Novel gas chromatographic headspace techniques for measuring Single-component liquid isotherms

In this study, a novel headspace technique, based on liquid calibration, was developed and compared to the standard headspace or vapor calibration technique. The technique was applied for the measurements of single component liquid adsorption isotherms of xylene isomers, ethylbenzene and toluene on a commercial NaX (13X) zeolite. In comparison to the vapor calibration technique, the liquid calibration technique provided more effective means by faster generating liquid isotherms with more accuracy and less computational complexity. The isotherms were measured at 30, 60 and 90 °C using both headspace techniques, and the results were found reasonably consistent. Among the alkylaromatic compounds studied, the NaX zeolite was more selective to toluene and showed the lowest selectivity to m-xylene. In contrast to larger adsorption capacity of toluene compared to ethylbenzene and p-xylene, the isosteric heats of adsorption indicated that ethylbenzene and p-xylene created stronger bonds to the NaX sites. The effects of solute concentration in the liquid phase were investigated with regard to the adsorption capacity and selectivity. The results indicates that the adsorbent selectivity is generally dependent on the concentration of the solute in the solution.