Study For Promoting SAPO-34 Molecular Sieve Preparative Technology And Its Effect On Conversion Of Chloromethane To Light Olefins

Methane by halogen methane process to produce light olefin avoids the high energy consumptive way of methane prepared syngas process. This technology is simple, and has high selectivity for light olefins, thus becomes a hotpot of research on new technology to produce light olefins. In order to provide basic data for the study and development for SAPO-34 catalytic conversion of chloromethane to light olefins, this paper on the basis of the research of the established work in our team, from three aspects to enhance catalytic properties of SAPO-34 molecular sieve in conversion of chloromethane to light olefins, such as the preparation of SAPO-34 molecular sieve factors, improve the diffusion properties of the catalyst and optimizing acid strength of the catalyst.Firstly, SAPO-34 molecular sieve were synthsized by hydrothermal synthesis method. Template and silicon content affectting the physical and chemical properties of SAPO-34 molecular sieve was studied. Meanshile, the performance of the SAPO-34 molecular sieve catalytic chloromethane to light olefins were investigated. The results show that the samples synthetic with TEA or TEAOH as template agent as catalyst is beneficial to propylene generated, and the deactivation rate slow. The samples synthetic with MOR and DEA as template agent as catalyst has high initial conversion rate of chloromethane, but deactivation rate fast. With the ratio of SiO2/Al2O3 increased in synthetic materials, the acid strength of SAPO-34 molecular sieve were enhanced, the chloromethane conversion rate increased, but the secondary reactions such as hydrogen transfer enhanced, resulted to decrease of light olefin selectivity decreased. T=450℃, WHSV=1.89h-1, the initial chlromethane conversion can reach 85%, the catalyst life time was about 3h.Secondly, the small size of SAPO-34 molecular sieve was prepared by co-templates or seed crystal assisted method, and as catalyst to the conversion of chloromethane to produce light olefins.The result shows that small size of SAPO-34 molecular sieve catalytic chloromethane presented a relatively stable catalytic activity, and the hydrogen transfer reaction in the reaction process was suppressed, catalyst deactivation rate slower than conventional SAPO-34 molecular sieve, light olefin selectivity increased. Mesoporous SAPO-34 molecular sieve were synthesized by hydrothermal synthesis method with HTAB as multilevel channel template. It was presented more stablility and high catalytic activity in the conversion of chloromethane to light olefins. The main product selectivity was remained. The carbon deposition on the mesoporous SAPO-34 molecular sieve was reduced by 25%.The SAPO-34 was modified by impregnation method over metallic salt solutions. 425℃,WHSV=1.89h-1, the initial chlromethane conversion can reach 85%, the catalyst life time was about 6h while the selectivity of main products invariable in chloromethane conversion. The selectivity of ethylene and propylene were closed to 40%. The stability of modified SAPO-34 was reduced with the increasing impregnation time.