(611c) Novel Polymeric Solid Acid Catalysts for Cellulose Hydrolysis
Biofuel derived from lignocellulosic biomass is one of the leading renewable energy to replace fossil-base transportation fuels. The main drawback of the current biochemical processing of biomass is the cost of pretreatment, cellulase enzymes as well as the slow enzymatic hydrolysis process. A synthetic enzyme mimic polymeric solid acid catalyst overcomes all these limitations. Dual functional polymeric solid acid catalysts are synthesized in order not only to catalyze cellulose hydrolysis but also to facilitate its dissolution. The acidic polymeric chain, poly (styrene sulfonic acid) (PSSA) immobilized on a glass/membrane substrate via atom-transfer radical polymerization (ATRP) catalyzes biomass hydrolysis. Its neighboring poly (vinyl imidazolium chloride) (PIL) chain grafted via UV-initiated radical polymerization helps solubilize lignocellulosic biomass and enhance the catalytic activity. UV-initiator 4-ethoxy-5-oxo-4,5-diphenylpentanoic acid (BEE-COOH) was successfully synthesized and immobilized prior to UV polymerization. Cellulose hydrolysis was conducted in 1-methyl-3-ethylimidazolium chloride [EMIM]Cl as well as in aqueous solution. An optimal ratio of the two polymer chain densities as well as optimal polymer chain lengths were found for achieving highest catalytic conversion of cellulose substrates. These polymeric catalysts are stable in ionic liquid solvents and maintain high catalytic activity after more than 12 repeated runs. Our novel polymeric solid acid catalysts demonstrate total reducing sugar (TRS) yield over 94% after 12 runs in [EMIM]Cl. Methods for ionic liquid regeneration and reuse were also developed. More importantly the catalytic activity of these polymeric acids can be further tuned by ring substitution and copolymerization. These polymeric solid acids are reusable, environmental friendly and potentially superior catalysts for many other organic reactions requiring acid catalysts. Theoretical investigations are conducted to obtain fundamental insight into their high catalytic activity.