Study On The Coupling Of Char Pyrolysis And Coal Catalytic Depolymerization For Increase Of Tar

Coal tar is the liquid product produced by coal pyrolysis,and it is an important chemical raw material.Nowadays,tar is still important or even only source of aromatic compounds and heterocyclic compounds with heteroatoms such as nitrogen,sulfur or oxygen.Tar is widely used in agriculture,industry,defense,civil industry and so on.In recent years,with the profound transformation of energy structure and increasingly serious environmental problems in China,the clean and efficient utilization of coal is of great importance in the strategic safety of energy supply and building the resource conserving and environment-friendly society.Therefore,the technology of tar from coal pyrolysis is a very economic and society–effective technology route.For traditional tar from coal pyrolysis technology,such as coal hydropyrolysis,the high cost of pure hydrogen atmosphere and the complex operation and equipment for this process seriously restrict its industrial operation.Based on it,our research group proposed a new coal pyrolysis process containing hydrogen generating from the reaction of char at relatively high temperature under the condition of coal-char coupling.The effect of this process on coal pyrolysis was studied.This paper firstly investigated the pyrolysis experiments of char from preliminary studies under high temperature with catalyst.The results showed that the catalyst can promote the cracking of oxygen containing functional groups in char and generated more gaseous oxygenates such as H₂O,CO,CO₂,and promoted the thermal condensation reaction of char,so that the output of H₂and CH₄ increased significantly.Then the coal-char coupled pyrolysis in different bed temperatures and hydrogenation pyrolysis at different hydrogen concentrations of Inner Mongolia lignite were investigated.The experimental results showed that:in the coupled pyrolysis process,the degree of char polycondensation increased with the increase of char bed temperature,so more active hydrogen was beneficial to stabilize the free radical fragments produced by coal pyrolysis,thus increasing the yield and light degree of tar.Content of phenol,benzene and naphthalene compounds substituted side chain increased in tar from this process,which maybe caused by the opening of large aromatics under the action of active hydrogen.The active hydrogen and small volume hydrocarbon free radicals can stabilize tar precursor fragment reducing the combination of tar fragments and char fragments,so the yield of char decreased,the degree of polymerization of char increased,In the process of hydrogenation pyrolysis of Inner Mongolia lignite,with the increase of hydrogen concentration,the tar yield was increased,the yield of the char was gradually reduced,the content of light components in tar is increased and the content of heavy components was reduced,It showed that the increase of hydrogen concentration can increase the conversion of coal and promote the degree of light quality of the obtained tar.After adding the catalyst ZnCl₂,in the process of coupled catalytic depolymerization,the experimental results showed that:the catalyst made the coal tar yield increase further during the coupled pyrolysis process,and the water yield increased obviously.The yield of the char further reduced,which indicated that the conversion of coal was increased by the catalyst.The results of hydrogenation catalytic depolymerization showed that after adding catalyst ZnCl₂,the tar yield was further increased and the yield of the char was reduced,which indicated that catalyst can improve the conversion of coal pyrolysis in hydrogen.The results showed that coal-char coupled pyrolysis for improving tar yield and quality was an innovative and promising coal pyrolysis technology.