Adsorption equilibrium of methane and carbon dioxide on zeolite 13X: Experimental and thermodynamic modeling

Abstract

A static, volumetric method has been used to determine the adsorption equilibrium of CH4 and CO2 and their binary mixtures on 13X molecular sieves at various temperatures between 273 and 343K. Pressures for the pure component data extend up to 10bar, while all binary data were obtained at 4bar and 6bar. The measured pure isotherms were regressed using different isotherm equations and the regressed parameters were applied to different thermodynamic models such as ideal adsorbed solution theory (IAST), vacancy solution theory (VST) and real adsorbed solution theory (RAST). CH4/CO2 system that deviate from ideality is not well represented by IAST and VST, whereas RAST which include activity coefficient in the adsorbed phase as characterizing parameter for non-ideality, show a much better representation of the binary equilibria. Experimental selectivities CO2/CH4 range from 26 to 2 at different pressure and temperatures. It is concluded that zeolite 13X suitable for natural gas industrial separation with yCO2<0.2 at 303K and 4bar. For landfill gas upgrading, where yCO2<0.45, zeolite 13X can be successfully applied at 303K, 4bar and 303K, 6bar and 323K, 4bar.