Desenvolvimento de um novo processo para a produção de ésteres monoalquílicos epoxidados a partir de matérias-primas renováveis

Abstract

The aim of this study was to produce epoxidized monoalkyl esters (EMAE), a valuable class of oleochemicals used in a wide range of products and industries, from used soybean cooking oil (USCO) and fusel oil by a chemoenzymatic three-step process. This process proceeds via first enzymatic hydrolysis of USCO to produce free fatty acids (FFA). In this step, five microbial lipases with different specificities were tested as biocatalysts. Full hydrolysis of USCO was obtained after 3 h of reaction under vigorous stirring (1500 rpm) using a non-specific lipase from Candida rugosa (CRL). Afterwards, monoalkyl esters (MAE) production via esterification of FFA and fusel oil in a solvent-free system was conducted using lipase Eversa® Transform 2.0 (ET 2.0) immobilized via physical adsorption on poly(styrenenedivinylbenzene) (PSty-DVB) beads as biocatalyst. Different water removal strategies (closed and open reactors in the presence or absence of molecular sieves at 5% m.m-1 ) on the reaction were evaluated. Maximum FFA conversion around of 64.3 ± 2.3% (open reactor after 30 min of reaction) and 73.5 ± 0.4% (closed reactor after 45 min of reaction) was achieved at 40 °C using a stoichiometric FFA:fusel oil molar ratio (1:1), absence of molecular sieves and 5 mg of immobilized protein per gram of reaction mixture. Under such conditions, maximum FFA conversion was only of 30.2 ± 2.7% after 210 min of reaction in closed reactor using soluble lipase. Reusability tests revealed better retention of the original activity of immobilized ET2.0 (around of 82%) after eight successive batch esterification reactions conducted in an open reactor. Finally, the produced MAE were epoxidized via Prilezhaev reaction, a classical chemical epoxidation process, using hydrogen peroxide and formic acid as a homogeneous catalyst. The products were characterized by standard methods and identified by proton nuclear magnetic resonance (1H NMR). Maximum conversion of unsaturated bonds into epoxy groups around of 33%, with an experimental epoxy oxygen content (OOCexp.) of 1.75-1.78% and selectivity (S) of 0.81, was achieved using both produced MAE (open or closed reactors). These results show that this new process can be a promising approach for value-added oleochemicals production from low-cost and renewable raw materials.