Energy & Fuels 2008, 22, 671–674
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Biodiesel from Rice Bran Oil: Transesterification by Tin Compounds Sandra Einloft,* Tatiana O. Magalhães, Augusto Donato, Jeane Dullius, and Rosane Ligabue Pontifícia UniVersidade Católica do Rio Grande do Sul, Faculdade de Química/PGETEMA, P.O. Box 1429, CEP 90619-900, Porto Alegre, Brazil ReceiVed August 24, 2007. ReVised Manuscript ReceiVed October 23, 2007
The transesterification of rice bran oil with methanol has been studied in the presence of sulfuric acid (H2SO4), tin chloride dihydrate (SnCl2 · 2H2O), tin 2-ethylhexanoate (Sn(C8H15O2)2), dibutyl tin oxide ((C4H9)2SnO), and dibutyl tin dilaurate ((C4H9)2Sn(C12H23O2)2), known commercially as DBTDL. Through the comparative analysis among the catalysts, we observed that the complex DBTDL presented the best performance, with a yield of 68.9% in 4 h using molar ratio 400:100:1 (methanol:oil:catalyst). These results evidenced the viability of the use of metallic compounds as catalysts in the obtainment of biodiesel, an interesting alternative to basic and acid catalysis.
1. Introduction In the 1970s, the Brazilian government created a National Program to the utilization of ethanol obtained from sugar cane. Since that time, anhydrous ethanol and mixtures of it with gasoline have been used as a combustible in Otto cycle motor vehicles in Brazil. This experience is one of the most successful examples in the world in terms of biocombustibles.1 In January 2005, the Brazilian government created a Biodiesel National Program, allowing the addition of 2% biodiesel into petroleum diesel for use in Diesel motors. The additional 2% biodiesel will be obligatory in 2008, and in 2013, the biodiesel content that must be added in the petroleum diesel will be 5% (Law no. 11097/2005).2 These actions will contribute to reducing dependence on fossil resources as fuels. An alternative fuel for diesel engines can be obtained through transesterification reaction of vegetable oils or animal fats with an alcohol such as ethanol or methanol producing a mixture of fatty acid esters of low alkyl-chain alcohols called biodiesel. This reaction occurs in the presence of a catalyst, the most common system using acids or alkyl catalysts such as metal alkyl hydroxides or alkoxides and sulfuric acid, as show in Figure 1.3–7 A great triglyceride source can be found worldwide for biodiesel production among rapeseed, soybean, sunflower, palm, and corn oils which are well-known and have been described in many articles.4,6,8–10 The methanolysis of the native Brazilian * Corresponding author. E-mail:
[email protected]. Tel./Fax: 55 51 33203549. (1) Holanda, H. O. Biodiesel Inclusão e a Social, Câmara dos Deputados; Coordenação de Publicações: Brasília-DF, 2004. (2) Biodiesel. O novo combustível do Brasil-Programa Nacional de Produção e Uso de Biodiesel. www.mme.gov.br (accessed 2006). (3) Gerpen, J. V. Fuel Process. Technol. 2005, 90, 1097–1107. (4) Ma, F.; Hanna, M. A. Bioresour. Technol. 1999, 70, 1–15. (5) Abreu, F. R.; Lima, D. G.; Hamú, E. H.; Einloft, S.; Rubim, J. C.; Suarez, P. A. Z. J. Am. Oil Chem. Soc. 2003, 80, 601–604. (6) Fukuda, H.; Kondo, A.; Noda, H. J. of Biosci. Bioeng. 2001, 92, 405–416. (7) Vicente, G.; Martínez, M.; Aracil, J. Bioresour. Technol. 2004, 92, 297–305. (8) Lang, X.; Dalai, A. K.; Bakhshi, N. N.; Reaney, M. J.; Hertz, P. B. Bioresour. Technol. 2001, 80, 53–62.
Figure 1. Transesterification reaction of triglycerides with alcohol.
oils of the Savannah and Amazon regions were described in the literature.11 At current production levels, biodiesel requires a subsidy to compete directly with petroleum-based fuels.3 In spite of the beneficial effects of this combustible, which is biodegradable, nontoxic, and renewable, cost is still as a major impediment for the wider biodiesel commercialization.12 In this sense, the use of byproduct to biodiesel production can be an alternative to deal with the price problem. Rice bran a coproduct of rice milling is a low-cost feedstock option for biodiesel production, since it contains 15–25% rice bran oil which can be used as vegetable oil for the transesterification reaction with alcohol to produce the methyl esters.12,13 In the literature, we can find some examples of biodiesel obtained from rice bran oil. Among them, a study using two commercially immobilized lipases, Novozym 435 and IM 60 as catalysts for the reaction of the rice bran oil and methanol, showed that a conversion over 98% can be reached in 6 h when catalyzed by Novozym 435.14 In another study a two-step acidcatalyzed methanolysis process was applied for the efficient conversion of rice bran oil into fatty acid methyl ester (FAME), which reached more than 98% of conversion in FAME in less than 8 h.12 The use of a biodiesel fuel derived from the rice (9) Barnwal, B. K.; Sharma, M. P. Renewable Sustainable Energy ReV. 2005, 9, 363–378. (10) Srivastava, A.; Prasad, R. Renewable Sustainable Energy ReV. 2000, 4, 111–133. (11) Abreu, F. R.; Lima, D. G.; Hamú, E. H.; Wolf, C.; Suarez, P. A. Z. J. Mol. Catal. A, Chem. 2004, 209, 29–33. (12) Zullaikah, S.; Lai, C.; Vali, S. R.; Ju, Y. Bioresour. Technol. 2005, 96, 1889–1996. (13) Danielski, L.; Zetzl, C.; Hense, H.; Brunner, G. J. Supercrit. Fluids 2005, 34, 133–141. (14) Lai, C.; Zullaikah, S.; Vali, S. R.; Ju, Y. J. Chem. Technol. Biotechnol. 2005, 80, 331–337.
10.1021/ef700510a CCC: $40.75 2008 American Chemical Society Published on Web 11/27/2007
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Figure 2. Products of the reaction of rice bran oil with methanol. Table 1. Typical Fatty Acid Composition (percent) of Rice Brain Oil and Other Refined Vegetable Oils fatty acids
rice bran oil
rice bran oila
soybeana
palma
palmitic oleic linoleic saturated/unsaturated
18.7 43.4 37.9 0.28
14.7 42.2 37.8 0.21
10.4 24.8 52.5 0.19
40.2 43.3 9.0 0.86
a
Table 2. Results Obtained for the Reaction between Rice Bran Oil and Methanol at 60 °C with Different Catalysts and Reaction Timesa entry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Literature data.12
bran oil was tested as an alternative fuel for agriculture fuel engines. The characterization of emissions for both net and blended biodiesel fuels, and for conventional fuels, showed that the use of a biodiesel based on rice bran oil resulted in lower carbon monoxide, carbon dioxide, and smoke emissions, without any increase in nitrous oxide emissions.15 Brazil is a main producer of rice especially in South Brazil which has a great rice production industry. Rice bran is a byproduct and is used mainly as animal feed since it has some enzymes that degrade the rice bran acidifying the oil. Only a small quantity of oil is transformed in comestible oil (> Zn2+ > Pb2+ = Hg2+.11 Rice bran oil has a free fatty acid content superior to 3%, thus, according to the literature, the acid catalysis is the most appropriate to prevent saponification reaction,12 which creates a difficult separation of the products from glycerol. In all of the reactions shown in Table 2, methanol was used as an alcohol keeping the ratio among the reactants constant. The influence of different tin compounds as well as the reaction time was studied. Note that the conditions are not optimized for the maximum reaction yield, because our goal was to compare these catalysts and observe their behavior with a reaction time. Although the stoichiometric proportion is 1 mol of oil to 3 mol of alcohol (as show in Figure 1), an excess of alcohol was used to shift the equilibrium toward the formation of esters and to facilitate the glycerin separation at the end of the reaction. As evidenced from Table 2 and Figure 3, in these reaction conditions, the best result for biodiesel synthesis was obtained with DBTDL (entry 4). The yield was 68.9% methyl esters in a reaction time of 4 h. In the same conditions, an acid catalyst presented a yield of 37.4%. The same behavior was evidenced in literature; the authors stated that tin compounds, such as Sn(3hydroxy-2-methyl-4-pyrone)2(H2O)2, were more efficient when compared to traditional methods of transesterification using NaOH and H2SO4 as catalysts.11,19 It is worth to noting that kinetics behaviors of acid catalysts are different when compared to tin compounds; while the reaction catalyzed by acid starts at a slow rate, continues at a faster rate, and then slows again as the reaction nears completion,20–22 the reaction catalyzed by tin compounds reaches a maximum yield and then decreases with time probably due (18) Schuchardt, U.; Sercheli, R.; Vargas, R. M. J. Braz. Chem. Soc. 1998, 9, 199–210. (19) Abreu, F. R.; Alves, M. B.; Macêdo, C. C. S.; Zara, L. F.; Suarez, P. A. Z. J. Mol. Catal. A, Chem. 2005, 227, 263–267. (20) Ferrari, R. A.; Oliveira, V. S.; Scabio, A. Quím. NoVa 2005, 28, 19–23.
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Table 3. Main Characteristics of Biodiesel Fuel Obtained from Rice Bran Oil with Tin Catalyst characteristics viscosity at 40 °C (mm2/s) density at 20 °C (kg/m3)
specification specification diesel biodiesel 2.5 – 5.5 820 – 880
2.5 – 5.5
B2 3.14 835
B100
ASTM method
5.36 D445 884
D4052
to the reverse reactions as show in Figure 3.5 The ligand effect in the behavior of tin compounds in the transesterification reaction, that is, the fact that tin compounds can be more or less active when compared to sulfuric acid, is depicted in Figure 3. This behavior can be attributed to the chemical structure which plays an important role in transesterification reaction, modifying both the solubility in the reaction medium and/or the Lewis acidity of the metallic center.11 3.3. Fuel Properties of Biodiesel. The main diesel fuel properties specified in Brazil were determined for methyl esters obtained from the rice bran oil. The properties of both biodiesel and diesel fuels are depicted in Table 3. The analysis of Table (21) Freedman, B.; Butterfield, R. O.; Pryde, E. H. J. Am. Oil Chem. Soc. 1986, 63, 1375–1380. (22) Noureddini, H.; Zhu, D. J. Am. Oil Chem. Soc. 1997, 74, 1457– 1463.
3 shows that biodiesel obtained from rice bran oil is a strong candidate as an alternative to diesel as already described for other oils.9 The use of triglycerides directly as a fuel is not recommended mainly due to their high viscosity. Conversion of triglycerides into methyl esters through the transesterification process reduces the molecular weight to one-third and reduces the viscosity by about one-eighth, allowing the use of biodiesel in existing engines without any modification.3,9 4. Conclusion In summary, we have shown that in the reaction conditions studied tin compounds are active for rice brain oil transesterification reactions using methanol and the best result was obtained when DBTDL was used as a catalyst. Rice bran oil, a byproduct of the rice industry, is a potentially low-cost feedstock for biodiesel production, being an interesting alternative to fuel produced from renewable sources. Acknowledgment. The financial support of Associação dos Arrozeiros de Uruguaiana and Fapergs is gratefully acknowledged. S.E. expresses her appreciation for fellowships granted by CNPq. EF700510A
