The Preparation And Preparation Of Core-shell Catalyst For Synthesis Of Light Olefins From Syngas

Light olefins are the most fundamental and the most important basic feedstocks in chemical industry,and they are mainly derived from naphtha steam cracking present.China is a country with abundant coal,but deficient gas and oil resources;Thus utilization of coal,natural gas and biomass instead of crude oil to produce light olefins is of great strategic significance to avoid dependence on imported crude oil.In this paper,Fischer-Tropsch catalyst with core-shell structure prepared by combining Fischer-Tropsch iron catalyst and SAPO-34 sieve used in methanol-to-olefins reaction,which can convert syngas to light olefins directly by outer layer's catalytic cracking sites.SAPO-34 molecular sieve was synthesized by static hydrothermal method.The effects of the silica-alumina ratio and water on the structure and acidity of the synthesized molecular sieve were investigated.Studies have shown that as silica to alumina ratio of the synthesis liquid increased within a certain range,the crystallinity,specific surface area,average pore size,and acid amount of strong acid and weak acid increase.When the content of water in the synthetic liquid increases,no significant texture property change,but its acid amount increased.When the ratio of silica to alumina in the synthetic liquid is 0.6 and the water to aluminum molar ratio is 60,the best SAPO-34 molecular sieve sample was prepared.The prepared SAPO-34 molecular sieve was then coated on the surface of the iron-based Fischer-Tropsch catalyst by physical adhesion to obtain a core-shell structure catalyst.The method successfully prepared a well-coated and uniformly distributed molecular sieve shell layer.No cracks and pinholes were observed on the surface of the sample as proved from electron microscope data.A series of core-shell structure catalysts were then prepared with various promoters in the core layer iron-based catalyst.The effects of core-shell structure and promoters on catalytic performance were investigated at 325 ? and 1.0 MPa.The SAPO-34 molecular sieve was coated on the surface of the Fischer-Tropsch synthesis iron catalyst by dip coating,to prepare a core-shell Fe@SAPO-34 catalyst.Influence of the dip coating times and the ratio of dipping solution on the performance of the catalyst was investigated in the reaction conducted at 325 ?,1.0 MPa,4.5 SL·h^-1·g?cat?^-1,and synthesis gas H₂/CO was 1.0.