Biocatalytic production of isoamyl acetate from fusel oil in supercritical CO2

Abstract

Isoamyl acetate esters were enzymatically synthesized from fusel oil, a by-product generated in bioethanol industrial plants, in supercritical carbon dioxide (SC-CO2) using immobilized lipase (Lipozyme 435). Effects of enzyme load (2.5–10.0 %), substrates’ molar ratio (acetic anhydride to fusel oil; 1:1–4:1), acyl donor (acetic anhydride, ethyl acetate, and acetic acid) and solvent type (SC-CO2, n-hexane, and solvent-free system) on the biocatalytic isoamyl acetate conversion and the specific productivity were investigated. Higher volumetric expansions of the reaction medium were observed at higher temperature (60 °C) between 10 and 20 MPa. A monophasic system was observed at 15 MPa and 60 °C. Acetic anhydride and SC-CO2 were the best acyl donor and solvent, respectively. An elementary mathematical model was adjusted to the experimental data. 15 MPa, 60 °C, 2:1 substrates’ molar ratio and 2.5 % of enzyme concentration yielded the highest conversion (88.4 ± 0.5 %) and specific productivity (36.9 ± 0.2 %).