8-02: Pretreatment with alkali and oxygen to produce highly hydrolysable cellulose and sulfur-free lignin

Plant biomass is the major readily available renewable source to substitute oil for liquid biofuels and chemicals. Feasible utilization of cell wall components by the sugar route requires efficient methods to fractionate raw materials into utilizable non-carbohydrate fractions and readily hydrolysable cellulose fraction for hydrolysis. In this work we discuss a method which fractionates efficiently biomass using simple chemicals and mild process conditions, giving carbohydrates with high hydrolysability and low inhibitor content and lignin fraction with interesting technical properties.

Alkaline oxidative fractionation of woody materials and sugarcane bagasse was performed either with or without of Cu-catalyst at 100 - 140 ºC for 5 to 24 h.  A fibre fraction with high enzymatic hydrolysability and a solubilised fraction containing recoverable lignin, organic acids and some minor components were produced. Pretreatment was also efficient even without catalyst although the presence of the catalyst enhanced its performance. The enzyme dosage required for hydrolysis of the fibre was radically decreased as compared to materials obtained by steam explosion from the same raw materials. The demand of enzymes was decreased most significantly with long hydrolysis time, probably due to diminished inactivation and unproductive binding to the substrate. The binding of individual enzymes in total hydrolysis was studied by quantifying the major components of T. reesei cellulase system and A. niger β-glucosidase during hydrolysis by mixtures of purified enzymes. The results clearly show the promise of the new method and motivate further development and scale up work.