Enzymatic Pretreatment Of Bagasse Oxygen-alkali Pulping And Its Delignification Selectivity

Alkali-Oxygen pulping is a new,clean and environmentally compatible pulping method.However,the resulting pulp of carbohydrates seriously degradation which hinders its industrialization process.In this paper,laccase and hemicellulase were used to pretreat bagasse for studying the relationship between the microscopic structure of bagasse fiber and the penetration of cooking liquor.Then,using HO·and O₂^-·to treat the alkali-oxygen process pulp which pretreated by enzemy,the delignification ability and selectivity for them were studied.Finally,enzyme pretreated bagasse combined with controlled radical to improve the selectivity of bagasse alkali-oxygen pulping.The effect of enzemy pretreatment on bagasse raw material and penetration showed that it could improve the average pore size and specific surface area of the fiber.Thereby,the liquor penetration and reaction efficiency in the subsequent alkali impregnation process are further improved.Comprehensively judged the optimum conditions of laccase pretreatment were:enzyme dosage 80 U/g,t=6 h,pH=5,T=50°C;the optimum conditions of hemicellulose enzyme pretreatment were:enzyme dosage5 AXU/g,t=4 h,pH=8.5,T=50°C.The result showed that the micro-structure of bagasse raw material after hemicellulase pretreatment is better than that of laccase pretreatment,therefore the liquid penetration ability is better.The effect of enzemy pretreatment on radicals delignification selective showed that pulp from alkali-oxygen cooking for 1 h shows better delignification selectivity.The HO·treated the process pulps which pretreatment by enzemy showed that the delignification selectivity was better cooked at 1 h.When treated cooked 2 h pulps,the delignification selectivity decreased.The delignification ability of O₂^-·is limited for alkali-oxygen pulp,but delignification selectivity was significantly higher than that of HO·treated pulps.After radical treated the pulps,the laccase pretreated bagasse alkali-oxygen pulp was with better lignin degradation ability,and to the hemicellulase pretreated bagasse alkali-oxygen pulp delignification rate was faster and the resulting pulps has a lower Kappa number and a slightly higher viscosity.However,the delignification selectivity of both pulps is improved.The effect of adding radicals control agent on selectivity of delignification of bagasse alkali-oxygen pulping showed that the work was the best when added at 1 h of pulping.it's better than those of addtion of Vc and sodium 2-anthraquinonesulfonate at 2 h of cooking process.However,the pulping result was not ideal when added agent at 0 h of cooking process.When the agent was added at1 h of cooking process,lower Kappa number and higher viscosity pulp could be obtained after laccase pretreatment.the higher fine yield was obtained after hemicellulase pretreatment.