Optimization of Enzymatic Synthesis of Tricaprylin in Ionic Liquids by Response Surface Methodology

Ten 1,3-dialkylimidazolium-based ionic liquids (ILs) have been investigated as media for the enzymatic synthesis of tricaprylin, in comparison with the conventional organic solvent hexane. The results suggested that the esterification activity of Novozym 435 was higher than Lipozyme RM IM in all the ILs assayed. Novozym 435 showed higher catalytic activity in ILs with anions Tf2N- and PF6- than in BF4- and hexane. FTIR analysis of the secondary structure of the lipase indicated that a smaller decrease of the alpha-helix was observed in [C4MIM] Tf2N and [C4MIM] PF6 than [C4MIM] BF4 and hexane, indicating that the anions of ILs might be a key factor for the activity of lipase in ILs. Process parameters (amount of lipase, caprylic acid/glycerol molar ratio, temperature and their interactive effects) were optimized in 1-butyl-3-methylimidazolium hexafluorophosphate ([C4MIM] PF6) using Novozym 435 by response surface methodology. When the reactions were performed with the lipase amount of 6.1 % substrate mass at a caprylic acid/glycerol molar ratio of 4.5:1 and 66.7 degrees C, a higher yield was reached up to 92.4 %.