Enhancement of Cellulose Acid Hydrolysis Selectivity Using Metal Ion Catalysts

Abstract

Hydrolyzing the amorphous region of cellulose with high selectivity while protecting the crystalline region during acid hydrolysis of cellulose still remains a key technical barrier in cellulose hydrolysis and Microcrystalline Cellulose (MCC) production. This study investigated the effects of two transition metals (Fe3+ and Cu2+) on cellulose yield after acid hydrolysis, α-cellulose content and crystallinity of the Eucalyptus pulp cellulose. The correlations of metal ion catalysis and hydrolysis selectivity were studied and optimized using Orthogonal Experimental Design. The results showed that metal ion catalysts enhanced the selectivity of acid hydrolysis of amorphous cellulose region over crystalline region with enhanced hydrolysis conditions. Thus, high degree crystalline MCC was obtained. However, the selectivity did not show clear improvement with mild acid hydrolysis conditions. Overall, Fe3+ catalyst had better acid hydrolysis selectivity than Cu2+ catalyst. The factors that affect cellulose crystallinity follow the order: metal ion concentration > HCl concentration > hydrolysis temperature > hydrolysis time. The optimal conditions to get the highest crystallinity of cellulose were 0.4 mol/l Fe3+, 2.5 mol/l HCl, 80°C, 55 min at solid-liquid ratio of 1:15.