero catalyzedtransesterification (using toluene) and acid esterification(using H2SO4) prior to alkaline esterification to reducethe acid value from 22.0% to 2.0%. Sharma and Singh [3]also favored acid esterification prior to alkaline transesteri-fication with karanja oil as feedstock having FFA of 2.53%(5.06 mg KOH/g) using H2SO4. In the same manner, theacid value of jatropha which corresponds to 14% FFAwas reduced to less than 1% by using H2SO4 [9]. Table 1depicts the values of initial FFA of the feedstock, the levelreached after acid esterification and the amount of H2SO4

used. After treatment with acid catalyst, H2SO4, the freefatty acid (FFA) value is reduced to less than 2.0% to maketransesterification reaction feasible. Table 2 depicts theyield/conversion of biodiesel with different oils taken.The yield of biodiesel ranged from 56% from Chlorella

Table 2Yield of biodiesel with different feedstock

Oil taken for study Yield(%)

Conversion(%)

Reference

Karanja (Pongamia pinnata) 89.5 – [3]Tobacco (Nicotina tabacum) 91 – [7]Polanga (Calophyllum inophyllum) – 85 [8]Jatropha (Jatropha curcas) 99 – [9]Mahua (Madhuca indica) 98 – [10]Karanja (Pongamia pinnata) 97–98 – [11]Karanja (Pongamia pinnata) – 92/95 [14]Soybean (Glycine max) – 98.4 [15]Waste cooking oil 97.02 – [16]Canola oil (Brassica napus) 90.04 98 [19]Used frying oil 87.5 94 [19]Sunflower oil (Helianthus annuus) – Nearly

complete[20]

Chlorella protothecoides 56 – [21]Chlorella protothecoides – >80 [22]

Table 1Values of initial FFA content of different feedstock

Feedstock Initial FFA (%) FFA after treatment (%) Amount (%) and catalyst used Reference

Rubber oil 17.0 <2.0 0.5, H2SO4 [1]Karanja oil 2.53 0.95 0.5, H2SO4 [3]Tobacco oil 35.0 <2.0 1.0/2.0, H2SO4 [7]Polanga oil 22.0 <2.0 0.65, H2SO4 [8]Jatropha oil 14.0 <1.0 1.43, H2SO4 [9]Mahua oil 19.0 <1.0 1.0, H2SO4 [10]Karanja oil 2.53 0.3 KOH (appropriate amount) [11]– 37.96 ± 0.018 1.05 ± 0.018 2.0 Fe2SO4 [16]– 40.0 <1.0 – [18]

Y.C. Sharma et al. / Fuel 87 (2008) 2355–2373 2357

protothecoides to 99% from Jatropha curcas. The conver-sion of biodiesel ranged from more than 80% fromC. prothecoides to 98.4% from soybean oil.

Various oils have been in use in different countries asraw materials for biodiesel production owing to its avail-ability. Soybean oil is commonly used in United Statesand rapeseed oil is used in many European countries forbiodiesel production, whereas, coconut oil and palm oilsare used in Malaysia for biodiesel production [10–13].Transesterification of edible oils has also been carried outfrom the oil of canola and sunflower. Other edible andnon-edible oils, animal fats, algae and waste cooking oilshave also been investigated by researchers for the develop-ment of biodiesel [14–31]. Table 3 depicts the work carriedout for biodiesel production from various feedstocks underdifferent conditions. Type and amount of variables such asfeedstock, alcohol, molar ratio, catalyst, reaction tempera-ture, time duration, rate and mode of stirring affects theyield and conversion of biodiesel.

1.1. Various raw materials used as feedstock

Leung and Guo [19] compared the transesterificationreaction conditions of neat canola oil with used frying oil(UFO). A comparatively higher temperature (333 K),

higher molar ratio (7:1, methanol/UFO), and more amountof catalyst (1.1 wt% NaOH) was needed when compared toedible canola oil where optimal conditions were 315–318 K, 6:1 methanol/oil molar ratio and 1.0 wt% NaOH.However, comparatively a less time (20 min) was neededin UFO for completion of reaction in comparison to canolaoil where reaction time took 60 min. Non-edible oils usedfor transesterification mostly are the oils with higher freefatty acids such as rubber (Ficus elastica), jatropha (J. cur-

cas), karanja (Pongamia pinnata), mahua (Madhuca indica),polanga (Calophyllum inophyllum), tobacco (Nicotina taba-

cum), etc. In an attempt to reduce the cost of biodiesel, mic-roalgal oils have also been tried by researchers as a sourceof feedstock for the production of biodiesel due to theirhigher photosynthetic efficiency, higher biomass produc-tion and faster growth as compared to other energy crops[32–35]. Miao and Wu [21] reported production of biodie-sel from microalga C. protothecoides using 100% catalystquantity (based on oil weight) with 56:1 molar ratio ofmethanol to oil at temperature of 303 K in 4 h of reactiontime. The specific gravity of biodiesel produced reducedfrom initial value of 0.91 to a final value of 0.86. Xuet al. [22] obtained high quality and low cost biodiesel frommicroalgae C. protothecoides of heating value 41 MJ kg�1,density 0.864 kg L�1 and viscosity 5.2 � 10�4 Pa S at313 K. C. protothecoides have earlier been reported as afeedstock for aquaculture feeds, human food supplementsand pharmaceuticals [36–39].

Attributing to its low cost, waste cooking oil has alsobeen tried by researchers to develop biodiesel. The ideacomes from the fact that triglycerides comprise of greasesand oil. Oils are generally in liquid state at room tempera-ture, whereas greases and fats are in solid state at roomtemperature. Recycled grease is termed as waste greaseand is classified as yellow and brown grease dependingon free fatty acid composition [17]. The price of yellowgrease (FFA < 15%) ranges from $0.04 to $0.09 kg�1 whilethe price of brown grease (FFA > 15%) ranges between0.004 and $0.014 kg�1 [40]. Biodiesel development fromgrease can reduce its production cost. In United States,an estimate reveals that biodiesel production from 5.2 bil-lion kg/year of greases and animal fats could replace 1.5million gallons of diesel fuel. The major constraint of directapplication of waste frying oil lies in its higher amount of

Table 3Biodiesel production from different feedstock

YearRef

Feedstock Transesterificationstages

Alcohol Molarratio(methanolto oil)

Catalyst Reactiontemperature(K)

Duration Stirring Conversion/yield Reference

2004 Sunflower oil Single step Supercriticalmethanol

40:1 No catalyst 473–673(pressure200 bar)

10–40 min

– 78–96%conversion withincrease intemperature

[20]

SupercriticalethanolMethanol 5:1 Supercritical

CO2 + lipase (Novozym435) 30 wt% of oil

318 6 h 23% conversionEthanol 27% conversion

2005 Pongamia pinnata Single step Methanol 10:1 KOH (1% by wt) 378 1.5 h – 92% conversion [14]ZnO 83% conversionHb-Zeolite 393 24 h 59% conversionMontmorillonite 47% conversion

2005 Madhuca indica Two step Methanol 0.30–0.35v/v

1% v/v H2SO4 333 1 h – 98% yield [10]

0.25 v/v 0.7% w/v KOH – 1 h –2005 Rubber seed oil Two step Methanol 6:1 H2SO4 0.5% by volume 318 ± 5 20–

30 minMagnetic stirre – [1]

9:1 NaOH 0.5% by volume 318 ± 5 30 min2006 Chlorella

protothecoides

Methanol 56:1 Acid catalyst 303 More than 80%conversion

[22]

2006 Chlorella

protothecoides

Methanol 56:1 H2SO4 (100%) on thebasis of oil weight

303 4 h – 63% yield [21]

2006 Neat canola oil Single step Methanol 6:1 NaOH 1.0 wt% 318 15 min Magnetic stirri 1100 rpm inthe first stage ( min) and600 rpm in seco d stage

Ester content98 wt%

[19]

Used frying oil 7:1 NaOH 1.1 wt% 333 20 min Ester content94.6 wt%

2006 Nicotiana

tabacum L.(tobacco)

Two step Methanol 18:1 H2SO4 (1% with lowermolar ratio) (2% withhigher molar ratio)

333.0 ± 0.1 25 min Magnetic stirre 400 rpm Yield 91% in30 min

[7]

6:1 KOH (1% based on theoil wt.)

30 min

2358Y

.C.

Sh

arm

aet

al./F

uel

87

(2

00

8)

23

55

–2

37

3

r

ng10n

r

2006 Pongamia pinnata Single step Methanol 6:1 KOH (1% by weight) 338 2 h Mechanical stirrer 360 rpnm Yield 97–98% [11]12:1 1 h

2006 Soybean oil Methanol 4.5:1 TiO2/ZrO2 (11 wt% Ti) 448 2 h Conversion over95%

[23]Al2O3/ZrO2 (2.6 wt% Al)K2O/ZrO2 (3.3 wt% K) Conversion 100%

2006 Monosodiumglutamatewastewater

Two step Methanol 0.5 M 1 ml KOH (0.5 M) 333 10 min – Yield92.54 ± 2.00%

[24]12.5%, v/v 1 ml BF3 (12.5%, v/v) 353 5 min

2006 Soybean oil Single step alkalicatalyzed

Methanol 6:1 NaOH 318 10–20 min

Mechanical stirrer 900 rpm Yield 100% [25]Power ultrasonic (frequency19.7 KHz, power 150 W)Hydrodynamic cavitation(operation pressure 0.7 MPa)

2007 Jatropha,pongamia,sunflower,soybean, palm

Single step Methanol 3:1 NaOH/KOH (1 wt% ofoil)

– 2–4 h Stirring – [12]

2007 Calophyllum

inophyllum

Three step zerocatalysed

Methanol 6:1 Anhydrous H2SO4

(98.4%) 0.65% by volume338 2 h Mechanical stirring 450 rpm 85% yield in

90 min[8]

Acid catalysed 4 h Complete in 4 hreactionAlkali catalysed 9:1 KOH 1.5% by weight 4 h

2007 Jatropha curcas Two step acidcatalysed

Methanol 0.28 v/v H2SO4 1.43% v/v(3.5 + acid value, w/vKOH)

333 88 min >99% yield [9]

Alkali catalysed 0.16 v/v 24 min2007 Triolein Single step Ethanol 10:1 Anion exchange resin 323 60 min – 98.8% purity [26]

Cation exchange resin(heterogeneous catalyst)

2007 Sunflower oil Single step Methanol 13:1 Activated CaO (1 wt%) 333 100 min Helix stirrer 1000 rpm – [27]2007 Waste cooking oil Two step Methanol 10:1 Fe2SO4 368 4 h No stirring because boiling was

sufficient97.02% conversion [16]

6:1 KOH 338 1 h2007 Karanja Two step Methanol 8:1 H2SO4 318 ± 2 30 min Magnetic/mechanical 89.5% yield with

mechanical[3]

9:1 NaOH/KOH 30 min 85% yield withmagnetic

Y.C

.S

ha

rma

eta

l./Fu

el8

7(

20

08

)2

35

5–

237

32359

Fig. 1. Basic scheme for biodiesel production.


FFA. The FFA level of fresh soybean oil has been reportedto change from 0.04% to 1.51% after 70 h of frying at463 K [41]. Hence, due to higher FFA, direct conversionof waste restaurant oil and animal fats to biodiesel viaalkaline catalyst is not possible. The level of FFA, there-fore, is reduced by an acid catalyst.

Following this advantage, researchers have advocatedthe use of rendered animal fats and restaurant waste oilsas biodiesel feedstocks [18,42–47]. A major limiting factorof biodiesel is its inverse relationship between its oxidationstability and its cold flow properties. Saturated compoundshave good oxidation stability but poor cold temperatureproperties. Unsaturated compounds have better low tem-perature properties but fail in oxidation stability [12,17].Here, the waste oil product can be of advantage over theneat vegetable oil as they have a higher proportion of sat-urated fatty acids [17] and hence can provide better oxida-tive stability. Wang et al. [16] have achieved 97.02% yield ofbiodiesel from waste cooking oil of high acid value i.e.75.92 ± 0.036 mg KOH/g, by a two step catalysis process.

A novel method has been developed by Xue et al. [24]for the production of biodiesel from monosodium gluta-mate wastewater having COD of 10,000 mg/L. After treat-ment the COD removal was 85% with 10% formation ofcrude lipid. The crude lipid was biosynthesized by rhodo-torula glutinis by transesterification reaction with methylester yield of 92.54 ± 2.0%. Biodiesel has also been synthe-sized using triolein as a feedstock [26]. Fig. 1 depicts thebasic scheme for biodiesel production [48].

2. Production of biodiesel

2.1. Acid esterification

The acid value is a measure of the number of acidicfunctional groups in a sample and is measured in termsof the quantity of potassium hydroxide required to neutral-ize the sample. Acid value of the feedstock for alkalinetransesterification has to be reduced to less than 2.0 mgKOH/g [15,49–51]. However, other authors advocate it to

be less than 4.0 mg KOH/g [1,3]. The commonly used cat-alyst during acid esterification of neat oil is sulphuric acid(H2SO4) [1,3,7–10]. Nevertheless, this process too has adrawback as water is produced along with ester from thereaction of FFA with alcohol which inhibits the transeste-rification of glycerides [17]. For waste cooking oil too theacid employed is sulphuric acid [29–31]. But in this case,the conversion reported is low (82%) and the alcoholrequired for the reaction is high (200% excess of ethanol)[16]. Wang et al. [16] have, therefore, tried a new catalystFe2(SO4)3 (ferric sulphate) as an alternate to sulphuric acidand have reported much better conversion (97.02%). As,ferric sulphate is insoluble in oil, it was centrifuged fromthe liquid after acid esterification and reused for the nextbatch. High temperature and high concentration ofH2SO4 as catalyst could burn some of the oil which willthen cause low yield of biodiesel product.

2.2. Alkaline transesterification

For oil samples with FFA below 2.0%, alkaline transe-sterification is preferred over the acid catalyzed transesteri-fication as the former is reported to proceed about 4000times faster than the latter [2]. The common catalystemployed during alkaline transesterification at industriallevel application includes the homogeneous catalystssodium hydroxide, potassium hydroxide, etc.

The use of homogeneous catalyst such as sodiumhydroxide and potassium hydroxide has been successfulat industrial level for production of biodiesel. However,the biodiesel and glycerin produced have to be purified toremove the basic catalyst and need its separation by wash-ing with hot distilled water twice or thrice. Thus, heteroge-neous catalyst has also been tried by researchers toovercome this drawback of time consumption and colossalconsumption of water. The heterogeneous catalyst can beseparated from the final product by filtration which checkstime consumption and prevents the consumption of largevolume of water. The filtered solid then can be reused.The application of a heterogeneous catalyst, CaO has been


tested by Grandos et al. for its feasibility [27]. The experi-ments confirmed that CaO could be used as a catalyat forthe transesterification reaction without significant deactiva-tion up to eight runs with significant amount of CaO.

Leung and Guo [19] tried three different homogeneouscatalysts i.e. sodium hydroxide (NaOH), potassiumhydroxide (KOH), and sodium methoxide (CH3ONa).The optimum requirement of the catalyst were 1.1, 1.3and 1.5 wt% for NaOH, CH3ONa, and KOH respectivelyfor the maximum ester content. The amount of NaOHrequired was less than the amounts of both the CH3ONaor KOH for the same conversion of fatty acid methyl esteras NaOH has lower molar mass (40 g/mol), compared toCH3ONa (54 g/mol) and KOH (56 g/mol).

However, in terms of yield, CH3ONa proved to be a bet-ter catalyst than NaOH and KOH because CH3ONa disso-ciates into CH3O� and Na+ and does not form any wateras side product. On the other hand, NaOH and KOHforms sodium (or potassium) methoxide when dissolvedin methanol and produces water. This water then reactswith Na+ (or K+) to form sodium (or potassium) soaps.

Potassium methoxide (KOCH3) has also been used as analkali catalyst by dissolving potassium hydroxide in meth-anol [52]. Sharma and Singh [3] reported better yield withNaOH as a catalyst over KOH while using magnetic stir-rer. Whereas, when mechanical stirrer was adopted theyield was same with equal amount of NaOH and KOH(0.5 wt%). However, during the separation of the finalproducts from glycerol, KOH was more convenient. Potas-sium soaps being softer than sodium soaps did not blockthe bottom of separating funnel unlike latter and wereremoved easily. Hence, KOH as catalyst is preferred overNaOH at industrial level application [3,19].

The base catalyzed reaction is reported to be very sensi-tive to the purity of the reactant. FFA content should notexceed beyond a certain limit. The efficiency of the reactionwas affected to some extent when FFA content exceeded0.5 wt% [28]. However, when the feedstock is waste cook-ing oil, the limit of FFA is a bit relaxed and FFA contenta little beyond 1.0 wt% did not have any effect on themethyl ester conversion [16,53]. The amount of catalyst(KOH) required was 1.0 wt% to reach 97.02% conversionof biodiesel.

Ramadhas et al. [1] have reduced the acid value to lessthan 2.0% through acid catalyst followed by alkalinetransesterification. The amount of catalyst used for alka-line transesterification ranged between 0.3% and 1.0%.The maximum conversion efficiency was reported at 0.5%of NaOH during alkaline transesterification. Excessamount of catalyst gave rise to formation of an emulsion.This increased the viscosity and led to the formation ofgels. Conversion efficiency decreased to 60% when the cat-alyst amount was increased to 0.8% (wt of NaOH/wt ofoil). However, esterification also did not take place withoutsufficient amount of the catalyst.

Srivastava and Verma [54] used sodium methoxide solu-tion prepared by dissolving NaOH (28.5 g) and methanol

(2.0 kg) as an alkaline catalyst for transesterification.Sahoo et al. [8] used alkaline transesterification after reduc-ing the free fatty acid value from 44 mg KOH/g (i.e. 22%)to less than 4 mg KOH/g (i.e. <2%) through zero catalyzedand acid catalyzed transesterification. 1.5% by weight ofpotassium hydroxide was found sufficient for the maximumyield of ester. Sarin et al. [12] prepared a series of biodieselfrom the edible oils such as sunflower, soybean, palm andnon-edible oils such as jatropha and karanja. The catalystused was either NaOH or KOH with 1 wt % of oil.

The amount of alkali catalyst was calculated on thebasis of the amount needed to neutralize the unreactedacids plus 0.35% for virgin oil which came out to be0.55% w/v KOH [9]. 1.0% KOH was reported as the opti-mal amount for alkaline transesterification reaction ofkaranja oil by Meher et al. [11] and Karmee and Chadha[14]. Karmee and Chadha also tried Hb-Zeolite, montmo-rillonite K-10 and ZnO but the conversion of fatty acidmethyl ester was less. Around 83% conversion with ZnOwas possible only with a longer reaction time of 24 h. Evenlesser conversions of 59% and 47% were achieved with Hb-Zeolite and montmorillonite K-10, respectively, in compar-ison to 92% achieved by KOH.

While using the refined karanja oil, the conversionreached to 99% with 0.5% of NaOH or CH3ONa [14].1% KOH was optimum amount of catalyst even with usedfrying oil reported by Marinkovic and Tomasevic [55].Ghadge and Raheman [10] calculated the amount of cata-lyst to be 0.7% w/v KOH as the cumulative sum of 0.5% forcatalyst plus the amount needed to neutralize the unreactedacids (2 mg KOH/g) i.e. 0.2%. NaOH was used as a cata-lyst by Ji et al. [25] with power ultrasonic and hydrody-namic cavitation methods and found the methodssuperior as compared to mechanical stirring. The amountof KOH used for the transesterification of tobacco (Nicoti-

ana tabacum) oil after acid esterification as reported by Vel-jkovic et al. [7] is 1.0% (based on oil weight) with a yield of91%. Using the same oil Usta got a yield of 86%. Hence,the two step process of acid and alkaline esterificationcan be expected to yield a better result when compared toone step base catalyzed transesterification [56]. In anattempt to find a new catalyst, Furuta et al. [23] testedamorphous zirconia solid catalysts, TiO2/ZrO2 (11 wt%Ti) and Al2O3/ZrO2 (2.6 wt% of Al) and reported morethan 95% conversion. The reason for this is the amphotericnature of zirconia. However, the temperature required wasquite high i.e. 448–473 K.

The homogeneous catalysts require neutralization andseparation steps from the reaction mixture. To accomplishthis, water, solvents and energy are needed. To overcomethese, heterogeneous based catalysts have been tested byresearchers, where separation is possible without usingsolvent and shows easy regeneration. The nature of thefinal product has been less corrosive in character and thewhole process is termed safer, cheaper and more environ-ment friendly [57]. The heterogeneous catalyst being usedby researchers include alkaline–earth oxides, zeolites,


hydrotalcites, MgO and CaO [27,57–62]. In addition, reac-tor heating was not needed when MgO was used as a cat-alyst in batch process [57].

Another method where neither acid nor base catalyst isrequired is non-catalytic transesterification where super-critical methanol is used instead of methanol and nearlycomplete conversion is achieved. The reason is that, theoil and supercritical methanol exist in the single phase[20,63–67]. The advantage with supercritical methanol isthat the conversion gets 95% complete in 10 min. But atthe same time, higher molar ratio (40:1) is employed. Thesupercritical condition is based on the effect of relationshipbetween pressure and temperature upon the thermophysi-cal properties of the solvent, such as dielectric constant,viscosity, specific weight and polarity. There is a decreasein the dielectric constant of methanol in supercritical state.Fig. 2 depicts the influence of temperature and alcohol usedin the synthesis of biodiesel. In methanol, conversionincreased from 78% to 96% with increase in temperature.The conversion was even higher with supercritical ethanol

Fig. 2. Synthesis of biodiesel at various temperatures in supercritical (a)methanol, (b) ethanol (j) 473 K, (�) 523 K, (N) 573 K, (.) 623 K, (�)673 K.

as the solubility parameter of ethanol is closer to the solu-bility parameter of the oil. But, high temperature and highpressure conditions i.e. 573 K and 20 MPa are needed forthe reaction to proceed and complete. [13,20]. Anotheradded advantage with heterogeneous based catalyst is thelesser consumption of catalyst. As per the study by Zhanget al. [29] annually 88 tonnes of sodium hydroxide isneeded for 8000 tonnes of biodiesel production. While asper the simulation study by Dossin et al. [57] the require-ment of MgO will be only 5.7 tonnes for 100,000 tonnesproduction of biodiesel.

3. A special reference to karanja

Among the several indigenous plant species, karanja isone of the medium sized plants found in several parts ofIndia. The plant is also said to be highly tolerant to salinityand is reported to be grown in various soil textures viz.stony, sandy and clayey. Karanja can grow in humid aswell as subtropical environments with annual rainfall rang-ing between 500 and 2500 mm. This is one of the reasonsfor wide availability of this plant species. The constituentsof karanja oil viz. furanoflavones, furanoflavonols, chro-menoflavones, flavones and furanodiketones make the oilnon-edible and hence the oil is underutilized. The presenceof these constituents, however, gives the oil antifungalcharacteristics and enhances its application in medicinalointments. The woody part of the tree is still in use by tri-bal people where the plant is locally available such asbrushing of teeth. The oil expelled from the seeds is alsoburned during the festival of lighting to purify the environ-ment. All these applications are at local or regional leveland 94% of the oil from plant is still underutilized. Thepresent production of karanja oil approximately is 200 mil-lion tons per annum [11]. However, its production poten-tial is much more i.e. 135,000 million tones per annum[8]. The time needed by the tree to mature ranges from 4to 7 years and depending on the size of the tree the yieldof kernels per tree is between 8 and 24 kg. The oil contentextracted by various authors ranges between 30.0 to 33%[3,14]. The oil is used by common people due to its low costand easy availability. The fatty acid composition of karanjaoil has been reported in Table 4. Karanja oil comprises of

Table 4Different fatty acids present in karanja oil [107]

Fatty acid(commonname)

Systematic name Formula Structure wt%

Palmitic Hexadecanoic C16H32O2 16:0 10.6Stearic Octadecanoic C18H36O2 18:0 6.8Oleic cis-9-octadecenoic C18H34O2 18:1 49.4Linoleic cis-9, cis-12-octadecadienoic C18H32O2 18:2 19.0Arachidic Eicosanoic C20H40O2 20:0 4.1Gadoleic 11-eicosenoic C20H38O2 20:1 2.4Behenic Docosanoic C22H44O2 22:0 5.3Lignoceric Tetracosanoic C24H48O2 24:0 2.4

Table 5Test method and limits of biodiesel along with its comparison with karanja oil methyl ester [12]

Property (units) ASTM 6751 test method ASTM 6751 limits IS 15607 test method IS 15607 limits Karanja oil methyl ester

Flash point (�C) D-93 Min. 130 IS 1448 P:21 Min. 120 141Viscosity at 40 �C (cSt) D-445 1.9–6.0 IS 1448 P:25 2.5–6.0 4.16Sulphated ash (mass%) D-874 Max. 0.02 IS 1448 P:4 Max. 0.02 0.002Sulphur (mass%) D-5453 Max. 0.05 ASTM D 5453 Max. 0.005 0.003Cloud point (�C) D-2500 NA IS 1448 P:10 NA 4Copper corrosion D-130 Max. 3 IS 1448 P:15 Max. 1 1Cetane number D-613 Min. 47 IS 1448 P:9 Min. 51 55.1Water and sediment (vol. %) D-2709 Max. 0.05 D-2709 Max. 0.05 0.03CCR 100% (mass%) D-4530 Max. 0.05 D-4530 Max. 0.05 <0.01Neutralization value (mg, KOH/gm) D-664 Max. 0.80 IS 1448 P:1/Sec. 1 Max. 0.50 0.10Free glycerin (mass%) D-6584 Max. 0.02 D-6584 Max. 0.02 0.01Total glycerin (mass%) D-6584 Max. 0.24 D-6584 Max. 0.25 0.01Phosphorus (mass%) D-4951 Max. 0.001 D-4951 Max. 0.001 <0.001Distillation temperature D-1160 90% at 360 �C Not under spec. – 90%Oxidation stability, h NA NA EN 14112 Min. 6 h 2.35


29.2% saturated fatty acids and 70.8% unsaturated fattyacids. The maximum proportion comprises of oleic acid(cis-9-octadecenoic) i.e. 49.4%, whereas, gadoleic acid(11-eicosenoic, 2.4%) and linoceric acid (tetracosanoic,2.4%) are in traces. Table 5 depicts the ASTM 6751 andIS 15607 test methods and limits for biodiesel. In respectof karanja, it is observed that it meets all the specificationof American Society for Testing and Materials (ASTM)and Indian Standards but fails in oxidation stability test.Hence, appropriate methods have to be devised to makethe karanja oil methyl ester fit for commercialization.

For the transesterification reaction, Sharma and Singh[3] advocated for 8:1 molar ratio during acidic esterificationso as to reduce the acid value below 2 mg KOH/g i.e. 1.0%FFA. For the alkaline transesterification reaction, theauthors advocate 9:1 molar ratio for the completion ofthe reaction. Mechanical stirrer produced better resultsthan magnetic stirrer and resulted in higher yield (89.5%)in 1 h with 0.5% H2SO4 and 0.5% NaOH at 318 ± 2 K.Meher et al. [11] have neutralized the oil by using potas-sium hydroxide to reduce the acid value of the oil from5.06 mg KOH/g to 0.6 mg KOH/g. The yield of 97.0–98.0% was achieved in 2 h with 6:1 molar ratio (metha-nol:oil); and in 1 h with 12:1 molar ratio. The optimumtemperature was 338 K with the rate of stirring 360 rpmand 1% KOH as catalyst. Karmee and Chadha [14] havereported 92% conversion with karanja oil using 10:1molar ratio (methanol:oil) at 333 K with 1.0% KOH byweight.

4. Effect of different parameters on production of biodiesel

4.1. Effect of molar ratio

Ramadhas et al. [1] and Sahoo et al. [8] reported 6:1molar ratio during acid esterification and 9:1 molar ratio(alcohol:oil) during alkaline esterification to be the opti-mum amount for biodiesel production from high FFA rub-ber seed oil and polanga seed oil respectively. Sharma and

Singh [3] used similar two step transesterification and took8:1 molar ratio for acid esterification and 9:1 molar ratiofor alkaline esterification for optimum yield of biodieselproduction from karanja oil. Veljkovic et al. [7] used 18:1molar ratio during acid esterification and 6:1 molar ratioduring alkaline esterification. Meher et al. [11] carried outinvestigation with 6:1 molar ratio during acid esterificationand 12:1 molar ratio during alkaline esterification. Insteadof taking molar ratio, Tiwary et al.[9] and Ghadge andRaheman [10] used volume as a measure of ratio. WhileTiwary et al. used 0.28 v/v (methanol/oil) during acidesterification and 0.16 v/v (methanol/oil) during alkalineesterification, Ghadge and Raheman used 0.30–0.35 v/v(methanol/oil) during acid esterification and 0.25 v/v(methanol/oil) during alkaline esterification. Karmee andChadha [14] used a single step transesterification andhave achieved 92% conversion by taking 10:1 molarratio.

Presence of sufficient amount of methanol during thetransesterification reaction is essential to break the glycer-ine-fatty acid linkages [68]. But excess of methanol shouldbe avoided. Increasing the molar ratio of methanol/oilbeyond 6:1 neither increases the product yield nor the estercontent, but rather makes the ester recovery process com-plicated and raised its cost. Leung and Guo [19] suggestedthat methanol has polar hydroxyl group which can act asan emulsifier causing emulsification. Thus separation ofthe ester layer from the water layer becomes difficult. Miaoand Wu [21] have reported that addition of large quantityof methanol, i.e. 70:1 and 84:1 molar ratio slowed down theseparation of the ester and glycerol phases during the pro-duction of biodiesel. 56:1 molar ratio was reported to beoptimum for transesterification of microalgal oil.

4.2. Effect of moisture and water content on the yield of

biodiesel

Kusdiana and Saka [69] observed that water couldpose a greater negative effect than presence of free fatty

Fig. 3. Plots for yields of methyl esters as a function of water content intransesterification of triglycerides.

Fig. 4. Effect of FFA on the yield of methyl ester during alkali catalyzedtransesterification.

Fig. 5. The variation of product specific gravity with reaction time underdifferent molar ratio of methanol to oil. Reaction conditions: 303 K,160 rpm, 100% catalyst quantity based on oil weight.


acids and hence the feedstock should be water free.Romano [70] and Canakci and Van Gerpen [5] insistedthat even a small amount of water (0.1%) in the transeste-rification reaction would decrease the ester conversionfrom vegetable oil. Demirbas [13] too reported a decreasein yield of the alkyl ester due to presence of water andFFA as they cause soap formation, consume catalystand reduce the effectiveness of catalyst. Srivastava andVerma [54] removed the moisture content from the vege-table oil by heating in oven for 1 h at 383 K. Meher et al.[11] too reported a precautionary step to prevent moistureabsorbance and maintenance of catalytic activity by pre-paring the fresh solution of potassium hydroxide andmethanol. Ellis et al. [52] found that even a small amountof water in the feedstock or from esterification reactionproducing water from FFA might cause reduction in con-version of fatty acid methyl ester and formation of soapinstead. At the same time the presence of water had apositive effect in the yield of methyl esters when methanolat room temperature was substituted by supercriticalmethanol. However, no explanation for this has been pro-vided. [13]. Fig. 3 depicts the influence of water contenton yield of methyl esters. It is observed that acid catalystis most prone to presence of water followed by alkalinecatalyst. No effect on ester content was observed whensupercritical methanol was used. The presence of waterhad negligible effect on the conversion while using lipaseas a catalyst [20,71].

4.3. Effect of free fatty acids

Free fatty acids (FFAs) content after acid esterificationshould be minimal or otherwise less than 2% FFAs. TheseFFAs react with the alkaline catalyst to produce soapsinstead of esters. Fig. 4 depicts the effect of FFAs on theyield of methyl ester during alkali catalysed transesterifica-tion. There is a significant drop in the ester conversionwhen the free fatty acids are beyond 2% [72].

4.4. Effect of temperature

The temperature maintained by the researchers duringdifferent steps range between 318 and 338 K. The boilingpoint of methanol is 333.7 K. Temperature higher than thiswill burn the alcohol and will result in much lesser yield. Astudy by Leung and Guo [19] showed that temperaturehigher than 323 K had a negative impact on the productyield for neat oil, but had a positive effect for waste oil withhigher viscosities.

4.5. Effect of stirring

Stirring can play an important role in the yield of biodie-sel production. Meher et al. [11] conducted the transesteri-fication reaction with 180, 360 and 600 revolutions perminute (rpm) and reported incomplete reaction with180 rpm. The yield of methyl ester was same with 360

Table 6Comparison of different technologies to produce biodiesel

Variable Alkali catalysis Lipase catalysis Supercritical alcohol Acid catalysis

Reaction temperature (K) 333–343 303–313 512–658 328–353Free fatty acid in raw materials Sapanofied products Methyl esters Esters EstersWater in raw materials Interference with reaction No influence – Interference with reactionYield of methyl esters Normal Higher Good NormalRecovery of glycerol Difficult Easy – DifficultPurification of methyl esters Repeated washing None – Repeated washingProduction cost of catalyst Cheap Relatively expensive Medium Cheap


and 600 rpm. Sharma and Singh [3] reported that mode ofstirring too plays a vital role in the transesterification reac-tion. The yield of biodiesel increased from 85% to 89.5%when magnetic stirrer (1000 rpm) was replaced withmechanical stirrer (1100 rpm). A plausible explanationmay be a thorough mixing of the reactants by mechanicalstirrer.

4.6. Effect of specific gravity

Lower value of the specific gravity of the final product isan indication of completion of reaction and removal ofheavy glycerine. The influence of molar ratio, temperatureand catalyst quantity on the specific gravity of the biodieselwas studied by Miao and Wu [21]. The specific gravity ofthe product decreased sharply up to 2 h of reaction timeusing 30:1 molar ratio and up to 4 h of reaction time using45:1 and 56:1 molar ratio after which it was almost con-stant. The best process combination reduced the productspecific gravity from 0.912 to 0.864 with 100% catalyst,56:1 molar ratio at 303 K in 4 h of reaction time. Fig. 5depicts the change in specific gravity with reaction timeunder different molar ratio of methanol to oil. A compari-son of different technologies to produce biodiesel is shownin Table 6 [48].

5. Biodegradability of biodiesel

Biodiesel is reported to be highly biodegradable in fresh-water as well as soil environments. 90–98% of biodiesel ismineralized in 21–28 days under aerobic as well as anaero-bic conditions [73–75]. Biodiesel has been reported toremove twice the amount of crude oil from sand as conven-tional shoreline cleaners [76]. Biodiesel increases the biode-gradability of crude oil by means of cometabolism. More

Table 7Biodegradability of fossil diesel

%degradation

No. ofdays

Reference

Artificially contaminated soils 67 109 [77]Using soil columns 81 310 [78]Fuel contaminated soil in the arctic 90–95 365 [79]Under aerobic conditions 42 30 [80]Under anaerobic conditions 18 50 [80]

than 98% degradation of pure biodiesel after 28 days isreported by Pasqualino et al. [73] in comparison to 50%and 56% by diesel fuel and gasoline respectively. Also,the time taken to reach 50% biodegradation reduced from28 to 22 days in 5% biodiesel mixture and from 28 to 16days in case of 20% biodiesel mixture at room temperature.The biodegradability of the mixture was reported toincrease with addition of biodiesel. Table 7 depicts the bio-degradability of fossil diesel under different conditions [77–80].

6. Stability of biodiesel

Biodiesel, chemically is fatty acid methyl ester if alcoholused during transesterification is methanol or fatty acidethyl ester in case of ethanol. This ester molecule will gethydrolyzed to alcohol and acid in the presence of air. Con-version of ester into alcohol will lead to reduction in flashpoint whereas conversion of ester into acid will increase thetotal acid number. This makes the biodiesel unstable onstorage [12]. The stability of biodiesel also depends onthe feedstock used for the biodiesel production. The feed-stock with larger proportion of saturated fatty acids willbe more stable than those having larger proportion ofunsaturated fatty acids. But again, higher portion of satu-rated fatty acid lowers the low temperature properties suchas cloud and pour points. Hence, a major drawback of bio-diesel lies in its tradeoff between the level of saturation ofbiodiesel and its cold flow properties [12,17]. The oxidationstability of biodiesel is not dependent on the total numberof double bonds but on the total number of bis-allylic sites(the methylene CH directly adjacent to the two doublebonds). These esters undergo auto-oxidation which isdependent on the number and position of the double bondsand forms by-product such as acids, esters, aldehydes,ketones, lactones, etc. [12,81–83].

Fatty acid methyl esters form a radical next to the dou-ble bond during the oxidation process. This radical bindswith the oxygen in air, which is a biradical to form peroxideradical. A new radical is created from the fatty acid methylester by this peroxide radical which binds with oxygen inair. This augments the auto-oxidation cycle at an exponen-tial rapid rate whereby 100 new radicals are created quicklyfrom one single radical resulting in the formation of a seriesof by-products. The fuel thus gets deteriorated as there isformation of sediment and gum. Peroxide formation


through this route leads to obligomerization even at ambi-ent temperature. As the deterioration of biodiesel is attrib-uted to the formation of peroxide in the initial step, theremedy suggested is to prevent peroxide formation duringthe stages of biodiesel manufacture and throughout its dis-tribution chain [12,81]. As biodiesels are primarily madefrom vegetable oils which do contain naturally occurringantioxidants such as tocopherols, sterols and tocotrienolsand these remain in the biodiesel during the process ofmanufacture. However, the distillation and purificationstep destroys these natural antioxidants and hence becomesprone to oxidation. Synthetic antioxidants such as phenolictypes or aminic types have to be added to make it stableand hence acceptable in market [12,81,83–85]. Sarin et al.[12] suggested blending jatropha biodiesel with palm bio-diesel to reduce the antioxidant dosage by 80–90% to main-tain good oxidation stability.

7. Kinetics of the reaction

Transesterification reaction consists of a sequence ofreversible reactions [52].

ð1Þ

In the first step, triglycerides are converted to diglycerideswhich get converted to monoglycerides in the nextstep. In the third and last step, monoglycerides are

Fig. 6. Simulated concentration profile of glycerol (G), tri-glyceride (TG),di-glyceride (DG), mono-glyceride (MG) and fatty acid methyl ester(FAME) during transesterification.

converted to glycerol. In each of the steps an ester isformed. Thus three esters are obtained from one triglycer-ides molecule.

TGþM$K1

K4

DGþ FAME ð2Þ

DGþM$K2

K5

MGþ FAME ð3Þ

MGþM$K3

K6

Gþ FAME ð4Þ

where, TG, triglycerides; DG, diglycerides; MG, mono-glycerides; M, methanol and FAME, fatty acid methylesters.

The values of rate constants for forward reactions, K1,K2 and K3, are found to be 5.00, 4.93 and 29.67 dm3 mol�1

min�1 and the values of the rate constants of backwardreactions involved in the kinetics of biodiesel development,K4, K5, and K6 are reported to be 3.54, 2.99 and0.79 dm3 mol�1 min�1. A software MATLAB 6.1 was usedto generate concentration profile of glycerol, tri-,di-, andmonoglycerides and fatty acid methyl ester. Fig. 6 showsthe concentration profiles of all components in which a pla-teau is reached at equilibrium [52].

8. Diesel engine emissions and performance of biodiesel

Researchers worldwide are on a consensus that biodie-sel, irrespective of the feedstock used results in a decreasein the emissions of hydrocarbons (HC), carbon monoxide(CO), particulate matter (PM) emissions and sulphur diox-ide (SO2). Only oxides of nitrogen (NOx) are reported toincrease which is due to oxygen content in the biodiesel[86–94]. It is also said to be carbon neutral as it contributesno net carbon dioxide to the atmosphere [95–97]. However,in a study conducted by Sahoo et al. [8] the NOx emissionfrom 100% biodiesel lowered to 4% for polanga seed oil.This is attributed by the authors to difference in enginegeometry, compression ratio, less reaction time and tem-perature. A remarkable decrease in the emission of unburnthydrocarbon was observed. 40% reduction of CO2 emis-sions was observed for B20 and B100 biodiesel. Thermalefficiency of the engine also improved by 0.1%. Smokeemissions reduced by 35% in the case of B60 biodiesel.The results were obtained without any engine hardwaremodifications. Other authors have suggested various strat-egies to eliminate the NOx emission. Szybist et al. [98] sug-gested to change the chemical composition of feedstock byincreasing the methyl oleate and addition of cetane improv-

Table 8Emission impact of 20 vol% biodiesel for soybean based biodiesel added toan average base diesel fuel

Percent change in emissions

NOx (nitrogen oxides) +2.0PM (particulate matter) �10.1HC (hydrocarbons) �21.1CO (carbon monoxides) �11.0


ers. This reduces the iodine value. Boehman et al. [99] andKegl [100] recommended to retard the injection timingwhich could lead to decrease in NOx emission. Nabiet al. [101] advocated for the exhaust gas recirculation toreduce the NOx emission.

Kegl [102] stressed on the importance of fuel injectionsystem to reduce the engine emissions as well as fuel con-sumption. Author suggests that pressure squareness (ratioof mean to maximum injection pressure) should be at max-imum and fuelling in the first part of injection has to be lessto reduce NOx emission. Simultaneously, the fuelling in thelast part of injection should be less to reduce the smokeemissions. Shahid and Jamal [103] reported that blend ofbiodiesel till B20 (20% biodiesel and 80% diesel) would

Table 9List of 26 indigenous plant meeting US, Germany and European standards (a oil

Sources Oil SN IV CN Fatty acid composi

Rhus succedanea Linn 39.5a 204.0 92.6 52.22 16:0 (25.4); 18:1 (46Annona reticulate Linn 42.0b 203.6 87.2 53.47 14:0 (1.0); 16:0 (17.Ervatamia coronaria

Stapf41.6b 201.1 76.0 56.33 16:0 (24.4); 16:1 (0.2

(0.2); uk (0.2)Thevetia peruviana

Merrill67.0a 201.5 84.0 57.48 16:0 (15.6); 18:0 (10

Basella rubra Linn 36.9b 202.9 85.3 54.00 14:0 (0.4); 16:0 (19.Canarium commune Linn 73.0a 204.6 77.3 55.58 16:0 (29.0); 18:0 (9.Celastrus paniculatus

Linn52.0a 236.6 77.5 51.9 1:0 (2.0); 2:0 (1.7); 1

Terminalia bellirica Roxb 40.0b 198.8 77.8 56.24 16:0 (35.0); 18:1 (24Vernonia cinerea Less 38.0a 205.2 68.5 57.51 14:0 (8.0); 16:0 (23.Corylus avellana 57.5a 200.5 84.51 54.50 14:0 (3.2); 16:0 (3.1Jatropa curcas Linn 40.0b 202.6 93.0 52.31 14:0 (1.4); 16:0 (15.Putranjiva roxburghii 41.8a 199.6 82.9 54.99 16:0 (8.0); 18:0 (15.Calophyllum apetalum

Wild47.5a 200.4 97.6 51.57 16:0 (8.0); 18:0 (14.

Calophyllum inophyllum

Linn65.0a 201.4 71.5 57.3 16:0 (17.9); 16:1 (2.

Mesua ferrea Linn 68.5a 201.0 81.3 55.10 14:0 (0.9); 16:0 (10.Azadirachta indica 44.5a 201.1 69.3 57.83 16:0 (14.9); 18:0 (14Moringa concanensis

Nimmo35.5b 199.7 76.0 56.32 16:0 (9.7); 18:0 (2.4

Moringa oleifera Lam 35.0a 199.7 75.4 56.66 16:0 (9.1); 16:1 (2.1Pongamia pinnata Pierre 33.0b 196.7 80.9 55.84 16:0 (10.6); 18:0 (6.Ziziphus mauritiana Lam 33.0b 198.6 81.8 55.37 16:0 (10.4); 18:0 (5.Sapindus trifoliatus Linn 45.5a 195.0 64.5 59.77 16:0 (5.4); 18:0 (8.5Schleichera oleosa Oken 40.0b 193.0 57.9 61.55 16:0 (1.6); 16:1 (3.1)Madhuca indica JF Gmel 40.0b 202.1 74.2 56.61 14:0 (1.0); 16:0 (17.Mimusops hexendra

Robx47.0a 202.0 62.2 59.32 16:0 (19.0); 18:0 (14

Pterygota alata Rbr 35.0b 202.6 98.4 51.09 16:0 (14.5); 18:0 (8.Holoptelia integrifolia 37.4b 208.7 49.9 61.22 14:0 (3.5); 16:0 (35.

be safe above which it would cause maintenance problemand might damage the engine. A study on comparison ofcarbonyls emissions from diesel and biodiesel blend wascarried by Correa and Arbilla [104]. Higher emission offormaldehyde, acetaldehyde, acrolein, acetone, propional-dehyde, and butyraldehyde was observed from B2, B5,B10 and B20 blends than neat diesel. However, significantreduction in emission in terms of benzaldehyde wasobserved from biodiesel blends.

Srivastava and Verma [54] have reported the HC, COand NO emissions from karanja oil methyl ester to beslightly higher as compared with petrodiesel. HC emissionof diesel at maximum load was 85 ppm, while that of bio-diesel was 120 ppm due to poor mixing with air. CO emis-sion of diesel at maximum load was reported to be 0.18%as compared to 0.21% of biodiesel and NO emission wasreported to be 12% higher than that of biodiesel. Maximumthermal efficiency of methyl ester and brake specific fuelconsumption of the biodiesel were quite close to that of die-sel and hence the authors were of the view that karanja oilmethyl ester can replace diesel as an alternative fuel. Table8 depicts emission impact of 20 vol% for soybean basedbiodiesel. It can be seen that there is a significant reduction

from kernel, b oil from seeds, osa: other saturated acids, uk: unknown) [107]

tion (%)

.8); 18:2 (27.8)2); 16:1 (4.2); 18:0 (7.5); 18:1 (48.4); 18:2 (21.7)); 18:0 (7.2); 18:1 (50.5); 18:2 (15.8); 18:3 (0.6); 20:0 (0.7); 20:1 (0.2); 22:0

.5); 8:1 (60.9); 18:2 (5.2); 18:3 (7.4); 20:0 (0.3); 22:0 (0.1)

7); 16:1 (0.4); 18:0 (6.5); 18:1 (50.3); 18:2 (21.6); 18:3 (0.4); 20:4 (0.7)7); 18:1 (38.3); 18:2 (21.8); 18:3 (1.2)6:0 (25.1); 18:0 (6.7); 18:1 (46.1); 18:2 (15.4); 18:3 (3.0)

.0); 18:2 (31.0); osa (10.0)0); 18:0 (8.0); 18:1 (32.0); 18:2 (22.0); 20:0 (3.0); 22:0 (4.0)); 18:0 (2.6); 18:1 (88.0); 18:2 (2.9); uk (0.2)6); 18:0 (9.7); 18:1 (40.8); 18:2 (32.1); 20:0 (0.4)0); 18:1 (56.0); 18:2 (18.0); 20:0 (3.0)0); 18:1 (48.0); 18:2 (30.0)

5); 18:0 (18.5); 18:1 (42.7); 18:2 (13.7); 18:3 (2.1); 24:0 (2.6)

8); 18:0 (12.4); 18:1 (60.0); 18:2 (15.0); 20:0 (0.9).4); 18:1 (61.9); 18:2 (7.5); 20:0 (1.3)); 18:1 (83.8); 18:2 (0.8); 20:0 (3.3)

); 18:0 (2.7); 18:1 (79.4); 18:2 (0.7); 18:3 (0.2); 20:0 (5.8)8); 18:1 (49.4); 18:2 (19.0); 20:0 (4.1); 20:1 (2.4); 22:0 (5.3); 24:0 (2.4)5); 18:1 (64.4); 18:2 (12.4); 20:0 (1.8); 20:1 (2.6); 22:0 (1.2); 22:1 (1.7)); 18:1 (55.1); 18:2 (8.2); 20:0 (20.7); 22:0 (2.1); 18:0 (10.1); 18:1 (52.5); 20:0 (19.7); 22:0 (4.0); 22:1 (0.9); gadolic acid (8.4)8); 18:0 (14.0); 18:1 (46.3); 18:2 (17.9); 20:0 (3.0).0); 18:1 (63.0); 18:2 (3.0); 20:0 (1.0)

5); 18:1 (44.0); 18:2 (32.4); uk (1.0)1); 16:1 (1.9); 18:0 (4.5); 18:1 (53.3); 20:0 (1.1); uk (1.4)

Table 10List of 11 species meeting the US biodiesel standards on the basis of fatty acid composition, SN, IV and CN (a oil from kernel, b oil from seeds, osa: othersaturated acids, uk: unknown) [107]

Sources Oil SN IV CN Fatty acid composition (%)

Vallaris solanacea

Kuntze33.0b 198.3 104.7 50.26 16:0 (7.2); 18:0 (14.4); 18:1 (35.3); 18:2 (40.4); 20:0 (1.8); 22:0 (0.4); 24:0 (0.5)

Balanites roxburghii

Planch43.0a 188.9 109.9 50.46 16:0 (17.0); 16:1 (4.3); 18:0 (7.8); 18:1 (32.4); 18:2 (31.3); 18:3 (7.2)

Croton tiglium Linn 45.0b 203.9 102.9 49.9 14:0 (11.0); 16:0 (1.2); 18:0 (0.5); 18:1 (56.0); 18:2 (29.0); 20:0 (2.3)Hydnocarpus wightiana

Blume63.0a 210.5 102.1 49.25 16:0 (1.8); 18:1 (6.9); hydnocarpic acid (48.7); gorlic acid (12.2); chaulmoogric acid (27.0);

chaulmoogtic homolog (3.4)Mappia foetida Milers 48.0b 200.7 101.3 50.70 16:0 (7.1); 18:0 (17.7); 18:1 (38.4); 18:3 (36.8)Perilla frutescens

Britton40.5b 199.0 193.9 30.09 18:1 (9.8); 18:2 (47.5); 18:3 (36.2); osa (6.5)

Aphanamixis

polystachya Park35.0a 203.8 109.1 48.52 16:0 (23.1); 18:0 (12.8); 18:1 (21.5); 18:2 (29.0); 18:3 (13.6)

Princeptia utilis Royle 37.2a 201.9 108.4 48.94 14:0 (1.8); 16:0 (15.2); 18:0 (4.5); 18:1 (32.6); 18:2 (43.6); 24:0 (0.9) uk (1.4)Meyna laxiflora Robyns 38.5b 202.8 101.3 50.42 16:0 (18.8); 18:0 (9.0); 18:1 (32.5); 18:2 (39.7)Aegle marmelos correa

Roxb34.0b 202.5 114.9 48.30 16:0 (16.6); 18:0 (8.8); 18:1 (30.5); 18:2 (36.0); 18:3 (8.1)

Tectona grandis Linn 44.5a 200.9 111.3 48.31 14:0 (0.2); 16:0 (11.0); 18:0 (10.2); 18:1 (29.5); 18:2 (46.4); 18:3 (0.4); 20:0 (2.3)


in HC (21%), CO (10%), PM (11%) and 2.0% increase inNOx emission [105].

9. Indian scenario

India imports more than 40% of its edible oil require-ment and hence non-edible oils are used for the develop-ment of biodiesel. India is a agrarian nation and has richplant biodiversity which can support the development ofbiodiesel. India also has a vast geographical area with agri-cultural lands as well as wastelands on which oil bearingplants can be planted. Common non-edible oil bearingplants and trees include neem, karanja, mahua, jatropha,etc. The oil yields from these species at present are insuffi-cient to meet the demand for raw material on large scaleproduction of biodiesel. Hence, there has been governmentinitiatives and interest from few private firms to enhancethe production and distribution facilities of biodieselthroughout the country. The Petroleum Ministry has seta target for biodiesel to meet 20% of India’s diesel demand.Government’s initiative has resulted in large scale planta-tion of J. curcas in the state Andhra Pradesh. Oil and Nat-ural Gas Corporation (ONGC) has planned to build anexport oriented refinery at kakinada in Andhra Pradeshwhich will have a annual production capacity of 5.5–7.5million tonnes [106].

Azam et al. [107] have studied the profile of 75 indige-nous plant species of India containing 30% or more oil intheir seed, fruit or nut. Out of these plants, based on sapon-ification number, iodine value, cetane number and fattyacid composition, 26 species were found to be most suitablefor use as biodiesel and they met the biodiesel standards ofUSA (ASTM D 6751-02, ASTM PS 121-99), Germany(DIN V 51606) and European Standard Organization(EN 14214). Another 11 plant species met the specificationsof US biodiesel standards. Authors predicts that cultiva-tion of Azardirachta indica or P. pinnata on 40.09 million

and 19.9 million ha, respectively, will meet the target of100% replacement of imported biodiesel which amountedto 87.5 million tons in 2003–2004. These 37 species arelisted in Tables 9 and 10. Among these species, jatropha(Jatropha curcas), karanja (P. pinnata), neem (A. indica),mahua (Madhuca indica) and polanga (Calophyllum

inophyllum) have catched the attention of researchers andbiodiesel manufacturer in India and feasibility of rest ofthe plant species still remains unexplored.

10. Cost of biodiesel

Various factors contributing to the cost of biodieselinclude raw material, other reactants, nature of purifica-tion, its storage, etc. However, the major factor which con-tributes the cost of biodiesel production is the feedstock,which is about 80% of the total operating cost [108]. Costof biodiesel reported by Zhang et al. [29] is US $0.5 l�1

as compared to US $0.35 for normal diesel. Bender in hisreview has reported the cost of biodiesel to be US$0.30 l�1 and US $0.69 l�1 when the fuel was producedfrom soybean and rapeseed respectively. The intact oilseedwas taken as starting material while calculating the cost.Canakci and Van Gerpen while using a small pilot scaleplant in a batch process estimated the cost to be US$0.42 l�1 while using refined, bleached and deodorized soy-bean oil. The profits from glycerol and capital cost foroperation was not included [109,110].

Haas et al. [111] in a study of review on biodiesel pro-duction cost found the feedstock to contribute a substantialportion in production cost. A process model was preparedby the author to estimate biodiesel production costs. Tak-ing all the factors into account viz. raw material (vegetableoil, methanol, catalysts), utilities (electricity, etc.), labour,supplies, general works and depreciation, the cost of bio-diesel was estimated to be US $0.561 l�1. The coproductglycerol as 80% w/w aqueous solution was valued to be


US $0.034 l�1 and reduced the production cost of biodieselby 6% on deduction of this value from original cost. Hence,the gross operating cost of biodiesel was estimated to beUS $0.527 l�1, of which the feedstock comprised 87.36%of the overall cost of biodiesel production.

Nas and Berktay [112] too concluded that feedstock costis the major component contributing to the cost of biodie-sel production. In a comparison of feedstock viz. soybeanoil and yellow grease (recycled cooking oil from restau-rants), it was estimated that yellow grease is quite lessexpensive that soybean oil. On the contrary, the supplyof yellow grease is limited and has other applications andhence it cannot be used on a large scale production. Aneight year comprehensive study (from 2004–2005 to2012–2013), on the price rise of petroleum diesel, yellowgrease and soybean oil is reported. Cost of petroleum hasbeen estimated to rise from 0.67 to 0.75 (i.e. 11.94%increase). Biodiesel fuel obtained from yellow grease is esti-mated to rise from 1.41 to 1.55 (i.e. 9.93% increase). Biodie-sel fuel from soybean oil will rise from 2.54 to 2.80 (i.e.10.24% increase). Author is of opinion that biodiesel willnot be produced at a cost comparable with that of petro-diesel unless the soybean oil price decline.

Table 11Instrumentation involved in characterization of biodiesel

Feedstock Instrument involved for characteriz

Tobacco High performance liquid chromatogPolanga seed oil High performance liquid chromatogPongamia pinnata (i) HPLC (Perkin-Elmer series 2

(ii) H NMR Bruker DPX 300 sp(iii) Gas chromatograph (for ana

Jatropha, Pongamia, sunflower,soybean, palm

(i) GC (Model HR/GC/5300) [f(ii) Thin layer chromatography

Pongamia pinnata Gas chromatography (Nucon, IndiaWaste cooking oil Gas chromatography (GC) equippe

lm) and a FIDNeat and used frying oil (i) HP 6890 series II Gas Chrom

(ii) Thin layer chromatographySunflower oil (i) Gel permeation chromatogra

(ii) Gas chromatograph (GC), NMicroalgal oil CE-440 elemental analyzer (for deteMicroalga chlorella protothecoides Gas Chromatography–mass spectroSoybean oil (i) X-ray diffractometer

(ii) GPC with an RI (refractive(iii) Gas chromatography–mass s

Lipid extracted from the cell of R.

glutinis

Gas chromatograph

Triolein HPLC system (Hitachi, Ltd, TokyoSunflower oil For FAME determination Agilent 6

For catalyst characterization(i) Balzer Prisma quadrupole m

(ii) Seifert 3000 XRD diffractom(iii) VG Escalab 200 R spectrom(iv) Nicolet 5700 Fourier tran

cryodetector)Biopiles Gas chromatography–mass spectromCanola, corn, peanut, olive, waste

vegetableGas chromatography

Castor oil (i) Size exclusion chromatograp(ii) Fourier-transformed infrared

Biodiesel comprises of 11% oxygen by weight whichimprove the combustion process and hence has reducedemissions in terms of hydrocarbon, carbon monoxide andparticulate emissions but increases nitrogen oxide emis-sions. Nitrogen oxide emissions from biodiesel can bereduced by adding cetane enhancers that are di-tert-butylperoxide at 1% or 2-ethylhexyl nitrate at 0.5%. However,addition of these enhancers will increase the cost of biodieselproduction. Nevertheless, reduction in emission of oxides ofnitrogen is desired as they are ozone precursors and afterreaching stratosphere it will result in ozone layer depletion.

In Indian context, the government has fixed the price ofbiodiesel delivered at refineries to be Rs. 26.50 l�1. Thisrate of biodiesel has been fixed after the Indian governmenthas provided subsidies in order to encourage its application[113].

The cost of biodiesel after blending with petrodiesel willreduce as the cost of biodiesel becomes less significant inblended form. At present, biodiesel can be blended with80% petrodiesel (B20) without any engine modification. B100 (100% biodiesel) costed US $3.76 per gallon of biodie-sel in USA in June 2006, whereas, B 20 (20% biodiesel and80% petrodiesel) costed US $2.98 per gallon of biodiesel.

ation Reference

raph [7]raph [8]00) equipped with refractive index detector (shodex RI 71)ectrometer (Bruker, Rheinstetten, Germany)lysis of fatty acid composition of karanja oil)

[11]

or fatty acid composition of vegetable oils)(TLC)

[12]

) equipped with a FID detector [14]d with a capillary column (SPBTM-5, 30 m � 0.32 mm � 0.25 [16]

atograph with a 3365/II GC-chemstation and a FID(TLC)

[19]

ph (GPC)ucon 5765, India

[20]

rmining elemental composition of biodiesel) [21]metric analysis [22]

index) detector, (carrier: THF)pectrometer

[23]

[24]

, Japan, D-7000 interface, L-7100 [26]890 GC with a HP INNOwax capillary column [27]

ass spectrometer (QMS 200)eter (equipped with a PW gonimeter)eter (equipped with a hemispherical electron analyzer)sform spectrophotometer (equipped with an Hg-col-Te

eter [79][85]

hy (SEC)spectroscopy

[104]


11. Instrumentation involved in biodiesel production

For production of biodiesel, there are some primarysteps. If kernel or seeds are taken as starting materials, infirst step the raw oil is to be expelled from the kernel bymechanical crusher. This raw oil is in fact feedstock fordevelopment of biodiesel. After feedstock is obtained,beakers, measuring flasks, test tubes, separating funnels,etc. are needed up to development of biodiesel. Practicallyno instruments are needed till its development. Most of theinstruments are used for characterization of the biodieselproduct. Further, the instruments used for characterizationcan be divided into the categories of minor and majorequipments. Viscometer, cetane number analyzer, etc. areminor equipments. Flash point, cloud point, pour point,etc. are also determined by minor instruments. Majorinstruments are however, needed for chemical characteriza-tion of biodiesel product. Gas chromatograph, gas chro-matograph–mass spectrometer, high performance liquidchromatograph, fourier transformed infrared spectrome-ter, elemental analyzer etc. are the major instruments usedfor chemical characterization of the product. The majorinstruments are listed in Table 11.

12. Conclusions

Biodiesel is derived from a varied range of vegetable oil(edible and non-edible), animal fats, used frying oil, wastecooking oil and wastewater. The edible oil in use at presentis soybean, sunflower, canola, palm. The non-edible oil usedas feedstock for biodiesel production includes J. curcas, P.pinnata, M. indica, F. elastica, A. indica, C. inophyllum,etc. The main advantage in its usage is attributed to lesserexhaust emissions in terms of carbon monoxide, hydrocar-bons, particulate matter, polycyclic aromatic hydrocarboncompounds and nitrited polycyclic aromatic hydrocarboncompounds. Biodiesel is said to be carbon neutral as moreof carbon dioxide is absorbed by the biodiesel yieldingplants than what is added to the atmosphere when used asfuel. Exhaust emissions of NOx can be controlled by adopt-ing certain strategies such as change in composition of feed-stock, addition of cetane improvers, retardation of injectiontiming, exhaust gas recirculation, etc.

Transesterification is the process successfully employedat present to reduce the viscosity of biodiesel and improveother characteristics. Methanol being cheaper is the com-monly used alcohol during transesterification reaction.Among the catalysts, homogeneous catalysts such as sul-phuric acid, sodium hydroxide, potassium hydroxide arecommonly used at industrial level production of biodiesel.Heterogeneous catalysts such as calcium oxide, magnesiumoxide and others are also being tried to decrease the cata-lyst amount and production cost of biodiesel. Transesteri-fication reaction can be completed even without catalystby using supercritical methanol but it will increase the pro-duction cost of biodiesel as it is energy intensive. The molarratio of alcohol to oil required is 3:1 by stoichiometry, but

excess molar ratio has been used for biodiesel productionfor better yield in lesser time. The molar ratio employedduring acid esterification is between 6:1 and 18:1 whereasthe molar ratio used alkaline transesterification rangesbetween 5:1 and 12:1 after reducing the acid value to lessthan 2.0% approximately. The temperature ranges between318 and 338 K as the boiling point of methanol is 337.7 Kand heating beyond this temperature would burn metha-nol. However, higher temperature is employed while usingsupercritical methanol (473–573 K). Depending on thefeedstock taken; amount and type of alcohol and catalyst;temperature employed; mode and rate of stirring; there isdifference in the yield of biodiesel which varied from 80to 100%. The percent conversion of biodiesel also rangedbetween 80% and 100%.

Another added advantage of biodiesel is that it is biode-gradable in nature. When used as blend along with dieselfuel, it shows positive synergic effect of biodegradation bymeans of cometabolism. Major disadvantage of biodieselis the inverse relationship of oxidation stability of biodieselwith its low temperature properties which includes cloudpoint and pour point. Higher composition of saturated fattyacids in feedstock will increase the oxidation stability of bio-diesel but will lower its cloud and pour points. Whereas,higher composition of unsaturated fatty acids will enhancethe cloud point and pour point of biodiesel but will have apoor oxidation stability. Hence, a balance has to be main-tained between the ratio of saturates and unsaturates forthe oil to be used as a feedstock for biodiesel production.

Edible oils are in use in developed nations such as USAand European nations but developing nations are not selfsufficient in the production of edible oils and hence haveemphasized in the application of a number of non-edibleoils. In a country like India, which is rich in plant biodiver-sity, there are many plant species whose seeds remainunutilized and underutilized have been tried for biodieselproduction. These species have shown promises and fulfillsvarious biodiesel standards. However, there still is paucityin terms of all the standards which should be fulfilled forthe large commercial application and its acceptance frompublic and governing bodies.

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