Synthesis And Modification Of SAPO-47/SAPO-34 Intergrowth Molecular Sieves And Their Application In MTO Reaction

Ethylene and propylene are important chemical raw materials,and in recent years the demand is rising year by year.However,with the depletion of oil resources,it is urgent of finding an alternative to oil energy.China is rich in coal resources and the coal price is low,also the methanol synthetized by coal is oversupply,so the technology of methanol to olefin has become a a very important alternative to oil route.In the reaction of methanol to olefin,catalyst is the most important.The mainly used catalyst is ZSM-5,SAPO-34,SAPO-18,SSZ-13,etc.However,at present all the catalysts are easy deactivation by carbon deposition,and have a short catalytic lifetime.In order to improve the catalytic activity and prolong the life of catalyst,we get the research results are as follows:1)SAPO-34?SAPO-47 and SAPO-47/SAPO-34 intergrowth molecular sieves were prepared by one step crystallization method and the catalytic performance was investigated by methanol to olefin reaction?MTO?.The MTO results showed that SAPO-47/SAPO-34 intergrowth molecular sieves synthesized by one step crystallization has the highest selectivity of ethylene,good selectivity of ethylene and propylene and long catalytic life.2)Hierarchical porous SAPO-47/SAPO-34 intergrowth molecular sieves were prepared by alkali treatment and one step synthesized by PEG2000.Trough MTO reaction,the catalytic results showed that the hierarchical porous SAPO-47/SAPO-34intergrowth molecular sieves has longer catalytic life than SAPO-47/SAPO-34intergrowth molecular sieves.And the catalytic life of hierarchical porous SAPO-47/SAPO-34 intergrowth molecular sieves synthesized by one step crystallization is longer than that prepared by alkali treatment.The catalytic life of hierarchical SAPO-47/SAPO-34 was 720 min which 2 times as the life of SAPO-47/SAPO-34 intergrowth molecular sieves.3)The hierarchical porous SAPO-47/SAPO-34 intergrowth molecular sieves was modified by lithium acetate,and applied it in MTO reaction.The catalytic results showed that the ethylene selectivity was decreased,but the propylene selectivity was greatly increased when the hierarchical molecular sieves was modified by Li.And the most important thing is that the selectivity of ethylene and propylene is the same as before modified while the catalytic life was prolonged by 2 times and reached1260min.4)The cause of catalyst deactivation were analyzed.The byproduct of methanol to olefin reaction was analyzed by GC-MS/MS,and the deactivated molecular sieves were characterized by FT-IR and NH₃-TPD.The results showed that for the small pore molecular sieves such as SAPO-34 and SAPO-47,methane and ethane were easily produced as the byproduct and the component of the carbon deposition was small molecular weight aromatic.As for hierarchical SAPO-47/SAPO-34 and Li doped hierarchical SAPO-47/SAPO-34,C₄⁺?C₅⁺?C₆⁺were easily produced as the byproduct and the component of the carbon deposition was big molecular weight aromatic.