A novel FTIR method for studying mixed gas adsorption at low concentrations:: H2O and CO2 on NaX zeolite and γ-alumina

The modeling and measurement of mixed gas adsorption at low concentrations (ppm level) is an important part of the design of an adsorptive purification process, but has received little attention so far. This work introduces a new technique for the measurement of the equilibrium adsorbed amounts of a multicomponent mixture of gases/vapors on an adsorbent pellet based on Fourier-transform infrared spectroscopy (FTIR). The technique consists of first calibrating the infrared absorption peak areas with known adsorbed amounts of the different components in the adsorbate mixture using single gases/vapors. By measuring the IR peak areas of the adsorbates on the sorbent in contact with the gas mixture, the actual amounts of the sorbate can be determined. The method is fairly simple, quick, and accurate even at low concentrations provided the adsorbates exhibit strong distinct peaks and the sorbent is at least partially infrared-transparent. The utility of this method is demonstrated by measuring the binary gas adsorption of CO2 and H2O-vapor at low concentrations on two adsorbents: 13X (NaX) zeolite molecular sieve, and gamma -Al2O3. In the low CO: concentration range, the amount of CO2 adsorbed seemed to be significantly enhanced in the presence of H2O in trace amounts. The adsorption data was fit to the Doong-Yang potential theory model, and the ideal (and real) adsorbed solution theory (IAS) of Myers and Prausnitz. with the Dubinin-Astakhov equation as the basis. (C) 2001 Elsevier Science Ltd. All rights reserved.