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Communication Biofuel Obtained from Transesterification by Combined Catalysis Manuel F. Rubio-Arroyo,*,† Miguel A. Ayona-Argueta,† Martha Poisot,‡ and Guillermo Ramı´rez-Galicia‡ Instituto de Quı´mica, UniVersidad Nacional Auto´noma de Me´xico, Circuito Exterior Ciudad UniVersitaria, 04510, Coyoacan, Mexico DF, Mexico, and UniVersidad del Papaloapan, Circuito Central 200, Parque Industrial, 68301, Tuxtepec, Oaxaca, Mexico ReceiVed August 13, 2008. ReVised Manuscript ReceiVed March 25, 2009 A conversion of 99.05% sunflower oil into biofuel using a combined catalysis between tin oxide supported in mesoporous material (MM) and sodium hydroxide, without adding an step to separate the catalyst in the biofuel formation, was performed in our laboratory.1 The use of combined catalysis brought an improvement in conversion with respect to the alkaline catalysis. It is well-known that biofuel production via transesterification of oils and fats with alcohols of low molecular weight has being developed for a long time; in 1986, the first kinetic studies were performed.2 Afterward, studies concluded that this kind of reaction is carried out via alkaline or acid catalysis and the best molar relation of alcohol/oil is 6:1 for alkaline medium and 30:1 for acid medium at 45 °C and 1 h of reaction.3 The use of heterogeneous catalysts with acid character, such as SnO2 sulfated, B2O3/ZrO2, or zeolites shows a lower reaction yield and longer reaction time than using the homogeneous alkaline catalysts; therefore, this kind of catalysis is not economically convenient. However, alkaline catalysis owns the disadvantage of producing soap, which must be removed to provide a highquality biofuel, consequently increasing the operational costs. Several techniques have been developed to decrease the production costs; for example, U.S. patent 2005080280 A1 improves a continue separation method of alkaline catalysis.4 Furthermore, a combination of acid and alkaline catalysts has proven to improve the reaction yield, combining sulfuric acid as a first step and sodium or potassium hydroxide as a second step, to reduce the fatty acid free in the reagents. However, the operational costs have been increased, and several dangerous wastes are formed. Patent W02005063954 explains the application of organometallic compounds as catalysts, such as the alkylic oxide of tin, but this method uses an additional step.5 This work shows results derived from using tin oxide supported on MM material combined with sodium hydroxide, without an * To whom correspondence should be addressed. Telephone: +5256224420. Fax: +52-56162217. E-mail:
[email protected]. † Universidad Nacional Auto ´ noma de Me´xico. ‡ Universidad del Papaloapan. (1) Rubio-Arroyo, M. F.; Ayona-Argueta, M. A. Me´todo de Transesterificacio´n para obtener un Biocombustible basado en la Aplicacio´n de una Cata´lisis Combinada. Oct 28, 2007; MX/a/2007/012523. (2) Freedman, B.; Butterfield, R. O.; Pryde, E. H. J. Am. Oil Chem. Soc. 1986, 63, 1375–1380. (3) Lotero, E.; Liu, Y.; Lopez, E. D.; Suwannakan, K.; Bruce, D. A.; Goodman, J. G., Jr. Ind. Chem. Res. 2005, 44, 5353–5363. (4) Yoo, J.-W. Process for preparing an alkylester of fatty acid with high purity via one-step continuous process. W003066567, Aug 14, 2003. Yoo, J.-W. Process for producing alkylester of fatty acid in a single-phase continuous process. US2005080280, April 14, 2005.
Figure 1. N2 adsorption-desorption isotherm of the obtained MM.
additional step to separate the catalyst in the biofuel formation. Our results show a reaction yield higher than that reported in the literature, with a similar temperature. The biofuel synthesis was performed by a combined catalysis. A mixture of 230 mL of NH4OH, 250 mL of H2O, and 1 g of cetyl trimethyl ammonium bromide (CTAB) was homogenized, and 4 mL of tetraethyl orthosilicate (TEOS) was dropped with stirring to 350 rpm for 2 h. The solution was filtered and dried at room temperature. The solid was calcined to 550 °C for 4 h. The obtained material was subjected to the nitrogen physisorption test. The result is in Figure 1, while the X-ray powder diffraction data are shown in Figure 2 for the MM and in Figure 3 for the catalyst. The surface area of the MM is 1331.96 m2/g, and the
10.1021/ef800661v CCC: $40.75 2009 American Chemical Society Published on Web 04/03/2009
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Figure 2. X-ray diffraction (XRD) pattern for MM. Figure 4. 1H NMR spectrum of biofuel obtained from homogeneous transesterification alkaline catalysis, using only NaOH.
Figure 3. XRD pattern for catalyst.
pore volume is 0.9732 cc/g, with a pore diameter of 29.22 Å. The surface characterization of the catalyst (SnO2/MM) is 1179.28 m2/g as the surface area, while the pore volume is 0.6857 cc/g, with 23.26 Å pore diameter. With regard to the support impregnation, a tin solution was prepared with 0.136 g of SnCl4 · 5H2O, dissolved in 5 mL of distillated water, dried at 100 °C for 1 h, and calcined at 550 °C for 3 h. The catalyst was obtained at 10% weight with respect to the support. The biofuel synthesis has been carried out, heating 35.73 g of sunflower oil to 50 °C and 0.178 g of catalyst SnO2/MM with stirring to 300 rpm. On the other hand, a solution of 0.275 g of NaOH in 36 mL of methanol was prepared. This solution was added to the previous mixture of sunflower oil/SnO2/MM with stirring to 300 rpm. The acid value of the sunflower oil is 0.084 mg of KOH/g and, in the presence of SnO2/MM, 0.087 mg of KOH/g. The new mixture was kept at 45 °C and atmospheric pressure. After 2 min, the solution color changed from yellow to amber. After 15 min, the temperature has been increased up to 63 °C for methanol distillation starting and held for 30 min. The distillation was carried out using a cooling apparatus to prevent biofuel contamination. The dark amber solution formed was left to cool at room temperature, washed 2 times with water, and separated in three liquid phases: glycerin and heterogeneous catalyst (white liquid), water, and the biofuel. According to a qualitative analysis of the flame test, the tin content in the biofuel was discarded, indicating that lixiviation of the catalyst in the reaction does not appear. Figure 6 shows the infrared spectrum obtained from the sample: the strong signals of 1700 and 1200 are assigned to C-O and CdO bonds of methyl ester. Some properties of the biofuel are density at 0.869 g/cm3, kinematic (5) Kumar, G. A.; Kumar, B. A.; Savita, K. Improved process for preparing fatty acid alhylesters using as biodiesel. W0200550663954, July 14, 2005.
Figure 5. 1H NMR spectrum of biofuel obtained from the transesterification via combined catalysis.
Figure 6. Infrared (IR) spectrum of biofuel obtained from the transesterification via combined catalysis.
viscocity at 35 °C at 2.3 mm2/s, and boiling point at 298 °C at 0.77 atm. The heterogeneous catalyst was separated from glycerin by means of washing with water and later filtration. The conversion yield is 99.05%. This percentage was calculated by integration of RMN spectra, in agreement with the following equation:6 2AME C ) 100 × 3AR-CH2
( )
(6) Knothe, G. Trans. ASAE 2001, 44, 193–200.
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where C is the conversion of triacylglycerol feedstock (vegetable oil) to the corresponding methyl ester, AME is the integration value of the protons of the methyl esters (the strong singlet peak), and AR-CH2 is the integration value of the methylene protons. The factors 2 and 3 derive from the fact that the methylene carbon possesses two protons and the alcohol (methanol-derived) carbon has three attached protons. Figure 4 shows the nuclear magnetic resonance (NMR) spectrum of biofuel from homogeneous transesterification alkaline catalysis, using only a solution of 0.275 g of NaOH in 36 mL of methanol; the reaction time was also 2 min. The signal in 3.667 ppm indicates the methyl ester (-CO2CH3) formation, and the signal in 2.3 ppm is the signal of hydrogen adjacent to methyl ester. Both of these signals could be used to quantify the biofuel production. Figure 5 shows the NMR spectrum of biofuel obtained from the transesterification via combined catalysis described in this paper. Signals at 3.661 and 2.3 ppm were obtained, and the
Communications
integration of these signals, AME ) 2.771 and AR-CH2 ) 1.865, corresponds to 99.05% of conversion. This conversion is higher than obtained in Figure 2 of 92.96%, corresponding to conventional catalysis. The NMR spectra were carried out using Eclipse Jeol equipment at 300 MHz, with CHCI3 as the solvent. The error associated with this technique is 5.66%,7 which is why the difference found between both catalytic reactions is 0.34%, supporting the positive influence of the combined catalysis path. The action of the heterogeneous catalyst on the oil tends to modify the relation between the aliphatic chain and the double bonds, contributing to the esterification reactions of free fatty acids before the reaction. This relation was 7:1, and after the reaction, this relation changed to 11.5:1, with methanol in alkaline medium. EF800661V (7) Pedrido, M. L.; Bortolato, S.; Gonzalez, M.; Olivieri, C.; Boschetti, C. Composition of biodiesel blends with gas oil using near infrared spectroscopy. LabCiencia 3, 2008.
