Adsorption equilibria and kinetics of propane and propylene in silica gel

Adsorption equilibrium isotherms for propane and propylene on narrow pore s ilica gel (NSG) and wide pore silica gel (WSG) were measured by gravimetry in the temperature range 303-343 K and at pressures up to 101 kPa. The isot herms were correlated by the generalized Dubinin isotherm and Polanyi's the ory. Both adsorbents have a higher affinity for propylene. The loading at 1 00 kPa of propylene is 2 and 0.7 mmol/g on NSG and WSG, respectively. These loadings are 1.5 higher than those for propane with both adsorbents. The h eat of adsorption estimated by the Clausius-Clapeyron equation decreases wi th the degree of coverage. Adsorption kinetics in the same temperature rang e was studied by the zero-length column method using the long time response . The diffusion of propane and propylene in both silicas is controlled by K nudsen diffusion. The pore diffusivities determined in the temperature rang e 303-343 K are 2.4 x 10(-3)-2.8 x 10(-3) and 1.7 x 10(-3)-2.4 x 10(-3) cm( 2)/s for propane and propylene on NSG, respectively. For WSG these values a re 6.4 x 10(-3)-9.9 x 10(-3) cm(2)/s for propane and 6.6 x 10(-3)-12.1 x 10 (-3) cm2/s for propylene. Average tortuosity factors of 2.5 for NSG and 2.0 for WSG were obtained.