Comparison between XRF and EPMA applied to study the ionic exchange in zeolites

Zeolites are crystalline aluminosilicates consisting of SiO 4 and AlO 4 tetrahedral as primary units. One peculiar characteristic of zeolites is the ion exchange capacity defined as the capacity to locate specific cations in the framework of zeolites; it depends on the chemical composition and varies with the structure of the zeolite and with the cation nature. This work studies the exchange of the Na + monovalent cation of 5A and 13X synthetic zeolites by the Ca 2+ bivalent cation present in a CaCl 2 solution. X-ray fluorescence (XRF) and electron probe microanalysis (EPMA) techniques were used to determine the cation exchange capacity (CEC). The efficiencies of the two X-ray detectors were compared and the minimum detection limits of the zeolite elements were calculated. Although both techniques differ in the sample excitation mode, the results obtained were compatible. The results showed that the CEC was higher for the 5A zeolite, in agreement with its lower SiO 2 /Al 2 O 3 ratio and its greater BET area. It was also found that the amount of Na + ions exchanged by Ca 2+ ions was in complete agreement with the corresponding molar balance. The determination of the CEC using X-ray spectroscopy techniques can be considered a novelty as XRF and EPMA techniques permit to analyze the sample directly

High-Pressure Methane Adsorption in 5A Zeolite and the Nature of Gas-Solid Interactions

Experimental adsorption isotherms for methane in 5A zeolite over the pressure range 0–5 MPa have been obtained and analyzed using a statistical thermodynamical formulation which relates the observed macroscopic thermodynamic quantities to microscopic gas–solid interactions. The efficiency of the zeolite as a methane storage system has thus been evaluated

High-pressure Methane Adsorption on Natural and Synthetic Zeolites

The adsorption isotherms of methane on synthetic (5A and 13X) and natural (Erionite) zeolites at different temperatures have been obtained through the use of a high-pressure volumetric adsorption apparatus over the pressure range 0–5 MPa. The isotherms have been analyzed on the basis of a statistical thermodynamic adsorption model, variation in the temperature allowing calculation of the isosteric heat of adsorption. The results show that these zeolites are highly efficient for methane storage at moderately low pressure (0.5–1 MPa)

High-Pressure Methane Adsorption on NaX and NaY Zeolites with Different Si/Al Ratios

One method of increasing the storage capacity of compressed natural gas, an alternative for vehicular fuel, is by adsorbing it on to microporous solids such as zeolites or activated carbons. NaX and NaY zeolites with different Si/Al ratios have been synthesized and characterized. Experimental adsorption isotherms for CH 4 on these zeolites have been obtained at different temperatures over a pressure range of 0–5 MPa using a high-pressure volumetric apparatus. Isosteric heats of adsorption have been estimated and the isotherms analyzed applying a statistical thermodynamic model. The efficiency of this solid as a methane storage system has been evaluated and compared with other sorbents. Encouraging results have been obtained