Study On Coupling Production Of Light Aromatic Hydrocarbons From Methanol/Hami Lignite Pyrolysis Components Catalyzed By Modified HZSM-5

China's low-rank coal reserves account for more than 50%of the country's total proven coal reserves,and its chemical structure has more side chains,higher hydrogen and oxygen content,high volatile matter,high water content,easy to natural,low calorific value.Pyrolysis of low-rank coal is the key direction of low-rank coal utilization.Hydropyrolysis or catalytic hydropyrolysis of coal can increase the yield of tar and the content of light components to some extent.However,due to the high cost of hydrogen production,high requirements on equipment and operation for hydropyrolysis,high price of the catalyst used,and difficulty in recycling,the industrial application is limited.Small molecular alcohol,as a substance with high hydrogen content(H/C_eff=2),can be used as a good hydrogen donor for the catalytic upgrading of biomass pyrolysis components.In this study,methanol was applied in the pyrolysis and quality improvement process of low-rank coal,the directional conversion of methanol and low-rank coal pyrolysis components is used to produce light aromatic hydrocarbons.HZSM-5 is widely used in catalytic conversion of coal or biomass due to its excellent shape selection selectivity and anti-carbon deposition.In this paper,HZSM-5 and modified HZSM-5 were used as catalysts to improve the selectivity of directional conversion of high value-added aromatic hydrocarbon products during coal pyrolysis.In this study,benzyl phenyl ether,catechol and o-ethyltoluene were used as model compounds for coal pyrolysis,and methanol was added during catalytic pyrolysis.The results showed that the addition of methanol promoted the deoxidation of benzyl phenyl ether and catechol,and significantly increased the selectivity of light aromatic hydrocarbons(benzene,toluene,xylene,BTX).However,excessive methanol can lead to the production of polymethylbenzene.However,the products from the co-catalytic pyrolysis of methanol and o-ethyltoluene are mainly trimethylbenzene,with the content up to 80%,which is attributed to the methanol providing methyl group to the system,resulting in methylation reaction of the products,and then producing polymethylbenzene.The coupling reaction between methanol and pyrolysis components of Xinjiang Hami lignite was investigated,which was selected as the representative of low-rank coal.For the convenience of comparison,we first investigated the pyrolysis and catalytic pyrolysis behavior of Hami lignite without methanol in the system.The study showed that the addition of ZSM-5 catalyst could effectively improve the selectivity of pyrolysis product BTX.When methanol is added to the system,the generation of light aromatic hydrocarbons between methanol and lignite pyrolysis components is significantly improved under the action of ZSM-5 catalyst,especially for xylene.Methyl provided by methanol can make benzene and toluene generated during coal pyrolysis to methylation reaction,thus generating xylene.The addition amount of methanol had an optimal value,leading to the maximum selectivity of light aromatic hydrocarbons.However,the selectivity of light aromatic hydrocarbons decreased with the increase of methanol dosage,which was attributed to the deepening of methylation reaction caused by excessive methanol and the generation of a large number of by-products.Further examines the modified HZSM-5 for methanol/metal components of low rank coal pyrolysis of coupling reaction,the results show that metal load in ZSM-5products can significantly increase the selectivity of light aromatic hydrocarbon,oxygen containing compounds have lower at the same time,it is attributed to metal and acid active centers that promote the conversion of hydrocarbons such as dehydrogenation,deoxygenation,cracking,polymerization,cyclization,and aromatization.At the same time,making ZSM-5 into a hollow structure can further improve the selectivity of light aromatic hydrocarbons,which is attributed to the fact that the hollow HZSM-5 also has a mesoporous channel structure,which is convenient for the diffusion of volatiles and prolong the catalyst life.On this basis,the coupling reaction of metal-modified hollow HZSM-5 for methanol/low-rank coal pyrolysis components was further investigated,and the results showed that the modified hollow HZSM-5 significantly increased the yield of BTX in liquid products.