Energy & Fuels 2008, 22, 3889–3893
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Mixtures of Vegetable Oils and Animal Fat for Biodiesel Production: 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 when mixtures with different fat contents are used as raw materials, and (iii) to understand how mixture composition influences biodiesel quality. Production yields varyed from 81.7 to 88.8 wt %; furthermore, the obtained products fulfilled most of the determined quality specifications according to European biodiesel quality standard EN 14214. 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 a model 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 in reducing the iodine value of biodiesel to acceptable values. Considering the use of virgin or waste vegetable oils, it was concluded that waste frying oil might be an alternative raw material to obtain a biodiesel fulfilling European standard at a lower cost.
Introduction Biodiesel consists of a mixture of fatty acid alkyl esters, used as an alternative fuel in compression-ignition engines; it is obtained from renewable resources, such as vegetable oils and animal fats, which makes it biodegradable and nontoxic. Furthermore, biodiesel contributes for the reduction of CO2 emissions, because of the fact that production comprises a closed carbon cycle.1,2 Biodiesel also presents very low sulfur content, high cetane number, and good characteristics regarding storage and transportation, which makes it a very attractive alternative fuel.1,3,4 Biodiesel might be produced by transesterification, which is a three-step reversible reaction that converts the initial triglyceride into a mixture of alkyl esters and glycerol, in the presence of a catalyst (Figure 1). At an industrial scale, biodiesel production is mainly made using virgin vegetable oils. The current great obstacle for biodiesel production is the high price of those raw materials; also, the use of food oils for biodiesel production is controversial, which is the reason why studying alternatives is of major importance. There are many studies reporting the transesterification of different types of vegetable oils; on the contrary, few studies can be encountered regarding the conversion of * To whom correspondence should be addressed. Telephone: +351-225081688. Fax: +351-22-5081449. E-mail:
[email protected]. (1) Bozbas, K. Biodiesel as an alternative motor fuel: Production and policies 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 of biodiesel production by transesterificationsA review. Renewable Sustainable Energy ReV. 2006, 10 (3), 248–268. (4) VenkatReddy, C. R.; Oshel, R.; Verkade, J. G. Room-temperature conversion of soybean oil and poultry fat to biodiesel catalyzed by nanocrystalline calcium oxides. Energy Fuels 2006, 20 (3), 1310–1314.
animal fat. This is probably due to the fact that animal fat use at a larger scale is limited; also, a high degree of free fatty acids gives rise to difficult production processes.5 Studies regarding the mixture of raw materials for biodiesel production are currently limited; however, in a study by Meneghetty et al.,6 the use of castor oil, which had a viscosity of 225.8 mm2 s-1 at 40 °C enabled biodiesel production by mixing it with either soybean or cottonseed oil. In a study by Lebedevas et al.,7 the use of three component mixtures also allowed for the reduction of emission and harmful components of the fuel. Soybean oil has a high iodine value; therefore, the product obtained using this raw material alone often does not fulfill the European biodiesel standard EN 14214. On the other hand, animal fat is known to have a low iodine value, and therefore, its use in mixtures with soybean oil will probably result in a fuel with improved iodine values (lower than the limit). The use of wastes as raw materials for biodiesel production has three major advantages: (i) does not compete with the food market, (ii) recycles waste, and (iii) reduces production costs.8 The great amount of waste animal fat, produced at several (5) Ngo, H. L.; Zafiropoulos, N. A.; Foglia, T. A.; Samulski, E. T.; Lin, W. Efficient two-step synthesis of biodiesel from greases. Energy Fuels 2008, 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 origin for the production of biodiesel fuel: Quality, motor properties, and emissions of harmful components. Energy Fuels 2006, 20 (5), 2274–2280. (8) Wang, Y.; Ou, S.; Liu, P.; Xue, F.; Tang, S. Comparison of two different processes to synthesize biodiesel by waste cooking oil. J. Mol. Catal. A: Chem. 2006, 252 (1-2), 107–112.
10.1021/ef8005383 CCC: $40.75 2008 American Chemical Society Published on Web 10/15/2008
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slaughterhouses and other meat-processing units, might be an attractive and cheap raw material. One of the great concerns regarding the use of animal fat as a raw material for biodiesel production is its cold-weather properties and oxidation stability; however, it is known that the obtained fuel might be used in 100% in boilers for heat generation. Other waste materials that can be used for biodiesel production are the waste-frying oils.8-11 Because of the scarce availability of these low-cost materials, their use at an industrial scale is limited; however, their mixture with other raw materials might be an attractive alternative. The current knowledge regarding the use of mixtures of raw materials including wastes is yet very scarce. Aiming to improve this knowledge, 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 when mixtures with different fat contents are used as raw materials, and (iii) to understand how mixture composition influences biodiesel quality. Experimental Section General. The soybean oil used was from the brand “olisoja” and was donated by Sovena, SA, Portugal. This oil met Portuguese specifications for food oil. The pork lard was from the brand “Dilop Carnes” and was purchased at the food market. The waste frying oil was obtained from a voluntary collection system implemented at the Faculty and consisted of waste frying oil from different domestic sources. The same mixture of waste frying oils was used in all experiments. The reagents used during biodiesel production procedures were methanol (99.5%, analytical grade, Fischer Scientific), sodium hydroxide powder (97%, reagent grade, Aldrich), and anhydrous sodium sulfate (99%, analytical grade, Panreac). Biodiesel production was performed in three steps: pretreatment of raw material, synthesis, and purification. Raw Materials Pretreatment. Waste frying oil was filtered under vacuum, dehydrated using anhydrous sodium sulfate (left overnight), and finally again filtered under vacuum. The pork lard was first heated at 100 °C to eliminate residual water and cooled to near the reaction temperature (60 °C). Raw Materials Characterization. Different properties of the starting raw materials were determined: (i) composition [using gas chromatography (GC) according to EN 14103 (2003) and NP EN ISO 5508 (1996)], (ii) acid value, by volumetric titration according to the standard NP EN ISO 660 (2002), (iii) iodine value, by volumetric titration using Wijs reagent, according to the standard ISO 3961 (1996), and (iv) water content, using coulometric Karl Fischer titration. Biodiesel Synthesis. Synthesis of biodiesel was carried out by transesterification. The mixtures of vegetable oil and fat were prepared considering the increase in the fat fraction of the mixture, varying from 0 to 1 (w/w), in 0.2 intervals. The fat was weighted and added to the reactor, which already contained the necessary amount of vegetable oil (soybean oil or waste frying oil). A defined amount 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 at the reaction temperature. The catalyst concentration was chosen (9) Al-Widyan, M. I.; Al-Shyoukh, A. O. Experimental evaluation of the 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 frying oils. Waste Manage. 2006, 26 (5), 487. (11) Zheng, S.; Kates, M.; Dube, M. A.; McLean, D. D. Acid-catalyzed production of biodiesel from waste frying oil. Biomass Bioenergy 2006, 30 (3), 267–272.
Dias et al. according to a previous study by Dias et al.12 At this point, the reaction started; the reactor consisted of a 1 L flat-bottom flask immersed in a temperature-controlling bath, equipped with a watercooled condenser and a magnetic stirrer. Suggested by the literature review, the reaction occurred for 60 min under vigorous stirring; at the end of the reaction, products were left to settle for 1 h to allow for the separation of the two phases: biodiesel and glycerol. Biodiesel Purification. Both phases were separated, and excess methanol was recovered from each phase, using a rotary evaporator under reduced pressure. Biodiesel was then filtered (S&S, grade 589/1) and washed, first with 50% (v/v) of an acid solution (0.2% HCl) and then repeatedly with 50% (v/v) of distilled water until the pH of the washing water was the same as the distilled water. The filtering stage was adopted because of the fact that it significantly improved the washing stage, reducing emulsion formation. Regarding biodiesel dehydration, different procedures were adopted to evaluate which would be the best one. Such procedures were based on the use of an anhydrous salt and evaporation at reduced pressure under different conditions. Biodiesel Characterization. The biodiesel quality was evaluated according to the European biodiesel standard EN 14214 (2003). The following parameters were determined: (i) acid value, by volumetric titration according to the standard EN 14104 (2003), (ii) kinematic viscosity, determined at 40 °C using glass capillary viscometers according to the standard ISO 3104 (1994), (iii) density, determined using a hydrometer method according to the standard EN ISO 3675 (1998), (iv) flash point, using a rapid equilibrium closed cup method according to the standard ISO 3679 (2004), (v) copper corrosion, using a copper strip test according to the standard ISO 2160 (1998), (vi) water content, by Karl Fischer coulometric titration according to the standard NP EN ISO 12937 (2003), (vii) ester and linolenic acid methyl ester contents by GC according to the standard EN 14103 (2003), and (viii) iodine value, determined from ester content according to annex B of EN 14214 (2003). With regard to chromatographic analysis, a Dani GC 1000 DPC gas chromatograph (DANI Instruments S.p.A.), with an AT-WAX (Heliflex capillary, Alltech) column (30 m, 0.32 mm internal diameter and 0.25 µm film thickness) was used. The injector temperature 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, using a split flow rate of 50 mL/min (split ratio of 1:25), and the volume injected was 1 µL.
Results and Discussion Raw Materials Properties. The fatty acid composition and the mean molecular weight (calculated from the composition) as well as some other measured properties of the starting raw materials are presented in Table 1. Considering the typical fatty acid composition of vegetable oils as determined using GC,13 the waste frying oil composition indicates that both soybean and sunflower oil might be present; the low C18:3 content and the content in C18:1 might indicate that sunflower is present in a higher amount.13 As expected, the acid value of the soybean oil was lower than the waste frying oil; however, much higher acid values have been reported for waste frying oils.8,14 The low acid value found might indicate a smaller degree of both oxidation and hydrolysis reactions. This can be justified because the waste frying oils were from a domestic source and they (12) Dias, J. M.; Alvim-Ferraz, M. C. M.; Almeida, M. F. Comparison of the performance of different homogeneous alkali catalysts during transesterification 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 Oils and 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 vegetable oil derived fuels in diesel engines. Prog. Energy Combust. Sci. 1998, 24 (2), 125–164.
Mixtures of Oils and Fat for Biodiesel Production
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Figure 1. Transesterification of triglycerides (overall reaction). Table 1. Starting Raw Materials Properties Including Acid Value, Iodine Value, Water Content, Fatty Acid Composition (wt %), and Mean Molecular Weighta raw material properties acid value (mg of KOH/g) iodine value (g of I2/100 g) water content (wt %) fatty acid composition (wt %) miristic (C14:0) palmitic (C16:0) palmitoleic (C16:1) heptadecenoic (C17:1) stearic (C18:0) oleic (C18:1) linoleic (C18:2) linolenic (C18:3) arachidic (C20:0) eicosenoic (C20:1) eicosadienoic (C20:2) eicosatrienoic (C20:3) behenic (C22:0) docosadienoic (C22:2) lignoceric (C24:0) mean molecular weight (g/mol) a
waste frying oil
soybean oil
pork lard
0.21 127 0.04
0.71 67 0.03
0.82 117 0.05
nd 11.0 nd nd 3.3 25.4 53.6 5.3 0.4 0.3 0.0 nd 0.4 0.2 0.1 874.0
1.3 23.7 2.2 0.4 12.9 41.4 15.0 1.0 0.2 0.9 0.7 0.2 nd nd nd 861.6
nd 8.4 0.2 nd 3.7 34.6 50.5 0.6 0.4 0.4 nd nd 0.8 nd 0.3 877.5
nd ) not detected.
Table 2. Biodiesel Production Yields (wt %) Using Different Vegetable Oil/Lard Mixtures as Raw Materials lard fraction (wt)
soybean oil/ lard mixture
waste frying oil/ lard mixture
0 0.2 0.4 0.6 0.8 1
88.8 87.4 85.2 87.6 88.6 81.7
82.2 87.1 87.6 85.2 88.0 81.7
might have been exposed to high temperatures for short periods.15 Pork lard also presented a low acid value, probably resulting from pretreatment processes; however, the commonly referred value for commercial lard is slightly higher (1.3 mg of KOH/g of fat).16 Yield. Biodiesel production yields are presented in Table 2. They varied from 81.7 to 88.8 wt %. Production using only soybean oil as raw material presented a yield almost 7% higher than when using only waste frying oil or lard as raw materials; however, considering all oil/lard mixtures, the differences between yields were less than 3.4%. (15) C¸etinkaya, M.; Karaosmanogˇlu, F. Optimization of base-catalyzed transesterification reaction of used cooking oil. Energy Fuels 2004, 18, 1888–1895. (16) Codex Alimentarius Commission (CAC). Codex standard for fats and oils from animal sources (CODEX-STAN 211-1999). In Fats, Oils and Related Products, 2nd ed.; Joint FAO/WHO Food Standards Program. Food and Agriculture Organization of the United Nations: Rome, Italy, 2001; Vol. 8.
Table 3. Dehydration Methods Used and Final Water Contents of the Biodiesel Samples soybean oil/lard mixture lard fraction dehydration water content (wt) method (wt %) 0 0.2 0.4 0.6 0.8 1
AS Ev40/45 Ev65/90 Ev45/90 Ev40/45 Ev40/45
0.127 0.154 0.095 0.153 0.155 0.114
waste frying oil/lard mixture dehydration method
water content (wt %)
AS Ev90/210 Ev80/90 Ev90/120 Ev90/120 Ev40/45
0.100 0.040 0.100 0.045 0.056 0.114
Effect of Different Dehydration Treatments in Biodiesel Water Content. High water contents will improve biodiesel degradation because of hydrolysis,17 therefore affecting the storage life of the fuel. The standard limit according to EN 14214 is 0.05 wt %. With the objective of selecting an appropriate dehydration method, each sample produced was subjected to a different treatment. The following treatments were performed: 30 wt % of anhydrous salt (AS) or evaporation (163 mbar) including heating at 40 °C during 45 min (Ev40/45), heating at 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 heating at 90 °C during 3 h and 30 min (Ev90/210). Table 3 shows which samples were used in each treatment as well as the final water contents. The same dehydration treatment led to different final water contents depending upon the water content after the washing stage. When evaporating during 1 h and 30 min, the effect of increasing the temperature was mainly noted when going from 45 to 65 °C. The increase in evaporation time was not very much reflected in terms of decreasing biodiesel water content; however, independent of the sample used, a great decrease in the biodiesel water content was observed when increasing the temperature from 45 to 90 °C. Considering the obtained results, evaporation at 90 °C, 163 mbar, and a holding time of 3 h and 30 min seemed to be enough to ensure that biodiesel samples fulfill the European biodiesel standard EN 14214. Biodiesel Composition. Biodiesel composition resulting from the transesterification of soybean and waste frying oil mixed with lard was evaluated, aiming its prediction when mixtures with different lard contents are used as raw materials. It was postulated that the fatty acid content of biodiesel corresponded to the weighted average of its content in each component of the mixture, therefore Cmix ) CoilXoil + ClardXlard S Cmix ) (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 (17) Leung, D. Y. C.; Koo, B. C. P.; Guo, Y. Degradation of biodiesel under different storage conditions. Bioresour. Technol. 2006, 97 (2), 250– 256.
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Dias et al.
Table 4. Fitting of Fatty Acid Content (wt %) of Biodiesel versus Lard Mass Fraction Incorporated in the Oil and Linear Regression Parametersa fatty acid mixture C14:0 C16:0 C18:0 C18:1 C18:2 C18:3 C20:0 C20:1 C22:0
sb/l wfo/l sb/l wfo/l sb/l wfo/l sb/l wfo/l sb/l wfo/l sb/l wfo/l sb/l wfo/l sb/l wfo/l sb/l wfo/l
a
b
r2
1.3 1.3 12.2 15.3 9.3 9.1 15.8 6.8 -37.5 -35.3 -4.5 0.3 -0.1 -0.2 0.6 0.5 -0.5 -0.9
0.0 0.1 11.1 8.5 3.3 3.8 26.0 34.8 53.2 50.2 5.2 0.6 0.4 0.4 0.3 0.4 0.5 0.9
0.991 0.989 0.994 1.000 0.993 1.000 0.952 0.994 0.993 1.000 0.892 0.995 0.987 0.997 0.985 0.996 0.878 1.000
p value Coil Clard Clard - Coil
