CO2 selective adsorption from CO2/CH4 mixtures and regeneration of X zeolites by Li and K modification using various regeneration strategies

Natural gas purification before liquefaction necessitates the use of efficient adsorbents with high selective CO 2 adsorption and easy regeneration. Because of its efficiency and ease of operation, the ion exchange is widely employed to adjust zeolites’ CO 2 adsorption. However, few in-depth mechanistic studies have been undertaken on cation substitution regulation of pore structure and gas–solid interaction, as well as their synergistic effects on CO 2 selective adsorption and zeolite regeneration. In this study, we synthesized Li + and K + -modified 13X and examined their material characteristics, thermodynamics, adsorption kinetics, and the adsorption–desorption performance under various desorption methods. The results showed that the variation in pore structure and gas–solid interaction with cation radius is non-monotonic, resulting in 13XLi and 13XK having better CO 2 selective adsorption than 13X. All zeolites are extremely stable after 10 adsorption–desorption cycles in each regeneration setting. 13X outperforms 13XLi and 13XK in CO 2 desorption at 30 °C, owing to its large non-micropore volume and low gas–solid interaction. 13XK has the lowest CO 2 desorption rate at low temperature but the highest at high temperature, owing to the flat micropore distribution and the progressive gas–solid interaction. Approximately 100 % regeneration of 13XK is achieved with CH 4 purging (150 mL/min) at 150 °C, owing to its smallest cumulative pore volume at 0.5 nm. This research could help to develop efficient cation-modified X zeolites for CO 2 deep removal from CH 4 streams prior to liquefaction, as well as advance the in-depth understanding of cation substitution mechanisms.