Critical Admission Temperature of H2 and CH4 in Nanopores of Exchanged ERI Zeolites

Abstract

Due to the nanoporous nature of zeolitic materials, they can be used as gas adsorbents. This paper describes the effect of critical admission temperature through narrow pores of natural ERI zeolites at low levels of coverage. This phenomenon occurs by adsorption of CH4 and H2 on pores in natural erionite. The zeolite was exchanged with aqueous solutions of Na+, Mg2+, and Ca2+ salts at different concentrations, times, and temperatures of treatment. Experimental data of CH4 and H2 adsorption were treated by the Langmuir equation. Complementarily, the degree of interaction of these gases with these zeolites was evaluated by the evolution of isosteric heats of adsorption. The Ca2+ and Mg2+ cations favor the adsorption phenomena of H2 and CH4. These cations occupy sites in strategic positions Ca1, Ca2, and Ca3, which are located in the nanocavities of erionite zeolites and K2 in the center of 8MR. Following the conditions of temperature and the exchange treatment, ERICa2 and ERINa3 samples showed the best behavior for CH4 and H2 adsorption.

Crystal Chemical and Structural Characterization of Natural and Cation-Exchanged Mexican Erionite

“…Notably, no Fe was detected in the fibers, in agreement with previous results obtained on erionite fibers from Oregon, USA [36,37]. On this basis, the presence of Fe previously detected in the sample by X-ray fluorescence spectroscopy may be attributed to impurity phases [38], possibly clays.…”

“…Pristine erionite has been labelled ERIN (N = natural). The porosity and the adsorption capacity of CO 2 , CH 4 and H 2 from both pristine and ion-exchanged samples were evaluated in previous works [38,42]. Results showed that ERINa3, EriCa2 and EriMg2 samples (see Supplementary Materials) have the best textural properties and adsorption capacity compared to the ion-exchanged analogue ones.…”

“…In recent years, several studies have been published aimed at describing the crystal chemical characteristics of fibrous erionite samples from the typical localities [34][35][36][37] as well as on cation-exchanged samples. Mexican erionite from Agua Prieta, Sonora has already been characterized from a morphological, thermal and textural point of view [11,38]. In fact, this zeolite has been studied for industrial applications in gas and liquid adsorption processes [39][40][41].…”

“…In fact, this zeolite has been studied for industrial applications in gas and liquid adsorption processes [39][40][41]. Specifically, the selected erionite samples, both pristine and ionic exchanged, occupied in the present investigation were studied by Hernandez and Quiroz in CO 2 [42] and CH 4 [38] adsorption processes at zero degrees of coverage where the interactions between cations in the zeolitic cavities and gas molecules are more representative. According to the data reported, the main variations in CO 2 adsorption occurred in the ERINa3 (0.155 mmol/g) and EriCa2 (0.11 mmol/g) and ERIMg2 (0.05 mmol/g) samples compared to the pristine ERIN sample (0.08mmol/g) at a temperature of 473 K and 10 mm Hg of pressure.…”