Adsorption isotherms of carbon dioxide and methane on CHA-type zeolite synthesized in fluoride medium

High-silica CHA-type zeolite was synthesized in fluoride medium using fumed silica as silica source. Adsorption isotherms of CO₂ and CH₄ were measured over pressure range of 0–1100 kPa and at temperatures of 298, 323, 353, and 393 K. The isotherms follow a typical Type-I shape according to the BDDT classification. All adsorption isotherms are well described by Langmuir, Toth and Sips isotherms. Adsorptive performance of the zeolite was compared with other CHA-type zeolites, i.e. SAPO-34, Si-CHA and SSZ-13 using ideal adsorption solution theory. The modeling results revealed that the zeolite has a high CO₂/CH₄ selectivity, e.g. 6.70 for an equimolar mixture at 298 K and 100 kPa. Isosteric heats of adsorption for both CO₂ and CH₄ were reasonably constant (20.6 and 24.1 kJ mol⁻¹ at loading of 0.02 mol kg⁻¹ for CH₄ and CO₂, respectively) showing that the adsorbent is energetically homogenous.