Efficient and green esterification of glycerol with capric acid to medium chain glycerides catalyzed by two dimensional planar ZSM-5 directional immobilization of lipase

Abstract

A series of Candida antarctica lipase B (CALB) catalysts immobilized on two-dimensional planar ZSM-5 zeolite (denoted as xCAL/ZSM-5-P) were developed for the efficient and green esterification of capric acid (CA) and glycerol (Gly) to synthesize medium-chain glycerides (MCGs). Comprehensive characterizations, including X-ray diffraction, Fourier-transform infrared, scanning electron microscopy, transmission electron microscopy, N₂ physisorption, and thermogravimetric analysis, confirmed the successful immobilization and uniform dispersion of lipase of CALB on ZSM-5-P via sulfhydryl modification. The framework structure of ZSM-5-P remained structurally intact after immobilization. The CAL/ZSM-5-P catalysts exhibited outstanding catalytic performance in the esterification reaction. Notably, the 9CAL/ZSM-5-P catalyst achieved the highest CA conversion of 66.94 %, with nearly 100 % selectivity toward MCGs—substantially outperforming bare ZSM-5-P (without immobilized lipase), which showed only 0.19 % conversion. Additionally, 9CAL/ZSM-5-P demonstrated excellent catalytic stability and chemical robustness. A possible mechanism for the CALB/ZSM-5-P-catalyzed esterification of CA to MCGs was also proposed. This approach provides both theoretical insight and practical guidance for developing MCGs as food emulsifiers and functional oils via heterogeneous catalytic esterification using immobilized lipase in the food industry.