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Energy & Fuels 2007, 21, 3746–3747
Biodiesel Production from Vegetable Oil Mixtures: Cottonseed, Soybean, and Castor Oils Simoni M. Plentz Meneghetti,*,† Mario R. Meneghetti,† Tatiana M. Serra,† Daniela C. Barbosa,† and Carlos R. Wolf‡ Laboratório de Oleoquímica, Instituto de Química e Biotecnologia, UniVersidade Federal de Alagoas, Maceió, Alagoas, CEP 57072-970, Brazil, and Faculdade de Química, UniVersidade Luterana do Brasil, Canoas, Rio Grande do Sul, CEP 92420-280, Brazil ReceiVed January 23, 2007. ReVised Manuscript ReceiVed July 6, 2007 The use of vegetable oils and their derivatives as a source of energy, replacing mainly fossil fuel, brings forth not only a new element to the energetic matrix of a nation but also new tendencies on economical, social, and environmental issues.1 Biodiesel is now the most important product of this new trend. It is a renewable fuel, which can now be produced mainly by the transesterification reaction, using vegetable oils and shortchain alcohols in the presence of catalysts. In terms of environmental quality, biodiesel, as other biofuels, is advantageous if compared to fossil fuels, because its use will allow for an important reduction of COx, SOx, and particulated compounds in the atmosphere.2 In Brazil, the Programa Nacional de Produção e Uso de Biodiesel (PNPB/National Program of Production and Use of Biodiesel) foresees a progressive increase of biodiesel addition to fossil diesel, generating one of the most important programs of fuel substitution in the world. Also, the Brazilian biodiesel program is not only based on one kind of vegetable oil. Because of the great social, economical, and regional diversities of the country, many different sources of oils are under investigation.3,4 Particularly, in northeastern Brazil, there is a strong stimulation involving a castor plantation, where this culture is well-adapted and can reach high productivity. Castor oil almost entirely comprises a mixture of triglycerides, predominantly containing (ca. 89%) the ester form of an unsaturated and hydroxylated fatty acid, the ricinoleic acid, (9Z,12R)-12-hydroxy-9-octadecenoic acid. The presence of this hydroxylated fatty acid derivative in such high amounts imparts several unique chemical and physical properties.2 In comparison to other vegetable oils, castor oil presents much higher viscosity and polarity.2,5 Such properties are exploited in various industrial applications for this oil, including the production of coatings, plastics, and cosmetics.6 * To whom correspondence should be addressed: Instituto de Química e Biotecnologia, Universidade Federal de Alagoas, Av. Lourival de Melo Mota, s/n Cidade Universitária, 57072-970, Maceió-AL, Brazil. Telephone: +55-82-32141373. Fax: +55-82-32141384. E-mail:
[email protected]. † Universidade Federal de Alagoas. ‡ Universidade Luterana do Brasil. (1) Crabbe, E.; Nolasco-Hipolito, C.; Kobaiashi, G.; Sonomoto, K.; Ishizaki, A. Process Biochem. 2001, 37, 65–71. (2) Kulkarni, M. G.; Sawant, S. B. Eur. J. Lipid Sci. Technol. 2003, 105, 214–218. (3) Lima, P. C. R. O Biodiesel e a Inclusão Social, Estudo sobre recursos Minerais, Hídricos e Energéticos, Consultoria Legislativa, Câmara dos Deputados, Governo do Brasil, Brasília, DF, 2004. (4) Produção de combustíveis líquidos a partir de óleos vegetais. Coordenadoria de Informações Tecnológicas, Ministério da Indústria e Comércio (MIC), Governo do Brasil, Brasília, DF, 1985. (5) Conceição, M. M.; Candeia, R. A.; Dantas, H. J.; Soledade, L. E. B.; Fernandes, V. J.; Souza, A. G. Energy Fuels 2005, 19, 2185–2188. (6) Gunstone, F. D. The Chemistry of Oil and Fats, 1st ed.; Blackwell: New York, 2004; p 276.
Table 1. Fatty Acid Composition (%) of Soybean, Cottonseed, and Castor Oils fatty acid
soybean oil
cottonseed oil
myristic (14:0) palmitic (16:0) palmitoleic (16:1) stearic (18:0) oleic (18:1) linoleic (18:2) linolenic (18:3) ricinoleic [18:1(OH)] total C-18
0.4 14.0 2.4 23.5 51.2 8.5
1.0 22.0 1.0 3.0 19.0 54.0 1.0
85.6
77.0
castor oil 1.8
11.2 87.0 98.2
Castor oil has a viscosity of ca. 225.8 mm2 s-1 at 40 °C. This value is far higher than the viscosities of conventionalcomposition oils. As a consequence, biodiesel obtained from castor oil also features high viscosity, which, if one considers the current stage of cycle-diesel engines, will enable its use only as a mixture, under limited content, with fossil diesel or other less viscous biodiesel. In Brazil, this viscosity requirement stands between 2.5 and 5.5 mm2 s-1 at 40 °C.7 Envisaging the necessity of more knowledge on alternatives to mixtures preparation, in this work, the methanolysis of mixtures of castor oil with soybean oil or cottonseed oil have been examined with the purpose of assessing the possibility of carrying out transesterification reactions for biodiesel production from oil mixtures. The transesterification reactions of a mixture of different vegetable oils, soybean/castor oils and cottonseed/ castor oils, using methanol as the transesterification agent and sodium hydroxide as the catalyst have been studied to produce biodiesel. The yield of the biodiesel formation reaction and some physico-chemical properties of the biodiesel produced from the oil mixtures were evaluated. It was observed that there was no appreciable trend to preferably transesterify one specific oil in both oil mixtures. The addition of soybean or cottonseed oil to castor oil improves the purification process of the biodiesel produced when compared to that produced from pure castor oil. Transesterification reactions were performed in a 50 mL batch reactor equipped with a reflux condenser and a magnetic stirrer. The reaction mixture containing methanol, the catalyst (NaOH), vegetable oils (castor, cottonseed, or soybean oil) or their mixtures, with the molar ratio of alcohol/oil/catalyst of 34:6:1, had been refluxed at the boiling point of the respective alcohol for an appropriate period of time (1, 2, 4, 6, 8, or 10 h). After this time, the alcohol was recovered by distillation and the remaining mixture was neutralized and washed 3 times with (7) Portaria 310, 12/27/2001-ANP. legis_biodiesel.asp (accessed Jan 2007).
10.1021/ef070039q CCC: $37.00 2007 American Chemical Society Published on Web 09/15/2007
http://www.anp.gov.br/petro/
Communications
Energy & Fuels, Vol. 21, No. 6, 2007 3747
Table 2. Yields in Biodiesel from the Transesterification Reaction of Mixtures of Soybean/Castor Oils and Cottonseed/Castor Oils soybean/castor oils biodiesel
cottonseed/castor oils biodiesel
mixture of soybean/castor oils or cottonseed/castor oilsa
total yield in biodieselb,c
average percentage composition of the biodiesel obtained, relative to the oils usedb,c
100:0 75:25 50:50 25:75 0:100
87 83 85 87 81
100:0 76:24 53:47 28:72 0:100
total yield in biodieselb,c
average percentage composition of the biodiesel obtained, relative to the oils usedb,c
77 80 86 85 81
100:0 73:27 49:51 25:75 0:100
a Prior to the transesterification reaction. b As determined by GC, according to the experimental procedure. c Average of different reaction times, from 1 to 10 h.
distilled water. The phase separation was carried out by gravity in a separatory funnel. The biodiesel yield was determined by gas chromatography (GC) and expressed in terms of the percentage (wt %) of fatty acid methyl esters (FAMEs) formed. Before chromatographic characterization, the mixture was dried in the presence of MgSO4, as a desiccant agent and centrifugated. The kinematic viscosity values were determined following the standard method (ASTM D445), and the density was determined with a DMA35N density meter from Anton Paar. Table 1 presents the compositions in terms of fatty acids of the oils used in this study. Soybean and cottonseed oils have a typical composition encountered in the majority of the vegetable oils. However, as already mentioned, castor oil has a nonconventional composition, which explains some of its distinct properties.4 All transesterification reactions, regardless of the reaction time, achieved yields higher than 70%, and in all cases, there was a tendency toward slight decreasing yields at higher reaction times.8–10 The methanolysis reactions of mixtures of soybean/ castor oils and cottonseed/castor oils were carried out in the ratios of 25:75, 50:50, and 75:25 (wt/wt) and carried out under the same conditions applied to the no mixed oils, e.g., with a typical molar ratio of alcohol/oil/catalyst of 34:6:1 and refluxed at the boiling point of the alcohol for an appropriate period of time (1, 2, 4, 6, 8, or 10 h). Table 2 shows the results in terms of the total biodiesel yield and average percentage composition of the biofuel obtained, respectively, for the mixtures of soybean/ castor oils and cottonseed/castor oils. The total yields in biodiesel obtained from methanolysis of the mixtures, under the experimental conditions employed, reached average values that are comparable to those observed for the individual oils. It is possible to infer that there is no significant proportional variation between different biofuels, which is an indication that the average values shown in Table 2 are quite representative of the methanolysis process. This also demonstrates the viability of biodiesel production from mixtures of vegetable oils and methanol as an alcoholysis agent, because there is no appreciable trend to preferably transesterify either soybean, cottonseed, or castor oil when they are mixed. (8) Meneghetti, S. M. P.; Meneghetti, M. R.; Wolf, C. R.; Silva, E. C.; Lima, G. E. S.; Coimbra, M. A.; Soletti, J. I.; Carvalho, S. H. V. J. Am. Oil Chem. Soc. 2006, 83, 819–822. (9) 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, 601–604. (10) Meneghetti, S. M. P.; Meneghetti, M. R.; Wolf, C. R.; Silva, E. C.; Lima, G. E. S.; Silva, L. L.; Serra, T. M.; Cauduro, F.; Oliveira, L. G. Energy Fuels 2006, 20, 2262–2265.
It is important to remark that the workup process for biodiesel purification, normally via washings with aqueous solutions and subsequent phase separations, is difficult when castor oil is used as a raw material. In this case, strong emulsions are formed and centrifugation must be employed.8,10 This is, in part, due to the singular chemical composition of castor oil, as mentioned elsewhere.2 This problem is not observed in great extension when biodiesel is obtained from neat soybean or cottonseed oil. Thus, in the case of the transesterification of mixtures (castor oil and soybean or cottonseed oil), the purification and separation processes are facilitated and decantation by gravity can be employed. These observations represent an important contribution of this work for biodiesel production from castor oil, allowing its use as a suitable raw material. The biodiesel thus obtained presents physico-chemical properties, which are directly linked to the characteristics of the vegetable oils from which it was produced. As already mentioned in the introductory section of this work, castor oil has a relatively high viscosity (225.8 mm2 s-1 at 40 °C), as compared to the viscosities of soybean oil (30.6 mm2 s-1 at 40 °C) and cottonseed oil (34.6 mm2 s-1 at 40 °C). As a result, biodiesel produced from castor oil will also feature high viscosity and, in this case, may only be used as a mixture with fossil diesel or other less viscous biodiesel, as mentioned earlier. It is important to point out that, despite the disadvantage of the high viscosity, the biodiesel produced from castor oil presents an excellent lubricity,11 which is also an important feature for fuels, thus justifying its use under adequate contents. The results presented herein allow for the immediate insertion of castor oil and viabilization of its use as a raw material in biodiesel production. Besides, one envisages the possibility of producing biodiesel with tailored, custom-designed characteristics, without the need of a physical mixture step after the production process. It is important to mention that the production of biodiesel by methanolysis of oily mixtures may be improved through further development and the optimization of processes to obtain biodiesel with high purity. Acknowledgment. Financial support from the CTEnergPROSET program, CAPES, CNPq, FINEP, FAPEAL, and FAPERGS are gratefully acknowledged. T.M.S. expresses her appreciation for fellowships from CNPq. EF070039Q (11) Goodrum, J. W.; Geller, D. P. Bioresour. Technol. 2005, 96, 851– 855.
