Synthesis And Modified Of SAPO-34 Molecular Sieves And Study Of Catalytic Performance In 1-butene Cracking

Propylene is one of the most important basic chemical raw materials.Traditional methods for producing propylene cannot meet the market demand for propylene as the demand for propylene derivative products has maintained strong growth.In recent years,the craft of butene catalytic cracking for preparing propylene received widespread attention.As the core of butene catalytic cracking reaction,the choice of catalysts becomes the focus of the research.SAPO-34 molecular sieves with CHA structure showed good catalytic performance in butene cracking reaction and exhibited high propylene selectivity.In this paper,the SAPO-34 and modified SAPO-34 molecular sieves have been synthesized by hydrothermal synthesis method,and the synthesized molecular sieves were characterized by XRD,SEM,and NH3-TPD techniques and so on,and we investigated the catalytic performance of the molecular sieves in 1-butene catalytic cracking reactions.Firstly,we synthesized SAPO-34 molecular sieves successfully by hydrothermal synthesis in this paper.And we studied the effect of the silicon content on the synthesis of SAPO-34 molecular sieves,the experimental data showed that the acid properties were influenced by the silicon content,the higher the silicon content,the stronger the acid.The conversion of 1-butene on catalysts increased with the silicon content.However,the selectivity of propylene decreased as the silicon content increased.The catalyst which had lowest silicon content exhibited highest propylene selectivity.And we used different types of template to synthesized SAPO-34 molecular sieves to study the effect of the template type on the synthesis of SAPO-34.The ability to introduce silicon to the skeleton of molecular sieves and the various types of template have a strong correlation,which affects the acid properties of the catalysts.The sample synthesized with TEA had the most amounts of acid and the strongest acid while the sample synthesized with DMCHA had the least amount of acid and the weakest acid.The sample synthesized with TEA exhibited the highest conversion of 1-butene and the lowest selectivity of propylene during the catalytic cracking reaction.The sample synthesized with DMCHA exhibited the lowest conversion and the highest selectivity of propylene during the reaction.We used impregnation and hydrothermal synthesis to modify SAPO-34 molecular sieves with cerium and manganese respectively.The modified molecular sieves were characterized by XRD,SEM,and NH3-TPD techniques and so on.And the samples were used in 1-butene catalytic reaction to test the catalytic performance.Analyzing the experimental data of SAPO-34 and the impregnated samples,we found that the amount of acid decreased and the acid strength weakened after impregnation.And the conversion of the samples impregnated with metal and its weak acid strength had a positive correlation.The stronger the weak acid was,the higher the conversion was.And the propene selectivity was related to the ratio of the amount of strong and weak acid,the higher the ratio,the lower the selectivity,which showed that strong acid isn't beneficial to the production of propene.The two rules had no connection with the types of metal.And we found the effect of cerium on weak acid is greater while manganese had a larger effect on strong acid.And the acid properties changed a lot after hydrothermal treatment.Comparing the data of SAPO-34 with the modified samples,we found the conversion on catalysts and the propene selectivity were related to the strong acid properties.The stronger the acid was,the higher the conversion was.However,the propene selectivity decreased when the strong acid strength increased,which showed the strong acid doesn't contribute to the production of propene.And manganese had a bigger impact on strong acid.By comparing different methods of modifying,the conversion on samples modified by hydrothermal method is better than that by impregnation,and the catalytic life is longer.The propene selectivity on samples modified by impregnation is higher than that by hydrothermal method when the metal is cerium.And the propene selectivity on samples modified by hydrothermal method is higher than that by impregnation when the metal is manganese.