Study On The Oxygen-alkali Pulping Of Bagasse Pretreated By Wet Storage And Its Delignification Selectivity

In recent years,with the steady development of China's paper industry and national economy,the demand and production of paper products increased rapidly.However,the shortage of paper-making resources has not been solved,which restricts the rapid development of China's paper industry.Yunnan Province has abundant sugarcane resources in China.The bagasse,the remaining fiber material after sugar extraction,is a good raw material for pulping and papermaking.Therefore,the bagasse resources in Yunnan for pulping and papermaking is of great strategic significance.In this paper,the delignification selectivity of bagasse alkali-oxygen pulping was studied by combining wet storage pretreatment with free radical control during cooking.Firstly,the effect of wet storage on the properties of bagasse raw materials was investigated,the alkali-oxygen cooking process pulp of bagasse after wet storage was treated by a self-made free radical production system,then the effects of free radicals on the alkali-oxygen cooking of bagasse after wet storage were studied.Secondly,the optimized conditions of alkali-oxygen cooking reaction by adding free radical controllers in the process of alkali-oxygen cooking was discussed.At last,XRD,FT-IR,SEM and BET were used to analyze the properties and microstructures of pulp and wet storage pretreatment bagasse,and the mechanism of improving the alkali-oxygen pulping effect by combining wet storage pretreatment with free radical control was studied.The effect of wet storage pretreatment on the properties of bagasse raw materials was shown as follows:the dissolution of small molecules resulted in the change of pore size distribution of fibers,which has an important impact on the subsequent alkali impregnation.The bagasse was pretreated with tap water for 16 days,the proportion of pore diameter with greater than 50 nm was the highest in bagasse fibers,and lead to the alkali impregnation is the best.The bagasse was pretreated with bleaching waste-water for 12 days,the proportion of pore diameter with greater than 50 nm is thehighest,and resulted in the alkali absorption effect is best,the result was similar to that of the16 days.The pretreatment with bleaching waste-water was more efficient than that of tap water to improve the properties of bagasse.The alkali-oxygen pulping of tap water and bleaching wastewater pretreated bagasse is with good pulping properties,the yield,viscosity and whiteness of bagasse oxygen-alkali pulp are higher when the kappa numbers of the pulps are similar.The effect of wet storage pretreatment on delignification of oxygen free radicals was shown as follows:the bagasse was mainly as fibre fasciculus when the cooking was heated to the max temperature,and the pulp contained a lot of lignin,when the pulp was treated with hydroxyl radicals,the lignin was removed effectively,the viscosity was reduced slightly,and the delignification selectivity was good.Furthermore,the bagasse after cooked at the max temperature for 1 h,the pulp was separated well,when the pulp was treated with hydroxyl radicals,delignification selectivity decreased with the prolonging of pretreatment time.Compared with bagasse pretreated with tap water,hydroxyl radicals selectivity delignification of bagasse after bleaching waste-water pretreated was better.The delignification ability of superoxide anion free radicals was lower than that of hydroxyl radicals in the process of alkali-oxygen cooking,but its delignification selectivity and the viscosity of pulp were higher.The results of the combination wet storage pretreatment and free radical control agents to improve the alkali-oxygen pulping properties were shown as follows:with the extending of pulping time,the content of pore size less than 10 nm decreased,but the content of pore size greater than 10 nm increased,meanwhile,the crystallinity of the fibers increased at first and then decreased during the alkali-oxygen cooking.The addition MgSO₄ protective agent is beneficial to improve pulping effect when it was added at the beginning of cooking.Compared with the pulping effect of MgSO₄protective agent,it could obtain pulp with similar kappa number and higher yield and viscosity when the addition of hydroxyl radical inhibitor?ascorbic acid?or superoxide anion radical accelerator?sodium anthraquinone-2-sulfonate?were add at the max temperature for 1h.