Adsorption Kinetics of CO₂, O₂, N₂, and CH₄ in Cation-Exchanged Clinoptilolite

Abstract

The rate of adsorption of pure CO 2 , O 2 , N 2 , and CH 4 on natural untreated clinoptilolite-rich volcanic tuff (Cp) from Tehuacan (Puebla, Mexico), and on cation-exchanged clinoptilolite samples (Ca-Cp, K-Cp, and Na-Cp) has been measured at 20 °C using a glass high-vacuum volumetric apparatus. The X-ray diffraction pattern of Cp showed that the main crystalline phases correspond to clinoptilolite-heulandite and minor amounts of mordenite, cristobalite, feldspar (albite), quartz, smectite, and opal. The adsorption rates of gases in the initial period (t < 180 s) were measured with a custom acquisition data card capable of registering pressure and time data five times per second, simultaneously. The influence of cation exchange on adsorption kinetics of the gases depended on the gas-adsorbent contact time (t). In the initial period, the adsorption rate of all gases on all samples decreased in the order Ca-Cp > K-Cp > Cp > Na-Cp, and the affinity decreased in the order CO 2 . N 2 > O 2 > CH 4 , whereas at equilibrium (t f ∞ s) the adsorption uptake decreased in the sequence CO 2 . CH 4 > N 2 > O 2 . The slow adsorption of methane in Na-Cp was probably due to diffusional difficulties as a result of channel blockage by Na + cations. By cation exchange of Cp an adsorbent can be tailored for the separation of N 2 /O 2 , N 2 /CH 4 , and CO 2 /CH 4 mixtures.

Advances in principal factors influencing carbon dioxide adsorption on zeolites

“…For example, the erionites, mordenites, clinoptilolites and chabazite can adsorb only the molecules which possess kinetic diameter with a maximum of 4.3, 3.9, 3.5-3.8 and 4.3 Å, respectively, indicating that the CO 2 adsorption (diameter = 3.3 Å) is not limited by this steric factor [12,16,43,57]. Moreover, it has been showed by Aguilar-Armenta et al [7] that the require period for reach the middle of the capacity of CO 2 , O 2 or N 2 adsorption on Na-clinoptilolite and Caclinoptilolite is proportional to diameter of the adsorbed molecules (CO 2 < O 2 < N 2 ).…”

“…In this matter, an analysis of the CO 2 adsorption on zeolites KX, BaX and LaX has effectively indicated that the zeolite KX was the most basic among these three zeolites [28]. In contrast, a study of CO 2 adsorption on the clinoptilolite has indicated that the substitution of Na + and K + by Ca 2+ caused a rise of the basicity of the framework oxygen acting as basic center [7]. The basic strength and the capacity of CO 2 adsorption of zeolites might also be increased significantly by occlusion of alkali metal oxides.…”

“…This assemblage gives rise to diverse framework structures including those shown in figure 1. The packing of zeolite structure allows the formation of regular cavities joint by the channels, where the molecules with an appropriate size such as the gas as CO 2 4 tetrahedron by SiO 4 tetrahedron (figure 2) [6,7]. The CO 2 usually undergoes a physical adsorption (physisorption) and chemical adsorption (chemisorption) at the surface of zeolites.…”

Development of an Active Film With Natural Zeolite as Ethylene Scavenger

“…Studies indicate that the generation of negative charge of aluminosilicate minerals is due to the isomorphic substitution between silicon and aluminum atoms. The adsorption properties of gaseous substances depend largely on the exchangeable cations that are much more important for zeolites with a porous structure 23,24) .…”

A Review of Layered Double Hydroxides as Intermediate-temperature CO2 Adsorbents

“…Low-temperature Adsorbents. Low-temperature adsorbents mainly including zeolite based adsorbents [4,5], carbon based adsorbents [6,7] and metal organic framework based adsorbents [8][9][10] always have received extensive attention, especially in recent years. Zeolites are porous crystalline aluminosilicates, whose framework of SiO 4 and AlO 4 joined together in various regular arrangements through shared oxygen atoms.…”