Energy & Fuels 2005, 19, 1735-1741
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Production of Diesel-Like Fuel and Other Value-Added Chemicals from Pyrolysis of Animal Fat Adenike O. Adebanjo, Ajay K. Dalai,* and Narendra N. Bakhshi Catalysis and Chemical Reaction Engineering Laboratories, Department of Chemical Engineering, University of Saskatchewan, Saskatoon, Canada Received November 23, 2004. Revised Manuscript Received May 6, 2005
Pyrolysis of lard was performed in a fixed-bed reactor to produce a diesel-like fuel. Lard was fed into the reactor at 5 g/h using N2 (3 × 10-5-7 × 10-5 m3/min) as carrier gas. The liquid product obtained at a temperature of 600 °C, carrier gas flow rate of 5 × 10-5 m3/min, and quartz packing particle size of 0.7-1.4 mm has a cetane index of 46, specific gravity of 0.86, and a higher heating value of 40 MJ/kg. This study shows that there is a potential for producing diesel-like liquid from pyrolysis of lard. It also identifies the pyrolysis of animal fats as a source of highcalorific-value (68-165 MJ/m3) gaseous fuel.
1. Introduction Alternative fuel development is important for securing the supply of future transportation fuels, as well as for cleaner fuel utilization. Among the alternative and renewable fuel sources being considered are various types of fats and oils derived from plant and animal sources. Quick1 noted that these fats and oils have potential as diesel engine fuels but there is a need for continued and concentrated research. Following this, considerable research has been done on pyrolysis of vegetable oils to produce chemicals and diesel-like fuel.2-5 These studies were carried out using oils extracted from soybean, castor, palm tree, babassu, pequi, and canola. The studies included the effects of temperature on the type of products obtained, effects of co-feeding steam, and the characterization of the gas and liquid products. Some of these studies were conducted in batch and fixed-bed flow reactors, whereas others were conducted in a standard ASTM distillation apparatus, in which cracking and distillation occur simultaneously in the same unit. Different types of vegetable oils produce large differences in the composition of the thermally decomposed oil. Production of chemicals such as alkanes, alkenes, alkadienes, aldehydes, ketones, aromatics, and carboxylic acids was possible. The properties of the liquid fractions of the thermally decomposed vegetable oil are similar to those of diesel fuels. For example, pyrolyzed soybean oil contains 79% * Author to whom correspondence should be addressed. E-mail:
[email protected]. Tel: (306) 966-4771. Fax: (306) 966-4477. (1) Quick, G. R. ASAE paper No. 80-1525; ASAE: St Joseph, MI, 1980. (2) Alencer, J. W.; Alves, P. B.; Craveiro, A. A. J. Agric. Food Chem. 1983, 31, 1268-1270. (3) Schwab, A. W.; Bagby, M. O.; Freedman, B. Fuel 1987, 66, 13721378. (4) Idem, R. O.; Katikaneni, S. P. R.; Bakhshi, N. N. Energy Fuels 1996, 10, 1150-1162. (5) Lima, D. G.; Soares, V. C. D.; Ribeiro, E. B.; Carvalho, D. A.; Cardoso, E. C. V.; Rassi, F. C.; Mundim, K. C.; Rubim, J. C.; Suarez, P. A. Z. J. Anal. Appl. Pyrolysis 2004, 71, 987-996.
carbon and 11.88% hydrogen, has low viscosity, and has a high cetane number compared to pure vegetable oils. The cetane number of pyrolyzed soybean oil is enhanced to 43 from 37.9. Its viscosity is reduced to 10.2 from 32.6 mm2/s at 38 °C.3 However, it exceeds the specified value of 7.5 mm2/s for diesel fuel. The pyrolyzed vegetable oils possess acceptable amounts of sulfur, water, and sediment and give acceptable copper corrosion values but unacceptable ash, carbon residue amounts, and pour point. Pyrolysis, assisted by solid catalysts, has also been reported for vegetable oils,6-8 and it was noted that the product selectivity is strongly affected by the presence and nature of heterogeneous catalysts. The liquid product, however, was similar to gasoline. A catalytic steam reforming process is being utilized to convert triglycerides to value-added products such as hydrogen. Marquevich et al.9 studied the production of hydrogen by catalytic steam reforming of sunflower oil in a fixedbed reactor with a commercial nickel-based catalyst. This oil was completely converted to hydrogen, methane, and carbon oxides, except for the runs performed at the lowest temperatures and a steam-to-carbon ratio (S/C) of 3. The hydrogen yield ranged from 72% to 87% of the stoichiometric potential, depending on the S/C and the catalyst temperature. Pyrolysis of animal fats however, has not been studied to the same extent as vegetable oils. Green Oasis EnviroEconomics, Inc.10 employed a one-step process of thermal cracking and distillation to convert animal tallow into a diesel-like product having a flash point of 60 °C, perfect distillation curve, and a pour point of -28 (6) Dandik, L.; Aksoy, H. A. Fuel Process. Technol. 1998, 57, 8192. (7) Prasad, Y. S.; Bakhshi, N. N.; Mathews, J. F.; Eager, R. L. Can. J. Chem. Eng. 1986, 64, 278-284. (8) Katikaneni, S. P. R.; Adjaye, J. D.; Idem, R. O.; Bakhshi, N. N. J. Am. Oil Chem. Soc. 1998, 75, 381-391. (9) Marquevich, M.; Coll, R.; Montane, D. Ind. Eng. Chem. Res. 2000, 39, 2140-2147. (10) Green Oasis EnviroEconomics, 1999; http://www.greenoasis.com/product/overview.html
10.1021/ef040091b CCC: $30.25 © 2005 American Chemical Society Published on Web 06/18/2005
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°C. The use of animal fat instead of vegetable oil to produce alternative diesel is an effective way to reduce the raw material cost because its cost is estimated to be about half the price of virgin vegetable oil.11 Because meats cannot be produced without the simultaneous production of fat, a large amount (about 27.9 million metric tons per year globally12) of animal fat is unavoidably produced in the process of supplying meat. Also, due to the recent Bovine Spongiform Encephalopathy (BSE) crisis, the use of animal-derived products to feed cattle is now severely restricted.13 Therefore, using animal fat as fuel could also help to solve the problem of waste disposal.14 In this present investigation, lard was used as a representative feed material for animal fats. The choice of lard was based on the fact that it is readily available in a pure form. The objective of this work was to investigate the potential for production of a diesel-like fuel, other chemicals, and high-heating-value gas from lard pyrolysis. The effects of temperature, residence time, and particle size of the inert (quartz) packing on the quality of liquid product, the composition, and heating value of product gas were studied. 2. Experimental Section The lard used in this study was produced by Sobeys in Stellarton Toronto and obtained from a retail outlet. The carbon (C), hydrogen (H), and nitrogen (N) analysis of the lard was performed on a CHN analyzer (Perkin-Elmer 2400). The wt% of O2 in the lard was obtained by difference. The lard was also analyzed for sulfur and nitrogen using ANTEK 900 sulfur and nitrogen (N/S) analyzer. The lard’s fatty acid composition was determined by POS Pilot Plant Corporation, Saskatoon, using gas chromatography. 2.1. Pyrolysis of Lard. Pyrolysis reactions were conducted at atmospheric pressure in a continuous fixed-bed inconel alloy microreactor (310 mm long, 10 mm i.d.). Quartz chips (about 5 g), occupying a height of 70 mm in the reactor, were held on a plug of quartz wool placed on a supporting mesh inside the microreactor. The reactor was heated by a furnace with temperature control by a series SR22 microprocessor-based autotuning PID temperature controller (Shimaden Co. Ltd., Tokyo, Japan) using a K-type thermocouple placed on the furnace side of the annulus between the furnace and the reactor. Another thermocouple (in a thermowell) was used to monitor the temperature at the center of the reactor. All temperatures were maintained to within (2.0 °C. Lard is a solid at room temperature; however, it melts at about 37 °C. It was therefore preheated to 40 °C and then fed to the reactor using a programmable syringe pump (Genie model YA-12) at a flow rate of 5 g/h. The desired flow rate of the carrier gas (N2) was maintained by using a needle valve and a mass flow meter (Top-trak model 822). Each experiment was run for 0.5 h. The liquid products were collected with the help of a condenser attached to the bottom of the reactor outlet. The gaseous products were collected in a gas collector by the downward displacement of brine solution of NaCl. The experimental setup is shown in Figure 1. After each run, the reactor was cooled and weighed to determine the amount of retained products (char + residue). The condensate (liquid product) was also weighed. (11) Supple, B.; Howard-Hildige, R.; Gonzalez-Gomez, E.; Leahy, J. J. J. Am. Oil Soc. Chem. 1999, 79, 175-178. (12) Gunstone F. D. http://www.britanniafood.com/german/ invite_05.htm#three. (13) Chaala A.; Roy, C. Environ. Sci. Technol. 2003, 37, 4517-4522. (14) Wiltsee, G. Proceedings of Bioenergy Conference, Madison, WI, October 4-8, 1998; pp 956-963.
Adebanjo et al.
Figure 1. Schematic diagram of experimental setup for pyrolysis of lard: (1) brine solution tank, (2) gas collector, (3) two way valves, (4) sampler, (5) lard feed pump, (6) quartz chips packing, (7) furnace, (8) reactor, (9) ice condenser, (10) condensate collector, (11) nitrogen cylinder, (12) needle valve, (13) mass flow meter, and (14) check valve. 2.2. Gas Product Analysis. The product gas was analyzed for its composition using two GCs (HP5890 and HP5880A). The HP5890 is equipped with a thermal conductivity detector (TCD) and Carbosive S II column (3000 mm, 3.18 mm i.d.), and it analyses H2, CO, CO2, and CH4, whereas the HP5880A equipped with a flame ionization detector and a Chromosorb102 column (1800 mm, 3.18 mm i.d.) was used to analyze for hydrocarbons. Standard gas mixtures were used for calibration. After normalization of the components, an average molecular weight was calculated for the gaseous product. The weight of the gas fraction was determined from this average molecular weight and the total volume of gas evolved during the run. 2.3. Liquid Product Analysis and Characterization. Analytical chromatograms of the liquid product were obtained on an FID Varian 3400 GC equipped with a capillary column (26 m × 0.32 mm) by using DB-1 column having 100% dimethylpolysiloxane as the stationary phase. The compounds present in the liquid product were identified using a VG-250SE mass spectrometer (MS) coupled to a Fisons GC 8000 series (model 8060) which was equipped with a 95% dimethylpolysiloxane capillary column. The densities of the liquid products were determined using a density meter (Parr, Model DMA 35) at 25 °C according to the method of ASTM D5002. The density meter was calibrated using distilled water. The viscosities were determined using a digital cone and plate viscometer (Brookfield, Model LVDV-1+, Brookfield Engineering Laboratories, Stoughton, MA) at 40 °C. The temperature of the sample was maintained within (0.5 °C with a constant-temperature bath (Julabo F20). Brookfield standard fluid 100 was used to calibrate the viscometer. The heat of combustion of the liquid was measured using an oxygen bomb calorimeter (Parr 1341) according to ASTM D240 using benzoic acid as the primary standard. The boiling point distribution of the petroleum fraction in the product was determined by GC-simulated distillation (Model CP 3800) according to ASTM D2887. Standard hydrocarbon mixtures were used to calibrate the GCsimulated distillation. ASTM D976 was used to calculate the cetane index (CI) as a function of mid-boiling point and density of the liquid according to the formula:
CI ) 454.74 - 1641.416(G) + 774.74(G)2 - 0.554(T50) + 97.803(log T50)2 (1) where T50 ) mid-boiling temperature (°C) and G ) specific gravity at room temperature.
Diesel-Like Fuel from Pyrolysis of Animal Fat
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Table 1. Physical Properties and Fatty Acid Composition of the Feed (Lard) Physical Properties density @40 °C (kg/m3) higher heating value (MJ/kg) viscosity @40 °C (mPa‚s) Composition, wt% of Total Fatty Acids C10:0 (capric) C12:0 (lauric) C14:0 (myristic) C15:0 (pentadecanoic) C16:0 (palmitic) C16:1 (palmitoleic) C17:0 (magaric) C18:0 (stearic) C18:1n9 (oleic) C18:2 (linoleic) C18:3 (R-linolenic) C18:4 (octadecatetraenoic) C20:0 (arachidic) C20:1 (eicosenoic) C20:2 (eicosadienoic) others
940 39.6 36.4 0.1 0.1 1.4 0.1 24.1 2.4 0.4 14.0 39.4 14.2 0.8 0.1 0.2 0.7 0.5 1.4
3. Results and Discussion The physical properties of the lard, as well as its fatty acid composition, are given in Table 1. The data in Table 1 indicate that the feed has a high heating value (39.6 MJ/kg) and viscosity (36.4 mPa‚s). The heating value measurement was accurate to within (2.0%. The lard contained large quantities of palmitic, stearic, oleic, and linoleic acid moieties. Its overall elemental analysis showed 77.3 wt% C, 12.2 wt% H, and 10.5 wt% O. Traces of sulfur (
