Effects Of Residual Acid From Pre-hydrolysis On Subsequent Kraft Pulping Performance Of Acacia Wood

Pre-hydrolyzed kraft pulping is widely used in the production of dissolved pulp as a pulping method with high consistency with biomass comprehensive utilization.As for the pre-hydrolysis kraft pulping,it has been shown that the pre-hydrolysis process can enhance the delignification of the subsequent kraft pulping process and improve the pulping efficiency.In the earlier exploration experiment,we found that the kraft pulping process of wood after pre-hydrolysis was incomplete and lignin removal was difficult.The reasons may be various,one of the main reasons is due to the water absorption of wood,wood after pre-hydrolysis residual part contains the pre-hydrolysis process of organic acid pre-hydrolysis solution,this part of the organic acid will consume cooking liquor,the subsequent sulfate pulping form adverse effects.Therefore,ultrasonic washing method was used to wash the wood after pre-hydrolysis,and the residual acid in the wood was eluted.the changes of main chemical components of wood and hydrolysate during pre-hydrolysis,pulp properties and black liquor during pre-hydrolysis were analyzed respectively,so as to explore the effect of pre-hydrolysis residual acid on the kraft pulping performance of acacia wood.For the pre-hydrolysis process,the changes of main components of acacia wood and pre-hydrolysis solution under different pre-hydrolysis intensities were studied.it was found that with the increase of P-factor?prehydrolysis intensity index?,the yield of prehydrolysis wood chips decreased continuously due to the degradation of components in wood chips,and reached a stable level when P-factor was large.The content of total cellulose,pentosan,lason lignin and acid-soluble lignin in wood decreased with the increase of P-factor,while the content of alcohol-benzene extractive increased with the increase of P-factor.With the increase of p factor,the ph value of prehydrolysis solution decreased rapidly at first and then tended to be gentle.the change trend of organic acid content in the corresponding prehydrolysis solution was basically opposite to the ph value.with the increase of P-factor,the organic acid content in the prehydrolysis solution increased continuously,and also increased with the increase of p factor.The ash content of solid matter in the prehydrolysis solution increased firstly and then tended to be gentle.For sulfate pulping process,the pulping conditions were as follows:the highest temperature was 165?,the liquid ratio was 1:4,the heating time was 60 min,the holding time was 150 min,the amount of alkali?calculated as Na₂O?was 15%,and the degree of vulcanization was 30%.For pre-hydrolyzed wood chip without ultrasonic washing,with that increase of P-factor,both the crude pulp yield and the fine pulp yield decrease first and then keep stable.The kappa number of the slurry increases with the increase of P-factor,and the viscosity decreases with the increase of P-factor.The performance of that pre-hydrolyzed wood chip pulp aft ultrasonic washing show that the crude pulp yield of the pulp is reduced as a whole compared with the condition without washing,while the fine pulp yield of the pulp is increase,the slag pulp yield is reduced,the kappa number of the corresponding pulp is reduced,and the lignin removal effect in the pulping process is obviously improved.In addition,due to the effect of ultrasonic treatment,the viscosity of the slurry is reduced.Different from the phenomenon that the degree of polymerization of the fibers decreased with the decrease of the viscosity of the fibers,the analysis of the morphology of the fibers showed that the length and width of the fibers remained basically stable with the increase of the p factor.The fiber length of the pulp after ultrasonic washing of pre-hydrolyzed wood chips decreased,but the width of the fiber increased significantly.the curl of the fiber increased under the condition of low p factor and decreased with the increase of p factor.For the analysis of pulping black liquor,with the increase of the degree of prehydrolysis,the ph value and residual alkali content of kraft pulping black liquor show a trend of decreasing at first and then gradually changing.The solid content of black liquor increased;Under the condition of low hydrolysis strength,the viscosity of black liquor tends to be stable after decreasing.under the condition of high hydrolysis strength?P-factor>500?,the viscosity of black liquor rises again.The lignin content in black liquor was relatively stable under the condition of P-factor<200.with the increase of hydrolysis intensity,the lignin content gradually decreased,and slightly increased under the condition of P-factor>500.The ph value and residual alkali content of the black liquor were increased after ultrasonic washing.the ph value and residual alkali content of the black liquor increased slightly under the condition of low degree of hydrolysis.under the condition of P-factor>500,the ph value and residual alkali content increased obviously compared with the black liquor without washing.The solid content and organic matter content of black liquor after ultrasonic washing were increased.Under the condition of P-factor>200,the lignin content in black liquor was higher than that of black liquor without ultrasonic washing and pre-hydrolyzed wood,and the viscosity of black liquor was higher.The pretreatment also has a great influence on the physical strength properties of the paper sheet made by subsequent kraft pulp pulp.with the increase of P-factor,the tear index,tensile index and burst index of the hand-made sheet show a decreasing trend in different degrees.Ultrasonic washing also has an adverse effect on the physical strength of the paper sheet,and the physical strength of the hand-made sheet of wood pretreated by ultrasonic washing is reduced compared with the condition without ultrasonic washing.