Design of a sustainable process for enzymatic production of ethylene glycol diesters via hydroesterification of used soybean cooking oil

Abstract

The aim of this study was to produce diol diesters, an important class of synthetic esters with lubricant properties, via enzymatic hydroesterification of used soybean cooking oil (USCO). Initially, free fatty acids (FFAs) were produced through hydrolysis of USCO catalyzed using powder lipase extract from Candida rugosa. Afterwards, different diols and FFAs were esterified using Eversa® Transform 2.0, a low-cost liquid lipase derived from Thermomyces lanuginosus, immobilized via interfacial activation on polystyrene-divinylbenzene (PSty-DVB) beads as biocatalyst. The immobilization improved its catalytic activity and the best performance was observed using ethylene glycol (EG). Thus, it was selected for further ester production optimization. The effect of relevant factors on EG diesters production was assessed through a central composite rotatable design (CCRD). As a result, full OH conversion was achieved at 65 °C using EG:FFA molar ratio of 1:3% and 18% of mass of heterogeneous biocatalyst per mass of starting materials after 40 min of reaction. Maximum OH conversion was only 32.5% using soluble lipase under such conditions. The prepared biocatalyst retained ≈ 37% of its original activity after seven successive esterification batches. Viscosity index (166.2 ± 18.2), pour point (–9 ± 2 °C) and density at 20 °C (0.8794) values of the produced EG diesters were similar to other EG esters produced from soybean oil in literature and commercial synthetic neopolyol esters.