Chromatographic Study on the Adsorption and Diffusion of Light Hydrocarbons in ZSM-5 and USY Zeolites

Single-component sorption/diffusion of methane, ethane, propane, n-butane, isobutane, cyclohexane, and toluene in ZSM-5 and USY zeolites has been measured by a chromatographic method in the temperature range of 373-599 K. It is shown that the adsorption equilibrium constants decreased with the increase of the temperature, while it increased with the increase of the atomic number of carbon in the adsorbate molecule. The adsorption energies increased with the increase of molecular weights of the adsorbate molecules. The adsorption energy follows the order: methane < ethane < propane < n-butane < cyclohexane < toluene. The diffusivities in the micropore were larger at higher temperatures. The diffusivities in the micropore increased with the decrease of critical sizes of adsorbate molecules, for example, ethane > propane > n-butane > cyclohexane > toluene. The diffusion coefficients are found to be influenced by the critical molecular size, electronic effect, and configuration of sorbate molecules. In comparison to the diffusion data in ZSM-5 and USY zeolites, it is confirmed that the zeolite channel also plays a vital controlling/deciding role in the penetration and diffusion.