Experimental & Theoretical Studies of Selectivity & Heats of Adsorption of Gaseous Mixtures in Zeolites: Effect of Pore Size and Electric Field

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Abstract CTS 9610030 The PIs propose to develop theories of multicomponent adsorption capable of making reliable predictions of selectivity and heats of adsorption. Since reliable experimental data are scarce, the objective of this proposal is to measure thermodynamic excess functions: the excess Gibbs free energy ((Ge) and heat of mixing ((He). The excess Gibbs free energy contains information about adsorbed-phase activity coefficients and the selectivity; the heat of mixing is needed to determine the change in temperature of the system during adiabatic operation of pressure-swing-adsorption (PSA) processes. These excess functions of adsorbed mixtures will be determined with a microcalorimeter which measures simultaneously the selectivity and the individual heats of adsorption of the components of the mixture. Statistical mechanical theories of adsorption lead naturally to the prediction of theoretical values of excess functions. Therefore precise experimental data on selected real measures are desirable as test material against which the usefulness of competing theories can be judged. The systems chosen for initial studies are: 1. CH4 and C2H6 in silicate at low loading. 2. CO2 and C2H6 in NaX. 3. CO2 and C2H4 in NaX. 4. CHF2CHF2 (HFC-134) and CF3CH2F (HFC-134a) in Li, Na, K, Rb, Cs cation-exchanged forms of X and Y zeolites. 5. CH4 and SF6 in cylindrical, one-dimensional pored composed of 10, 12, and 14 membered rings. These five systems were selected to isolate the principal variables which determine selectivity: the pore size and electric field inside the micropores of the zeolite and the polarity, size, and shape of the adsorbate molecules. The significance of the proposed measurements is that they will provide a systematic way of handling the temperature dependence of adsorption of single gases and multicomponent mixtures, which is critical for the design of adsorptive separation processes.