Mixtures of Vegetable Oils and Animal Fat for BiodieselProduction: Influence on Product Composition and Quality

Joana M. Dias, Maria C. M. Alvim-Ferraz,* and Manuel F. Almeida

LEPAE, Faculdade de Engenharia, UniVersidade do Porto,R. Dr. Roberto Frias, Porto 4200-465, Portugal

ReceiVed July 4, 2008. ReVised Manuscript ReceiVed August 18, 2008

Studying alternative raw materials for biodiesel production is of major importance. The use of mixtures,namely, by incorporating wastes, is an environmental friendly alternative and might reduce production costs.The objective of the present work was (i) to study biodiesel production using vegetable oils (virgin and waste)mixed with animal fat, (ii) to analyze the variations in biodiesel composition, aiming its prediction whenmixtures with different fat contents are used as raw materials, and (iii) to understand how mixture compositioninfluences biodiesel quality. Production yields varyed from 81.7 to 88.8 wt %; furthermore, the obtained productsfulfilled most of the determined quality specifications according to European biodiesel quality standard EN14214. Minimum purity was only achieved using waste frying oil or soybean oil alone as raw material; however,it ranged from 93.9 to 96.6 wt %, always being close to the limit (96.5 wt %). It was possible to establish amodel to be used for predicting composition and some parameters of biodiesel resulting from the mixtures,and it could be estimated that the use of at least 12% lard in a soybean oil/lard mixture would be effective inreducing the iodine value of biodiesel to acceptable values. Considering the use of virgin or waste vegetableoils, it was concluded that waste frying oil might be an alternative raw material to obtain a biodiesel fulfillingEuropean standard at a lower cost.

Introduction

Biodiesel consists of a mixture of fatty acid alkyl esters, usedas an alternative fuel in compression-ignition engines; it isobtained from renewable resources, such as vegetable oils andanimal fats, which makes it biodegradable and nontoxic.Furthermore, biodiesel contributes for the reduction of CO2

emissions, because of the fact that production comprises a closedcarbon cycle.1,2 Biodiesel also presents very low sulfur content,high cetane number, and good characteristics regarding storageand transportation, which makes it a very attractive alternativefuel.1,3,4 Biodiesel might be produced by transesterification,which is a three-step reversible reaction that converts the initialtriglyceride into a mixture of alkyl esters and glycerol, in thepresence of a catalyst (Figure 1).

At an industrial scale, biodiesel production is mainly madeusing virgin vegetable oils. The current great obstacle forbiodiesel production is the high price of those raw materials;also, the use of food oils for biodiesel production is controver-sial, which is the reason why studying alternatives is of majorimportance. There are many studies reporting the transesteri-fication of different types of vegetable oils; on the contrary,few studies can be encountered regarding the conversion of

animal fat. This is probably due to the fact that animal fat useat a larger scale is limited; also, a high degree of free fatty acidsgives rise to difficult production processes.5

Studies regarding the mixture of raw materials for biodieselproduction are currently limited; however, in a study byMeneghetty et al.,6 the use of castor oil, which had a viscosityof 225.8 mm2 s-1 at 40 °C enabled biodiesel production bymixing it with either soybean or cottonseed oil. In a study byLebedevas et al.,7 the use of three component mixtures alsoallowed for the reduction of emission and harmful componentsof the fuel. Soybean oil has a high iodine value; therefore, theproduct obtained using this raw material alone often does notfulfill the European biodiesel standard EN 14214. On the otherhand, animal fat is known to have a low iodine value, andtherefore, its use in mixtures with soybean oil will probablyresult in a fuel with improved iodine values (lower than thelimit).

The use of wastes as raw materials for biodiesel productionhas three major advantages: (i) does not compete with the foodmarket, (ii) recycles waste, and (iii) reduces production costs.8

The great amount of waste animal fat, produced at several

* To whom correspondence should be addressed. Telephone: +351-22-5081688. Fax: +351-22-5081449. E-mail: aferraz@fe.up.pt.

(1) Bozbas, K. Biodiesel as an alternative motor fuel: Production andpolicies in the European Union. Renewable Sustainable Energy ReV. 2008,12 (2), 542–552.

(2) Van Gerpen, J. Biodiesel processing and production. Fuel Process.Technol. 2005, 86 (10), 1097–1107.

(3) Meher, L. C.; Vidya Sagar, D.; Naik, S. N. Technical aspects ofbiodiesel production by transesterificationsA review. Renewable SustainableEnergy ReV. 2006, 10 (3), 248–268.

(4) VenkatReddy, C. R.; Oshel, R.; Verkade, J. G. Room-temperatureconversion of soybean oil and poultry fat to biodiesel catalyzed bynanocrystalline calcium oxides. Energy Fuels 2006, 20 (3), 1310–1314.

(5) Ngo, H. L.; Zafiropoulos, N. A.; Foglia, T. A.; Samulski, E. T.; Lin,W. Efficient two-step synthesis of biodiesel from greases. Energy Fuels2008, 22 (1), 626–634.

(6) Meneghetti, S. M. P.; Meneghetti, M. R.; Serra, T. M.; Barbosa,D. C.; Wolf, C. R. Biodiesel production from vegetable oil mixtures:cottonseed, soybean, and castor oils. Energy Fuels 2007, 21 (6), 3746–3747.

(7) Lebedevas, S.; Vaicekauskas, A.; Lebedeva, G.; Makareviciene, V.;Janulis, P.; Kazancev, K. Use of waste fats of animal and vegetable originfor the production of biodiesel fuel: Quality, motor properties, and emissionsof harmful components. Energy Fuels 2006, 20 (5), 2274–2280.

(8) Wang, Y.; Ou, S.; Liu, P.; Xue, F.; Tang, S. Comparison of twodifferent processes to synthesize biodiesel by waste cooking oil. J. Mol.Catal. A: Chem. 2006, 252 (1-2), 107–112.

Energy & Fuels 2008, 22, 3889–3893 3889

10.1021/ef8005383 CCC: $40.75 2008 American Chemical SocietyPublished on Web 10/15/2008

slaughterhouses and other meat-processing units, might be anattractive and cheap raw material. One of the great concernsregarding the use of animal fat as a raw material for biodieselproduction is its cold-weather properties and oxidation stability;however, it is known that the obtained fuel might be used in100% in boilers for heat generation. Other waste materials thatcan be used for biodiesel production are the waste-fryingoils.8-11 Because of the scarce availability of these low-costmaterials, their use at an industrial scale is limited; however,their mixture with other raw materials might be an attractivealternative.

The current knowledge regarding the use of mixtures of rawmaterials including wastes is yet very scarce. Aiming to improvethis knowledge, the objective of the present work was (i) tostudy biodiesel production using vegetable oils (virgin andwaste) mixed with animal fat, (ii) to analyze the variations inbiodiesel composition, aiming its prediction when mixtures withdifferent fat contents are used as raw materials, and (iii) tounderstand how mixture composition influences biodieselquality.

Experimental Section

General. The soybean oil used was from the brand “olisoja”and was donated by Sovena, SA, Portugal. This oil met Portuguesespecifications for food oil. The pork lard was from the brand “DilopCarnes” and was purchased at the food market. The waste fryingoil was obtained from a voluntary collection system implementedat the Faculty and consisted of waste frying oil from differentdomestic sources. The same mixture of waste frying oils was usedin all experiments. The reagents used during biodiesel productionprocedures were methanol (99.5%, analytical grade, FischerScientific), sodium hydroxide powder (97%, reagent grade, Aldrich),and anhydrous sodium sulfate (99%, analytical grade, Panreac).Biodiesel production was performed in three steps: pretreatmentof raw material, synthesis, and purification.

Raw Materials Pretreatment. Waste frying oil was filteredunder vacuum, dehydrated using anhydrous sodium sulfate (leftovernight), and finally again filtered under vacuum. The pork lardwas first heated at 100 °C to eliminate residual water and cooledto near the reaction temperature (60 °C).

Raw Materials Characterization. Different properties of thestarting raw materials were determined: (i) composition [using gaschromatography (GC) according to EN 14103 (2003) and NP ENISO 5508 (1996)], (ii) acid value, by volumetric titration accordingto the standard NP EN ISO 660 (2002), (iii) iodine value, byvolumetric titration using Wijs reagent, according to the standardISO 3961 (1996), and (iv) water content, using coulometric KarlFischer titration.

Biodiesel Synthesis. Synthesis of biodiesel was carried out bytransesterification. The mixtures of vegetable oil and fat wereprepared considering the increase in the fat fraction of the mixture,varying from 0 to 1 (w/w), in 0.2 intervals. The fat was weightedand added to the reactor, which already contained the necessaryamount of vegetable oil (soybean oil or waste frying oil). A definedamount of methanol (6:1 molar ratio to oil) premixed with NaOH(0.8 wt % of the starting mixture weight) was added to the reactor,which already had 100 g of the raw material mixture, preheated atthe reaction temperature. The catalyst concentration was chosen

according to a previous study by Dias et al.12 At this point, thereaction started; the reactor consisted of a 1 L flat-bottom flaskimmersed in a temperature-controlling bath, equipped with a water-cooled condenser and a magnetic stirrer. Suggested by the literaturereview, the reaction occurred for 60 min under vigorous stirring;at the end of the reaction, products were left to settle for 1 h toallow for the separation of the two phases: biodiesel and glycerol.

Biodiesel Purification. Both phases were separated, and excessmethanol was recovered from each phase, using a rotary evaporatorunder reduced pressure. Biodiesel was then filtered (S&S, grade589/1) and washed, first with 50% (v/v) of an acid solution (0.2%HCl) and then repeatedly with 50% (v/v) of distilled water untilthe pH of the washing water was the same as the distilled water.The filtering stage was adopted because of the fact that itsignificantly improved the washing stage, reducing emulsionformation. Regarding biodiesel dehydration, different procedureswere adopted to evaluate which would be the best one. Suchprocedures were based on the use of an anhydrous salt andevaporation at reduced pressure under different conditions.

Biodiesel Characterization. The biodiesel quality was evaluatedaccording to the European biodiesel standard EN 14214 (2003).The following parameters were determined: (i) acid value, byvolumetric titration according to the standard EN 14104 (2003),(ii) kinematic viscosity, determined at 40 °C using glass capillaryviscometers according to the standard ISO 3104 (1994), (iii) density,determined using a hydrometer method according to the standardEN ISO 3675 (1998), (iv) flash point, using a rapid equilibriumclosed cup method according to the standard ISO 3679 (2004), (v)copper corrosion, using a copper strip test according to the standardISO 2160 (1998), (vi) water content, by Karl Fischer coulometrictitration according to the standard NP EN ISO 12937 (2003), (vii)ester and linolenic acid methyl ester contents by GC according tothe standard EN 14103 (2003), and (viii) iodine value, determinedfrom ester content according to annex B of EN 14214 (2003). Withregard to chromatographic analysis, a Dani GC 1000 DPC gaschromatograph (DANI Instruments S.p.A.), with an AT-WAX(Heliflex capillary, Alltech) column (30 m, 0.32 mm internaldiameter and 0.25 µm film thickness) was used. The injectortemperature was set at 250 °C, while the flame ionization detector(FID) temperature was set at 255 °C. The carrier gas used was N2,with a flow of 2 mL/min. Injection was made in a split mode, usinga split flow rate of 50 mL/min (split ratio of 1:25), and the volumeinjected was 1 µL.

Results and Discussion

Raw Materials Properties. The fatty acid composition andthe mean molecular weight (calculated from the composition)as well as some other measured properties of the starting rawmaterials are presented in Table 1. Considering the typical fattyacid composition of vegetable oils as determined using GC,13

the waste frying oil composition indicates that both soybeanand sunflower oil might be present; the low C18:3 content andthe content in C18:1 might indicate that sunflower is present ina higher amount.13 As expected, the acid value of the soybeanoil was lower than the waste frying oil; however, much higheracid values have been reported for waste frying oils.8,14 Thelow acid value found might indicate a smaller degree of bothoxidation and hydrolysis reactions. This can be justified becausethe waste frying oils were from a domestic source and they

(9) Al-Widyan, M. I.; Al-Shyoukh, A. O. Experimental evaluation ofthe transesterification of waste palm oil into biodiesel. Bioresour. Technol.2002, 85 (3), 253–256.

(10) Felizardo, P.; Neiva Correia, M. J.; Raposo, I.; Mendes, J. F.;Berkemeier, R.; Bordado, J. M. Production of biodiesel from waste fryingoils. Waste Manage. 2006, 26 (5), 487.

(11) Zheng, S.; Kates, M.; Dube, M. A.; McLean, D. D. Acid-catalyzedproduction of biodiesel from waste frying oil. Biomass Bioenergy 2006, 30(3), 267–272.

(12) Dias, J. M.; Alvim-Ferraz, M. C. M.; Almeida, M. F. Comparisonof the performance of different homogeneous alkali catalysts duringtransesterification of waste and virgin oils and evaluation of biodiesel quality.Fuel 2008, 87 (17-18), 3572–3578.

(13) Rossel, J. B. Classical analysis of oils and fats. In Analysis of Oilsand Fats; Hamilton, R. J., Rossel, J. B., Eds.; Elsevier Applied Science:London, U.K., 1986.

(14) Graboski, M. S.; McCormick, R. L. Combustion of fat and vegetableoil derived fuels in diesel engines. Prog. Energy Combust. Sci. 1998, 24(2), 125–164.

3890 Energy & Fuels, Vol. 22, No. 6, 2008 Dias et al.

might have been exposed to high temperatures for shortperiods.15 Pork lard also presented a low acid value, probablyresulting from pretreatment processes; however, the commonlyreferred value for commercial lard is slightly higher (1.3 mg ofKOH/g of fat).16

Yield. Biodiesel production yields are presented in Table 2.They varied from 81.7 to 88.8 wt %. Production using onlysoybean oil as raw material presented a yield almost 7% higherthan when using only waste frying oil or lard as raw materials;however, considering all oil/lard mixtures, the differencesbetween yields were less than 3.4%.

Effect of Different Dehydration Treatments in BiodieselWater Content. High water contents will improve biodieseldegradation because of hydrolysis,17 therefore affecting thestorage life of the fuel. The standard limit according to EN14214 is 0.05 wt %. With the objective of selecting anappropriate dehydration method, each sample produced wassubjected to a different treatment. The following treatments wereperformed: 30 wt % of anhydrous salt (AS) or evaporation (163mbar) including heating at 40 °C during 45 min (Ev40/45), heatingat 45, 65, and 80 °C during 1 h and 30 min (Ev45/90, Ev65/90,and Ev80/90), heating at 90 °C during 2 h (Ev90/120), and heatingat 90 °C during 3 h and 30 min (Ev90/210). Table 3 shows whichsamples were used in each treatment as well as the final watercontents. The same dehydration treatment led to different finalwater contents depending upon the water content after thewashing stage. When evaporating during 1 h and 30 min, theeffect of increasing the temperature was mainly noted whengoing from 45 to 65 °C. The increase in evaporation time wasnot very much reflected in terms of decreasing biodiesel watercontent; however, independent of the sample used, a greatdecrease in the biodiesel water content was observed whenincreasing the temperature from 45 to 90 °C. Considering theobtained results, evaporation at 90 °C, 163 mbar, and a holdingtime of 3 h and 30 min seemed to be enough to ensure thatbiodiesel samples fulfill the European biodiesel standard EN14214.

Biodiesel Composition. Biodiesel composition resulting fromthe transesterification of soybean and waste frying oil mixedwith lard was evaluated, aiming its prediction when mixtureswith different lard contents are used as raw materials.

It was postulated that the fatty acid content of biodieselcorresponded to the weighted average of its content in eachcomponent of the mixture, therefore

Cmix )CoilXoil +ClardXlardSCmix ) (Clard -Coil)Xlard +Coil (1)

where Cmix is the fatty acid content (wt %) of the mixture, Clard

is the fatty acid content (wt %) of the lard, Coil is the fatty acid

(15) Cetinkaya, M.; Karaosmanoglu, F. Optimization of base-catalyzedtransesterification reaction of used cooking oil. Energy Fuels 2004, 18,1888–1895.

(16) Codex Alimentarius Commission (CAC). Codex standard for fatsand oils from animal sources (CODEX-STAN 211-1999). In Fats, Oils andRelated Products, 2nd ed.; Joint FAO/WHO Food Standards Program. Foodand Agriculture Organization of the United Nations: Rome, Italy, 2001;Vol. 8.

(17) Leung, D. Y. C.; Koo, B. C. P.; Guo, Y. Degradation of biodieselunder different storage conditions. Bioresour. Technol. 2006, 97 (2), 250–256.

Figure 1. Transesterification of triglycerides (overall reaction).

Table 1. Starting Raw Materials Properties Including AcidValue, Iodine Value, Water Content, Fatty Acid Composition

(wt %), and Mean Molecular Weighta

raw material properties soybean oil pork lardwaste frying

oil

acid value (mg of KOH/g) 0.21 0.71 0.82iodine value (g of I2/100 g) 127 67 117water content (wt %) 0.04 0.03 0.05fatty acid composition (wt %)

miristic (C14:0) nd 1.3 ndpalmitic (C16:0) 11.0 23.7 8.4palmitoleic (C16:1) nd 2.2 0.2heptadecenoic (C17:1) nd 0.4 ndstearic (C18:0) 3.3 12.9 3.7oleic (C18:1) 25.4 41.4 34.6linoleic (C18:2) 53.6 15.0 50.5linolenic (C18:3) 5.3 1.0 0.6arachidic (C20:0) 0.4 0.2 0.4eicosenoic (C20:1) 0.3 0.9 0.4eicosadienoic (C20:2) 0.0 0.7 ndeicosatrienoic (C20:3) nd 0.2 ndbehenic (C22:0) 0.4 nd 0.8docosadienoic (C22:2) 0.2 nd ndlignoceric (C24:0) 0.1 nd 0.3

mean molecular weight (g/mol) 874.0 861.6 877.5

a nd ) not detected.

Table 2. Biodiesel Production Yields (wt %) Using DifferentVegetable Oil/Lard Mixtures as Raw Materials

lard fraction(wt)

soybean oil/lard mixture

waste frying oil/lard mixture

0 88.8 82.20.2 87.4 87.10.4 85.2 87.60.6 87.6 85.20.8 88.6 88.01 81.7 81.7

Table 3. Dehydration Methods Used and Final Water Contentsof the Biodiesel Samples

soybean oil/lard mixture waste frying oil/lard mixture

lard fraction(wt)

dehydrationmethod

water content(wt %)

dehydrationmethod

water content(wt %)

0 AS 0.127 AS 0.1000.2 Ev40/45 0.154 Ev90/210 0.0400.4 Ev65/90 0.095 Ev80/90 0.1000.6 Ev45/90 0.153 Ev90/120 0.0450.8 Ev40/45 0.155 Ev90/120 0.0561 Ev40/45 0.114 Ev40/45 0.114

Mixtures of Oils and Fat for Biodiesel Production Energy & Fuels, Vol. 22, No. 6, 2008 3891

content (wt %) of the oil, Xoil is the weight fraction of oil, andXlard is the weight fraction of lard.

In fact, it was found that the fatty acid content of biodieselwas linearly correlated to the mass fraction of lard incorporatedin the raw material, with a determination coefficient r2 > 0.88and p value < 0.05 (probability of falsely rejecting the nullhypothesis, using a F test) for fatty acids corresponding to >96%of the biodiesel composition. Table 4 shows the linear regressionparameters. From those, it was possible to verify that the slope(a) was similar to the difference between the fatty acid contentin fat and oil (Clard - Coil) and also that the intercept (b) wassimilar to the fatty acid content in the oil (Coil) and differenceswere lower than 5%. Such results show that eq 1 might be usedto predict the fatty acid content of biodiesel resulting frommixtures of soybean oil/lard and waste frying oil/lard whenmixtures with different lard contents are used.

Biodiesel Quality. As it can be observed in Table 5, allproduced samples fulfilled the European standard limit in termsof acid value, kinematic viscosity, density, flash point, coppercorrosion, and linolenic methyl ester content. High flash pointsindicate effective methanol recovery, which should be reflectedin low methanol contents of biodiesel. Kinematic viscosity wasslightly higher for mixtures using waste frying oil; however, itwas always within the standard limits according to EN 14214.Among the measured parameters, methyl ester content (purity)

and iodine value were the ones that were not fulfilled by allsamples. It was verified that the minimum purity of biodiesel(96.5 wt %) was only achieved when using waste frying oil orsoybean oil alone as raw material (Figure 2); when using 100%lard, lowest purity was obtained (94.4%). The lowest purityobtained using lard alone led to a decrease in biodiesel puritywith an increased incorporation of lard, despite the high yieldsobtained. However, it should be referred that purity might beimproved, namely, by increasing either catalyst concentration(for instance, 1 wt %) or temperature (for instance, 65 °C). 12,18

As for the composition, it was postulated that the parameterof the biodiesel obtained from the mixture corresponded to theweighted average of the parameter of biodiesel resulting fromeach component. Therefore

Pmix )PoilXoil +PlardXlardSPmix ) (Plard -Poil)Xlard +Poil (2)

where Pmix is the parameter of biodiesel from the mixture, Plard

is the parameter of biodiesel from the lard, Poil is the parameterof biodiesel from the oil, Xoil is the weight fraction of oil, andXlard is the weight fraction of lard.

A linear correlation was also found between some of thequality parameters and the lard fraction incorporated in the oil;those parameters were iodine value, density, viscosity, methylester content, and linolenic methyl ester content. Such correla-tions had r2 > 0.79 (p < 0.05), except in the case of viscosityand methyl ester content of biodiesel resulting from the mixtureof waste frying oil and lard. Table 6 shows the linear regressionparameters of the fitting. It was possible to verify that,considering the fittings with determination coefficients > 0.8,the slope (a) was similar to the difference between the propertyin fat and oil (Plard - Poil) and also that the intercept (b) wassimilar to the property of the oil (Poil) (differences were lessthan 3.5%). The very low determination coefficient foundregarding biodiesel viscosity resulting from waste frying oil/lard mixtures might be explained by the fact that biodieselsamples obtained from these two raw materials had very similarviscosities and experimental errors were much more reflected.The results showed that eq 2 might be used to predict theproperty of biodiesel resulting from mixtures of soybean oil/lard and waste frying oil/lard when mixtures with different lardcontents are used for the following properties: iodine value,

(18) Leung, D. Y. C.; Guo, Y. Transesterification of neat and used fryingoil: Optimization for biodiesel production. Fuel Process. Technol. 2006,87 (10), 883–890.

Table 4. Fitting of Fatty Acid Content (wt %) of Biodieselversus Lard Mass Fraction Incorporated in the Oil and Linear

Regression Parametersa

fatty acid mixture a b r2 p value Coil Clard Clard - Coil

C14:0sb/l 1.3 0.0 0.991 <0.0001 nd 1.3 1.3wfo/l 1.3 0.1 0.989 <0.0001 nd 1.3 1.3

C16:0 sb/l 12.2 11.1 0.994 <0.0001 11.0 23.7 12.7wfo/l 15.3 8.5 1.000 <0.0001 8.4 23.7 15.4

C18:0 sb/l 9.3 3.3 0.993 <0.0001 3.3 12.9 9.6wfo/l 9.1 3.8 1.000 <0.0001 3.7 12.9 9.2

C18:1 sb/l 15.8 26.0 0.952 <0.001 25.4 41.4 16.0wfo/l 6.8 34.8 0.994 <0.0001 34.6 41.4 6.9

C18:2 sb/l -37.5 53.2 0.993 <0.0001 53.6 15.0 -38.6wfo/l -35.3 50.2 1.000 <0.0001 50.5 15.0 -35.5

C18:3 sb/l -4.5 5.2 0.892 <0.05 5.3 1.0 -4.4wfo/l 0.3 0.6 0.995 <0.0001 0.6 1.0 0.3

C20:0 sb/l -0.1 0.4 0.987 <0.0001 0.4 0.2 -0.1wfo/l -0.2 0.4 0.997 <0.0001 0.4 0.2 -0.2

C20:1 sb/l 0.6 0.3 0.985 <0.0001 0.3 0.9 0.6wfo/l 0.5 0.4 0.996 <0.0001 0.4 0.9 0.5

C22:0 sb/l -0.5 0.5 0.878 <0.01 0.5 nd -0.5wfo/l -0.9 0.9 1.000 <0.0001 0.8 nd -0.8

a Coil, fatty acid content of oil; Clard, fatty acid content of lard; a,slope; b, intercept; r2, determination coefficient; p, probability value(using a F test); sb, soybean; wfo, waste frying oil; nd, not detected.

Table 5. Quality Parameters of Biodiesel from Oil/LardMixtures and the Respective Standard Limits According to

EN 14214

property results EN 14214

acid value (mg of KOH/g) 0.02-0.10 <0.5kinematic viscosity at 40 °C (mm2 s-1)

lard/soybean oil mixture 4.46-4.71 3.50-5.00lard/waste frying oil mixture 4.67-4.77

density at 15 °C (kg m-3) 875.7-883.6 860-900flash point (°C) 174-179 >120copper corrosion (3 h/50 °C) all samples class 1a class 1methyl ester content (wt %) 93.9-96.6 >96.5linolenic methyl ester content (wt %)

lard/soybean oil mixture 1.0-5.3 <12.0lard/waste frying oil mixture 0.6-1.0

iodine valuea (g of I2/100 g)lard/soybean oil mixture 67-127 <120lard/waste frying oil mixture 67-117

a Calculated from the methyl ester composition.

Figure 2. Methyl ester content (wt %) of biodiesel samples obtainedusing different mixtures of vegetable oil and lard.

3892 Energy & Fuels, Vol. 22, No. 6, 2008 Dias et al.

density, viscosity (considering soybean/lard mixtures only),methyl ester content (considering soybean/lard mixtures only),and linolenic methyl ester content.

The iodine value gives the degree of unsaturation of thebiodiesel samples. The existence of double bonds might leadto polymerization of glycerides by heating, which could leadto gum formation.19 As expected, the increase in the lard fractionled to a decrease in the iodine value. In the case of the mixturewith soybean oil, this had a positive effect because biodieselobtained from soybean oil alone does not meet the standardspecification according to EN 14214. From the linear model, itwas possible to estimate that the use of 12% lard in the soybean/lard mixture would decrease the biodiesel iodine value to themaximum limit according to the European biodiesel standard.Therefore, the incorporation of lard in the soybean oil was foundto be effective in reducing the iodine value of biodiesel toacceptable values.

Overall, in terms of using virgin or waste oil, the mixturebehavior was not very different, which can indicate thatincorporating waste frying oil might be a good alternative toobtain a biodiesel that fulfils European standard at a lower cost.

Conclusions

Synthesis of biodiesel by transesterification of several rawmaterial mixtures of virgin/waste frying oil/pork lard results inyields varying from 81.7 to 88.8 (wt %). Evaporation at 90 °C,163 mbar during 3 h and 30 min was established as an efficientdehydration method for biodiesel production using such rawmaterial mixtures.

Biodiesel met the European biodiesel quality standard EN14214 in terms of acid value, viscosity, density, flash point,

copper corrosion, and linolenic acid methyl ester content usingdifferent incorporation percentages of lard in soybean oil andwaste frying oil. Methyl ester content (purity) and iodine valuewere the ones that were not fulfilled in some cases. Minimumpurity was achieved when using waste frying oil or soybeanoil alone as raw material; however, it was always close to thelimit (93.9-96.6 wt %).

It was postulated and confirmed by a linear model that (i)the fatty acid content of biodiesel corresponds to the weightedaverage of its content in each component of the mixture and(ii) the parameter of the biodiesel obtained from the mixturecorresponded to the weighted average of the parameter ofbiodiesel resulting from each component. For the first, it couldbe applied for fatty acids corresponding to >96% of thebiodiesel composition (linear fittings with determination coef-ficient r2 > 0.88 and p value < 0.05). For the second, it couldbe applied for iodine value, density, viscosity (consideringsoybean/lard mixtures), methyl ester content (consideringsoybean/lard mixtures), and linolenic methyl ester content (linearfittings with determination coefficient r2 > 0.79 and p value <0.05). It was predicted that the use of at least 12% lard in asoybean oil/lard mixture would be effective in reducing theiodine value of biodiesel to acceptable values.

Considering all studied production and quality parameters,there was not much difference regarding the use of refined orwaste oil, which can indicate that the use of waste frying oilmight be a good alternative to obtain a biodiesel that fulfilsEuropean standard EN 14214 at a lower cost.

Acknowledgment. J. M. Dias thanks the FCT for the fellowshipSFRD/BD/22293/2005.

EF8005383

(19) Encinar, J. M.; Gonzalez, J. F.; Rodrıguez-Reinares, A. Biodieselfrom used frying oil. Variables affecting the yields and characteristics ofthe biodiesel. Ind. Eng. Chem. Res. 2005, 44, 5491–5499.

Table 6. Fitting of Some Quality Parameters of Biodiesel from Oil/Lard Mixtures versus Incorporated Lard Fraction and LinearRegression Parametersa

property mixture a b r2 p value Poil Plard Plard - Poil

iodine value (g of I2/100 g)sb/l -59 127 0.991 <0.0001 127 67 -60wfo/l -50 118 1.000 <0.0001 117 67 -50

density (kg m-3)sb/l -7.9 883.4 0.993 <0.0001 883.6 875.7 -7.8wfo/l -7.4 883.4 0.989 <0.0001 883.4 875.7 -7.6

viscosity (mm2 s-1)sb/l 0.25 4.46 0.815 <0.05 4.46 4.71 0.25wfo/l 0.02 4.70 0.040 0.705 4.69 4.71 0.02

methyl ester content (wt %)sb/l -2.5 96.3 0.788 <0.05 96.6 94.4 -2.2wfo/l -2.5 96.1 0.615 0.0647 96.3 94.4 -1.9

linolenic methyl ester content (wt %)sb/l -4.5 5.2 0.892 <0.05 5.3 1.0 -4.4wfo/l 0.3 0.6 0.995 <0.05 0.6 1.0 0.3

a Poil, property of oil; Plard, property of lard; a, slope; b, intercept; r2, determination coefficient; p, probability value (using a F test); sb, soybean; wfo,waste frying oil.

Mixtures of Oils and Fat for Biodiesel Production Energy & Fuels, Vol. 22, No. 6, 2008 3893