Energy & Fuels 2008, 22, 2061–2066
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Comparing Biofuels Obtained from Pyrolysis, of Soybean Oil or Soapstock, with Traditional Soybean Biodiesel: Density, Kinematic Viscosity, and Surface Tensions† Kenneth M. Doll,*,‡ Brajendra K. Sharma,‡,§ Paulo A. Z. Suarez,‡,| and Sevim Z. Erhan‡ Food and Industrial Oil Unit, National Center for Agricultural Utilization Research, United States Department of Agriculture, Agricultural Research SerVice, 1815 North UniVersity Street, Peoria, Illinois 61604, and Department of Chemical Engineering, PennsylVania State UniVersity, UniVersity Park, PennsylVania 16802 ReceiVed January 30, 2008. ReVised Manuscript ReceiVed March 7, 2008
A product with diesel-like properties was synthesized by a pyrolysis method, from either edible soybean oil or an inedible soybean soapstock starting material (PD and SD, respectively). Some physical properties of the material were studied, neat and in blends, with both high- and low-sulfur diesel fuels (HSD and LSD) and at a range of different temperatures. The kinematic viscosities at 40 °C were 4.5 mm2 s-1 for PD and 3.8 mm2 s-1 for SD, which were reduced in a linear fashion by the addition of HSD or LSD. The densities of the fuels at 40 °C were 0.853 and 0.844 g mL-1, very similar to the density of HSD. The surface tensions of the compounds, also at 40 °C, were 27.1 mN m-1 for PD and 26.2 mN m-1 for SD. A comparison to traditional biodiesel was made and, overall, lead to the conclusion that the pyrolysis products are a viable alternative.
Introduction The use of bio-based fuels has dramatically increased in recent years,1–3 and with the cost of petroleum going well over predictions,4,5 the biodiesel movement is unlikely to end soon. The United States government has successfully encouraged the use of bio-based products,6 through various regulations and tax incentives, to the point where there are currently almost 100 biodiesel plants in operation or under construction.7 The industry is currently trying to overcome the challenges of feedstock cost and availability.2 There are a couple of different methods in which vegetable oil can be made into a fuel. Direct use of vegetable oil as a fuel † Disclaimer: The use of trade, firm, or corporation names in this paper is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by the United States Department of Agriculture or the Agricultural Research Service of any product or service to the exclusion of others that may be suitable. * To whom correspondence should be addressed. E-mail: kenneth.doll@ ars.usda.gov. ‡ United States Department of Agriculture. § Pennsylvania State University. | Current address: LMC-UnB, CP 4478, CEP 70919-970, Brasília, DF, Brazil. (1) Tullo, A. New life for old plants. Chem. Eng. News 2007, 85 (7), 53–55. (2) Gunstone, F. Update on food and nonfood uses of oils and fats. INFORM 2007, 18 (8), 573–574. (3) Pruszko, R. Rendered fats and oils as a biodiesel feedstock. INFORM 2006, 17 (7), 431–433. (4) Van Arnum, P. Analysts say oil at $50 per barrel is possible. Chem. Mark. Rep. 2004, 266 (6), 1–2. (5) Viswanathan, P. Oil price threat. Chem. Mark. Rep. 2005, 267 (12), 1. (6) Hagstrom, J. USDA to set requirements for agencies to purchase bio-based products. 2005, www.govexec.com. (7) Howell, S. Biodiesel gains record momentum. INFORM 2006, 17 (Biorenewable Resources #1), 9.
was demonstrated a century ago,8 although its viscosity is not ideal and its use can cause deposit buildup and engine failure in modern engines. Most commonly, the triacylglyceride structures of oil are reacted with an alcohol in a simple transesterification reaction to form traditional biodiesel (BD) using acid,9 base,10,11 enzymatic,12 or heterogeneous13–16 catalysis. Although this route is commonly practiced, it has some drawbacks. The main drawback is the requirement of a large amount of alcohol, usually methanol, where at least 3 mol of alcohol are consumed for every 1 mol of triacylglyceride reacted. Despite some recent developments on conversion of biomass (8) Knothe, G. The history of vegetable oil-based diesel fuels. In The Biodiesel Handbook; Knothe, G., Ed.; AOCS Press: Champaign, IL, 2005; pp 4–16. (9) Di Serio, M.; Tesser, R.; Dimiccoli, M.; Cammarota, F.; Nastasi, M.; Santacesaria, E. Synthesis of biodiesel via homogeneous Lewis acid catalyst. J. Mol. Catal. A: Chem. 2005, 239 (1–2), 111–115. (10) Haas, M. J.; Scott, K. M.; Marmer, W. N.; Foglia, T. A. In situ alkaline transesterification: An effective method for the production of fatty acid esters from vegetable oils. J. Am. Oil Chem. Soc. 2004, 81 (1), 83–89. (11) Zhou, W.; Konar, S. K.; Boocock, D. G. B. Ethyl esters from the single-phase base-catalyzed ethanolysis of vegetable oils. J. Am. Oil Chem. Soc. 2003, 80 (4), 367–371. (12) Xu, Y.; Du, W.; Liu, D.; Zeng, J. A novel enzymatic route for biodiesel production from renewable oils in a solvent-free medium. Biotechnol. Lett. 2003, 25 (15), 1239–1241. (13) Macedo, C. C. S.; Abreu, F. R.; Tavares, A. P.; Melquizedeque, B. A.; Zara, L. F.; Rubim, J. C.; Suarez, P. A. Z. New heterogeneous metaloxides based catalyst for vegetable oil trans-esterification. J. Braz. Chem. Soc. 2006, 17 (7), 1291–1296. (14) Abreu, F. R.; Alves, M. B.; Macedo, C. C. S.; Zara, L. F.; Suarez, P. A. Z. New multi-phase catalytic systems based on tin compounds active for vegetable oil transesterificaton reaction. J. Mol. Catal. A: Chem. 2005, 227 (1–2), 263–267. (15) Suppes, G. J.; Dasari, M. A.; Doskocil, E. J.; Mankidy, P. J.; Goff, M. J. Transesterification of soybean oil with zeolite and metal catalysts. Appl. Catal., A 2004, 257 (2), 213–223. (16) Tesser, R.; Di Serio, M.; Santacesaria, E.; Guida, M.; Nastasi, M. Kinetics of oleic acid esterification with methanol in the presence of triglycerides. Ind. Eng. Chem. Res. 2005, 44 (21), 7978–7982.
10.1021/ef800068w CCC: $40.75 2008 American Chemical Society Published on Web 04/17/2008
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to methanol,17 it is usually derived from natural gas or other fossil fuel sources. To make matters worse, often, the alcohol must be used in excess to obtain a complete reaction. The production of glycerol, once seen as a valuable co-product of the reaction, is now regarded as a problem,18–20 at least until there are enough facilities for its refining. This glycerol byproduct must be completely removed to obtain a fuel that will meet current specifications.21 Alternative routes to a biobased fuel have been studied, including methods that use dimethyl carbonate22 or short-chain carboxylic acids as fuel components. These systems do not produce the glycerol byproducts but still require significant inputs, and their product fuels have not been studied in detail. Another interesting method for the production of vegetableoil-based fuel is through pyrolysis. Pyrolysis of vegetable oil is well-studied,23–26 and its use to produce fuels dates back 60 years.27,28 Pyrolyzed vegetable oil (pyrodiesel, PD) does not produce the undesired crude glycerol byproduct, a possible advantage given its current low value. Similar to biodiesel, pyrolysis will work on a variety of feedstocks, both edible and inedible. However, pyrolysis only requires a predrying step for use with soy soapstock. Traditional biodiesel alternatives have shown industrial applicability as well. For example, renewable diesel fuel made from animal fats may soon be incorporated into a large industrial-scale process in a joint collaboration between a food industry giant and a large petrochemical producer.29 A recent report contained a method for the synthesis of a PD and a study of the chemical composition of the resultant product.30 However, there are other studies that should be performed before the product can be used as fuel. Internal combustion engines require efficient fuel atomization before fuel combustion. Atomization of liquids is an old topic in science31–34 and well-studied in the bio-based fuels area.35–38 It is influenced by many factors, including the injector properties (17) Zhu, L.-F.; Du, L.; Li, X.-B.; Li, G.-T.; Zhang, J. Process conditions for preparing methanol from cornstalk gas. J. EnViron. Sci. 2007, 19 (5), 628–632. (18) Kirschner, M. Chemical profile: Glycerine. Chem. Mark. Rep. 2005, 267 (4), 31. (19) de Guzman, D. Supply pressures continue for global oleochemicals market. Chem. Mark. Rep. 2005, 267 (4), 16. (20) Rattay, J. B. GlycerinesHow sweet it is. INFORM 2006, 17 (5), 285. (21) Torrey, M. Biodiesel standards. INFORM 2007, 18 (7), 432–433. (22) Fabbri, D.; Bevoni, V.; Notari, M.; Rivetti, F. Properties of a potential biofuel obtained from soybean oil by transmethylation with dimethyl carbonate. Fuel 2007, 86 (5–6), 690–697. (23) Fortes, I. C. P.; Baugh, P. J. Study of analytical on-line pyrolysis of oils from macauba fruit (Acrocomia sclerocarpa M.) via GC/MS. J. Braz. Chem. Soc. 1999, 10 (6), 469–477. (24) Idem, R. O.; Katikaneni, S. P. R.; Bakhshi, N. N. Thermal cracking of canola oil: Reaction products in the presence and absence of steam. Energy Fuels 1996, 10 (6), 1150–1162. (25) Alencar, J. W.; Alves, P. B.; Craveiro, A. A. Pyrolysis of tropical vegetable oils. J. Agric. Food Chem. 1983, 31 (6), 1268–1270. (26) Fortes, I. C. P.; Baugh, P. J. Study of calcium soap pyrolysates derived from macauba fruit (Acrocomia sclerocarpa M.). Derivatization and analysis by GC/MS and CI-MS. J. Anal. Appl. Pyrolysis 1994, 29 (2), 153–167. (27) Chang, C.-C.; Wan, S.-W. China’s motor fuels from Tung oil. Ind. Eng. Chem. 1947, 39 (12), 1543–1548. (28) Schwab, A.; Dykstra, G.; Selke, E.; Sorenson, S.; Pryde, E. Diesel fuel from thermal decomposition of soybean oil. J. Am. Oil Chem. Soc. 1988, 65 (11), 1781–1786. (29) Hess, G. Tax break for biofuel targeted. Chem. Eng. News 2007, 85 (41), 35–38. (30) 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. Diesel-like fuel obtained by pyrolysis of vegetable oils. J. Anal. Appl. Pyrolysis 2004, 71 (2), 987–996.
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as well as the nature of the fuel. A useful equation describing the atomization characteristic of a fuel (eq 1) has been derived.35,37 K)
(
Ffuel
We Fatmosphere Re
)
1⁄3
We ∝ 1/γRe ∝ 1/ν
(1)
where K ) characteristic, F ) density, We ) Weber number, Re ) Reynolds number, γ ) surface tension, and ν ) kinematic viscosity. Two physical parameters of the fuel that must be governed to obtain the desired low characteristic number (K) are the kinematic viscosity (ν) and the surface tension (γ). The viscosity is considered the more important of the two factors and was the primary reason why earlier work37 recommended that fuel blends used in direct injection motors should contain no more that 34% vegetable oil. The American Society for Testing and Materials (ASTM) standard,21,39 D6751-07b, requires a kinematic viscosity of 1.9–6 mm2 s-1 at 40 °C. Herein, we characterize the products of a previously developed pyrolysis process, using two different feedstocks: refined soybean oil and soapstock. The results are compared to commercially available soy methyl esters (biodiesel, BD). The materials are studied neat but also in incremental blends with ordinary diesel fuel, the more probable use in the United States. The kinematic viscosity, density, and surface tension of all of the above materials are studied at a variety of temperatures. It is also worth discussing that that there are many other properties that a bio-based fuel must possess in addition to the ones mentioned herein before it can be considered a true diesel alternative. These include cetane number, lubricity, cold flow behavior, corrosion, iodine value, and acid value. The cetane number of these fuels has been studied in a previous paper.30 It was found to be 50.1 when soybean oil was used as a feedstock, and an even better value of 52.7 was obtained when palm oil was used as a feedstock. These values are considerably above the requirement of 47, set in ASTM standard D6751-07b.39 The study of the other parameters of PD and SD have also indicated that they will enhance the lubricity of petroleum-based diesel fuels; they will meet copper corrosion and oxidative stability (31) Rutland, D. F.; Jameson, G. J. Theoretical prediction of the sizes of drops formed in the breakup of capillary jets. Chem. Eng. Sci. 1970, 25 (11), 1689–1698. (32) Strutt, J. W. Investigation of the character of the equilibrium of an incompressible heavy fluid of variable density. Proc. London Math. Soc. 1883, 14, 170–177. (33) Zhang, X.; Basaran, O. A. Dynamic surface tension effects in impact of a drop with a solid surface. J. Colloid Interface Sci. 1997, 187 (1), 166– 178. (34) Bousfield, D. W.; Keunings, R.; Marrucci, G.; Denn, M. M. Nonlinear analysis of the surface tension driven breakup of viscoelastic filaments. J. Non-Newtonian Fluid Mech. 1986, 21 (1), 79–97. (35) Allen, C. A. W.; Watts, K. C.; Ackman, R. G. Predicting the surface tension of biodiesel fuels from their fatty acid composition. J. Am. Oil Chem. Soc. 1999, 76 (3), 317–323. (36) Allen, C. A. W.; Watts, K. C. Comparative analysis of the atomization characteristics of fifteen biodiesel fuel types. Trans. ASAE 2000, 43 (2), 207–211. (37) Msipa, C. K. M.; Goering, C. E.; Karcher, T. D. Vegetable oil atomization in a DI diesel engine. Trans. ASAE 1983, 26 (6), 1669–1672. (38) Doll, K. M.; Moser, B. R.; Erhan, S. Z. Surface tension studies of alkyl esters and epoxidized alkyl esters relevant to oleochemically based fuel additives. Energy Fuels 2007, 21 (5), 3044–3048. (39) American Society for Testing and Materials (ASTM). ASTM International Designation: D 6751-07b standard specification for biodiesel fuel blend stock (B100) for middle distillate fuels. ASTM Int., 2007, D 6751-07b, 1–8.
Physical Properties Studies of Biofuels and Blends
requirements; and at blends up to 10%, they will have a negligible effect on the petroleum diesel pour point and cloud point.
Energy & Fuels, Vol. 22, No. 3, 2008 2063 Table 1. Fuel Blends (% w/w) Prepared and Used in This Work: High- and Low-Sulfur Content Diesel (HSD and LSD, Respectively), Biodiesel (BD), and Diesel-like Fuels Prepared from Soybean Oil (PD) and Soybean Soapstock (SD) sample
Experimental Section Materials. Alkali-refined soybean oil and soybean soapstock were obtained from ADM Packaged Oils (Decatur, IL) and were used as received without further purification. Biodiesel (BD, methyl soyate; trade name SoyGold) was obtained from Ag Environmental Products (Lenexa, KS). Low- and high-sulfur petrodiesel fuel (up to 15 ppm for LSD and 50 ppm for HSD, respectively) were obtained from Chevron-Phillips (Pascagoula, MS). All other materials were acquired from Aldrich Chemical Co. and were used as received. Pyrolysis Experiments. Diesel-like pyrolytic fuel (PD) was obtained from the pyrolysis of soybean oil followed by atmospheric distillation of the product using an adapted method published elsewhere.30 Pyrolysis experiments were carried out at 350 °C using a round-bottom three-necked 5 L flask equipped with a side condenser. The soybean oil (2 L) was introduced in the flask and then heated by an external electric resistance heating mantle. When the temperature inside the reactor achieved 350 °C, the vegetable oil was pyrolyzed and vaporized. The vapor feed left the flask via a side condenser at temperatures ranging from 200 to 250 °C. The condensation resulted in the production of two liquid fractions in the collector: an aqueous fraction and an organic fraction. These fractions were separated by decantation, and the organic phase was distilled using standard laboratory techniques. The fractions that distilled above 200 °C were recovered and used as PD. Alternatively, diesel-like pyrolytic fuel (SD) was obtained after pyrolysis of dried soybean soapstock. The soapstock was first dried at 150 °C until a constant weight was obtained. The dried soapstock was pyrolyzed, and the product was collected, using similar experimental procedures as those described for soybean oil. Sample Preparation. Data were collected on 35 samples corresponding to blends of HSD, LSD, BD, PD, and SD. They were prepared at room temperature using a balance (Mettler PM2000, (0.01 g). Their compositions are displayed in Table 1. Viscosity and Density Measurements. Kinematic viscosity and density, at 20 and 40 °C, were determined following ASTM method D7042, using an Anton Paar Stabinger (Ashland, VA) SVM3000 viscometer. Each sample was run in triplicate, and an average value is reported. The precision is within the limits of the ASTM method specification. Surface-Tension Analysis. Surface-tension measurements were taken with a Sita t60 bubble pressure tensiometer (SITA GmbH, Desden, Germany/Future Digital Scientific, Bethpage, NY) using Sita online version 2.1 software. Software-controlled dilutions and temperature control were handled by an Ingenieurbüro (Staufen, Germany) Cat M 26 stir plate and an Ingenieurbüro (Staufen, Germany) CAT contiburette µ-10M-C burette using Sita Labtool V1 software. They were all controlled by an IBM (White Plains, NY) Pentium 4 computer with a 3.0 GHz processor and a Windows XP operating system. The T-60 tensiometer records the surface tension versus bubble lifetime. The curves all showed the trend of a decreasing surface tension with an increasing bubble lifetime, at lifetimes less that 1 s. With bubble lifetimes >1 s, the value of the surface tension was constant and the curves became flat. A bubble lifetime of at least 4 s was used in all of these measurements, well into the flat region of the curve, ensuring that any dynamic surfacetension effects did not alter the measured values. The system was calibrated using pure water with the built in calibration function on the tensiometer. The water was obtained from a Barnstead (Dubuque, IA) Nanopure system and had a measured resistance of >18 MΩ cm-1. The surface tensions of several organic solutions
BD PD SD LSD HSD LSD/BD02 LSD/BD05 LSD/BD10 LSD/BD20 LSD/BD50 HSD/BD02 HSD/BD05 HSD/BD10 HSD/BD20 HSD/BD50 LSD/PD02 LSD/PD05 LSD/PD10 LSD/PD20 LSD/PD50 HSD/PD02 HSD/PD05 HSD/PD10 HSD/PD20 HSD/PD50 LSD/SD02 LSD/SD05 LSD/SD10 LSD/SD20 LSD/SD50 HSD/SD02 HSD/SD05 HSD/SD10 HSD/SD20 HSD/SD50
BD (g)
PD (g)
SD (g)
LSD (g)
HSD (g)
200 200 200 200 200 4.47 10.08 19.98 40.22 99.94 5.37 9.94 20.74 39.97 99.91
196.10 190.28 180.16 160.33 100.27 196.00 190.07 179.96 160.14 100.16 4.03 10.36 20.16 40.00 99.90 4.05 10.15 19.97 40.00 100.34
196.09 190.13 180.15 160.24 100.25 196.05 189.96 179.99 159.96 100.00 3.01 7.68 15.00 30.07 75.03 3.01 7.54 15.75 30.21 75.12
147.06 142.56 135.09 120.08 75.23 147.07 142.61 135.03 30.21 75.75
were also measured and found to agree with literature values, before the surface-tension measurements of samples were undertaken.
Results and Discussion The pyrolysis method was applied to both edible soybean oil as well as soapstock. The results gave a material similar to that obtained in the past (Figure 1).30 In that reference, the composition of the pyrolysis mixture was analyzed using gas chromatography–mass spectrometry methods. The identification of the structures was performed with the mass spectra, and the characterization was further confirmed by Fourier transform infrared (FTIR) spectroscopy. The cetane number, acid index, and sulfur wt % and density of pyrodiesel were all shown to be suitable for fuel use. The kinematic viscosities of the compounds at 20 and 40 °C are reported (Table 2), along with a comparison to traditional biodiesel. The viscosities of all of the biofuels meet the standards set for biodiesel.21,39 However, both the pyrolysis product made from edible soybean oil, PD, and traditional biodiesel, BD, are close to the maximum specification of 6.0 mm2 s-1.21,39 They are also considerably higher than the measured value for petroleum-based diesels. The SD product has a slightly lower viscosity, closer to that observed in the petroleum products. Biodiesel is most commonly used as a mixture with petrochemical diesel. Hence, measurement of the viscosities (ν) of a series of blends of the pyrodiesel fuels with LSD and HSD is also important. We made blends of fuels with contents ranging from 2 to 50 wt % of the PD, SD, and for comparison, BD (Table 1). These values, as well as the unblended values,
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Figure 1. Structure of a triacylglyceride oil and the proposed structures of the fuels studied herein. All of the biofuel mixtures will have a slightly varied composition depending upon feedstock and processing conditions. Table 2. Kinematic Viscosities (ν) and Densities (G) of Pyrolyzed Oleochemical Fuel, Made from Soybean Oil (PD) and Soapstock (SD), Traditional Biodiesel (BD), and Traditional Diesel Fuel in Low-Sulfur (LSD) and High-Sulfur (HSD) Varietiesa
fuel type
kinematic viscosity (ν) at 20 °C (mm2 s-1)
density (F) at 20 °C (g mL-1)
kinematic viscosity (ν) at 40 °C (mm2 s-1)
density (F) at 40 °C (g mL-1)
PD SD BD HSD LSD
6.0 5.5 5.2 3.9 3.3
0.867 0.858 0.881 0.858 0.822
4.5 3.8 4.1 2.7 2.2
0.853 0.844 0.867 0.844 0.809
a
The measurements were made at 20 and 40 °C.
correspond to the most probable real world uses of bio-based fuels. The results at 40 °C (Figures 2 and 3) show that in each case, as the quantity of biofuel is increased, ν also increased in a proportionate amount. For example a 50% mixture of PD, ν
Figure 2. Plot of the kinematic viscosities (ν), at 40 °C, of fuel mixtures of low-sulfur diesel (LSD) mixed with PD and SD and traditional biodiesel (BD).
Physical Properties Studies of Biofuels and Blends
Energy & Fuels, Vol. 22, No. 3, 2008 2065 Table 3. Surface Tensions (γ) of Pyrolyzed Oleochemical Fuel, Made from Soybean Oil (PD), and Soapstock (SD), Traditional Biodiesel (BD), and Traditional Diesel Fuel in Low-Sulfur (LSD) and High-Sulfur (HSD) Varietiesa
fuel type
surface tension (γ) at 23 °C (mN m-1)
surface tension (γ) at 40 °C (mN m-1)
surface tension (γ) at 60 °C (mN m-1)
PD SD BD HSD LSD
27.5 27.1 34.2 26.5 25.6
27.1 26.2 29.8 25.1 25.1
24.8 23.9 26.7 24.2 22.7
a The measurements were made using bubble pressure tensiometry at 23, 40, and 60 °C.
Figure 3. Plot of the kinematic viscosities (ν), at 40 °C, of fuel mixtures of high-sulfur diesel (HSD) mixed with PD and SD and traditional biodiesel (BD).
Figure 6. Plot of the surface tensions (γ), at 40 °C, of fuel mixtures of low-sulfur diesel (LSD) mixed with PD and SD and traditional biodiesel (BD). Figure 4. Plot of the densities (F), at 40 °C, of fuel mixtures of lowsulfur diesel (LSD) mixed with PD and SD and traditional biodiesel (BD).
Figure 7. Plot of the surface tensions (γ), at 40 °C, of fuel mixtures of high-sulfur diesel (HSD) mixed with PD and SD, and traditional biodiesel (BD). Figure 5. Plot of the densities (F), at 40 °C, of fuel mixtures of highsulfur diesel (HSD) mixed with PD and SD and traditional biodiesel (BD).
of 4.5 mm2 s-1 and LSD, ν of 2.2 mm2 s-1, had a measured ν of 3.1 mm2 s-1, essentially halfway between the two values. Traditional biodiesel has ν values, both neat and in blends, approximately halfway between the values for the two pyrolysis products. Overall, any of the fuels, either neat or in any blends, will meet the ν specifications21 for biodiesel. However, from a consideration of atomization efficiency (eq 1), a lower viscosity fuel will result in a better (lower) atomization characteristic number. Using a linear fit to the data in Figure 3, the maximum amount of each biofuel-blended HSD, which would still have
a kinematic viscosity below the middle of the specification range, ν ∼ 3.95 mm2 s-1, was calculated. PD could be incorporated at 71%; BD could be incorporated at 91%; and the SD product could be used in any amount. Slightly more biofuel could be used in LSD blends (Figure 2), because of its lower neat viscosity: PD at 81%, BD at 96%, and SD, again, could be used in any amount. The density (F) of the pyrolyzed fuels (Table 2) and blends (Figures 4 and 5) were slightly higher than that of LSD but lower than the measured value in traditional BD. The density measurements of the blends varied, as expected, in a fairly linear manner. Mixtures that contained more bio-based fuel were denser than those with more petroleum-based diesel. A notable exception was the mixture of the least dense bio-based fuel, SD, with the most dense petroleum diesel, HSD. Their densities
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were equal, as was the density of all of their blends. This is a potential convenience for those making fuel blends. In a similar manner, the surface tensions (γ) of both the neat fuels (Table 3) and the blends (Figures 6 and 7) were taken at multiple temperatures. The γ of both of the petrochemical diesel fuels was in the expected range of 20–25 mN m-1, common for hydrocarbons.40 The traditional biodiesel had γ somewhat higher, probably because of the oxygen-containing ester moieties contained on each molecule. The pyrolysis product contains both alkyl- and oxygen-containing structures; therefore, as expected, its surface tension is higher than that of a pure hydrocarbon but lower than a pure ester. Surface-tension results for blends of liquids can be somewhat difficult to predict. Often, fractional components of a mixture will affect γ in a way that does not correlate well with the amount of that component.35 However, in our case, the γ of the fuels (Figures 6 and 7) did show a predictable increase in γ as the amount of biofuel in the blend was increased.
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advantages compared to traditional biodiesel. The biggest advantage is that there is no requirement for a large amount of alcohol and correspondingly no production of byproduct glycerol. Another advantage is that the feedstock requirements for the pyrolysis may be less stringent, as demonstrated by the synthesis of a high-quality product from either edible soybean oil or inedible soapstock. From viscosity, density, and surfacetension points of view, the biofuel made from soapstock is the most similar to petroleum-based diesel. Overall, the use of this methodology offers an alternative to help meet the pressing fuel needs of the world. Acknowledgment. We acknowledge Ms. Donna I. Thomas for surface-tension measurements and Richard H. Henz for viscosity and density measurements. Professor P. A. Z. Suarez also thanks CNPq for a research fellowship. EF800068W
Conclusion The use of fuels derived from biomass is important for the future. The use of pyrolysis products has a couple of potential
(40) Quayle, O. R. The parachors of organic compounds. An interpretation and catalogue. Chem. ReV. 1953, 53 (3), 439–589.
