Effects Of Different Systems On The Product Distribution Of Lignin Depolymerization

Lignin is a kind of unqualitative aromatic polymers present in woody plants,the molecular structure contains phenylpropane and its derivatives,it is the main ingredient of almost all terrestrial plant cell walls.The lignin is treated by combustion to recover heat that used to generate steam and generate electricity in the paper production process.It cause great waste of resources.Lignin is the only material containing benzene ring in the regenerated plants.Therefore,it is necessary to break down lignin into aromatic platform molecules.This will reduce the dependence on oil will have important practical and far-reaching significance.In recent years,more and more researches have been made on the use of lignin depolymerization with different catalysts at high temperature.In many studies,supercritical depolymerization is highly efficient,The production of bio-oils and biochemicals can be product by depolymerization of biomass.The lignin is subjected to directional depolymerization by the addition of different catalysts.Based on the background above,the research content of this paper includes the following three aspects:(1)Preparation of hydrotalcite-like catalyst and ZSM-5 molecular sieve catalyst.(2)Preparation of poplar ethanol pulp lignin.(3)The effects of supercritical catalytic depolymerization of lignin under different catalytic systems were studiedExperimental results show:(1)The reaction of water and formic acid in the reaction system is helpful to improve the yield of phenol in the product.The molecular weight of the depolymerized product is small,Formic acid acts as a capping agent in the reaction,Repolymerization is unlikely to occur.(2)The specific surface area of hydro talc ite is the largest when n(Ni2+)/n(Mg2+)=1/4;When n(Ni2 +)/n(Mg2 +)>1/4,the hydrotalcite structure is destroyed.With the increase of n(Ni2+)/n(Mg2 +),the content of total phenol in the depolymerization product tends to rise,Especially in the Nil/4MgAl conditions,the total phenol achieve the highest yield,and have the highest ratio of hydroxyphenyl type products and the strongest deoxidation capacity.(3)With the increase of Si/Al ratio,the ZSM-5 zeolite particles became larger,the specific surface area increased first and then decreased,and the total phenol content increased first and then decreased,When the Si/A1 ratio is equal to 350,the specific surface area is the largest,the total phenol content is the most,and the demethoxy effect of the catalyst is the most obvious.(4)Lewis acid and Bronsted acid have different contributions to lignin catalytic depolymerization.Lewis acid affects the depolymerization yield,which is the active center of lignin catalysis?The free hydrogen in the Bronsted acid is subjected to hydrodeoxygenation with the methoxy group on the benzene ring,it can effectively inhibit the occurrence of repolymerization.The different forms of A1 in the catalyst directly affect the degree of lignin depolymerization.