Research For Alkylation Of Benzene With Methanol Over Modified ZSM-5and MCM-49

This article mainly includes the synthesis toluene and xylene product by alkylation of benzene with methanol. Two zeolite catalysts of ZSM-5and MCM-49were carried on the modification research, and difference of the alkylation performance between the two zeolites were compared.Using Platinum and Gallium to modify HZSM-5zeolite, the results showed that, certain amount of metal modification could improve shape-selective catalytic ability and the selectivity of objective product. Compared with HZSM-5, Pt/HZSM-5zeolite with loading of0.3%could improve selectivity of toluene from58%to72%, improve total selectivity of toluene and xylene from89%to94%, and descend selectivity of ethylbenzene from2.34%to1.35%. Ga/HZSM-5zeolite with loading of5%could improve conversion of benzene from45%to54%.According to the results of characterizations of XRD, XPS and TPD, the crystal structure of HZSM-5was not destroyed after Platinum and Gallium modification. Acid quantity and strength had been decreased. Ga existed at a high oxidation state form on the surface of zeolite.Compared alkylation performance of HZSM-5and HMCM-49as ratio of benzene and methanol was1:1, the results showed that, in terms of conversion of benzene and selectivity of toluene and xylene, HMCM-49 was better than HZSM-5. Increasing the ratio of benzene and methanol to3:1, selectivity of triethylbenzene had greatly reduced from5.32%to1.24%. Under this suitable ratio of benzene and methamol, studied the influence of reaction temperature and WHSV by single factor experiments, the results showed that WHSV had a more obvious influence on catalytic performance. Reaction temperature of500℃and WHSV=2h"1were determined as the appropriate reaction conditions. Using Platinum, Gallium, Phosphorus and Silicon to modify HMCM-49, the results of evaluation experiments showed that, conversion of benzene increased slightly, however, selectivity of toluene and xylene did not change significantly, and selectivity of ethylbenzene had increased.Using HCl under80℃prepared aluminated HMCM-49catalysts. The results showed that acid treatment could improve the alkylation activity of HMCM-49, conversion of benzene and yield of toluene had been increased, selectivity of objective products had decreased slightly. The aluminated HMCM-49which treated5hours by1mol/L HCl showed a better alkylation performance. Compared with non-treated HMCM-49, conversion of benzene had increased from26%to33%with good stability. Selectivity of toluene and xylene decreased from97%to96%. Besides, there was no propylbenzene in by-product generated. The characterization results showed that, the acid treatment took off a part of the framework aluminum, the crystallinity of zeolite reduced. The aluminated HMCM-49 which treated5hours by1mol/L HCl increased the surface area and pore volume, improved the diffusion properties of the product, increased conversion of benzene while enhancing the stability of the catalyst. Besides, the reduction of B acid and L acid lead to suppression the production of carbon in the reaction process. Also, it played an important role of delaying the deactivation of catalyst.