Effect of supercritical ammonia on the physical and chemical structure of ground wood

Pretreatment of hardwood biomass with supercritical ammonia dramatically enhances the susceptibility of the substrate to enzymic hydrolysis. The pretreatment of both hardwoods and softwoods increases the substrate nitrogen content via amidation reactions and increases total pore volume without increasing maximum pore width. Pretreatment does not significantly change the cellulose, hemicellulose, or lignin content of the substrates. Success of the pretreatment for hardwoods appears to result predominantly from cleavage of lignin-carbohydrate bonds and from increasing pore volume. The lower effectiveness against softwoods is apparently due to an inability to open the pore structure to allow penetration of cellulolytic enzymes. (Refs. 24).