HYBRID ADSORPTION DISTILLATION PROCESS FOR SEPARATING PROPANE AND PROPYLENE

The separation of propylene from a propane-propylene mixture by distillation is a energy-intensive process. A hybrid adsorption-distillation system has a great potential in reducing the energy consumption. A significant amount of energy can be saved relative to a process using only distillation, if a typical separation is carried out by distillation up to a propylene concentration of approximately 80% and then continuing the separation of propane from propylene by adsorption. A volumetric adsorption apparatus was designed to obtain the data at high pressures. The pure component data of propane and propylene were obtained on silica gel, molecular sieve 13X, and activated carbon. Although activated carbon has a greater capacity for both propane and propylene than either of the two adsorbents, it was only slightly selective for propylene. Silica gel has the greatest selectivity for propylene, which ranged from 2 to 4. None of the adsorbents was found to be selective for propane. The propane-propylene mixture behaved nonideally on the solid surface as indicated by the negative deviations of activity coefficients. The nonideality of the mixture can be attributed primarily to surface effects rather than to interactions between adsorbate molecules. A binary model has been proposed to predict mole fractions in the adsorbed phase and the total amount adsorbed from the pure component data. The pure component isotherm model of Hines et al. was extended to binary mixtures when the binary model was developed. Excellent agreement was obtained between experimental data and predicted values for mole fractions in the adsorbed phase, the total amount adsorbed, and adsorbed-phase activity coefficients.