Adsorption equilibria of CO2 and small hydrocarbons in AEI-, CHA-, SIT-, and RRO-type siliceous zeolites

AEI, CHA, and STT siliceous zeolites and RUB-41 (RRO) were prepared with low concentration of internal silanols and were characterized by X-ray diffraction, N-2 adsorption isotherms, electron microscopy, and Si-29 MAS NMR spectroscopy. Adsorption isotherms of methane, ethylene, ethane, propylene, propane, and CO2 were measured volumetrically on siliceous zeolites AEI, CHA, RRO, and SIT at various temperatures ranging from 273 K to 323 K up to a pressure of 101.3 kPa. The Clausius-Clapeyron equation was used to calculate the isosteric heats of adsorption. The amount adsorbed depends strongly on adsorbate polarizability in the low-pressure region, and on the adsorbent micropore volume in the high-pressure region. Adsorption entropy losses are independent of temperature and increase with increasing adsorption enthalpy. RRO showed the highest pure-component selectivity of CO2 over CH4, and potential for the separation of the natural gas mixtures AEI, CHA, and RRO-type materials showed potential for the kinetic separation of propylene/propane. (C) 2016 Elsevier Inc. All rights reserved.