Exploring the Potential of H-Zeolites as Heterogeneous Catalysts for the Chemical Recycling of Polysaccharides and Their Flexible Films

Abstract

Zeolites are a group of crystalline aluminosilicates with exchangeable cations and molecular-dimensioned micropores, which have successfully been applied to transform biomass and waste into biofuels. Herein, the effectiveness of acidic H-zeolites in biomass transformation and chemical valorization is demonstrated. In this process, the Brønsted/Lewis acid sites in zeolites catalyze the transition of carbohydrates into valuable chemicals. β-glucan polymer extracted from the lichen Usnea was catalytically converted into value-added molecules, such as glucose monomers. Particular challenges to elucidate the zeolite-catalyzed β-glucan conversion to glucose were addressed, namely: (i) water as the solvent, ii) hydrolysis of the biopolymer in an ionic liquid of 1-Butyl-3-vinylimidazolium bromide ([BVinIm]Br), and iii) reaction time of 30, 60, 120, and 240 min. Effective hydrolysis of β-glucan was achieved by H-zeolites (H-Beta, H-Mordenite, and H-ZSM-5), and the formed glucose was quantified through the dinitrosalicylic acid (DNS) method. Finally, applying H-zeolites as heterogeneous catalysts to prove the chemical recyclability of flexible films based on β-glucan was demonstrated as a step forward in integrating biopolymer-based materials into the circular economy.