Selective Separation Of Lignin In Hydrolysate Of Poplar

Energy crisis and environmental pollution promote the utilization of biomass which is sustainable and abundant.Biomass materials mainly consist of three components: cellulose,hemicelluloses and lignin,which can be used as raw materials for various bioproducts.Recently,pulp mills have become a significant platform of biorefinery.The prehydrolysis of wood prior to kraft cooking has been deemed as a significant facet for the biorefinery of forest biomass.Hot water can solubilize the majority of hemicelluloses and result prehydrolysis liquor(PHL)containing large quantities of hemicelluloses derived saccharides(HDSs)and non-saccharide compounds(NSCs)derived from lignin depolymerization and carbohydrate degradation.HDSs in PHL can be converted to many high-value products,such as xylitol,ethanol and food additives.The residual wood solid of hydrolysis still can be applied to dissolving-grade pulp.The whole process fits well with the concept of biorefinery.The selectivity of activated carbon(AC)towards to NSCs was studied in the process of HDSs purification.The presence of a substance in PHL may promote or weaken the adsorption of another substance,which affects the kinetics of adsorption and adsorption selectivity.In this paper,adsorption selectivity of AC towards to HDSs and NCSs were measured.The adsorption isotherms showed the priority of NSCs to be absorbed over HDSs at low AC level.However,high amount of AC made adsorption non-selective due to competitive adsorption between NSC and HDSs.The limited selectivity suggested that AC adsorption is infeasibility for HDSs purification,but applicable as a pretreatment method.A combined process including lime treatment and mixed bed ion exchange resin was employed to purify HDSs.In this paper,the optimized conditions of lime treatment were explored and breakthrough curves for non-saccharide organic compounds(NSOC)and HDSs on ion exchange resin were painted.The results showed NSOC removal was up to 44.2% with negligible HDSs loss,which is the optimized condition.The breakthrough curves of NSOC and HDSs showed selective retention toward NSOC,leading to 75% HDSs recovery with 95% purity at 17 bed volumes of exchange capacity.In addition,macroporous resin showed higher exchange capacity than gel resin as indicated by the triple processing volume.The remarkable selectivity of the combined process suggested the feasibility for HDSs separation fromPHL.In order to make use of HDSs effectively,the lignin in PHL must be removed on the basis of minimal HDSs loss.Lignin is mainly classified into three parts:macromolecular lignin,amphoteric lignin derivatives,and small lignin molecules.Lignins with different molecular weight need specific methods to remove.A variety of combined processes were explored to remove NCSs on the awareness of separation mechanism.A combined process consisting of lime treatment,resin adsorption,and gel filtration was proposed to separate HDSs from NSCs.The results showed that the macro-lignin impurities that accounted for 32.2% of NSCs were removed by lime treatment at 1.2% level with negligible HDSs loss.The majority of NSCs,lignin-derived phenolics,were eliminated by mixed bed ion exchange resin,elevating NSCs removal to 96.1% and lignin-derived phenolics removal to 88%.Gel filtration was applied to eliminate the remaining lignin,furfural and hydroxymethyl furfural(5-HMF)and obtained high purity oligosaccharides.