Separation Of Poplar Hemicellulose And Purification Of Xylo-oligosaccharides In The Pre-hydrolysis Liquor

Efficient separation and conversion of lignocellulosic materials is an effective method to achieve utilization of lignocellulosic materials,which is the inevitable trend of the social development.In the traditional process of pulping and papermaking,cellulose and part of hemicellulose in the raw materials were utilized,and the majority of lignin and part of hemicellulose were degraded and then combusted in alkali recovery system as garbage,which caused the waste of fiber resources and the pollution of environment.In this paper,pre-extracting hemicellulose from poplar chips by pre-hydrolysis with hot water was carried out.And the pre-hydrolysis liquor?PHL?with rich hemicellulose sugars was purified to remove contaminants,then the purified hemicellulose was applied to prepare functional xylooligosaccharides.Efficient use of components will be achieved by this method.The results will provide theoretical basis and technical support for the high value utilization of lignocellulosic materials.In this paper,the dissolution of carbohydrate components and the changes of acid-soluble lignin,acetic acid and aldehydes with the P factor were studied in the pre-hydrolysis process under different conditions.The results indicated that the optimum range of P factor was from 685 to 1225,under which the hemicellulose in poplar can easily be dissolved,and the total xylosugars yeild was 51.8%.The content of xylose,acid soluble lignin,acetic acid,furfural were proportional to the increase of P factor,while the content of xylo-oligosaccharides was increased and then decreased with the increase of P factor.When the P factor was 717,the content of xylo-oligosaccharides reached the maximum of 10.24 g/L,the total xylosugars yeild was 44.2%,and the content of xylose,acetic acid,furfural and other non-sugar were lower.And it was beneficial for the subsequent separation of xylose and xylo-oligosaccharides to obtain functional products,especially xylo-oligosaccharides with degree of polymerization in range from 2 to 6(XOS_DP2-6).In order to purify the xylosugars in the PHL at the P factor of 717,the activated carbon?AC?was applied for purification of PHL.The effects of adsorption time,the dosage of AC,and pH value of the PHL on the lignin removal and total xylosugars loss were discussed.The mechanism of lignin removal and the adsorption behavior of the lignin onto AC surface were explored.The results showed that the adsorption between AC and lignin was mainly affected by the electrostatic interaction between AC and lignin.The adsorption of lignin on the surface of AC greatly fit to heterogeneous adsorption.When AC adsorption process conditions were conducted at pH of 3.6 and 0.8%of activated carbon for 10 min,the lignin removal was 57.3%,and the total xylosugars loss was only 3.1%.The PHL after treatment of AC?AC-PHL?was treated with laccase combined with AC treatment.The effects of laccase dosage,treating time,treating pH,treating temperature and activated carbon dosage on the elimination of lignin were discussed.The results showed that the removal of lignin was 70.2%and the total xylosugars loss was 3.7%in the AC-PHL when 0.6%of AC was added and laccase treatment was conducted at 45°C,pH of 3.6 and laccase dosage of 1 U/g for 2 h with.After purification with AC,laccase and AC treatment,the final lignin removal was significantly increased to 87.3%,and the total xylosugars loss was 6.7%.A combined treatment of calcium hydroxide?CH?followed by activated carbon?AC?were experimented to purify PHL.The effect of Ca?OH?₂ and AC dosage were analysed.The results showed that the lignin was removed by forming lignin-calcium complexes and absorption onto CH particles.Furfural and lignin in PHL were efficiently removed,while content of acetic acid increased,and the total xylosugars was unchanged.The pH during the AC treatment process had significant influence on the adsorption efficiency of lignin onto AC,a high AC dosage will adsorb more XOS_DP>6 than XOS_DP2-6.The optimal conditions of combined treatment were of 0.6%Ca?OH?₂ dosage,0.4%of AC dosage and pH of 5,in which 67.7%of lignin,70.1%of furfural removals and 5.9%of total xylosugars loss were achieved.A combined treatment of laccase and xylanase treatment were empolyed to further purify CH-PHL.The effects of laccase treatment,xylanase treatment and laccase assisted xylanase treatment on the lignin removal and the yield of XOS_DP2-6were discussed.The results showed that laccase combined with xylanase treatment had better effect than single laccase or xylanase treatment,which can effectively removed lignin and improved the content of XOS_DP2-6 and the removal efficiency of lignin in subsequent AC treatment.The optimal conditions of laccase combined with xylanase treatment were laccase dosage of 1 U/g,xylanase dosage of 2 U/g,55°C,3h and pH 5.5,in which the removal of lignin was 51.8%and the content of XOS_DP2-6increased by 40.3%based on the original PHL,and here the XOS_DP2-6 accounted for66.5%of the total xylose content in original PHL.After the treatment of the laccase combined with xylanase,activated carbon was efficient to remove the lignin and furfural.Result showed that,after the combined treatment process of calcium hydroxide,laccas,xylanase and activated carbon treatment,the removal of lignin and furfural were 80.1%and 94%,respectively,and the content of XOS_DP2-6 increased by 37.8%which accounted for 65.3%of the total xylose content in original PHL.