Adsorption separation of CO2/CH4 gas mixture on the commercial zeolites at atmospheric pressure

Abstract

In this work, six kinds of the commercially common zeolites (NaX, CaX, NaA, CaA, ZSM-5 and Y) were selected as candidate for separating CO2 from CH4. In to study adsorption behavior of all zeolites and screen excellent adsorbents, adsorption experimental of pure gases was performed. NaX had the greatest adsorption amount of CO2 at 0.1MPa, and CaX had the highest affinity of CO2. The selectivity predicted by IAST model was 76 for NaX at 0.1MPa, yCH4=0.5, and 74 for CaA at 0.1MPa, yCH4=0.9. These two zeolites with excellent separation performance had been used for subsequent experiments about the effect of moisture and desorption. The moisture tremendously weakened separation performance of zeolites, and the pre-drying of zeolite and pre-dehydration of gas mixture is an essential step. The thermal desorption was more suitable for the regeneration of NaX and CaA than the vacuum desorption, and the CO2 adsorbed on zeolites could be wholly desorbed at 300°C. From the study of the adsorption heat and IR spectrum, we found that the adsorption of CO2 on NaX and CaA is a physical adsorption process in our experimental condition (atmospheric pressure and room temperature), because carbonate species have not been found in the zeolites after adsorbing CO2.