Capacity and kinetic measurements of methane and nitrogen adsorption on H⁺-mordenite at 243–303 K and pressures to 900 kPa using a dynamic column breakthrough apparatus

Abstract

A dynamic column breakthrough (DCB) apparatus was used to measure the capacity and kinetics of CH₄ and N₂ adsorption on zeolite H⁺-mordenite at temperatures in the range 243.8–302.9 K and pressures up to 903 kPa. Equilibrium adsorption capacities of pure CH₄ and pure N₂ were determined by these dynamic experiments and Langmuir isotherm models were regressed to these pure fluid data over the ranges of temperature and pressure measured. A linear driving force-based model of adsorption in a fixed bed was developed to extract the mass transfer coefficients (MTCs) for CH₄ and N₂ from the pure gas experimental data. The MTCs determined from single adsorbate experiments were used to successfully predict the component breakthroughs for experiments with equimolar CH₄ + N₂ gas mixtures in the DCB apparatus. The MTC of CH₄ on H⁺-mordenite at 902 kPa was 0.013 s⁻¹ at 302.9 K and 0.004 s⁻¹ at 243.6 K. The MTC of N₂ on H⁺-mordenite at 902 kPa was 0.011 s⁻¹ at 302.9 K and 0.005 s⁻¹ at 243.5 K. The values of the MTCs measured for each gas at a constant feed gas flow rate were observed to increase in a linear trend with the inverse of pressure. However, the apparent MTCs obtained at the lowest pressures studied (≈105 kPa) were systematically below this linear trend, because of the slightly longer residence time of helium in the mass spectrometer used to monitor effluent composition. Nevertheless, the pure fluid dynamic breakthrough data at these lowest pressures could still be reasonably well described using MTC values estimated from the linear trend. Furthermore, the results of dynamic breakthrough experiments with mixtures were all reliably predicted using the capacity and MTC correlations developed for the pure fluids.