Sorption and kinetics of CO2 and CH4 in binderless beads of 13X zeolite

The sorption equilibrium of CO2 and CH4 in binderless beads of 13X zeolite has been investigated between 313 and 373 K and pressure up to 4 atm. The amount adsorbed of CO2 and CH4 is around 5.2 mmol/g(ads) and 1.2 mmol/g(ads), respectively, at 313 K and 4 atm. Comparing these values with the ones in literature the value of CO2 is 20% higher than in CECA 13X binder pellets. It is also found that isotherms are pronounced Type I for CO2 and almost linear for CH4. The CO2 isotherms were modeled using a simple deviation from Langmuir isotherm that takes into account interaction between adsorbed molecules at adjacent sites (Fowler model) suggesting a moderate repulsion. Henry's constants range from 143 to 11.1 mmol/g(ads).atm for CO2 and 0.45 to 0.27 mmol/g(ads).atm for CH4 between 313 and 373 K, respectively. The heats of sorption at zero coverage are 43.1 kJ/mol for CO2 and 9.2 kJ/mol for CH4. The sorption kinetics has been investigated by the Zero-Length Column technique (ZLC). Recipes to analyze ZLC desorption curves in pellets of adsorbents are reviewed and it is derived a criteria which indicates that for the sorption rate be measured macroscopically the time of the experiment (that should be above a few seconds) is directly calculated with the following expression: t(0.1) >= 7.02 x 10(-2) r(c)(2)/D-c. Based on such criteria it is shown that crystal diffusivity of CO2 in 13X can be measured macroscopically by ZLC, being the same measurement for CH4 practically impossible. The crystal diffusivity of CO2 measured experimentally is 5.8 x 10(-15) m(2)/s and 1.3 x 10(-15) m(2)/s at 373 and 313 K. respectively. These values are comparable to the ones measured by a frequency response and pulse chromatography techniques reported in literature. The ZLC desorption curves for CH4 were measured under an equilibrium regime. (C) 2012 Elsevier Inc. All rights reserved.