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

Abstract

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.