Adsorption of methane and ethane in zirconium oxide pillared clays

In zirconium oxide pillared clays (A(BET) similar to 266 m(2) g(-1)), prepared with clays from different sources, the adsorption of pure methane and ethane, the more abundant hydrocarbon components of natural gas, were determined in the temperature range between 215 and 293 K up to the atmospheric pressure. The Langmuir model and the vacancy solution theory (VST) of Suwanayuen and Danner were used to fit the experimental data. As expected, the VST model leads to a better adjustment. The parameters obtained with this model were used to predict the binary adsorption isotherms. The data Predicted for mixtures were consistent with the experimental results obtained in the same volumetric apparatus used for the adsorption of pure components, analysing by gas chromatography the evolution of the fluid phase until the attainment of equilibrium. The results reveal a higher affinity towards ethane. The equilibrium selectivity towards ethane decreases when temperature and pressure increase, ranging from more than 100, at the lowest temperatures and pressures studied, to 3-4 near ambient temperature and atmospheric pressure. Even in the latter, less favourable situation, which in fact corresponds to the more usual working conditions, the phase diagram, predicted by the VST model indicates that the studied zirconium pillared clays are promising materials for ethane/methane separation. (C) 2001 Elsevier Science B.V. All rights reserved.