Biocatalytic esterification of caprylic acid with caprylic alcohol by immobilized lipase on amino-functionalized mesoporous silica

Abstract

Ordered mesoporous silica (MS) materials were prepared using Pluronic P123 (triblock copolymer poly(ethylene glycol)–block–poly(propylene glycol)–block–poly(ethylene glycol)) and poly(ethylene glycol) as dual templates, and functionalized with (3-aminopropyl)triethoxysilane using the postsynthesis-grafting method. Fourier-transform infrared spectroscopy, 29Si and 13C cross-polarization and magic angle spinning nuclear magnetic resonance, elemental analysis, small-angle X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and N2 adsorption–desorption were used to monitor the effect of surface functionalization on the structural and textural features of MS. MS was found to possess a short rod-shaped macrostructure and a two-dimensional hexagonal P6mm mesoscopic structure. After functionalization, the mesoscopic structure was retained and the interplanar spacing d (100) increased, whereas the pore diameters, pore volumes, and surface areas decreased. MS and functionalized MS were used as carriers to immobilize porcine pancreatic lipase (PPL). The immobilized PPL on both kinds of carriers were then employed to catalyze the hydrolysis of triacetin and esterification of caprylic acid with caprylic alcohol. All observed biocatalytic characteristics of PPL immobilized on functionalized MS were compared with those of PPL immobilized on MS. The hydrolysis activity of lipase immobilized on functionalized MS was almost twice that on MS. Functionalized MS immobilized PPL showed greater reusability, and its hydrolysis conversion was still retained at 24%, which was 15% higher than that of lipase immobilized on MS after the fifth reuse. The synthetic activity and effect of several parameters on caprylic caprylate production for immobilized PPL were investigated. Immobilized PPL exhibited significantly higher activity, with a caprylic acid conversion ratio of 67.47% when the reaction was catalyzed by PPL immobilized on functionalized MS. The corresponding value was 58.75% using PPL immobilized on MS at 50°C.