The sorption equilibrium of CO2 and CH4 in binderless beads of 13X zeolite was investigated between 313 and 373K and pressure up to 4 atm. The amount adsorbed of CO2 and CH4 was around 5.2 and 1.2mmol/gads, respectively, at 313K and 4atm. Comparing these values with the ones in literature the value of CO2 was 20% higher than in CECA 13X binder pellets. It was also found that isotherms were 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 11.1mmol/gads.atm for CO2 and 0.45 to 0.27mmol/gads.atm for CH4 between 313 and 373K, respectively. The heats of sorption at zero coverage were 43.1kJ/mol for CO2 and 9.2kJ/mol for CH4. The sorption kinetics was investigated by the zero-length column technique. Recipes to analyze zero-length column desorption curves in pellets of adsorbents were reviewed and it was 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) was calculated directly. Based upon such criteria it was shown that crystal diffusivity of CO2 in 13X could be measured macroscopically by ZLC, being the same measurement for CH4 practically impossible. The crystal diffusivity of CO2 measured experimentally was 5.8 x 10−15 and 1.3 x 10−15m2/s at 373 and 313K, respectively. These values were 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.

Sorption and Kinetics of CO2 and CH4 in Binderless Beads of 13X Zeolite. J.A.C.Silva, K.Schumann, A.E.Rodrigues: Microporous and Mesoporous Materials, 2012, 158, 219–28

Table 4

Self-Diffusion in Type-13X Zeolite