Removal Of Lignin From Pre-hydrolysis Liquor By Enzyme/Chemical Catalyzed Polymerization

Pre-hydrolysis of lignocellulose materials at high temperature with hot water before pulping is an important step for wood biomass refining.The pre-hydrolysis liquor(PHL)obtained by hot water pre-hydrolysis is rich in organic substances such as hemicellulose sugars,lignin.The carbohydrates in PHL can be used for production ofvaried high value-added products,but the lignin in PHL hinders the separation and purification of carbohydrates.Therefore,the removal of lignin from PHL is significance for the effective utilization of carbohydrates.In this paper,horseradish peroxidase/hydrogen peroxide(HRP/H₂O₂)and sodium molybdate/hydrogen peroxide(Na₂Mo O₄/H₂O₂)/systems were used to treat PHL,respectively,and the effects and the principle of the two systems on the removal of lignin from PHL.HRP was used to treat PHL,and the treatment conditions for lignin removal were optimizied.The combined processes of HRP and Ca²⁺were proposed and evaluated.The results show that the suitable conditions for lignin removal from PHL by HRP treatment are:HRP 1200-1500 U/L,p H 6.0,H₂O₂1.0 g/L,6 hours,and 25-35°C.After treatment of PHL at the suitable the 39%-43%of thedissolved lignin in PHL is removed.The results demonstrate synergy between HRP and Ca²⁺in lignin removal from PHL.HRP treatment in the presence of 60 mmol/L of Ca²⁺resulted in a lignin removal of 64.8%accompanied by a saccharide loss of 14.2%.HRP catalyzed both the polymerization and depolymerization of the lignin in the PHL.The HRP-catalyzed lignin polymerization rendered some lignin insoluble enabling it to be directly removed.The HRP-catalyzed depolymerization of lignin decreased its molecular weight with an evident increase in its carboxyl content.The insoluble complexes formed between the lignin with carboxyl and the Ca²⁺facilitated the removal of the depolymerized lignin.Na₂Mo O₄/H₂O₂was also used to treat PHL,and the conditions for removing lignin from PHL were optimized.The effects of combined processes of Na₂Mo O₄/H₂O₂treatment followed by polydiallyldimethylammonium chloride(PDADMAC)treatment,acidification or Ca²⁺treatment on lignin removal were studied.The results show that the suitable Na₂Mo O₄/H₂O₂treatment conditions for lignin removalfrom PHL are:Na₂Mo O₄dosage of0.25 g/L,p H 3.8,H₂O₂dosage of 2.0 g/L,treatment time of 1h at 70-90?.After treatement under optimized conditions,the dissolved lignin is 34.0-39%,respectively.The weight-averaged molecular weight(Mw)of insoluble lignin in PHL increases from 1327g/mo L to 1663 g/mo L after Na₂Mo O₄/H₂O₂treatment.The lignin polymerization catalyzed by Na₂Mo O₄/H₂O₂is benefit to the removal of the lignin.For the combined processes of Na₂Mo O₄/H₂O₂treatment followed by PDADMAC treatment,the lignin removal from PHL are 53.2%.In addition,in the combine processes,the sugar loss is less than 6%.The lignin model substance,Guaiacylglycerol-?-guaiacyl Ether(GG),was used to explore the mechanism of HRP treatment and Na₂Mo O₄/H₂O₂treatment for lignin removal from PHL.The results show that HRP treatment of GG can cause thebreakage some?-O-4bond,and then condense to new structures.The new formed condensed structures mainly include?-1,5-5?linkages and C-O linkages.and and Na₂Mo O₄/H₂O₂treatment of GG can also cause the breakage of some?-O-4 bond,and then condense to new structures.The new condensed structures mainly?-5?,?-1,and 5-5?connection.Na₂Mo O₄/H₂O₂treatment also causes the degradation of lignin model.In addition,both HRP treatment and Na₂Mo O₄/H₂O₂treatment can oxidize some aliphatic hydroxyl groups to carboxyl groups,and demethoxylation occurs during the treatments.