Kinetic modeling of immobilized-lipase catalyzed transesterification of n-octanol with vinyl acetate in non-aqueous media

Abstract

Organic esters are employed as solvents, fragrance, flavors, and precursors in a variety of industries. Particularly, aliphatic esters are greatly used in flavor industry, mainly as fixatives and modifiers, and aromatic esters in fragrance compositions. Esters are produced by a variety of methods among which esterification and transesterification with acid catalysts under reflux conditions are prominent. The use of biocatalysts provides an opportunity for carrying out reactions under milder conditions leading to better quality products suitable in fragrance and flavor industry. Transesterification of n-octanol with vinyl acetate was studied at 30 °C as a model reaction by employing different lipases as catalysts such as Psedomonas species lipase immobilized on diatomite, free Candida rugosa lipase. Novozym 435 (lipase B from Candida antarctica; immobilized on macro-porous polyacrylic resin beads) and Lipozyme IM 20 (Mucor miehei lipase immobilized on anionic resin). Novozym 435 was found to be the most active catalyst in heptane as a solvent. A conversion of 82% with 100% selectivity of n-octyl acetate was obtained at 30 °C in 90 min using equimolar quantities of the reactants with 0.833 g l⁻¹ of Novozym 435. Transesterification of other alcohols such as n-decanol, benzyl alcohol, cinnamyl alcohol, 2-ethyl-1-hexanol, 1-phenyl ethyl alcohol, and 2-phenyl ethyl alcohol was also studied with vinyl acetate. The analysis of the initial rate data and progress curve data showed that the reaction obeys the ternary complex bi–bi mechanism with inhibition by n-octanol. The experimental and theoretical values matched very well. The order of transesterification reactivity of vinyl acetate with various alcohols in presence of Novozym 435 under otherwise identical conditions at 30 °C was found to be as follows: n-octanol>n-decanol>benzyl alcohol>cinnamyl alcohol>2-ethyl-1-hexanol>2-phenyl ethyl alcohol>1-phenyl ethyl alcohol