Synthesis And Modified Of SAPO-18 Molecular Sieves And Study Of Catalytic Performance In 1-Butene Cracking

All along,olefins especially propylene is important chemical raw material in industry,as the market demand for propylene is growing,while traditional methods for preparing propylene cannot meet the market demand for propylene.In recent years,the craft of butene catalytic cracking for preparing propylene received widespread attention,ZSM-5 zeolite is commonly industrial catalyst used in this craft,however,the yield of propylene is lower,but the yield of polycyclic aromatic hydrocarbons is higher on ZSM-5 zeolite.Therefore,it is meaningful to hunt for a catalyst with a high propylene selectivity for butene catalytic cracking process.SAPO-18 molecular sieves with AEI structure showed good catalytic performance in butene cracking reaction.In this paper,the SAPO-18 molecular sieves have been synthesized by hydrothermal synthesis method,and we further synthesized metal modified MgSAPO-18 and Mg/SAPO-18 molecular sieves,synthesized molecular sieves characterized by XRD,SEM,XRF,TG and NH₃-TPD techniques,and investigated the catalytic performance of the molecular sieves in butene catalytic cracking reactions preparing light olefins.Firstly,we successfully synthesized SAPO-18 molecular sieves by hydrothermal synthesis in this paper.And further study the effect of the crystallization time,crystallization temperature,crystallization way and silicon content on the synthesis of SAPO-18 molecular sieves,the experimental data showed that within scope of the study,the suitable crystallization temperature is 165?,the suitable crystallization time is 72h,the suitable crystallization way is dynamic temperature program crystallization.Under the same reaction conditions,comparing the catalytic properties of SAPO-18 and ZSM-5 found that the selectivity of propylene and P/E of SAPO-18 is better than that of ZSM-5,but the amount of carbon of ZSM-5 is less than that of SAPO-18,these proved that the framework structure is an important factor affecting the catalytic properties of catalyst in butene cracking reaction.Under the same reaction conditions,comparing SAPO-18 molecular sieves with different silicon content found that SAPO-18 with lower Si content presenting better catalytic performance,propylene yield could reach 38.8wt%and propylene selectivity could reach 54.2wt%,these proved that the acid amount is also an important factor affecting the catalytic properties of catalyst in butene cracking reaction.We also modified SAPO-18 molecular sieves using Mg,MgSAPO-18 molecular sieves was synthesized by hydrothermal synthesis and Mg/SAPO-18 molecular sieves was synthesized by dipping,and applied them to butene catalytic cracking reaction.Comparing the catalytic properties of MgSAPO-18 and Mg/SAPO-18,we found that the catalytic performance of MgSAPO-18 is better than Mg/SAPO-18,and the amount of carbon of both is nearly.Comparing the catalytic properties of MgSAPO-18 with better catalytic properties and SAPO-18,we found that the catalytic performance of SAPO-18 is better,and the amount of carbon on MgSAPO-18 is lower.Last,the effect of reaction temperature and reaction space velocity on the catalytic properties of SAPO-18 in butene catalytic cracking reactions and the regeneration properties of SAPO-18 molecular sieves.The result showed that within the scope of our study,the appropriate reaction temperature is 500?,suitable reaction space velocity of 3.5h^-1 and the regeneration properties of SAPO-18 molecular sieves is good.