ARTICLE pubs.acs.org/EF
Evaluation of Two Purification Methods of Biodiesel from Beef Tallow, Pork Lard, and Chicken Fat Teresa M. Mata,*,† Nelson Cardoso,‡ Mariana Ornelas,‡ Soraia Neves,† and Nídia S. Caetano†,§ †
Laboratory for Process, Environmental and Energy Engineering (LEPAE), Faculty of Engineering, University of Porto (FEUP), Rua Doutor Roberto Frias, s/n, 4200-465 Porto, Portugal ‡ Faculty of Sciences, University of Porto (FCUP), Rua do Campo Alegre, s/n, 4169-007 Porto, Portugal § School of Engineering (ISEP), Polytechnic Institute of Porto (IPP), Rua Doutor Antonio Bernardino de Almeida, s/n, 4200-072 Porto, Portugal ABSTRACT: Beef tallow methyl esters (TMEs), pork lard methyl esters (LMEs), and chicken fat methyl esters (CMEs) were produced, purified, and characterized to evaluate their quality and compare two purification methods: (1) conventional neutralization, water washing, and drying and (2) purification using cationic exchange resins. Also, B20 blends [20% biodiesel (v/v) mixed with petroleum diesel] were characterized and evaluated. The conventional alkali-catalyzed transesterification process was used, with methanol as the reagent and KOH as the catalyst, yielding 76.8, 90.8, and 91.5% (w/w) CME, TME, and LME, respectively. The ester content of these biodiesels was below 96.5% (w/w), and the kinematic viscosity was high (ranging between 4.84 and 6.86 mm2/s), which poses restrictions to their use as fuel in vehicle engines, especially in low-temperature climates. Although it is not possible to use 100% biodiesel produced from these animal fats, blends of 20% biodiesel are viable with some advantages, such as the improved cold-flow properties [cold filter plugging point (CFPP) below 6 °C], lower kinematic viscosity (from 3.10 to 3.28 mm2/s), and higher heating value of the mixture (about 44.6 MJ/kg). Results also show that the resin purification helps to reduce biodiesel acidity and kinematic viscosity, while conventional water washing followed by adsorbent drying and filtration gives better results regarding water and alkaline metal (Na + K) content.
1. INTRODUCTION The commitment of the international community to significantly reduce emissions formalized in the Kyoto Protocol in December 1997 has been the main driver for the search of renewable sources of transportation fuels. Biodiesel is one of the envisaged options because it can contribute to reduce greenhouse gas (GHG) emissions by replacing fossil diesel and can also be used directly in compression ignition engines without significant changes by car manufacturers. Generally, biomass has a relatively low sulfur content; also, biofuels are generally considered CO2-neutral because, during their growth, plants remove CO2 from the atmosphere through photosynthesis, which is again released during the fuel combustion. For these reasons, the SO2 and CO2 direct emissions of biodiesel are smaller than fossil diesel,1 although depending upon the engine type, it may generate more NOx emissions for the same amount of energy delivered.2,3 Although biodiesel emissions may be smaller than those from fossil diesel at the usage stage, its environmental impact cannot be ignored from a life-cycle perspective. The main reason is that the cultivation, harvesting, transportation, and pretreatment of biomass are energy-consuming processes, contributing to significant emissions. Also, because of the large land areas required for their feedstock cultivation, especially as one envisions scaling up, there is concern about the impact of biofuels on the food supply chain, the biodiversity loss, and the carbon stock losses from soil because of land-use changes.4 For these reasons, the European Commission put forward a directive on the promotion of energy from renewable sources that meet the recommended r 2011 American Chemical Society
sustainability criteria.5 Additionally, a high priority is currently starting to be placed on the development of more sustainable conversion technologies for biofuels from nonfood feedstocks and the development of conditions to capitalize on the economic potential of biorefineries, seeking to obtain higher added-value bioproducts.6 Biodiesel is normally produced from a wide range of edible vegetable oils (e.g., rapeseed, soybean, sunflower, or palm oils), but their prices have recently suffered from speculation and are expected to increase even more in the future.7 This made biodiesel production from these feedstocks less competitive than fossil diesel and substantially reduced their production and usage. In this regard, low-cost feedstocks for biodiesel have increasingly drawn interest, such as waste frying oils8,9 and animal fats,10 byproducts of the meat- and fish-processing industries that cannot be used for human food purposes. Because most types of fatty waste materials consist of the leftover parts of a slaughtered animal, they contain fats, bones, and meat residues; therefore, the extraction process is necessary to separate them from the fat. Dependent upon the fatty residues to separate, the process varies, involving, for example, heating or solvent extraction. For example, because of their high levels of water content and biological and microbiological composition, animal byproducts can easily decompose if not stabilized, leading to environmental and sanitary problems. Thus, they are normally Received: July 12, 2011 Revised: September 20, 2011 Published: September 21, 2011 4756
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Energy & Fuels treated and sterilized by heat, in a process known as “rendering”, and transformed into fat and protein. Solvent extraction is also possible, as performed by Nebel and Mittelbach11 that tested nine solvents for extracting fat from meat and bone meal. These authors obtained as an extraction yield about 15% fat with all solvents, which is close to the fat content of meat and bone meal, and concluded that n-hexane is the most suitable solvent to perform the extraction, because it is relatively cheap and has a low boiling point. The traditional destination of animal fats was the production of soaps and pet food formulations.12 However, as a result of bovine spongiform encephalopathy (BSE), part of these applications has been lost and newer alternative uses have been developed, such as converting them into biodiesel. This not only represents a new application for a lower cost and environmental friendly feedstock but also contributes to solving a waste management problem. Animal fats stored at high temperatures for long periods and in the presence of moisture tend to accumulate free fatty acids (FFAs) because of the hydrolysis of triglycerides.13 Farahani et al.14 studied the stability of biodiesel from tallow and yellow grease stored over 10 months at temperatures ranging from 25 to 35 °C and with a relative humidity from 25 to 100%. They observed that biodiesel displayed more free water and sediment levels during cold months than after warm months. Ma et al.15 studied the effect of the catalyst, FFAs, and water in the transesterification of beef tallow, concluding that the presence of water has the most negative effect on the reaction yield and should be kept below 0.06% (w/w), while FFAs should be kept below 0.5% (w/w). The same conclusion was reached by Freedman et al.16 Normally, a pretreatment is needed to reduce or eliminate these contaminants (water and FFAs) that inhibit the transesterification reaction. They form soap in the presence of the alkali catalysts16 and increase the catalyst consumption, lowering the ester yield and rendering the ester and glycerol separation difficult.17 19 To reduce the water content one may heat the fat over 100 °C (to about 120 °C) to boil off any excess water present in the feedstock. The high acidity can be reduced, for example, by applying an acid-catalyzed transesterification in excess methanol to form biodiesel,20 an acid-catalyzed esterification of FFAs to esters,21 23 or even a heterogeneous catalyst basic or acidic in nature, such as hydrotalcite, MgO, or TiO2 grafted on silica, among others.24 Several authors have studied biodiesel production from beef tallow, pork lard, grease, or chicken fat as well as their properties. For example, Cunha et al.25 studied the production of biodiesel from beef tallow in a pilot plant using methanol as the reagent and KOH as the catalyst, concluding that a high-quality biodiesel can be obtained at a good conversion rate. However, to make this process economically viable, there is the need to improve the methanol and glycerin recovery. Similarly, Araujo et al.10 studied the transesterification of beef tallow by homogeneous catalysis with a methanolic solution of KOH, by heating and preliminary formation of a microemulsion, concluding that a high reaction yield (96.26%) can be obtained even from beef tallow with high acidity (about 3.6%). Guru et al.3 studied the combustion of B10 biodiesel from chicken fat in a direct-injection diesel engine and analyzed the resulting exhaust gases, concluding that the engine torque does not change significantly but the specific fuel consumption increases by 5.2% because of the lower heating value of biodiesel.
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Concerning the exhaust gases, these authors verified that the CO and smoke emissions decreased by 13 and 9%, respectively, but the NOx emissions increased by 5%. Issariyakul et al.26 studied a two-step process (acid-catalyzed esterification followed by alkali-catalyzed transesterification) for biodiesel production from waste fryer grease containing about 5 6% (w/w) FFAs. These authors used methanol, ethanol, and mixtures of methanol/ethanol as reagents, to profit from the better solvent property of ethanol and the rapid equilibrium of methanol, with KOH as the catalyst. Results show that more than 90% of the ester content can be obtained when the two-step process is used by comparison to 50% of the ester content by a single-step process with the alkaline catalyst. In the case of mixed alcohol, a relatively smaller amount of ethyl esters is obtained together with methyl esters. Tashtoush et al.27 performed experiments to determine the optimum conditions for converting animal fats into ethyl and methyl esters, concluding that absolute ethanol (containing no water) performs better than absolute methanol (containing no water) because ethanol gives lower viscosity for a maximum mass conversion of 78%. The optimum temperature for the transesterification reaction is 50 °C, during 2 h maximum. Lee et al.28 studied biodiesel production from lard and restaurant grease by enzymatic and alkali-catalyzed transesterification and obtained a maximum conversion of 74%. Similarly, Lu et al.29 studied the enzymatic transesterification of lard to produce biodiesel and determined the optimal operating conditions for the reaction, for which 87.4% of biodiesel was obtained. Hsu et al.30 also studied the enzymatic catalyzed transesterification of tallow and grease using ethanol as the reagent, concluding that the reaction yields 95% ethyl esters and it is possible to reuse the matrix-immobilized enzyme 5 times without activity loss of the catalyst. Bhatti et al.31 studied the effect of various parameters (e.g., reaction temperature, amount of acid catalyst, and oil/methanol molar ratio) in the reaction length and yield for producing biodiesel from animal fats (chicken and mutton tallow), using the acid-catalyzed esterification. These authors were able to obtain about 99% methyl esters, after 24 h, in the presence of acid (H2SO4), with about 98% fatty acids, as determined by gas chromatography (GC). These studies pointed out the difficulties inherent to the process of converting animal fats to biodiesel, especially as a result of the high water and FFA contents. Generally, it is concluded that this is a feasible process provided that the most adequate operating conditions are ensured for each specific case. Thus, one should start by performing an analytical characterization of the animal fats to define the best process flowsheet and then characterize the resulting biodiesel to make improvements in the process. Almost complete methanolysis of triglycerides is usually not enough to fulfill the high-purity requirements of EN 14214:2003 for biodiesel quality. A key step in this process is the purification of the ester phase, normally involving neutralization of alkali (catalyst), followed by washing to remove traces of catalyst, methanol, soaps, and glycerol, among other impurities. Water washing is still widely used in many industrial units for biodiesel production, but currently, there is increasing interest in purification by ion-exchange resins, using magnesium silicate as a solid adsorbent, or by membrane extraction.32 34 In this regard, Berrios and Skelton32 compared three purification methods for biodiesel (water washing, ion-exchange resins, and magnesium silicate), concluding that, although glycerol and soap contents 4757
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Energy & Fuels have been removed in all three processes, it is necessary to remove methanol to avoid the saturation of the adsorbents. Canoira et al.33 compared dry and wet routes for purification of biodiesel obtained from a mixture of 50% (vol) animal fat and soybean oil. The dry route consists of the treatment of the biodiesel with the adsorbent magnesium silicate. The wet route consists of a neutralizing step with a citric acid solution, water washing, and dehydration with a molecular sieve. Results show that a better biodiesel yield can be obtained in the wet purification route, but the rest of the parameters were almost identical. Also, in the wet route, the biodiesel oxidative stability, the total contamination, and the sulfur content were slightly better (out of the specifications for both routes). Glisic and Skala34 studied different biodiesel washing procedures using hot water by simulating the washing process with ASPEN plus software, supported by original experimental data. Results suggested that neutralization after the optimized washing process could be the best solution, because it significantly decreases the amount of wastewater, at the same time giving the desired purity of final products. Hence, this work compares two purification methods of raw biodiesel obtained from beef tallow, pork lard, and chicken fat wastes: (1) neutralization with acidulated water (AW) followed by water washing and drying by adsorption in MgO and (2) purification in cationic exchange resin (R; Lewatit GF 202). The quality parameters of biodiesel treated with AW and R were evaluated according to EN 14214:2003 and compared to determine the best treatment and purification method. These two purification methods have been chosen in this study to compare which one gives better results, because the first method is the traditional widely used method for biodiesel purification and the second method is starting to be applied to industrial processes (e.g., there is already one Portuguese’s biodiesel company using it). The use of cationic exchange R for biodiesel purification claims to reduce the water consumption and avoid wastewaters, simplifying the process and reducing production costs. Also, B20 blends of 20% biodiesel (v/v) mixed with petroleum diesel were characterized for these animal fats.
2. MATERIALS AND METHODS 2.1. Fats Extraction and Their Characterization. In this work, the waste animal fats (beef tallow, pork lard, and chicken fat) were collected from slaughterhouses and food-processing companies and were melted at around 110 °C.11 During this process, the fatty material lost about 70% of its moisture content. Then, the liquid fat was separated from solids by percolation and filtering to obtain the fat and remove gums, protein residues, and suspended particles. Fats were then characterized for the following properties: acid value [titrimetric method, according to NP EN ISO 660 (2002) standard], iodine number [titrimetric method using Wijs reagent, according to ISO 3961 (1996) standard], kinematic viscosity (determined at 40 °C, using a glass capillary viscometer, Cannon-Fenske routine viscometer, series 200, according to EN ISO 3104 standard), and higher heating value of the fats [determined using an oxygen bomb calorimeter, according to American Society for Testing and Materials (ASTM) method D240-87]. All reactants used in the experimental determinations were of analytical grade. 2.2. Biodiesel Synthesis. In this work, beef tallow methyl esters (TMEs), pork lard methyl esters (LMEs), and chicken fat methyl esters (CMEs) were produced by the alkali-catalyzed transesterification, using methanol as the reagent and KOH as the catalyst. A methanol/ fat molar ratio of 6:1 was used,16 with about 0.8% (w/w) KOH catalyst
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to fat. This is the most used process industrially for biodiesel production, where triglycerides (main components of oils and fats) react with a lowmolecular-weight alcohol (usually methanol), catalyzed by a base (NaOH or KOH), thus producing a mixture of fatty acid methyl esters (FAMEs), known as biodiesel, and glycerol (byproduct). Therefore, to a previously heated sample of 500 g of animal fat was added about 4 g of pure KOH (from Labsolve) dissolved in 150 mL of pure methanol (from Labsolve) in a 1 L screw cap flask. The reaction mixture was first vigorously shaken for about 1 min and then stirred for 2 h in a thermostatic bath (Selecta, Unitronic), at a constant temperature of 60 °C with stirring of 60 revolutions per minute (rpm). After transesterification, the glycerol byproduct was separated from the resulting biodiesel in a separatory funnel. The excess methanol was removed through distillation, and the biodiesel was then purified. 2.3. Biodiesel Purification. To produce a highly purified biodiesel, the conventional purification process comprises several separation and purification techniques, such as gravitational settling, distillation, evaporation, and washing with water (for each liter of biodiesel, about 2 L of water is consumed for the washing step), acid, and absorbent (that needs to be reprocessed or disposed of after usage).35 In this work, two different biodiesel purification methods were used for comparison. (1) AW: hot water acidified with some drops of o-phosphoric acid [85%, pro analysis (p.a.), Fischer] was added to biodiesel to neutralize the excess residual KOH in the biodiesel phase, and then biodiesel was gently washed with distilled hot water at 85 °C in a separatory funnel, until the pH of the rinsing water was around 7. After washing, biodiesel was dried by the addition of about 2.5 g of an anhydrous adsorbent (MgO, pure, from Labsolve), followed by stirring for 15 min and then vacuum filtration through cellulose membranes (0.8 μm pore, 47 mm, from Whatman) to remove the adsorbent from the final purified biodiesel. (2) Cation-exchange (acidic) R: biodiesel was passed through a column (5 cm in diameter and 30 cm in length) packed with a 15 cm length of ion-exchange R (Lewatit GF 202) that retained the impurities (water, ions of K, and glycerol), at a mean flow rate of 2 bed volumes/h (or about 236 cm3/h). Lewatif GF 202 is a macroporous cation-exchange (acidic) R. The R beads are uniform, 0.65 mm in diameter, with a density of 1.24 g/mL and a bulk density of 0.740 g/mL. 2.4. Biodiesel Characterization. In this study, some of the most important quality parameters of biodiesel produced from beef tallow, pork lard, and chicken fat were evaluated according to the EN 14214:2003 standard that defines the quality requirements of FAMEs. The acid value was determined using a titrimetric method. The kinematic viscosity was determined at 40 °C, using glass capillary viscometers, according to the standard ISO 3104:1994. The density was determined at 15 °C, using a hydrometer method, according to the EN ISO 3675:1998 standard. The flash point was determined using a rapid equilibrium closed cup method, according to the standard ISO 367:2004. The copper corrosion was determined using a copper strip test, according to the standard ISO 2160:1998. The water content was determined by Karl Fischer coulometric titration, according to the standard NP EN ISO 12937:2003. The iodine number was determined by the titrimetric method using Wijs reagent, according to the EN 14111:2003 standard. The cold filter plugging point (CFPP) was determined using a standardized filtration equipment, according to the EN 1116:1997 standard. The FAME and linolenic acid methyl ester contents were determined by GC, according to the EN 14103:2003 standard. The chromatographic analysis was performed using a Dani GC 1000 DPC gas chromatograph (DANI Instruments S.P.A.) equipped with an AT-WAX (Heliflex Capillary, Alltech) column (30 m, 0.32 mm internal diameter, and 0.25 μm film thickness). The injector temperature was set to 250 °C, while the flame ionization detector (FID) temperature was set to 255 °C. The carrier gas used was N2, at a flow rate 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. 4758
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such as acid value, iodine number, kinematic viscosity, and higher heating values, were evaluated, as shown in Table 1. The iodine number of the animal fats used in this work (shown in Table 1) is lower than that of vegetable oils, such as soybean or rapeseed oils.36 Especially, beef tallow presents the smallest iodine number of the three types of fats, indicating a higher degree of the beef tallow fatty acid molecule saturation, in other words, a small amount of fatty acid compounds with double bonds. This property is also a direct indication of the better oxidative stability of fuel obtained from beef tallow. Consequently, the methyl esters produced from these have larger stability to the oxidation, as compared to methyl esters from vegetable oils.37 Beef tallow presented the largest acid value of the three types of fats analyzed, which indicates the occurrence of oxidation and hydrolysis reactions, especially during extended storage, which increased the FFA content and can ultimately affect the fuel quality of the resulting biodiesel (e.g., with a low ester content or high acid value that may cause corrosion problems in the engine or low fuel oxidation stability). Not only does the acid value of fat increase with a long-term storage but also the viscosity, peroxide value, and density increase, while the heat of combustion decreases.38 The oxidation of fatty materials is normally promoted by elevated temperatures, presence of light, exposure to air (oxygen), or extraneous materials, such as metals. Also, beef tallow presented the higher viscosity of the three fats analyzed. Although an acceptable value for the viscosity of biodiesel feedstocks is not defined, the high kinematic viscosity at 40 °C is a drawback for the usage of animal fats for biodiesel
Finally, the higher heating value was determined in a bomb calorimeter, following the ASTM D240-87 standard test method for the heat of combustion of liquid hydrocarbon fuels. 2.5. Biodiesel Blends (B20). FAMEs obtained from each type of animal fat (beef tallow, pork lard, and chicken fat) were mixed with petroleum diesel (of brand name “Galp Gforce” from Galp Energy S.A.) on a volume basis, i.e., at a ratio of 1:5 (v/v) of biodiesel/diesel, yielding blends of B20 (20% biodiesel mixed with diesel). The blend percentage was chosen according to national legislation, because in Portugal, it is possible to commercialize B100 (pure biodiesel) and blends up to B20. Also, the purpose of blending was to understand if all quality parameters of the commercial blends would fulfill the EN 14214:2003 standard without the need to use further additives. Thus, the blends were characterized following the same procedures described above for biodiesel.
3. RESULTS AND DISCUSSION 3.1. Characterization of Animal Fats. In this study, for the physical chemical characterization of animal fats, main parameters,
Table 1. Characterization of Pork Lard, Beef Tallow, and Chicken Fat parameter
pork lard beef tallow chicken fat
acid value (mg of KOH/g of fat)
0.63
1.07
0.56
iodine number (g/100 g of fat)
77.9
45.3
76.7
kinematic viscosity at 40 °C (mm2/s)
39.53
46.37
41.06
higher heating value (MJ/kg of fat)
39.5
38.9
39.6
Table 2. Characterization of TMEs, LMEs, and CMEs Comparing the Conventional Acid Neutralization and Water Wash (AW) to Purification in a Fixed Bed of Lewatit GF 202 R LMEs parameter
AW
CMEs R
AW
TMEs R
AW
R
EN 14214 limits
reaction yield (wt %)
91.4
91.4
76.8
76.8
90.8
90.8
density at 15 °C (kg/m3)
873
871
877
888
870
870
860 900
kinematic viscosity at 40 °C (mm2/s)
5.08
4.84
6.86
4.83
5.35
5.44
3.50 5.00
flash point (°C)
147
147
171
171
172
172
g120
CFPP (°C)
+5
+4
+3
+11
+10
+10
e +5a
water content (mg/kg) iodine number (g/100 g)
184 75.6
114 77.3
1201 78.8
1273 72.9
374 44.4
795 44.6
e500 e120
acid value (mg of KOH/g of fuel)
0.22
0.17
0.55
0.09
0.20
0.21
e0.50
Group I metals (Na + K) (mg/kg)
17.2
62.1
46.8
60.1
2.0
5.7
e5.0
copper strip corrosion (3 h/50 °C)
1B
1B
1B
1B
1B
1B
class 1
linolenic acid methyl ester (wt %)
3.38
2.18
1.80
1.50
0.63
0.65
e12.0
ester content (wt %)
80.74
83.00
73.80
83.68
84.40
81.15
g96.5
myristate (C14:0) (wt %) palmitate (C16:0) (wt %)
28.12
31.56
34.64
34.96
10.22 30.39
8.25 29.88
stearate (C18:0) (wt %)
11.62
11.19
4.94
4.94
16.72
17.57
oleate (C18:1) (wt %)
38.05
37.00
44.35
44.53
37.46
39.12
linoleate (C18:2) (wt %)
18.83
18.07
14.26
14.07
4.29
4.07
linolenate (C18:3) (wt %)
3.38
2.18
1.80
1.50
0.63
0.65
0.28
0.45
FAME composition
arachidate (C20:0) (wt %)
a
higher heating value (MJ/kg)
40.1
39.6
39.6
39.2
40.2
39.7
average MMfatb (g/mol) average MMbiodiesel (g/mol)
861.2 288.4
858.7 287.6
856.2 286.7
856.0 286.7
844.7 282.9
848.5 284.2
Limit for temperate climates. b MM is the molecular mass. 4759
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Table 3. Characterization of B20 Blends B20 parameter kinematic viscosity at 40 °C (mm /s) 2
CFPP (°C)
a
LMEs
CMEs
TMEs
diesel
3.15
3.28
3.10
2.69
6
8
10
5
Group I metals (Na + K) (mg/kg)
1.6
23.9
0.6
2.4
higher heating value (MJ/kg)
44.6
44.7
44.6
46.0
EN 14214 limits 3.50 5.00 e +5a e5.0
Limit for temperate climates.
production, because it represents the resistance to flow of an important fluid. Therefore, it can cause difficulties during the process of handling biodiesel production, which can be overcome by heating the fat still in the storage tank, particularly in the colder months of the year, which will increase the energy costs of the process. 3.2. Biodiesel Properties and Composition. Table 2 shows the results of the biodiesel (B100) characterization (from beef tallow, pork lard, and chicken fat) and the standard limit for each quality parameter evaluated. As shown in Table 2, biodiesel obtained after purification with both methods, AW and R, is similar in terms of the quality parameters evaluated. Several limit values of EN 14214:2003 were satisfied by these biodiesels from animal fats, except the kinematic viscosity, water content, Group I metals (Na + K), ester content, and CFPP for biodiesel obtained from some of the fat types. Results show that the transesterification reaction yield varied from 76.8% (for chicken fat biodiesel) to 91.4% (for pork lard fat biodiesel), and with an intermediate yield of 90.8% for beef tallow biodiesel. These yields are good results compared to what was expected, as reported in published studies of the same types of fat.26 30 The density of the biodiesel from fat did not show a significant difference depending upon the purification process, except for CMEs that had a higher density when the purification was performed with the ion-exchange R. Because animal fats have a high content of saturated fatty acids with a high molecular weight, the kinematic viscosity found for CMEs and LMEs purified with water (6.86 and 5.08 mm2 s 1, respectively) and for TMEs (5.35 and 5.44 mm2 s 1) was higher than the established standard limit (5.00 mm2 s 1). Only LMEs and CMEs purified with R fulfill the EN 14214:2003 requirements for viscosity. The kinematic viscosity is a measure of the fuel flow resistance and can be used to select the fatty acid profile in the biodiesel feedstocks. Thus, at the industrial level, the necessary feedstock mixtures are made to obtain a biodiesel with a viscosity under the standard limit. All of the biodiesel samples, LMEs, CMEs, and TMEs, satisfied the standard minimum limit of the flash point (120 °C). With a high flash point, biodiesel is safer to handle, transport, and store than fossil diesel. However, too high of a flash point, as is the case of the CMEs (171 °C) and TMEs (172 °C) obtained in this study, may cause ignition problems when biodiesel is used as fuel in the engine, together with poor atomization, poor vapor air mixing, low pressure, and incomplete combustion. For example, to overcome these problems, Guru et al.3 used an organic magnesium-based additive to study the combustion of chicken fat B10 biodiesel in a direct-injection diesel engine.
The CFPP property characterizes biodiesel according to its use in low temperatures, and it is particularly important in the case of Portugal, which has a strong variation of weather conditions between winter and summer, with average temperatures ranging from 0 to 30 °C, typical of Mediterranean climates. Biodiesel fuels derived from fats, having significant amounts of saturated fatty compounds, normally display higher CFPPs, because these compounds have higher melting points, and in a mixture, they crystallize at higher temperatures than the unsaturated fatty compounds.25 This is the case of CMEs and TMEs that displayed CFPP values of 11 and 10 °C, respectively, above the standard limit (5 °C), which are very high even for temperate climates. However, LMEs with CFPPs ranging from 4 to 5 °C can be used in temperate climates, being classified as grade A in this parameter. The water content of CMEs was very high, for either the acid water or R-purified samples, but LMEs presented very low water content for samples obtained with both purification processes. TMEs purified with water satisfied the standard maximum limit for water content (500 mg/kg), but the sample purified with R did not. The iodine number varied from 44.4 to 78.8 g of I2/100 g (values obtained for TME and CME biodiesels, respectively, both washed with AW). These values indicate that TME biodiesel has a higher degree of saturation of the carbon chains of FAMEs than biodiesel produced from the other types of fat. Only for the AW-purified TME biodiesel, the amount of Group I metals (Na + K) is within the standard minimum limit (5.0 mg/kg). The values obtained for this parameter suggest that the AW and R purification methods were not effective, leaving catalyst residues dissolved in the biodiesel. However, the AW purification process seems to be better than the R purification process because, for the former, the Group I metal values are lower. None of the biodiesel samples had ester content that satisfied the standard minimum limit (96.5%), being between 73.80% for CMEs and 84.40% for TMEs. Generally, LMEs and TMEs presented the best results in terms of the ester content. The low ester content is indicative of the need to improve the biodiesel production and purification processes.11 Also, the chromatographic analysis revealed that TMEs had a larger amount of saturated esters than CMEs and LMEs. The mass ratios of saturated/unsaturated esters obtained after purification with AW and R were 1.28 and 1.36 for TMEs, 0.66 and 0.75 for LMEs, and 0.6 and 0.6 for CMEs, respectively. These values are calculated by dividing the sum of the weight percentages of saturated esters by the sum of the weight percentages of unsaturated esters. Biodiesel acidity seems to be lower for biodiesel purified with R, although the acid values of these biodiesel samples are below the standard maximum limit (0.50 mg of KOH/g of fuel), except 4760
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Energy & Fuels for CMEs purified with AW. These results may be due to an insufficient contact time of the R with the biodiesel. 3.3. Properties of B20 Blends. To obtain a fuel quality complying with the EN 14214:2003 standard limits, B20 blends of 20% biodiesel mixed with 80% (v/v) diesel were prepared and evaluated. The quality parameters that did not fulfill the EN 14214:2003 limits for 100% biodiesel were determined in the B20 blends. Results are shown in Table 3. As shown in Table 3, only B20 blends of CMEs did not comply with the standard limit for the Group I metals (Na + K). However, an improvement of the biodiesel purification methods is expected to solve this problem. Blending TMEs, LMEs, and CMEs with diesel resulted in a significant decrease of the CFPP of the B20 blends to values lower than those observed for petroleum diesel alone. According to Dunn39, the slowdown in cooling or crystallization of these blends may be explained as a consequence of the interactions between the saturated monoalkyl ester molecules and the nonpolar petroleum diesel chains. In fact, at low temperatures, these molecules form bilayered structures, with polar carboxylic head groups aligned head to head and next to each other in the crystal interior, which makes it difficult to form crystals and, therefore, decreases the temperatures required for crystal formation.
4. CONCLUSION This work aimed to study the viability of producing biodiesel from three types of waste animal fats (beef tallow, pork lard, and chicken fat) as well as to compare two biodiesel purification methods: with AW and cationic exchange R. R purification seems to help reduce the biodiesel acidity and viscosity, while conventional water washing followed by adsorbent drying and filtration seems to give better results regarding Group I metal (Na + K) and water content. Although the water washing is very effective in removing contaminants, the R purification has the advantage of using no water, which decreases production costs and time, and avoids the liquid effluent, emulsion formation, and product loss. However, the high concentration of Group I metals (Na + K) can be a problem for CME commercialization even in blends. The transesterification reaction yield of these fats transformed into biodiesel is relatively low but can be increased by process improvement. The biodiesel quality was evaluated according to EN 14214:2003, showing that none of the biodiesel types matches all of the European standard limits, which also normally happens when vegetable oils are used. Therefore, biodiesel B100 (100% biodiesel) from these feedstocks cannot be used in car engines without blending or the introduction of further additives. For this reason, B20 blends were prepared by mixing 20% (v/v) biodiesel with petroleum diesel. The parameters that did not fulfill the requirements for biodiesel B100 were re-evaluated for these blends, showing that all of the TMEs, LMEs, and CMEs are good alternatives as blending components for petroleum diesel with improved cold-flow properties, with the TME biodiesel blend presenting the best performance. ’ AUTHOR INFORMATION Corresponding Author
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’ ACKNOWLEDGMENT The authors acknowledge Avibom Avicola S.A., Salpicarne Produtos de Salsicharia, Lda, and Negociantes de Gado de Baltar (NGB) S.A. for their kind supply of animal fat. Lanxess is greatly acknowledged for their kind offer of ion-exchange R used in this work. This work was only possible with the support of the LIDERA multidisciplinary program of the University of Porto. ’ REFERENCES (1) Demirbas, A. Progress and recent trends in biodiesel fuels. Energy Convers. Manage. 2009, 50, 14–34. (2) United States Environmental Protection Agency (U.S. EPA). A Comprehensive Analysis of Biodiesel Impacts on Exhaust Emissions; U.S. EPA: Washington, D.C., 2002; Draft Technical Report EPA420-P-02-001. (3) Guru, M.; Koca, A.; Can, O.; Cinar, C.; Sahin, F. Biodiesel production from waste chicken fat based sources and evaluation with Mg based additive in a diesel engine. Renewable Energy 2010, 35, 637–643. (4) Fritsche, U. R.; Sims, R. E. H.; Monti, A. Direct and indirect land-use competition issues for energy crops and their sustainable production—An overview. Biofuels, Bioprod. Biorefin. 2010, 4, 692–704. (5) European Committee for Standardization (CEN). EC Directive of The European Parliament and of the Council on the Promotion of the Use of Energy from Renewable Sources; CEN: Brussels, Belgium, 2008. (6) Kamm, B.; Hille, C.; Sch€ onicke, P.; Dautzenberg, G. Green biorefinery demonstration plant in Havelland (Germany). Biofuels, Bioprod. Biorefin. 2010, 4, 253–262. (7) United States Department of Agriculture (USDA). Vegetable Oil Prices Expected To Rise with Tighter Oil Market in 2007/08; USDA: Washington, D.C., June 2007; Oilseeds: World Market and Trade, Circular Series FOP 06-07. (8) Encinar, J. M.; Gonzales, J. F.; Rodriquez-Reinares, A. Ethanolysis of used frying oil. Biodiesel preparation and characterization. Fuel Process. Technol. 2007, 88, 513–522. (9) Sabudak, T.; Yildiz, M. Biodiesel production from waste frying oils and its quality control. Waste Manage. 2010, 30, 799–803. (10) Araujo, B. Q.; Nunes, R. C. R.; Moura, C. V. R.; Moura, E. M.; Cito, A. M. G. L.; Santos Junior, J. R. Synthesis and characterization of beef tallow biodiesel. Energy Fuels 2010, 24, 4476–4480. (11) Nebel, B. A.; Mittelbach, M. Biodiesel from extracted fat out of meat and bone meal. Eur. J. Lipid Sci. Technol. 2006, 108, 398–403. (12) Lefferts, L. Y.; Kucharski, M.; McKenzie, S.; Walker, P. Feed for Food-Producing Animals: A Resource on Ingredients, the Industry, and Regulation; The Johns Hopkins Center for a Livable Future, Bloomberg School of Public Health: Baltimore, MD, 2007. (13) Zullaikah, S.; Lai, C. C.; Vali, S. R.; Ju, Y. H. A two-step acidcatalyzed process for the production of biodiesel from rice bran oil. Bioresour. Technol. 2005, 96, 1889–1896. (14) Farahani, M.; Page, D. J. Y. S.; Turingia, M. P. Sedimentation in biodiesel and ultra low sulfur diesel fuel blends. Fuel 2011, 90, 951–957. (15) Ma, F.; Clements, L. D.; Hanna, M. A. The effects of catalyst, free fatty acids, and water on transesterification of beef tallow. Trans. ASAE 1998, 41, 1261–1264. (16) Freedman, B.; Pryde, E. H.; Mounts, T. L. Variables affecting the yields of fatty esters from transesterified vegetable oils. J. Am. Oil Chem. Soc. 1984, 61, 1638–1643. (17) Aranda, D. A. G.; Santos, R. T. P.; Tapanes, N. C. O.; Ramos, A. L. D.; Antunes, O. A. C. Acid-catalyzed homogeneous esterification reaction for biodiesel production from palm fatty acids. Catal. Lett. 2008, 122, 20–25. (18) Diaz-Felix, W.; Riley, M. R.; Zimmt, W.; Kazz, M. Pretreatment of yellow grease for efficient production of fatty acid methyl esters. Biomass Bioenergy 2009, 33, 558–563. (19) Alptekin, E.; Canakci, M. Optimization of pretreatment reaction for methyl ester production from chicken fat. Fuel 2010, 89, 4035– 4039. 4761
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