Research On The Production Of Aromatic Hydrocarbons From Catalytic Co-pyrolysis Of Lignin With Hydrogen-donor Reagent

Lignin,the second largest component of biomass,has a unique three dimensional aromatic ring structure and a wide range of sources.Therefore,lignin can be used to produce high-value aromatic chemicals such as benzene and toluene by fast pyrolysis.However,because of the low hydrogen content of lignin and the difficulty of removing the phenolic hydroxyl groups from the intermediates produced in pyrolysis process,the quality of the pyrolysis oil of lignin and selectivity of aromatic hydrocarbon in bio-oil are not high.In this research,black-liquor lignin and its model compounds were used as raw materials to co-pyrolysis with different liquid blends under metal modified catalysts for improving the yield and selectivity of aromatic compounds in pyrolysis products.The co-pyrolysis mechanism was derived to optimize the selection of blends and evolution of catalysts.Firstly,considering the distribution of aromatic products under different reaction temperatures in the prococess of phenethyl phenyl ether?PPE?,700?was selected as the reaction temperature for the co-pyrolysis process of lignin model compounds.The effect of three blends?methanol,diethyl ether and acetone?on the aromatic products during the co-pyrolysis process of lignin model compounds was investigated.It was found that the phenolic compounds was preferably promoted by the addition of methanol due to H·radical from the hydroxyl groups in the methanol preferentially react with PhO·radical in the co-pyrolysis process.The production of aromatic hydrocarbons especially toluene and xylene was promoted by the competitive reaction between CH₃·radical and H·radical from acetone.The functional groups of lignin monomeric model compounds had a significant impact on the type and yield of the thermal decomposition products.p-Xylene was the typical product in the co-pyrolysis of 4-methyl guaiacol and p-cresol while styrene was that of 4-ethyl guaiacol and phenol.Secondly,the co-pyrolysis of monomer model compounds and acetone with HZSM-5 catalyst and different metal modified catalysts?1%Ni/HZSM-5,1%Co/HZSM-5 and 1%Fe/HZSM-5?was investigated to study the effect on the distribution of aromatic compounds.It was found that the promotion of the total yield of aromatic hydrocarbons in different catalyst differed due to the type of model compounds.HZSM-5 catalysts and modified catalysts showed good selectivity to monomeric aromatic hydrocarbons due to the favorable MFI crystal structure.According to the proportion of model compounds in lignin,the selectivity analysis of the main monomer aromatic hydrocarbons benzene,toluene and p-xylene was calculated.It was found that 1%Co/HZSM-5 showed the best selectivity to benzene while 1%Fe/HZSM-5 showed the best selectivity to toluene and p-xylene.The 1%Ni/HZSM-5 catalyst obviously promoted the production of dimmer aromatic hydrocarbons and coke deposition.The small pore volume of 1%Ni/HZSM-5 may hinder the macromolecular compound to enter the internal pores of the catalyst,which increased the formation of dimmer aromatic hydrocarbons,and further coke deposition on the surface of the catalyst.Finally,the better blending agent?acetone?and better selectivity metal?Co and Fe?modified catalyst selected in the co-pyrolysis of model compounds were applied to the black liquor lignin catalytic co-pyrolysis experiments.In the study,the effect of flow rate of the blend acetone and metal load of catalysts on the distribution of the target aromatic hydrocarbons in the pyrolysis products was investigated to select the optimum conditions for co-catalytic pyrolysis of lignin.It was found that the total yield of the main aromatic hydrocarbons produced by the co-pyrolysis of lignin and acetone was the maximun at the acetone flow rate of 0.5 mL/min.Under this flow rate,the formation of aromatic compounds especially the monomer aromatic hydrocarbons from lignin was further promoted under the metal modified catalysts.1%Co/HZSM-5and 5%Fe/HZSM-5 catalysts had the high selectivity to aromatic compounds and the low carbon deposition among the same type metal modified catalysts.