Modification of SAPO-34 Adsorbent for Separation of CO2 from Natural Gas at Low Pressure; Effects of Acidity, Ion Exchange and Si/Al Ratio

Among the various processes for the separation of impurities from natural gas, adsorption by solid adsorbent because of the simplicity of the process, low cost and also capability to achieve the high purity gas, have been considered. The SAPO-34 adsorbent as a molecular sieve has pores the same as CO2 and larger than CH4, so this causes high CO2 separation from the natural gas. In this study, SAPO-34 has been modified by H3PO4 at various operating conditions in order to maximize removing of carbon dioxide from the natural gas. Modifications can change the Si/Al ratio of SAPO-34 that is leading to a change in the acidity of adsorbent via the ion exchange process. These changes have been analyzed by various techniques such as EDX, SEM, XRD, and BET. The effects of temperature and pressure on separation have been verified at 5, 20 and 35 °Ϲ and 3, 5 and 7 bar, respectively. The results indicated that by increasing pressure and decreasing temperature, the amount of adsorption is increased, but at very low temperatures and very high pressures, this trend was slightly reversed. Finally, by applying the design of experiments the temperature of 17.4 ºC and pressure of 4.6 bar represented the highest yield for removing CO2 from natural gas (95%).