Produção de biolubrificante catalisada por lipase imobilizada via adsorção física em sílica de casca de arroz funcionalizada

Abstract

Amorphous and mesoporous SiO2 from rice husks was prepared via thermochemical process and functionalized with triethoxy(amino)silane (3-APTES) to produce a support with high density of amino groups (Amino-SiO2). The functionalization step was confirmed by several techniques such as X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electronic microscopy (SEM), atomic force microscopy (AFM), N2 physisorption analysis and Rose Bengal dye adsorption (hydrophobicity test). The functionalized support was then applied in the preparation of active biocatalysts via physical adsorption of microbial lipase from Thermomyces lanuginosus (LTL). The effect of certain parameters, including pH of incubation, temperature, initial protein loading and time of incubation, in the adsorption of LTL on Amino-SiO2 was systematically evaluated. According to results, the functionalization step improved the adsorption of the enzyme on the support surface when compared to the non-functionalized support. Under optimal conditions (5 mM buffer sodium acetate pH 4.0, 25 °C and 20 min of incubation), maximum immobilized protein loading of 12.3 ± 0.1 mg/g was observed. This biocatalyst exhibited maximum activity in the hydrolysis of olive oil emulsion of 645.8 ± 6.9 IU/g. The adsorption of TLL on the functionalized support was a physisorption process. The experimental data of adsorption was well-fitted to the Langmuir isotherm model (R2 = 0. 9957). The catalytic activity of the biocatalyst in organic medium was also evaluated through the synthesis of esters by esterification reaction. Among them, the synthesis of decila oleate, through a design using central rotational compound design (DCCR), a tool that allowed to obtain optimal operating conditions (30 ºC, 21% m/v biocatalyst, 150 rpm and acid molar ratio: alcohol ratio of 1: 1). Therefore, obtaining maximum percent conversion of the ester at 180 and 105 minutes, of 87%, to a solvent-free system and an isooctane-containing system respectively. The reuse tests showed that the biocatalyst retained all of its original activity after eight successive reaction cycles in a solvent-free system. These results suggest that this biocatalyst can be successfully used in ester synthesis through a clean technology process due to its high catalytic activity and reuse.