Study On The Effect Of Pulping Process On Performance Of Prehydrolysis Kraft Dissolving Pulp Of Bamboo

As an important high value-added products of pulp and papermaking industry,dissolving pulp with high purity,less ash and high brightness has been widely used in production of textile and viscose.The reactivity of dissolving pulp is a significant parameter for the comprehensive evaluation of its product quality,and thus directly determines the quality and grade of dissolving pulp.Pulping process has a critical effect on the properties of unbleached pulp including cellulose molecular weight and its distribution,and then plays a decisive role on hemicellulose content,a-cellulose and reactivity of dissolving pulp.This paper studied on the effect of pulping process on primary chemical composition of green bamboo chips and pulps,cellulose molecular weight and its distribution,the composition of hydrolysate and black liquor,pulp reactivity with three typical alkaline pulping processes,i.e.,traditional kraft pulping—KP,separate pre-hydrolysate after prehydrolysis and then conduct the kraft pulping—S-KP,directly conduct the kraft pulping after prehydrolysis without separation process of hydrolysate-NS-KP),for figuring out the influencing mechanism of pulping process on dissolving pulp reactivity and the criterion for optimizing process.Also,the online measurement model of prehydrolysis and sulfate pulping process has been established.Finally,these researches will provide theoretical basis and technical guidance for producing high quality dissolving pulp of green bamboo.Thesis was studied firstly about the effect of hot water prehydrolysis process on green bamboo chemical components,cellulose molecular weight and its distribution and the mainly ingredients of hydrolysate.The results showed that both raising temperature and extending the hydrolysis time were helpful to the dissolution of hemicellulose and lignin.The dissolution of hemicellulose and a small amount of lignin was predominant at the lower prehydrolysis intensity(i.e.,low temperature and/or short time).However,the dissolution of cellulose was markedly increased at high prehydrolysis intensity,also the cellulose molecular weight began to significantly decline.The main hydrolysate of xylan would gradually transform from xylo-oligosaccharides to xylose and furfural with the increase of reaction time.Specifically,at the reaction temperature of 170?,the content of xylo-oligosaccharides was highest and accounted for more than 80%of dissolved xylan,and the total concentration of xylose was up to 33.9g/L.Considering the effect of the kraft pulping process on hemicellulose removal,this paper selected respectively 40min,80min,120min and 160min to carry out the next stage experiment.In addition,this paper established an online measurement model of prehydrolysis process using the UV-vis spectroscopy technology,i.e.,Removal rate of cellulose,%=5.7038 In[(A278-A600)*L:S]+11.604,R2=0.935.Removal rate of hemicellulose,%=24.486 In[(A278-A600)*L:S]+54.039,R2=0.943.Yield of hydrolysis,%=-10.56 In[(A278-A600)*L:S]+77.735,R2=0.954.The model realized the online detection for the removal rate of the three major components according to the liquid ratio and UV-Vis spectra,which provided a guidance role on increasing the stability of prehydrolysis process.The reseach involved the kraft pulping process showed that the removal rate of lignin had a significant difference using different pulping patterns.Specifically,S-KP pulping process could obtain higher lignin removal rate than NS-KP and KP process with the same alkaline charge and cooking intensity.Also,the S-KP process would obtain lower kappa number than traditional KP process.Moreover,the unbleached pulp using the NS-KP and S-KP pulping process had a lower pentosan and HexA content than KP process,and basically had reached the requirements of dissolving pulp.In spite of the hemicellulose was not completely removed after hydrolysis at 170? for 80min.Besides,the S-KP pulping process obtained higher pulp viscosity and better brightness stablity than the traditional KP pulp,and could effectively save the dosage of chemicals.The research about cellulose molecular weight and its distribution for three pulping processes showed that,,for obtaining the same lignin removal rate(kappa number=11)using S-KP process,more cellulose degrated using the process increasing hydrolysis time(hydrolysis time=80 min,cooking time=50 min)than using the process increasing cooking time(hydrolysis time 40min with cooking time 100 min).Comparably,the propotion of cellulose with logMw<4.55 increased nearly 2 times.For the NS-KP process,the effect of the hydrolysis time was more significant than that of alkaline charge on cellulose molecular weight,for the same kappa number about 11.For the traditional KP process,the cellulose with high molecular weight began to degrade as the alkaline charge was higher than 21%.Considering the variation of pulp performance and chemical consumption,the alkaline charge should be 17%-19%,21%-23%and 19%-21%respectively for S-KP process,KP process,and NS-KP process.Basis on above research,this paper established the online detection model of pulp kappa number for three different pulping process,the linear relation(R2)between the measured and predicted values were higher than 0.98.Finally,this paper chose three kinds of unbleached pulp,with closed kappa number(11)to conduct the ECF bleaching.The selected dosage of chemicals was as followed:chlorine dioxide of 1.9%on D0 stage,hydrogen peroxide of 0.5%on the stage of alkali treatment enhanced with H2O2,and chlorine dioxide of 0.38%on D-stage.After each bleaching stage,the lower kappa number and viscosity,the higher brightness,higher a-cellulose,higher Fock's reactivity,and narrower cellulose molecular weight distributio were obtained.Using the oprimal pulping process(S-KP),the dissolving pulp was with an a-cellulose of 96.89%,a brightness of 89.48%ISO.Moreover,the Fock's reactivity of dissolving pulp reached to 50.06%on the premise of obtaining very high viscosity up to 986.73mL/g.