Experimental investigation of CO2 separation by adsorption methods in natural gas purification

CO2 separation for natural gas purification by the adsorption method was studied in detail using volumetric adsorption apparatus. The crystalline phase and microstructure of the experimental sample were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Micromeritics ASAP 2020 instrument. The XRD pattern proves that the experimental sample consists of 13X zeolites. The SEM images show that the 13X zeolites expose a large number of micro-channels on the surface of the particles. The microporous volume is 0.22 cm3 (STP)/g. The ideal swing frequency for the adsorption tank can improve the adsorption performance of an adsorbent compared with a static adsorption tank. The pure CO2 adsorption experimental data agrees well with the extended Langmuir model. The Langmuir-Freundlich model correlates the CO2/CH4 mixture adsorption experimental data fairly well. The relative errors between the simulated results and the experimental data are very little, which indicates that these fitted models are correct. The average selectivity of CO2/CH4 in a static and swing adsorption tank are, respectively, 3.57 and 3.93, considerably higher than 1, indicating preferential CO2 adsorption over CH4 in CO2/CH4 mixtures. This also shows that the swing can improve CO2 separation for natural gas purification. For the three types of motion status, the temperature of the adsorption tank increased in the order swing 2 > swing1 > static state for pure CO2 adsorption in 13X zeolites. The temperature variation decreased as the pressure increased. The amplitude and time of temperature variations in the adsorption tank can explain the adsorption capacity and adsorption speed. This research will improve the efficiency of offshore natural gas exploitation, and will affect the optimization of energy structures.