DOI: 10.1002/cssc.200800077 Ionic Liquid Supported Acid/Base-Catalyzed Production of Biodiesel Alexandre A. M. Lapis, [a] Luciane F. de Oliveira, [a] Brenno A. D. Neto, [a, b] and Jairton Dupont* [a] There are considerable efforts in the search of sustainable and renewable energy sources as concerns related to energy, secur- ity and climate change become imperative. [1] Renewable bio- systems are therefore important alternatives to natural draina- ble sources. For example, biodiesel (mono-alcohol fatty acid esters) has become a good alternative for the large-scale sub- stitution of petroleum-based fuels. [2,3] Although there are tech- nological problems [4,5] associated with the alcoholysis of vege- table oils (Scheme 1) employing metal hydroxides (or alkox- ides) and inorganic acids, these are the most employed meth- ods among many others for the production of biodiesel. [6,7] Be- sides the use of volatile organic solvents that are toxic, separation of glycerol, reversibility of the transesterification re- action, the use of large quantities of water, and catalyst regen- eration are the major drawbacks associated with such acid or base catalyzed reaction. Among various alternative methodolo- gies that are currently under investigation, such as new cata- lysts [8,9] and enzymes, [10] the use of supported catalytic systems is one of the most promising. [11,12] In particular, imidazolium ionic liquids [13] have been success- fully used as liquid support for the enzymatic alcoholysis of vegetable oils. [14] This system has interesting effects on the production of biodiesel, such as the reaction yield, separation of the products, and selective capture of glycerol, but its high cost and long reaction times render its industrial application unpractical. Progress in the transesterification of vegetable oils has been achieved using metal catalysts supported in classical imidazolium ionic liquids, [15] acidic task-specific ionic liquids, [16] or Lewis acid catalysts immobilized in 1-n-butyl-3-methylimida- zolium tetrachlorindate. [17] However, the recycling of the cata- lyst is a major problem with these metal-supported ionic-liquid catalysts. We report herein that a simple acid or base catalyst in conjunction with ionic liquids comprises one of the most simple and efficient as well as environmentally sound catalytic systems for the production of biodiesel. Results and Discussion The simple base-catalyzed transesterification of soybean oil using a combination of ethanol and K 2 CO 3 (40 mol%) with vari- ous hydrophobic and hydrophilic ionic liquids at 70 8C (Figure 1) produced biodiesel in yields of 2–98% (Table 1). It is clear from the data in Table 1 that with the exception of ionic liquids 1d (BMI·OTf) and 1e (BMI·OH; entries 4 and 5, Table 1), all the others produce the biodiesel in high yields (> 96%) re- gardless of the nature of the anion or the alkyl groups on the imidazolium cations. However, ionic liquids 1b (BMI·BF 4 ) and 1c (BMI·PF 6 ) were not stable and decomposed after 2–3 h, since hydrolysis of the BF 4 and PF 6 anions under these basic [a] Dr. A. A. M. Lapis, Dr. L. F. de Oliveira, Prof. Dr. B. A. D. Neto, Prof. Dr. J. Dupont Laboratory of Molecular Catalysis Institute of Chemistry—UFRGS Av. Bento GonÅalves, 9500 Porto Alegre 91501-970 RS (Brazil) Fax: (+ 55)5133087304 E-mail: dupont@iq.ufrgs.br [b] Prof. Dr. B. A. D. Neto Centro de Pesquisas em Biologia Moleculare Funcional, Tecnopuc, PUCRS (Brazil) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cssc.200800077. The transesterification (alcoholysis) reaction was successfully ap- plied to synthesize biodiesel from vegetable oils using imidazoli- um-based ionic liquids under multiphase acidic and basic condi- tions. Under basic conditions, the combination of the ionic liquid 1-n-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMI·NTf 2 ), alcohols, and K 2 CO 3 (40 mol%) results in the produc- tion of biodiesel from soybean oil in high yields (> 98%) and purity. H 2 SO 4 immobilized in BMI·NTf 2 efficiently promotes the transesterification reaction of soybean oil and various primary and secondary alcohols. In this multiphase process the acid is almost completely retained in the ionic liquid phase, while the bio- diesel forms a separate phase. The recovered ionic liquid contain- ing the acid could be reused at least six times without any signifi- cant loss in the biodiesel yield or selectivity. In both catalytic pro- cesses (acid and base), the reactions proceed as typical multipha- sic systems in which the formed biodiesel accumulates as the upper phase and the glycerol by-product is selectively captured by the alcohol-ionic liquid-acid/base phase. Classical ionic liquids such as 1-n-butyl-3-methylimidazolium tetrafluoroborate and hexafluorophosphate are not stable under these acidic or basic conditions and decompose. Scheme 1. Alcoholysis of vegetable oils. ChemSusChem 2008,1,759–762 # 2008 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 759