Aproveitamento de resíduos agroindustriais para a produção enzimática de ésteres de interesse industrial

Abstract

In the last decades, a significant effort has been directed toward the development of new sustainable processes for recycling and managing agro-industrial waste, such as waste vegetable oils and lignocellulosic biomass waste. In this context, this work aimed to propose a new approach in the enzymatic production of solketal esters, a class of compounds of great interest in the oleochemical industry, via enzymatic hydroesterification of used soybean cooking oil (USCO). For such a purpose, a heterogeneous biocatalyst was initially produced, which the lipase Eversa® Transform 2.0 (ET2.0) was immobilized on particles of Acrocomia aculeata (macaúba) epicarp (peel), which underwent two acid pre-treatments and two treatments with 70% ethanol before immobilization. Subsequently, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FT-IR) analyses were performed to evaluate the influences of the pretreatment methods on macaúba epicarp particles. The biocatalyst was prepared via physical adsorption of ET2.0 at 25 °C in pH 5.0 (sodium acetate buffer – 5 mmol.L-1 ) offering a protein loading of 40 mg.g-1 of support. In this step, the maximum immobilized protein concentration of 25.2 ± 1.3 mg.g-1 was achieved after 15 hours of immobilization. Afterward, the complete hydrolysis of used soybean oil catalyzed by Candida rugosa lipase (CRL) was carried out to produce free fatty acids (FFAs). The enzymatic hydrolysis step for FFA production was performed in an emulsifier-free and buffer-free system using a mass ratio of oil:water of 40% m.m-1 , a CRL concentration of 3.2 g of commercial powder per kg of medium, 40 °C, and mechanical stirring at 1500 rpm. Following this step, esterification reactions were performed in open flasks containing 6 g of reaction medium consisting of a mixture of FFAs and solketal, mechanical agitation at 240 rpm, and a reaction time of 40 minutes. In this stage, the influence of relevant factors in the esterification step such as solketal:FFA molar ratio (1:1 to 1:4), reaction temperature (40 to 70°C), and biocatalyst concentration (5 to 20% m.m-1 ) was evaluated using a central composite rotatable design (CCRD). According to the results, a maximum acid conversion of approximately 72.5 ± 0.8% was achieved after 150 minutes of reaction conducted at 46 °C, 20% m.m-1 of biocatalyst, and a molar ratio of (1:1.6) of FFA:solketal. Under this condition, reusability tests were performed to analyze the stability of the biocatalyst. The biocatalyst retained 70% of its original activity after ten successive cycles. The production of solketal esters was confirmed by FT-IR and nuclear magnetic resonance spectroscopy (1H NMR and 13C NMR). These results demonstrate that the strategy proposed in this work is very attractive for the chemical industry, for establishing efficient and sustainable processes from agro-industrial waste (macaúba epicarp and waste oil).