Study On Catalyst Of Methanol To Propylene Reaction In Fixed-bed Reactor

MTP?Methanol to Propylene?process has greatly realistic and strategic significance.As we all know,Propylene is one of the most important organic raw materials for the synthesis of a variaty of important downstream chemical materials,which is mainly produced through oil process.Due to the increasing price of crude oil and the demand of light olefins,methanol to ethylene or ethylene&propylene process has greatly developed in recent years.What's more,coal and nature gas are the main raw material for methanol production,which are plentiful in our country.From the above,develop methanol to propylene process has great significance.In our research first applied HZSM-5?SiO₂/Al₂O₃=38?zeolite as research object.We investigated the effect of reaction conditions,such as reaction temperature,reaction weight space velocity and carrier gas flow rate on the MTP catalytic performance of HZSM-5 zeolite on a continuous fixed bed setup.The experimental result shows that the optimum operational condition is 450°C,WHSV:9.78 h^-1,carrier gas flow rate:20 ml/min.Then we selected the best catalyst support among Kaolin,SiO₂ and Al₂O₃.The final experimental result shows that Al₂O₃ is the most suitable catalyst support in MTP reaction process.Among the alkali and alkaline-earth metals which were used to modify HZSM-5 zeolites to enhance the activity of MTP,Mg modified HZSM-5 had the best catalytic performance.Mg neutralized acid sites which result in the reduction of total acid amount.Mg interacted with strong Br?nsted acid sites formed the ionic structure of Mg?OH?⁺which belongs to Lewis acid site.The increasement of Mg loading amount decreased the Lewis acid sites,total acid content and the relative crystallinity of modified zeolite,as a result,the catalyst activity of modified zeolite decreased.We determined that the optimal loading of Mg species was 4.0wt%,the yield of propylene was 8.83 wt%,P/E was2.07.The introduction of Al₂O₃,can produce mesopores and macropores which are able to reduce the diffusion resistance,and therefore promoting the diffusion of aromatics which are coke precursors,as a result,prolonged the service life of MTP catalyst.We added pore expending agent into Al₂O₃,the pore size and pore volume expended after modification.The stability of catalyst was enhanced,but the reduction of diffusion resistance leaded to the growing of aromatics,which resulted in the decrease of propylene yield.The optimal reaction condition of Mg modified catalyst was as follows:reaction temperature was 500°C,WHVS was 9.78 h^-1,no water in feed,the yield of propylene was 12.10 wt%.Among non-metals which were used to modify HZSM-5 zeolites to enhance the activity of MTP,P and H₄BF₄N?BF?modified HZSM-5 had the best catalytic performance.Introduce P could prevent HZSM-5 from eliminating aluminum and keep well the original crystallites,it showed up as high relative crystallinity.Besides the modulation of acid property,P modification enhanced the shape selectivity of catalyst pore.The optimal loadong amount of P was 6.0 wt%,the yield of propylene was 9.55 wt%.BF formed BF₃,HF species over HZSM-5 after modification,BF₃ belongs to Lewis acid,HF produces both Br?nsted acid and Lewis acid after interacting with HZSM-5 zeolite.New acid sites belongs to weak acid,so the amount and strength of strong acid sites decreased.The optimal loading amount of H₄BF₄N was 4.0 wt%,the yield of propylene was 12.47 wt%.The introduction of Al₂O₃ reduced the total acid amount,resulted in low methanol conversion?97.49 wt%?but high stability.BF species interacted with Al₂O₃ generated strong Br?nsted acid sites,which enhanced hydrogen transfer reaction to a certain extent,leaded to a slight reduction of the yield of light olefins.