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Energy & Fuels 2009, 23, 1136–1138
Transesterification of Castor Oil Using Ethanol: Effect of Water Removal by Adsorption onto Zeolite 3A Moˆnica C. G. Albuquerque,† Ce´lio L. Cavalcante, Jr.,*,† A. Eurico B. Torres,† Diana C. S. Azevedo,† and Expedito J. S. Parente, Jr.‡ Grupo de Pesquisa em Separac¸o˜es por Adsorc¸a˜o (GPSA), Departamento de Engenharia Quı´mica, UniVersidade Federal do Ceara´, Campus do Pici, Bl. 709, Fortaleza 60455-760, CE, Brazil, and Tecnologias Bioenerge´ticas (TECBIO), PARTEC, Rua Prof. Roˆmulo Proenc¸a, s/n, Pici, Fortaleza 60455-700, CE, Brazil ReceiVed NoVember 6, 2008. ReVised Manuscript ReceiVed January 12, 2009 1. Introduction Biodiesel oil can be produced from renewable sources and may be defined as a monoester of simple alcohol, such as ethanol, methanol, or propanol, bonded to long-chain fatty acids (C12-C22). Those come from saturated or unsaturated triglycerols or triacylglycerols from seeds (vegetable sources) or grease (animal sources).1-3 The castor plant is an oleaginous species cultivated in almost all of the tropical and subtropical zones. In Brazil, it can be found in several regions, mainly in the half-barren northeast. The oil extracted from the seed is its most important industrialized product.4,5 Currently, there is an increasing interest to obtain biodiesel from this source oil, because of its availability in poor rural areas and the possibility of making energy available in remote regions of the country.6-8 The technology of biodiesel production with methanol using basic homogeneous catalysis is widely known and employed industrially.9,10 On the other hand, the use of ethanol is still under development and optimization. Ethanol and methanol have similar fuel properties. However, ethanol is more advantageous because it is nontoxic, more biodegradable, and obtained from * To whom correspondence should be addressed. Telephone: (55) (85) 3366-9611. Fax: (55) (85) 3366-9601. E-mail:
[email protected]. † Universidade Federal do Ceara ´. ‡ Tecnologias Bioenerge ´ ticas (TECBIO). (1) Krinangkura, K.; Simamaharnoop, R. J. Am. Oil Chem. Soc. 1992, 69, 166. (2) Vicente, G.; Coteron, A.; Martinez, M.; Aracil, J. Ind. Crops Prod. 1998, 8, 29. (3) Freedman, B.; Pryde, E. H.; Mounts, T. L. J. Am. Oil Chem. Soc. 1984, 61 (10), 1638. (4) Ogunniyi, D. S. Castor oil: A vital industrial raw material. Bioresour. Technol. 2006, 97, 1086–1091. (5) Ndiaye, P. M.; Franceschi, E.; Oliveira, D.; Dariva, C.; Tavares, F. W.; Oliveira, J. V. Phase behavior of soybean oil, castor oil and their fatty acid ethyl esters in carbon dioxide at high pressures. J. Supercrit. Fluids 2006, 37, 29–37. (6) Albuquerque, M. C. G.; Jime´nez-Urbistondo, I.; Santamarı´a-Gonza´lez, J.; Me´rida-Robles, J. M.; Moreno-Tost, R.; Rodrı´guez-Castello´n, E.; Jime´nez-Lo´pez, A.; Azevedo, D. C. S.; Cavalcante, C. L., Jr.; MairelesTorres, P. CaO supported on mesoporous silicas as basic catalysts for transesterification reactions. Appl. Catal., A 2008, 334, 35. (7) Almeida, R. M.; Noda, L. K.; Gonc¸alves, N. S.; Meneghetti, S. M. P.; Meneghetti, M. R. Transesterification reaction of vegetable oils, using superacid sulfated TiO2-base catalysts. Appl. Catal., A 2008, 347, 100– 105. (8) Conceic¸a˜o, M. M.; Candeia, R. A.; Silva, F. C.; Bezerra, A. F.; Fernandes, V. J., Jr.; Souza, A. G. Thermoanalytical characterization of castor oil biodiesel. Renewable Sustainable Energy ReV. 2007, 11, 964– 975. (9) Crabbe, E.; Nolasco-Hipolito, C; Kobayashi, G.; Sonomoto, K.; Ishizaki, A. Process Biochem. 2001, 37, 65. (10) Zhang, Y.; Dube´, M. A.; McLean, D. D.; Kates, M. Bioresour. Technol. 2003, 89, 1.
renewable sources (better energy balance). Recently, there have been reports of studies on heterogeneous catalysts6,7 or porous adsorbents11,12 to enhance conversion and selectivity in the biodiesel processes. The transesterification reaction of vegetable oils using ethanol can be represented as KOCH3
ethanol + triglycerides 798 biodiesel + glycerol + soap H2O
Normally, a catalyst obtained from methanol and KOH is used for the alcoholysis homogeneous reaction. The formation reaction of the catalyst (methoxide ion) is represented as H3COH + K+OH- T H3CO-K+ + H2O The presence of water that was formed in the catalyst preparation will favor soap formation during the transesterification reaction, especially when using ethanol as a transesterification alcohol. The removal of water would then disfavor the saponification reaction, improving the overall performance of the transesterification reaction. It is thus of great interest from a practical point of view to study potential separation processes to be able to remove water simultaneously to the formation reaction of the catalyst as well as to the transesterification reaction, in processes using ethanol. In this study, we evaluate the possibility of enhancing the biodiesel conversions in homogeneous reactors using ethanol, by removal of water by adsorption in zeolite 3A, in both the catalyst formation and the transesterification steps. The results are compared to a typical homogeneous reaction without adsorbent. 2. Experimental Section 2.1. Adsorbent Characterization. Commercial zeolite 3A (Grace Davidson, Brazil) in pelletized form was used in the experiments and was chosen because of its high water selectivity.13 The average particle diameter (3.6 mm) was obtained using a Tyler/ Mesh system. Water picnometry was used to determine the solid (11) Cavalcante, C. L., Jr.; Azevedo, D. C. S.; Torres, A. E. B.; Albuquerque, M. C. G.; Belo, L. F.; Sousa, J. R.; Sousa, L. L.; Lucena, I. L.; Parente, E. J. S., Jr. Applications of adsorption technology for the optimization of processes for biodiesel production. In AIChE Annual Meeting 2005, Cincinnati, OH, 2005. (12) Sousa, L. L.; Lucena, I. L.; Sousa, J. R.; Belo, L. F.; Albuquerque, M. C. G.; Parente, E. J. S., Jr.; Torres, A. E. B.; Azevedo, D. C. S.; Cavalcante, C. L., Jr. Adsorption processes applied to biodiesel production from castor oil. In World Renewable Energy Congress IX, 2006, Florence, Italy; Full Proceedings, Elsevier, London, U.K., 2006; Vol. 1, p 6. (13) Ruthven. D. M. Principles of Adsorption and Adsorption Processes; John Wiley and Sons, Inc.: New York, 1984.
10.1021/ef8009684 CCC: $40.75 2009 American Chemical Society Published on Web 02/02/2009
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Energy & Fuels, Vol. 23, 2009 1137
Figure 1. Effect of the adsorbent/liquid ratio in the catalyst formation step (Wc), using tc ) 120 min [(b) Wc ) 0.0, (0) Wc ) 0.3, (O) Wc ) 0.4, and (4) Wc ) 0.5].
varied between 0.3 (which corresponds approximately to the stoichiometric amount of adsorbent needed to remove the water) and 0.5. The catalyst prepared in this system (ca. 30 g, after water removal from first step) was then applied in the homogeneous transesterification of castor oil (50 g) with ethanol (13.09 g) at 298 K, using a glass reactor connected to a water-cooled condenser, for 50 min. During the transesterification reaction, aliquots (ca. 3 mL) of the reaction mixture were taken every 10 min and analyzed by titration with 0.01 N HCl to quantify the concentration (wt %) of active catalyst present in the reactor, which would be directly affected by the presence of water in the mixture. With the previous removal of water in the catalyst formation step, the performance of the transesterification reaction should be enhanced when compared to catalysts prepared without water removal. We also evaluated the conversion of the transesterification reaction, defined as the ratio between the produced glycerol and the glycerol present in the castor oil. Case Two: Adsorbent Applied in Both Steps (Catalyst Formation and Transesterification). In this case, zeolite 3A was used in both steps of the biodiesel production, using solid mass ratios (Wc and Wt) set at 0.5 and 0.3, respectively. All other experimental conditions were maintained the same as for case one, varying only the contact time in the catalyst formation step. The overall performance was evaluated using the same methodology described before (concentration of active catalyst and transesterification conversion).
Figure 2. Effect of the adsorbent contact time during catalyst formation (tc) [(b) Homogeneous catalyst only; using adsorbent in both steps (Wc ) 0.5 and Wt ) 0.3), (0) 60 min, (4) 120 min, and (O) 180 min].
density (2.68 g/cm3). The apparent density (1.23 g/cm3) was determined from the average particles mass and the solid density. The particle porosity was 0.54. 2.2. Adsorption Experiments. The adsorbent samples were previously activated through a typical thermal treatment process up to 300 °C for at least 24 h, for water removal. To evaluate the effect of the relative amount of adsorbent used in our experiments, we defined a parameter, W (solid mass ratio), as the ratio between the mass of adsorbent to the total mass in the system (solid + liquid). Two types of experiments were performed. First, we studied the removal of water by adsorption in the catalyst formation. In the other situation, we studied the removal of water not only in the catalyst formation but also in the transesterification reaction. The experimental parameters of the first step (catalyst formation) and those of the second step (transesterification reaction) will have subscripts “c” and “t”, respectively. All reagents were analyticalgrade (Vetec, Brazil) and were used without further treatment. Castor oil was used as available in the local market. Spent adsorbent was subsequently used repeatedly (up to 10 times) following the same activation procedure (300 °C for at least 24 h), without any significant loss of performance. Case One: Adsorbent Applied Only in the Catalyst Formation Step. The catalyst formation was carried out using methanol (25 g) and KOH (8.33 g), in a glass reactor (1000 mL) connected to a water-cooled condenser, controlled temperature (298 K), and stirring (700 rpm), using zeolite 3A as an adsorbent. A contact period of 2 h was allowed for the water adsorption. In this case, Wc was
3. Results and Discussion For case one (water removal only in catalyst formation), the presence of an active catalyst with time is shown in Figure 1. We used the stoichiometric amount of adsorbent for water removal as the starting point (Wc ) 0.3), increasing to Wc ) 0.5 to evaluate its usage in excess. We observe qualitatively that less soap is formed with an increasing solid mass ratio (Wc), which allows the catalyst to remain active for a longer period of time. It seems that increasing Wc compensates for apparent deactivation of the adsorbent that might be occurring throughout the catalyst formation step. This solid mass ratio value (0.5) was then used in the subsequent experiments when the water adsorption removal was also evaluated for the transesterification reaction step (case two). For those experiments, the studied variable was the adsorption time in the catalyst formation (see Figure 2), with Wc and Wt fixed at 0.5 and 0.3, respectively. From Figure 2, the best results (higher concentration of active catalyst throughout the transesterification reaction) were noticed for 120 min of contact time in the catalyst formation step. These were significantly better than all of the other results, especially those observed when using only the homogeneous catalyst, thus indicating that using the adsorbent in both catalyst formation and transesterification reaction steps will enhance the production of biodiesel from castor oil using ethanol. The evaluation of the conversion values of the transesterification reaction of castor oil for all of our experiments (see Table
Table 1. Conversion Values (Castor Oil with Ethanol, at 298 K) case
experiment
catalyst formation
transesterification reaction
conversion (wt %)
only homogeneous catalyst
1
Wc ) 0.0, tc ) 180 min
Wt ) 0.0, tt ) 50 min
44.6
case 1
2 3 4
Wc ) 0.3, tc ) 180 min Wc ) 0.4, tc ) 180 min Wc ) 0.5, tc ) 180 min
Wt ) 0.0, tt ) 50 min Wt ) 0.0, tt ) 50 min Wt ) 0.0, tt ) 50 min
54.7 52.3 52.1
case 2
5 6 7
Wc ) 0.5, tc ) 60 min Wc ) 0.5, tc ) 120 min Wc ) 0.5, tc ) 180 min
Wt ) 0.3, tt ) 50 min Wt ) 0.3, tt ) 50 min Wt ) 0.3, tt ) 50 min
56.2 72.2 64.3
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1) confirmed our observations above. The best conversion result (using Wc ) 0.50, Wt ) 0.30, tc ) 120 min, and tt ) 50 min) is substantially higher than the value obtained at the experiment using only the homogeneous catalyst (72.2 versus 44.6 wt %).
Acknowledgment. The authors acknowledge financial support received from Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq).
Nomenclature
4. Conclusions A zeolite 3A commercial adsorbent was efficient for water removal in the alkaline catalyst used in the transesterification reaction for biodiesel production, with castor oil and ethanol as reagents. The use of adsorption to remove water also in the transesterification reaction reduced the soap formation (undesirable byproduct) and increased the concentration of active catalysts present in the reactor. Conversions much higher than the current homogeneous process were obtained when 3A adsorbent was used.
Fp ) adsorbent density (g/mL) Mp ) adsorbent particle mass (g) dp ) particle diameter (m) Wc ) solid mass ratio (adsorbent mass/total mass) in the catalyst formation step Wt ) solid mass ratio (adsorbent mass/total mass) in the transesterification reaction step tc ) time in the catalyst formation step (min) tt ) time in the transesterification reaction step (min) EF8009684
