Study Of Methyl Chloride To Olefins On H-ZSM-35/SiO₂（q） Composite Catalyst

Propylene plays an important role in modern chemical industry.Propylene is the basic raw material of plastics,synthetic rubber and synthetic fibers,and the main raw material of a range of chemicals and fine chemicals in modern chemistry.The level of industrialization in a country is usually measured by the production of propylene.In recent years,with the rapid development of China’s economy and the improvement of people’s living standards and quality of life,people’s demand for propylene and propylene derivatives has also been growing rapidly.Propylene production by traditional process is mainly based on petroleum,obtained by steam cracking and catalytic cracking.This traditional oil route is too dependent on increasingly depleted fossil energy to meet the growing demand for propylene,and the production process is bound to be accompanied by a large amount of energy consumption and the production of a large amount of carbon dioxide.Therefore,under the pressure of the increasingly severe situation of oil energy shortage and the global energy crisis,it is urgent to find alternative energy sources and develop non-petroleum propylene production technology.In recent years,with the steady increase of natural gas exploitation and proven reserves in China,many researchers are engaged in the research of replacing petroleum with natural gas to produce propylene.Among them,the two-step method using methane as raw material to produce propylene from halomethane is an ideal production route for non-petroleum production of propylene,and the reaction of chloromethane to propylene is the key of this route.Firstly,ZSM-35 molecular sieve and ZSM-35/SiO₂（q）composite catalyst were synthesized by static hydrothermal synthesis with pyrrolidine as the structural guide,sodium hydroxide as the base source,sodium metaaluminate as the aluminum source,and silica sol as the silicon source.The effect of crystallization temperature on crystallinity and quartz phase content of ZSM-35/SiO₂（q）composite catalyst was systematically studied by X-ray diffractometer.It was found that the quartz phase content of ZSM-35/SiO₂（q）composite catalyst could be adjusted by changing the crystallization temperature.A single ZSM-35 molecular sieve was obtained when the crystallization temperature was 150℃,160℃and170℃.ZSM-35/SiO₂（q）composite catalysts with different quartz phase contents were obtained at temperatures of 180℃,190℃and 200℃.The ZSM-35/SiO₂（q）composite catalyst after ammonium exchange has better catalytic performance in Me XTO reaction than the single H-ZSM-35molecular sieve.Then,a simple mechanical mixing method was used to physically mix quartz sand with a single H-ZSM-35molecular sieve,and the mechanical mixing SiO₂（q）+H-ZSM-35catalyst was prepared as a reference for SiO₂（q）/H-ZSM-35composite catalyst.The catalytic performance of the mechanically mixed SiO₂（q）+H-ZSM-35catalyst was compared with that of a single H-ZSM-35molecular sieve,and the existence of a special composite phase between the quartz phase SiO₂（q）and H-ZSM-35 in the SiO₂（q）/H-ZSM-35composite catalyst and the synergistic effect between the two phases in the chloromethane propylene（Me XTO）reaction were further investigated.Finally,the 49%H-ZSM-35/SiO₂（q）composite catalyst with good catalytic performance was selected for F modification to explore the influence of F modification on its catalytic performance in Me XTO reaction.F modified partial dealuminization of 49%H-ZSM-35/SiO₂（q）composite catalyst.Partial dealuminization reduced the molecular sieve grain size but did not significantly change the crystallinity and structural properties of 49%H-ZSM-35/SiO₂（q）.Dealuminization also resulted in the reduction of Si-（OH）-Al bridge bond of 49%H-ZSM-35/SiO₂（q）composite catalyst,which significantly reduced its strong B acid content.The strong B acid level is positively correlated with the hydrogen transfer reaction,and its reduction leads to the inhibition of the hydrogen transfer reaction,thereby reducing the selectivity of alkanes and high carbon products,and thus increasing the selectivity of propylene.The experimental results showed that when the concentration of F modified was 0.03M,the catalyst reaction performance was the best,and the conversion rate of chloromethane,propylene selectivity and yield were 85.9%,37.7% and 32.4%,respectively.