Performance evaluation of bimetallic ion exchanged clinoptilolite for potential equilibrium and kinetic adsorption separations of CO₂ from CO₂/ CH₄ mixture

The bimetallic ion exchanged clinoptilolites (M1xM2y-CPs, M1 = Li+, Na+ or Cs+, M2 = Li+ or Cs+, x, and y = the exchange degree of the first and second cation) were prepared. Their physic-chemical parameters were characterized using various methods. The results demonstrated that the relative crystallinity of M1xM2y-CPs gradually decreased with the increase of the secondary cationic introduction. Meanwhile, M1xM2y-CPs presented the surface fractal features, particularly, the values of M1xM2y-CPs were higher than that of single ion exchanged CPs, suggesting that the surface of M1xM2y-CPs was rougher and more disordered. The effects of the type, size, and distributions of the used various cations on the gas adsorption and separation properties were evaluated via their equilibrium adsorbed performances of CO2 and CH4 demonstrate. The results indicated that the CO2 uptake of NaxLiy-CP increased with the increase of Li+ exchange degree, in which, Na67.95Li17.15-CP presented the maximum adsorption capacity of 2.45 mmol/g for CO2. While, the CO2/CH4 selective factors of NaxCsy-CP were around 10.82-12.75 at 273 K and 9.92-12.44 at 298 K, much higher than that of other bimetallic ion exchanged samples. The breakthrough experiments displayed a longer breakthrough time and a stronger CO2 absorption capacity. The cycling tests indicated an excellent CO2 adsorption stability and reversibility. Furthermore, the kinetics adsorption of pseudo-first-order and intraparticle model were used to investigate their adsorption mechanism. Finally, the CO2 adsorption mechanism between the adsorption amount and the average total energy of the CO2 adsorption system was preliminary elucidated using Material Studio simulation software.