Synthesis Of High Performance SAPO-34 Molecular Sieve And Study On Its Performance Of Methanol To Olefins

Ethylene production is a measure of the level of industrial development in a country.At present,the production of ethylene mainly depends on non-renewable petroleum resources,and the ethylene output obtained from petroleum cannot meet the needs of the current market.Methanol is renewable,the source is wide,and the price is low.The methanol to olefin（MTO）can solve the problem of olefin shortage.SAPO-34 has suitable medium-strong acidity and unique pore structure of SAPO-34,which exhibits good low-carbon olefin selectivity in MTO reaction and is the best choice for MTO reaction catalyst.However,the single-pass catalytic life of SAPO-34 in the MTO reaction is short,and the catalyst needs to be continuously recycled.Therefore,increasing the single-pass reaction life of SAPO-34 becomes the key to large-scale industrial production of methanol to olefin.In this experiment,a series of SAPO-34 molecular sieves were synthesized by hydrothermal method in hydrothermal reactor and seed crystal assisted hydrothermal method using silica sol and phosphoric acid as silicon source and phosphorus source.The effect of templating agent type,aluminum source,crystallization time and seed morphology existsto the physicochemical properties of the synthetic molecular sieve was researed.The synthesized samples were characterized by XRD,SEM and NH3-TPD.The experimental results show that in the hydrothermal reactor,the pseudo-boehmite is used as the aluminum source,and TEA&TEABr and TEAOH are used as template to crystallize at 170°C for 72 h,which can synthesize small-sized flaky acidity and mild SAPO-34molecular sieves.In the hydrothermal reaction tube,the crystallization time can be shortened to 12 h at 200°C.Crystallizated in the hydrothermal reaction tube,additing a certain amount of crystallization residue or seed soaking solution can greatly increase the yield of SAPO-34,and the yield of the product synthesized by the conventional seed method is increased by about 20%.The atomic utilization rate of the reactants is greatly improved,and the amount of experimental waste liquid is reduced.In this experiment,methanol was used as raw material to evaluate the MTO reactivity of the synthesized SAPO-34 molecular sieve on a continuous fixed bed reactor.The results show that under the conditions of 450°C,0.2 MPa and 2 h^-1,the yield of diene in the MTO reaction of SAPO-34 synthesized by TEA&TEABr as template and hydrothermal reactor is 85.34%,and the catalyst life is 360 min.The hydrothermal reaction tube is used as the crystallization container,and the molecular sieve prepared by adding the seed soaking solution has a yield of84.34%diene and a catalyst life of 380 min.Therefore,the hydrothermal reaction tube is used as the crystallization container,TEA&TEABr is the template,and the SAPO-34 sample with a certain concentration of seed soaking solution is synthesized with higher diene selectivity and reaction life,and its crystallization time is shorter.The product has high yield and is a catalyst with high potential industrial value.