Study On Purification Of Eucalyptus Pre-hydrolysate And Pyrolysis Kinetics Of Subsequent Kraft Pulping Black Liquor Solid

Aiming at the problem that it is difficult to improve the purity of xylo-oligosaccharide prepared from the hydrolysate of dissolved pulp,eucalyptus wood chips were extracted from the source to investigate the influence of wood extracts in hydrolysate on the purity of xylo-oligosaccharide.Xylo-oligosaccharides in hydrolysate were purified by flocculation,adsorption and other technologies,and the process conditions were optimized to ensure the yield of xylo-oligosaccharides and remove lignin and other impurities.Finally,the effects of different pretreatment processes on the pyrolysis kinetic characteristics of the subsequent pulping black liquor solid were studied,in order to provide theoretical support for the corresponding black liquor combustion control.Firstly,the eucalyptus wood chips were pre-extracted with benzyl alcohol,and then the pre-hydrolysate was prepared by hot water pretreatment.Then the effects of benzyl alcohol extraction on the contents of lignin,furfural,hydroxymethylfurfural(HMF),xylo-oligosaccharide and total sugar in the pre-hydrolysate were contrastive analysis.At the same time,the influence of different sizes of wood chips on the contents of phenyl alcohol extract and pre-hydrolysate was also considered.The results showed that the total dissolved solids(TDS)in the pre-hydrolysate after the benzyl alcohol extraction decreased obviously,while the content of acid-soluble lignin increased,and the purity of xylose,xylo-oligosaccharide and total sugar increased.The smaller the size of wood chip,the higher the content of phenyl alcohol pre-extraction,the higher the purity of xylo-oligosaccharide and total sugar in pre-hydrolysate.Secondly,Ca O and PAC were used to purify the pre-hydrolysate in the purification process,to study the content changes of lignin,furfural,HMF,xylo-oligosaccharide and total sugar..The results showed that the purification effect of Ca O was better than that of PAC.When the dosage of Ca O was 1.5%,the purification effect was the best,the lignin removal rate reached 47.6%,the purity of xylo-oligosaccharide and total sugar were35.64% and 68.58%,respectively.Ca O powder combined with activated carbon was used to treat the prehydrolysate.The effects of the amount of activated carbon on the contents of lignin and furfural in the prehydrolysate were studied.The results showed that the removal rates of lignin,furfural and HMF were 80.75%,97.71% and 74.81%,respectively,and the purities of xylooligosaccharide and total sugar were 31.48% and 71.03%,respectively,when the amount of activated carbon was 1.0%.The effects of static adsorption and dynamic adsorption on the contents of lignin,furfural,HMF,xylose oligosaccharide and total sugar in the pre-hydrolysate were analyzed by using macroporous resin.The results showed that in the static adsorption process,when the adsorption time was 60 min,the purity of xylo-oligosaccharide and total sugar were28.36% and 57.36%,respectively,and the highest purity of xylo-oligosaccharide was achieved at this time.In the process of dynamic adsorption,the maximum purity of total sugar was 54.64% when the sample volume was 30 m L.When the injection volume was45 m L,the highest purity of xylo-oligosaccharide was 31.51%.Finally,the eucalyptus wood chips treated with different pretreatment conditions were processed by sulfate cooking,and the pyrolysis kinetics of the obtained black liquor was studied.The study showed that after the kraft cooking,the pulp yield of the pre-hydrolyzed wood chips was lower than that of the raw wood chips,and the solid content of the black liquor decreased.Through black fluid dynamics analysis:The pyrolysis of black liquor solid is generally divided into four stages: water evaporation stage;Organic cracking stage;Further decomposition and carbonization stage of polymer compounds;Alkali salt melting decomposition stage.The reaction order in the main area of pyrolysis of organic matter in black liquid solid is 4.After the pre-hydrolysis of black liquid solid,the activation energy increases and the frequency factor decreases.