A review of enhancement of lignocellulose enzymatic hydrolysis via hydrogen peroxide pretreatments
In the process of biomass conversion,the intricate structure and the presence of lignin in lignocelluloses hinder the saccharification of carbohydrate components through enzymatic hydrolysis.Pretreatment can remove lignin and destroy the physical and chemical structures of lignocelluloses,thus achieving efficient conversion of biomass to monosaccharide.Hydrogen peroxide is widely used in the pretreatment of lignocelluloses because of its strong oxida-tive degradation ability to lignin.Hydrogen peroxide pretreatment methods mainly consist of hydrogen peroxide-acid,hydrogen peroxide-alkali,and hydrogen peroxide-activator pretreatments.This review summarized the mecha-nism of lignin degradation in these hydrogen peroxide pretreatments.In acidic media,hydrogen peroxide acts as an electrophilic reagent by forming hydronium ion.The aromatic hydroxylation of hydronium ion by substitution/addi-tion reaction is the main reaction for degradation of lignin in acidic media of hydrogen peroxide.In alkaline medi-um,some active reaction substances(hydrogen peroxide anion,hydroxyl group radical,and superoxide anion radi-cal)are formed by the decomposition of hydrogen peroxide.The alkene and carbonyl groups of the side chain of lig-nin can be attacked by those active reaction substances with a nucleophilic reaction.In hydrogen peroxide-activator systems,hydrogen peroxide can be activated by transition metal ions to enhance the oxidation ability of the hydrogen peroxide for the lignin degradation.The improvements of enzymatic hydrolysis of lignocelluloses through hydrogen peroxide pretreatments were summarized.In the hydrogen peroxide pretreatment,hydrogen peroxide-acid pretreat-ment shows the strongest lignin removal ability and the higher improvement on the enzymatic hydrolysis of lignocel-luloses.The main lignin degradation products in hydrogen peroxide pretreatment were organic carboxylic acids and phenolic compounds.The advantages and disadvantages of various hydrogen peroxide pretreatments were compared.The feasibility of various hydrogen peroxide pretreatment methods was evaluated by economic analysis.Hydrogen peroxide-alkali pretreatment shows the lowest economic cost in those three hydrogen peroxide pretreatment methods.Gramineous plants are suitable for hydrogen peroxide-alkali pretreatment and wood materials are suitable for the hy-drogen peroxide-acid pretreatment.Finally,the development trend of hydrogen peroxide pretreatment was predicted and prospected based on the characteristics of these pretreatment methods.The decomposition of hydrogen peroxide,the design of reaction equipment,the safety of pretreatment systems,and the utilization of degradation products of lignocelluloses are the main research directions of hydrogen peroxide pretreatment in the future.In conclusion,hy-drogen peroxide pretreatments with low reagent dose,low temperature,and low system pressure were the main re-search direction of hydrogen peroxide pretreatment in the future.The objective of this work was to comprehensively review various hydrogen peroxide pretreatment methods and offer insights into potential research directions in the field of hydrogen peroxide pretreatment.
hydrogen peroxide pretreatmentoxidation of lignindegradation producteconomic analysisresearch strategy
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维普
