Catalytic membranes for simultaneous biomass hydrolysis and sugar separation

A catalytic membrane reactor has been developed to simultaneously catalyze hydrolysis of cellulosic biomass and separate the monomer sugars with improved sugar yields. An enzyme mimic catalyst has been synthesized by growing poly(styrene sulfonic acid) (PSSA) chains as well as poly (vinyl imidazolium chloride) ionic liquid (PIL) chains from the surface of ceramic membranes. These polymeric solid acid catalysts are able to facilitate cellulose dissolution and catalyze its hydrolysis reaction. PSSA catalyzes biomass hydrolysis whereas PIL helps solubilize the biomass and enhance the catalytic activity. Our solid acid catalysts demonstrate over 97% and 32% TRS yields from crystalline α-cellulose hydrolysis in ionic liquid [EMIM]Cl and aqueous solutions respectively. Moreover, these catalysts are able to convert cellulose directly to 5-hydroxymethylfurfural (HMF) with over 60% yield. These catalysts are stable and maintain high catalytic activity after repeated runs. 

A membrane reactor immobilized with our novel catalysts has been designed to simultaneously catalyze hydrolysis of biomass and separate the hydrolyzed sugars. The reactor has been tested using feed streams consisting of cellulose and hemicellulose in water, ionic liquid and water/ionic liquid mixtures.  Hydrolyzed low molecular weight sugars were collected in the permeate. Our results indicate the feasibility of hydrolyzing cellulose and hemicellulose in one step and removing hydrolyzed sugars simultaneously. By removing monomeric sugars as they are produced, sugar loss is minimized. A catalytic membrane reactor for simultaneous biomass hydrolysis and sugar separation could lead to the consolidation of three unit operations: pretreatment, biomass conditioning and enzymatic hydrolysis resulting in significant process intensification.