Synthesis And Modified Of SAPO-34 Molecular Sieves And Research On Adsorption And Separation Of CH₄/CO₂

Many natural gas produced contains a large amount of CO₂,which seriously affects the use of natural gas.Therefore,the separation of CO₂ from natural gas is of great significance to improve the calorific value and use of natural gas.This paper introduces common methods of CO₂ separation,such as membrane separation,chemical absorption,adsorption,etc.Among them,adsorption method is the most promising method for CO₂ separation due to its advantages of low energy consumption,simple equipment,easy operation and small pollution.The SAPO-34,modified SAPO-34 molecular sieves and SAPO-34/18 intergrown zeolites have been synthesized by hydrothermal synthesis method,and the synthesized molecular sieves were characterized by XRD,SEM,and NH₃-TPD techniques and so on.The adsorption properties of the synthesized adsorbents for CH₄/CO₂ adsorption separation were compared.Firstly,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 adsorbents.H⁺is the charge center of CO₂ adsorption,so it affects the adsorption performance.The sample synthesized with TEA had the most amounts of acid and the strongest acid.Therefore,the amount of H⁺achieves the most,the amount of CO₂ adsorbed achives the most and the adsorption performance is the best?the adsorption amount is 1.16 mmol/g,and the selectivity is 46.98?.The sample synthesized with DMCHA had the least amount of acid and the weakest acid.Therefore,the amount of H⁺achieves the minimum,the amount of CO₂ adsorbed achieves the minimum,and the adsorption performance is the worst?the adsorption amount is 0.33mmol/g,and the selectivity is 26.73?.And in this paper,the physical structure of the synthesized SAPO-34 molecular sieve and SAPO-34/18 intergrown zeolite sieve were analyzed and applied to the adsorption and separation of CH₄/CO₂.It was found that SAPO-34 molecular sieve was cubic crystal morphology and SAPO-34/18 intergrown zeolite was a plate-like morphology.The acidity of the two molecular sieves is extremely different,so the amount of H⁺and the adsorption amount of CO₂ are extremely different.SAPO-34 molecular sieve has good adsorption performance,while SAPO-34/18 intergrown zeolite hardly adsorbs CO₂.We used impregnation and hydrothermal synthesis to modify SAPO-34 molecular sieves with cerium and manganese respectively.The modified samples were applied to the adsorption and separation of CH₄/CO₂.By comparing SAPO-34 with the impregnated samples,it was found that,within a certain range,the adsorption performance increased with the increase of Ce and Mn load.When the load is 1%,the adsorption effect of molecular sieve is obviously higher than that of unmodified molecular sieve.When the metal load is increased to 5%,the adsorption effect of molecular sieve is better.However,when the metal load continues to increase to 10%,the molecular sieve adsorption performance decreased.SAPO-34 molecular sieves modified by different metals have different adsorption effects.The adsorption effect of Ce impregnated zeolite is higher than that of Mn impregnated SAPO-34 zeolite.By comparing the sample of SAPO-34 and hydrothermal synthesis modification,it was found that the sample acidity changed significantly after hydrothermal synthesis modification.At the same time,it was also found that the adsorption performance of adsorption separation CH₄/CO₂ was related to strong acid acidity.The stronger the acidity was,the more H⁺was.Compared with different modification methods,hydrothermal synthesis method can improve the adsorption performance more than immersion method.The adsorption performance of Ce modified adsorbents is greater than that of Mn modified adsorbents by either immersion method or hydrothermal synthesis method.