The Determination of Multicomponent Mass Transport Processes for Adsorptive Environmental Applications

The study of the kinetics of competitive adsorption of multicomponent gaseous mixtures on a solid adsorbent is important for a range of practical adsorptive processes. One such environmental application is carbon capture and storage (CCS), which includes the use of geological CO₂ storage methods as well as the pre-combustion capture of CO₂ from syngas and post-combustion separation from flue gases. The former includes the storage of CO₂ in depleted oil and gas reservoirs and coal seams; the latter uses one of a number of methods, including adsorption, to separate gaseous CO₂ from multicomponent gas flows. The kinetics of adsorption of CO₂/CH₄, CO₂/H₂ and CO₂/N₂ mixtures are of fundamental importance to the practical application of these CCS technologies, but their determination is practically challenging. Therefore, in this work we introduce a method in which flowing multicomponent gas mixtures such as these can be varied to within a mass flow accuracy of ±1% and the time-dependent displacement of one species by another measured with high accuracy. The displacement is determined by combining the gas composition signal from a close-coupled quadrupole mass spectrometer with the integration of the inlet and outlet mass flow rates. The technique is demonstrated by the data presented here on the time-dependent displacement of N₂ by CO₂ in Na-X zeolite at ambient temperature. Using the same apparatus equilibrium uptake isotherms are determined and the isosteric enthalpy of adsorption calculated from data measured at multiple temperatures.