Solvent-Free Catalytic Depolymerization of Cellulose to Water-Soluble Oligosaccharides

The use of cellulose is hampered by difficulties with breaking up the biopolymer into soluble products. Herein, we show that the impregnation of cellulosic substrates with catalytic amounts of a strong acid (e.g., H2SO4, HCl) is a highly effective strategy for minimizing the contact problem commonly experienced in mechanically assisted, solid‐state reactions. Milling the acid‐impregnated cellulose fully converts the substrate into water‐soluble oligosaccharides within 2 h. In aqueous solution, soluble products are easily hydrolyzed at 130 °C in 1 h, leading to 91 % conversion of the glucan fraction of α‐cellulose into glucose, and 96 % of the xylans into xylose. Minor products are glucose dimers (8 %), 5‐hydroxymethylfurfural (1 %) and furfural (4 %). Milling practical feedstocks (e.g., wood, sugarcane bagasse, and switchgrass) also results to water‐soluble products (oligosaccharides and lignin fragments). The integrated approach (solid‐state depolymerization in combination with liquid‐phase hydrolysis) could well hold the key to a highly efficient “entry process” in biorefinery schemes. Reactive milling: The impregnation of cellulosic substrates with catalytic amounts of strong acid minimizes the contact problems encountered in mechanically assisted, solid‐state reactions. As a result, full conversion of cellulose into water‐soluble oligosaccharides is achieved by milling within 2 h. Water‐soluble products are easily hydrolyzed at 130 °C in 1 h, leading to 91 % conversion of the glucan fraction of the substrate into glucose, and 96 % of the xylans into xylose (see picture).