| BTX is an important basic raw material for petrochemical industry.They mainly come from the aromatics reforming unit of refining and chemical industry.The technology of making full use of abundant sources of toluene and methanol as raw materials to produce xylene has good market value and application prospects.How to affect the alkylation reaction path and product distribution through the acid-base differential regulation and surface functional modification of the catalyst is a hot spot in research and development in recent years.This article first selects a ZSM-5 molecular sieve with a silicon-aluminum ratio of 50 as the toluene methanol alkylation catalyst,and changes the properties of the acidbase sites of the catalyst by acid modification,alkali modification,and metal oxide modification of the molecular sieve.To achieve the regulation of product distribution;Secondly,XRD and NH3-TPD were used to study the change of acidity of molecular sieves by different modification methods;ZSM-5 molecular sieves were further applied to the alkylation reaction of benzene/xylene and methanol to investigate the catalysis Performance and product distribution.The result obtained are summarized as follows:1.Select HZSM-5 molecular sieve as catalyst,the conversion rate of toluene reaches 59.5%,the selectivity of xylene is 62.5%,which is significantly better than 13X and NaY molecular sieves,and HZSM-5 molecular sieve with a silica-to-aluminum ratio of 50 is more conducive to occurrence Alkylation on benzene ring.2.Modification with basic oxides reduces the acidity of HZSM-5 molecular sieves,which is beneficial to increase the selectivity of xylene and inhibit the formation of heavy aromatics,but does not promote the conversion of toluene.3.The acid oxide used for the modification partially covered the surface of the HZSM-5 molecular sieve,and the acidity was significantly reduced.It also showed a decrease in toluene conversion and an increase in the selectivity of xylene,and it was related to the weak acidic and medium acidic sites of the catalyst.4.The acidity of HZSM-5 molecular sieve catalyst modified with noble metal or non-noble metal oxide is significantly reduced,but the conversion rate of toluene remains unchanged.The selectivity of xylene in non-noble metal oxide-modified catalysts is increased to more than 70%.Its mechanism needs to be further explored.5.Iron-molybdenum composite double metal oxide modified molecular sieve has good catalytic activity,the conversion rate of toluene is 58.5%,and the selectivity of xylene is 64.6%.Further applied to the alkylation reaction of benzene with methanol,the conversion rate of benzene 57.1%,the total selectivity of toluene and xylene can reach 90%,which is comparable to the data reported by industry. |
