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Energy & Fuels 2006, 20, 1310-1314
Room-Temperature Conversion of Soybean Oil and Poultry Fat to Biodiesel Catalyzed by Nanocrystalline Calcium Oxides Chinta Reddy Venkat Reddy, Reed Oshel, and John G. Verkade* Department of Chemistry, Gilman Hall, Iowa State UniVersity, Ames, Iowa 50011 ReceiVed December 26, 2005. ReVised Manuscript ReceiVed February 22, 2006
A promising route for the production of biodiesel (fatty acid methyl esters, FAMES) via transesterification of soybean oil (SBO) and poultry fat with methanol in quantitative conversions at room temperature has been developed using nanocrystalline calcium oxides as catalysts. Under the same conditions, laboratory-grade CaO gave only 2% conversion in the case of SBO, and there was no observable reaction with poultry fat. The soybean oil/methanol ratio in our protocol is 1:27. With our most active catalyst, deactivation was observed after eight cycles with SBO and after three cycles with poultry fat. Deactivation may be associated with one or more of the following factors: the presence of organic impurities or adventitious moisture and enolate formation by the deprotonation of the carbon alpha to the carboxy group in the triglyceride or FAMES. The biodiesel from our protocol meets the ASTM D-874 standard for sulfated ash for both substrates.
Introduction Biodiesel, a mixture of fatty acid methyl esters (FAMES), is a clean-burning fuel derived from vegetable oils or animal fat and is an advantageous alternative to fossil diesel fuel1,2 because of its biodegradability, biorenewable nature, very low sulfur content and toxicity, low volatility/flamability, good transport and storage properties, higher cetane number, and its salutary atmospheric CO2 balance for production. Treatments that circumvent the significant problems associated with the high viscosity of plant oils when used as engine fuels are its dilution, microemulsification, pyrolysis, and transesterification with methanol; the latter approach is used most commonly. The glycerin formed during transesterification is also important because of its numerous applications in the food, cosmetic, and pharmaceutical sectors.3 FAMES is not only currently useful as a diesel fuel additive, but it is also marketed as green industrial degreasing solvents; as diluents for pigments, paints, and coatings; and for military engine fuel applications.4 Reported routes for the conversion of plant oils to biodiesel have included the use of homogeneous strong base catalysts * Corresponding author. Fax: 01 (515) 294-0105. E-mail: jverkade@ iastate.edu. (1) For example, see: (a) Toda, M.; Takagaki, A.; Okamura, M.; Kondo, J. N.; Hayashi, S.; Domen, K.; Hara, M. Nature 2005, 438, 178. (b) Srivastava, A.; Prasad, R. Renewable Sustainable Energy ReV. 2000, 4, 111. (c) Shay, E. G. Biomass Bioenergy 1993, 4, 227. (d) Schwab, A. W.; Bagby, M. O.; Friedman, B. Fuel 1987, 66, 1372. (e) Freedman, B.; Butterfield, R. O.; Pryde, E. H. J. Am. Oil Chem. Soc. 1986, 63, 1375. (f) Freedman, B.; Pryde, E. H.; Mounts, T. L. J. Am. Oil Chem. Soc. 1984, 61, 1638. (g) Leclercq, E.; Finiels, A.; Moreau, C. J. Am. Oil Chem. Soc. 2001, 78, 1161. (h) Xie, W.; Peng, H.; Chen, L. J. Mol. Catal. A: Chem. 2006, 246, 24. (2) For reviews on transesterification of vegetable oils and animal fat to biodiesel, see: (a) Schuchardt, U.; Sercheli, R.; Vargas, R. M. J. Braz. Chem. Soc. 1998, 9, 199. (b) Kinney, A. J.; Clemente, T. E. Fuel Process. Technol. 2005, 86, 1137. (c) Haas, M. J. Fuel Process. Technol. 2005, 86, 1087. (d) Knothe, G. Fuel Process. Technol. 2005, 86, 1059. (e) Van Gerpen, J. Fuel Process. Technol. 2005, 86, 1097. (f) Lotero, E.; Liu, Y.; Lopez, D. E.; Suwannakaran, A.; Bruce, D. A.; Goodwin, J. G., Jr. Ind. Eng. Chem. Res. 2005, 44, 5353. (g) Fukuda, H.; Kondo, A.; Noda, H. J. Biosci. Bioeng. 2001, 92, 405. (3) (a) Vicente, G.; Martinez, M.; Aracil, J. Bioresource Technol. 2004, 92, 297. (b) Patel, D. C.; Ebert, C. D. TheraTech, Inc., Utah. U.S. Patent 4,855,294, 1989.
such as alkaline metal hydroxides, alkoxides, and acids such as HCl and H2SO4 as catalysts.2,5 Alkaline alkoxides and hydroxides are considerably more effective catalysts than acid catalysts and operate at lower temperatues.6 It may be noted that plant oils with high free fatty acid contents suffer soap formation in the presence of homogeneous alkaline catalysts, leading to product loss and problems with product separation and purification. Recently, Sn, Pb, Hg, and Zn complexes and enzymes have also been reported to catalyze this reaction under homogeneous conditions.5a,h Heterogeneous catalysts are advantageous for biodiesel production because of their reusability and consequently their more ecofriendly nature, and they also lend themselves to easier product separation and better product purity since water washes can be eliminated. Such catalysts based on guanidines or amines anchored to organic polymers have been reported which operate at the reflux temperature of the solvent employed.7 These approaches suffer from leaching of organic moieties attached to the support, with accompanying deterioration of the catalyst sites. Very recently, WO3/ZrO2 has been employed as a solid acid catalyst at 250 °C to produce biodiesel.8 Although the recyclability of the catalyst was not specifically addressed, it (4) (a) Wildes, S. Chem. Health Saf. 2002, 24. (b) Mushrush, G. W.; Beal, E. J.; Hughes, J. M.; Wynne, J. H.; Sakran, J. V.; Hardy, D. R. Ind. Eng. Chem. Res. 2000, 39, 3945. (5) (a) Shah, S.; Sharma, S.; Gupta, M. N. Energy Fuels 2004, 18, 154. (b) Dorado, M. P.; Ballesteros, E.; Lopez, F. J.; Mittelbach, M. Energy Fuels 2004, 18, 77. (c) Encinar, J. M.; Gonzalez, J. F.; Rodriguez, J. J.; Tejedor, A.; Energy Fuels 2002, 16, 443. (d) Chang, D. Y. Z.; Van Gerpen, J. H.; Lee, I.; Johnson, L. A.; Hammond, E. G.; Marley, S. J. J. Am. Oil Chem. Soc. 1996, 73, 1549. (e) Freedman, B.; Bagby, M. O. J. Am. Oil Chem. Soc. 1990, 67, 565. (f) Abreu, F. R.; Lima, D. G.; Hamu, E. H.; Einloft, S.; Rubim, J. C.; Suarez, P. A. Z. J. Am. Oil Chem. Soc. 2003, 80, 601. (g) Watanabe, Y.; Shimada, Y.; Sugihara, A.; Noda, H.; Fukuda, H.; Tominaga, Y. J. Am. Oil Chem. Soc. 2000, 77, 355. (h) Abreu, F. R.; Lima, D. G.; Hamu, E. H.; Wolf, C, Suarez, P. A. Z. J. Mol. Catal. A: Chem. 2004, 209, 29. (i) Schuchardt, U.; Vargas, R. M.; Gelbard, G. J. Mol. Catal. A: Chem. 1996, 109, 37. (6) (a) Formo, M. W. J. Am. Oil Chem. Soc. 1954, 31, 548. (b) Nye, M. J.; Southwell, P. H. Vegetable Oils Diesel Fuel: Seminar III, ARM-NC-28; Bagby, M. O., Pryde, E. H., Eds.; U.S. Department of Agriculture: Peoria, IL, 1983; p 78. (c) Harrington, K. J.; D’Arcy-Evans, C. Ind. Eng. Chem. Prod. Res. DeV. 1985, 24, 314.
10.1021/ef050435d CCC: $33.50 © 2006 American Chemical Society Published on Web 04/15/2006
ConVersion of Soybean Oil and Poultry Fat to Biodiesel
was stable for 100 h at 250 °C for at least 100 h. Sulfonated pyrolized carbohydrates1a have been employed successfully for the same purpose at 80-100 °C. This catalyst can be reused, but the number of cycles was not mentioned. Although some of the aforementioned protocols5 afford good product yields, they all have one or more disadvantages such as lack of catalyst reusability, handling difficulties, the need for elevated temperatures, multistep catalyst synthesis, and most importantly, frequent problems with adaptability to large-scale preparations. Therefore, we set out to seek a solid-catalyst protocol for the transesterification of soybean oil (SBO) and poultry fat that operates efficiently at room temperature. Nanosized materials have recently received much attention in view of their unusual physical9 and chemical10 properties. Enhancement in the reactivity of nanosized oxides is associated with their increased surface area, greater concentrations of highly reactive edge and corner defect sites, and unusual, stabilized lattice planes.10d It was anticipated that the greater activity of nanosized oxides might allow the transesterification of SBO and poultry fat to occur efficiently at room temperature, which would afford operational simplicity, low energy consumption, greater safety, and the possibility of fewer side reactions in the process compared with those requiring elevated temperatures.11 Experimental Section General. All reactions were performed in oven-dried glassware (90 °C). 1H NMR spectra were recorded at ambient temperature on a Varian VXR-300 MHz spectrometer using standard procedures. The chemical shifts were referenced to the residual peaks of CHCl3 in CDCl3 (ppm). Laboratory-grade CaO, methanol (HPLC grade), and tetrahydrofuran (HPLC grade) were purchased from Fischer chemicals and used without any further purification. Alkali-refined soybean oil was obtained from Cargill and was used without further purification. Virgin soybean oil (nonalkali treated) was obtained from Insta Pro International and was used without further purification. All nanocrystalline (NC) catalysts in various forms such as powder, pellets, and granules were purchased from NanoScale Materials, Inc. (www.nanmatinc.com) and were used as received. They were stored in a nitrogen-filled glovebox. All other solvents and chemicals were obtained from commercial sources and were used as received without further purification. Sulfated ash tests (ASTM-6751) were carried out by Magellan Midstream Partners, Kansas City, KS, or Harris Testing Laboratories, Houston, TX. The sunflower and canola oils (vegetable grade) used were products of ConAgra Foods, Irvine, CA. The peanut oil employed was produced by Planters Company, East Hanover, NJ. These vegetable oils were (7) (a) Schuchardt, U.; Vargas, R. M.; Gelbard, G. J. Mol. Catal. A: Chem. 1996, 109, 37. (b) Schuchardt, U.; Vargas, R. M.; Gelbard, G. J. Mol. Catal. A: Chem. 1995, 99, 65. (c) Peter, S. K. F.; Ganswindt, R.; Neuner, H.-P.; Weidner, E. Eur. J. Lipid Sci. Technol. 2002, 104, 324. (d) Sercheli, R.; Vargas, R. M.; Schuchardt, U. J. Am. Oil Chem. Soc. 1999, 76, 1207. (e) Suppes, G. J.; Dasari, M. A.; Doskocil, E. J.; Mankidy, P. J.; Goff, M. J. Appl. Catal., A 2004, 257, 213. (8) Furuta, S.; Matsuhashi, H.; Arata, K. Catal. Commun. 2004, 5, 721. (9) (a) Nanophase Materials: Synthesis, Properties, Applications; Hadjipanayis, G. C., Siegel, R. W., Eds.; Kluwer: London, 1994. (b) Fecht, H. J. Nanomaterials: Synthesis, Properties, and Applications; Edelstein, A. S., Cammarata, R. C., Eds.; Institute of Physics: Philadelphia, PA, 1996; p 105. (10) For a critical discussion on metal oxide nanocrystals, see: (a) Sun, N.; Klabunde, K. J. J. Am. Chem. Soc. 1999, 121, 5587. (b) Jeevanandam, P.; Klabunde, K. J. Langmuir 2002, 18, 5309. (c) Richards, R.; Li, W.; Decker, S.; Davidson, C.; Koper, O.; Zaikovski, V.; Volodin, A.; Rieker, T.; Klabunde, K. J. J. Am. Chem. Soc. 2000, 122, 4921. (d) Wagner, G. W.; Koper, O. B.; Lucas, E.; Decker, S.; Klabunde, K. J. J. Phys. Chem. B 2000, 104, 5118. (d) Stoimenov, P. K.; Klinger, R. L.; Marchin, G. L.; Klabunde, K. J. Langmuir 2002, 18, 6679. (e) Klabunde, K. J. Nanoscale Materials in Chemistry; Wiley-Interscience: New York, 2001. (11) Stambuli, J. P.; Stauffer, S. R.; Shaughnessy, K. H.; Hartwig J. F. J. Am. Chem. Soc. 2001, 123, 2677.
Energy & Fuels, Vol. 20, No. 3, 2006 1311 Scheme 1
Table 1. Preparation of Biodiesel from SBO at Room Temperature in the Presence of Various Nanosized Catalystsa entry
catalyst
time (h)
conversion (%)b
1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 none
24 24 24 24 24 48 48 24 48 24
>99 >99 >99 >99 6 no reaction no reaction no reaction no reaction no reaction
a Reaction conditions: nanosized catalyst (1 mmol), SBO (4.4 g), MeOH (15 mL), stirred vigorously at room temperature in the time indicated. b Based on 1H NMR spectroscopic integration (24 h was arbitrarily chosen as a reaction time for convenience).
purchased from a local grocery store. Biodiesel (a sample for comparison) was obtained from West Central Soy, Ralston, IA. The free fatty acid contents were determined by a standard titration method (AOCS Ca 5a-40) using phenolphthalein indicator.12 General Procedure for Catalyst Recycling in the Transesterification of SBO to FAMES. A round-bottom centrifuge tube containing the catalyst was equipped with a rubber septum and two magnetic stir bars for stirring efficiency. After flushing the tube with argon, soybean oil and MeOH were charged separately via syringe. The reaction was vigorously stirred at room temperature (23-25 °C), and progress of the reaction was monitored as follows. The extent of transesterification of soybean oil was monitored by solution 1H NMR spectroscopy. The relevant signals chosen for integration were those of methoxy groups in the FAMES (3.66 ppm, singlet) and those of the R-methylene protons present in all triglyceride derivatives (2.3 ppm, triplet) of the soybean oil.7d The conversion was calculated directly from the integrated areas of the aforementioned signals. Upon completion of the reaction, the reaction mixture was centrifuged and the vast majority of the supernatant was removed carefully by cannulation to avoid disturbing the catalyst. Excess methanol was removed from the separated supernatant liquid via rotavapor, leaving the FAMES and glycerol as separate phases. The FAMES were carefully decanted from the glycerol, which was analyzed for purity by 1H NMR analysis. The centrifuged catalyst, which was still submerged under a minimal volume of methanol/FAMES solution, was used for further recycling. The complete conversion of the soybean oil in methyl soyate was also seen visually by the disappearance of the immiscible soybean oil and methanol phases.
Results and Discussion Herein we investigated the efficacy of a series of nanocrystalline (NC) metal oxides for SBO transesterification (Scheme 1). We initially tested the activity of NC-CaO [a powder with crystallite size (CS) ) 20 nm, specific surface area (SSA) ) 90 m2/g] (1) in the transesterification of soybean oil at room temperature, which was essentially complete in 12 h. Under the same reaction conditions, commercial CaO [powder of CS ) 43 nm, SSA ) 1 m2/g] resulted in only 2% conversion in 12 h. We also evaluated NC-CaO [pellets of CS ) 20 nm, SSA (12) Horwitz, W. J.-Assoc. Off. Anal. Chem. 1976, 59, 658.
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Venkat Reddy et al.
Table 2. Transesterification of Alkali Refined SBO at Room Temperature with Methanol Using NC CaO’s in 24 h (unless Otherwise Stated)a entry
catalyst
cycle
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 1 2 3 4 1 2 3 4 1 2
1 1 1 1 2 2 2 2 3 3 3 3 4 4
conversion (%)b >99 >99 >99 >99c >99 >99 >99 >99 >99 >99 >99 >99 >99 >99
entry
catalyst
cycle
conversion (%)b
15 16 17 18 19 20 21 22 23 24 25 26 27 28
3 4 1 2 4 1 2 4 1 2 1 2 1 2
4 4 5 5 5 6 6 6 7 7 8 8 9 9
50 >99 >99 >99 >99 >99 >99 55 >99 >99d >99 >99e 64 >99f
a Reaction conditions: 4.4 g of SBO (alkali refined), NC CaO 1-4 (0.056 g), MeOH (15 mL) stirred vigorously at room temperature for 24 h under an argon atmosphere. Twenty four hours was arbitrarily chosen as a reaction time for convenience. Conversions in cycle 1 are with fresh catalysts, and those in cycles 2-9 are with catalyst recovered by centrifugation followed by decantation. b Based on 1H NMR spectroscopic integration. c Reaction takes place in 48 h. d After 36 h. e After 48 h. f After 72 h.
) 90 m2/g (2)], NC-CaO [powder of CS ) 40 nm, SSA ) 20 m2/g (3)], NC-CaO [granules of CS ) 40 nm, SSA ) 20 m2/g (4)], NC-MgO [powder of CS ) 4 nm, SSA ) 600 m2/g (5)], NC-ZnO [powder of CS ) 10 nm, SSA ) 70 m2/g (6)], NCAl2O3 [amorphous powder, SSA ) 550 m2/g, (7)], NC-TiO2 (amorphous powder, SSA ) 500 m2/g (8) and NC-CeO2 [powder of CS ) 7 nm, SSA ) 50 m2/g (9)]. Among these nanosized catalysts, 1-4 were found to be highly active as shown in Table 1. As expected, no observable reaction occurred in the absence of a catalyst (entry 10). Encouraged by these results, we examined the reusability of the NC-CaO’s in the room-temperature transesterification of SBO to FAMES. As seen in Table 2, NC 1 shows good catalytic performance in multiple cycles. NC 1 possesses an average particle size of 20 nm and a surface area of 90 m2/g, whereas these parameters for NC 3 are 40 nm and 20 m2/g, respectively. The higher SSA of NC 1 (owing to the smaller size of its crystallites) favors a higher concentration of the catalytically active methoxide anion than NC 3. The recyclability of NC 3 is moderate compared with that of NC 1 (Table 2, entries 3, 7, 11, and 15), reflecting the effect of fewer active catalyst sites and smaller surface area. For reasons that are not clear, NC 4, a granular form of NC 3, gave substantially better recyclability compared with that of its powder counterpart, NC 3 (Table 2, entries 4, 8, 12, 16, 19, and 22). Although the first cycle for NC 4 requires 48 h to reach 99% conversion (Table 2, entry 4), subsequent cycles are completed within 24 h. NC 2, a pelletized form of NC 1, would be attractive from the point of view of potential commercialization because of ease in handling. Although NC catalyst 2 is as efficient as NC catalyst 1, it does not recycle as well (entries 2, 6, 10, 14, 18, 21, 24, 26, and 28 in Table 2). The transesterification of alkali-refined SBO in the presence of NC 1 was successfully scaled up to 1240 mL under the reaction conditions in Table 2.13 It was also found that under these conditions NC 1 was also able to transesterify sunflower, peanut, and canola oils quantitatively (99% conversion) within 24 h at room temperature under the same conditions used for SBO as described Table 1, footnote a. Calcium methoxide is known to form on the surface of CaO,14 and because of its slight solubility in methanol, Ca(OMe)2 acts predominantly as a heterogeneous catalyst.14 We confirmed the (13) See the Supporting Information. (14) (a) Gryglewicz, S. Bioresour. Technol. 1999, 70, 249. (b) Tanabe, K.; Misono, M.; Ono, Y.; Hattori, H. New Solid Acids and Bases; Elsevier: Amsterdam, 1989.
formation of surface-bound Ca(OMe)2 on NC 1 by 13C MAS NMR spectroscopy.13 Apparently, the surfaces of NC 1 possess a substantial concentration of OH groups as was shown by their silylation with (CH3O)3SiCH3.13 Interestingly, under the conditions of Table 2, only ca. 3% conversion to FAMES was realized with the silylated catalyst, suggesting that surface-bound OH groups are converted to surface bound water groups upon reaction with methanol, thus liberating methoxide. This result demonstrates that surface -OH groups are very important in the present protocol as was shown earlier in other studies.15 SEM analysis revealed that fresh NC 1 consists of numerous crystallites with well-defined edges (Figure 1), while the same catalyst, which was partially deactivated after seven cycles, had formed aggregated polycrystallites with substantially less welldefined edges. The disappearance of edges and the agglomeration observed are consistent with catalyst deactivation. In general, virgin vegetable oils contain free fatty acids (1-5%), phospholipids, carotenes, tocopherols, and traces of water.16 Neutralization of the oil for feedstock purposes is accomplished by alkali refining or steam distillation. However, removal of free fatty acids is not required when the transesterification is carried at temperatures between 240 and 280 °C under high pressures (e.g., 9 MPa).7c Under these rigorous conditions, even inferior fats and virgin plant oils with high free fatty acid contents can be processed without prior neutralization. NC 1 showed good activity with virgin SBO as depicted in Figure 2. Although the first three cycles provided >99% conversions, decreasing conversions (96 and 74% conversions) were obtained in the fourth and fifth cycles, respectively. We determined that the free fatty acid content in the alkali refined and virgin SBO was 0.027% and 0.225%, respectively, by titration.12 Our data therefore show (as expected) that, at room temperature, the free fatty acid present in virgin SBO destroys the catalytic activity of NC 1 more quickly than in the case of the alkali-refined SBO (Table 2). To substantiate this conclusion, we examined the transesterification of a commercial sample of glyceryl tribenzoate to methyl benzoate. These reactions proceeded in near quantitative yields (92-94%) at room temperature for 10 consecutive cycles in 3.5 h in the first cycle and increasing to 6.0 h in the tenth cycle.13 The reason for the apparent deactivation of the catalyst in this case is not clear. It is possible that the carbon alpha to the (15) Choudary, B. M.; Mulukutla, R. S.; Klabunde, K. J. J. Am. Chem. Soc. 2003, 125, 2020. (16) Marckley, K. S. Fatty Acids, 2nd ed.; Interscience: New York, 1960.
ConVersion of Soybean Oil and Poultry Fat to Biodiesel
Energy & Fuels, Vol. 20, No. 3, 2006 1313
Figure 1. SEM photograph of NC 1 (left) and NC 1 recovered after seven cycles (right). Table 3. Transesterification of SBO with Different Molar Ratios of Methanol at Room Temperature in the Presence of NC 1 in 24 ha
Figure 2. Conversion obtained in recycling NC 1 in the transesterification of virgin SBO based on 1H NMR spectroscopic integration. Reaction conditions: NC 1 (0.25 g), SBO (25 mL), MeOH (100 mL) stirred vigorously at room temperature for 24 h (24 h was arbitrarily chosen as a reaction time for convenience). Conversion in cycle 1 is with fresh catalyst and those in cycles 2-5 are with recycled catalyst.
carboxybenzoate group is slowly deprotonated by the methoxy anion to form an enolate anion plus methanol. To test this hypothesis, we tried to detect the formation of enolate using Ca(OMe)2 in the presence of methyl phenylacetate by subsequent addition of dimethyl sulfate as a trap.17 However, no alkylation product was detected by 1H NMR spectroscopy, suggesting that formation of enolate does not occur or that the enolate is formed in undetectably low concentration. Transesterifications generally require a large excess of methanol to shift the equilibrium favorably. Using NC 1, we found that an SBO/MeOH ratio of 1:27 is suitable for obtaining high product yields as summarized in Table 3. It is clear from these results that the reaction requires 27 molar equivalents to reliably reach the 99% conversion level. In a separate experiment, we recovered unreacted methanol in 97% yield by simple distillation and reused it in a subsequent cycle successfully. It may be noted that, although our MeOH/SBO ratio appears to be somewhat high at room temperature, others have reported processes requiring up to 22 h operating with 40-275 molar excesses of methanol for the transesterification of plant oils at 70 °C or higher.1g,8 It is worth noting that, under the reaction conditions of entry 5 in Table 3, laboratory-grade CaO gave only a 2% conversion to FAMES. (17) Fruchart, J.-S.; Gras-Masse, H.; Melnyk, O. Tetrahedron Lett. 2001, 42, 9153.
entry
SBO/MeOH (molar ratio)
conversion (%)b
1 2 3 4 5 6 7
1:3 1:9 1:15 1:21 1:27 1:30 1:33
75 85 89 96 >99c >99c >99c
a Reaction conditions: Catalyst NC 1 (0.25 g), alkali refined SBO (22 g), MeOH (3 mL) in entry 1. b Based on 1H NMR spectroscopic integration. c Repeated twice.
Because the transesterification reaction with a heterogeneous catalyst is a three-phase system, it was believed that an appropriate cosolvent that would promote SBO/methanol miscibility would accelerate transesterification by enhancing contact of the reactants with the solid catalyst.18 Thus, the miscibility of SBO and methanol in the presence of THF was investigated over a range of added volume amounts appropriate to our optimized conditions. Thus, a mixture of SBO (5 mL), MeOH (15 mL), and THF (5 mL) in the presence of 0.056 g of NC catalyst 1 took only 6 h to reach 99% conversion to FAMES, whereas 12 h was required for complete conversion in the absence of THF. We also briefly investigated the conversion of waste poultry fat to biodiesel, which has previously been studied using soluble alkali metal hydroxides.2d-f,19 The results in Table 4 demonstrate that NC 1 is superior compared to NC 5-8. This protocol was successfully scaled-up to 60 g of poultry fat using NC 1, and the FAMES produced exhibited an encouragingly low value (0.003%) of sulfated ash content in the ASTM D-874 test. In (18) (a) Boocock, D. G. B.; Konar, S. K.; Mao, V.; Lee, C.; Buligan, S. J. Am. Oil Chem. Soc. 1998, 75, 1167. (b) Boocock, D. G. B.; Konar, S. K.; Mao, V.; Sidi, H. Biomass Bioenergy 1996, 11, 43. (19) (a) Wyatt, V. T.; Hess, M. A.; Dunn, R. O.; Foglia, T. A.; Haas, M. J.; Marmer, W. N. J. Am. Oil Chem. Soc. 2005, 82, 585. (b) Jordan, V.; Gutsche, B. Chemosphere 2001, 43, 99. (c) Cvengros, J.; Cvengrosova, Z. Biomass Bioenergy 2004, 27, 173. (d) Tashtoush, G. M.; Al-Widyan, M. I.; Al-Jarrah, M. M. Energy ConVers. Manage. 2004, 45, 2697. (e) Ma, F.; Hanna, M. A. Bioresour. Technol. 1999, 70, 1. (f) Muniyappa, P. R.; Brammer, S. C.; Noureddini, H. Bioresour. Technol. 1996, 56, 19.
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Conclusions
Table 4. Preparation of Biodiesel from Poultry Fat at Room Temperature in the Presence of NC 1, 5-8, and Commercial CaOa entry
catalyst
time (h)
conversion (%)b
1 2 3 4 5 6
1 laboratory-grade CaO 5 6 7 8
6.0 6.0 6.75 6.75 6.75 7.0
100 1 1 no reaction 1 1
a Reaction conditions: Catalyst (1 mmol), poultry fat (3.0 g), MeOH (10 mL), stirred vigorously at room temperature in the specified time. b Based on 1H NMR spectroscopic integration.
Table 5. Reusability of NC 1 for Poultry Fat Transesterification at Room Temperaturea cycle
time (h)
conversion (%)b
1 2 3 4
6.0 6.0 6.75 6.75
100 100 100 1
a Reaction conditions: NC 1 (1 mmol), poultry fat (3.0 g), MeOH (10 mL), stirred vigorously at room temperature for the time indicated. b Based on 1H NMR spectroscopic integration.
results for the smaller scale reactions summarized in Table 5, NC 1 was successfully recycled three times, although it failed in the fourth cycle. The lower recyclability compared with that realized in SBO transesterification (eight cycles, Table 2, entry 25) can be associated with the expectation of considerably higher concentrations of impurities in the poultry fat.
Nanocrystalline calcium oxide is an efficient catalyst for the production of environmentally compatible biodiesel fuel in high yields at room temperature using SBO and poultry fat as raw materials. We found that the biodiesel obtained by our protocol exhibited a sulfated ash value of 0.020-0.004%, which meets the ASTM D-874 diesel standard. It is noteworthy that the FAMES obtained from poultry fat gave an exceptionally low sulfated ash value (0.003%, ASTM D-874). Additionally, THF plays an important role under our conditions as a phase-merging agent to speed up the transesterification. The inherently higher activity and surface reactivity of NC 1 in the transesterification of SBO are due to higher surface area associated with small crystallite size and defects. Acknowledgment. We are grateful to the United Soybean Board and the USDA for grant support. We also thank Dr. Victor S.-Y. Lin for providing the SEM photographs. Supporting Information Available: Preparation of silylated NC 1, table of larger-scale transesterification results, reusability data for the transesterification of glyceryl tribenzoate, 1H and 13C NMR spectra for biodiesel from SBO using NC 1 and for a commerical sample, and 1H NMR spectra of FAMES from peanut, canola and sunflower oil. This material is available free of charge via the Internet at http://pubs.acs.org. EF050435D
