Influence of pore size of zeolite for CO2 capture

https://doi.org/10.1088/1468-6996/9/1/013007

“The pores size ofzeolites is another factor that might influence the capacity and rate of CO₂ adsorption. In fact, the size of pores must be appropriate to allow to the adsorbed molecules topenetrate within them. The relationship between the CO₂ adsorption capacity of zeolites and the size of their poresdepends particularly of the pressure (loading). Indeed, at low pressures, the density of the adsorbate is highest in the smaller pores while that is higher in larger poresat high pressures [44]. At the low pressures, the adsorbed molecules have the tendency to occupy the positions where the adsorbate-adsorbate interactions are less than the adsorbate-pore interactions, corresponding to the energetically most favorable positions. At high pressures, the adsorbed molecules might occupy the central region of the pores and the increase of their packing leads to the greater density [44–46]. This is corroborated by the fact that the affinity of the zeolite NaA for CO₂ is highest than that of zeolites NaX and NaY (affinity for the CO₂: NaA > NaX > NaY) at low pressures. This might be due in part to small pore diameter of zeolite A [16, 47, 48]. This high affinity of zeolite NaA allows a better selectivity for CO₂ in the presence of N₂ and O₂ than NaX and NaY. Moreover, since the CO₂ can also interact with the pore wall of zeolites, the CO₂ adsorption might be limited by the size of zeolites pores at high pressures because the CO₂–CO₂ interactions might prevent the adsorption of new molecules of CO₂ into the pore wall sites that are thus occupied by other molecules of CO₂ [12, 19, 21]. The shape of pores also seems to be important for the selective adsorption of CO₂. Inui et al [49] have suggested from a study of the CO₂ adsorption on the natural and synthetic zeolites (chabazite, clinoptilolite, clinoptilolite–smectite-Opal C.T., mordenite, ferrierite, mordenite–ferrierite–pielite, erionite, MS-5A,MS-4A, MS-13X, H-ZSM-5), which have different structures, that the zeolites having three-dimensional pore connection structure are more performing for the CO₂ separation.”