Temperature dependence of one-component permeation through a silicalite-1 membrane

The one-component steady-state permeation of gases through a silicalite-l zeolite composite membrane as a function of the temperature is studied from 190 to 680 K for light hydrocarbons, noble gases, and some inorganic gases. In general, with increasing temperature the permeance shows a maximum followed by a minimum. For gases weakly adsorbed the permeance has only a minimum and for gases strongly adsorbed only a maximum is observed in the permeance. The permeance for various,eases, for a feed pressure of 101 kPa, span four orders of magnitude. The lowest permeation is for i-butane at 300 K: a permeance of 0.07 x 10(-8) mol.m(-2).s(-1).Pa-1. The highest value is observed for methane: a permeance of 70 x 10(-8) mol.m(-2).s(-1).Pa-1 at about 240 K. A comparison between the isobars and the temperature dependence of the steady-state permeance, both at 101 kPa, shows that at the temperature where the amount adsorbed vanishes the permeance starts to increase. The temperature dependence of the steady-state fluxes through the silicalite-l membrane can be described only if two diffusion mechanisms are taken into account. For high occupancies the mass transport can be described by equilibrium adsorption followed by surface diffusion and for low occupancies the mass transport can be described by activated gaseous diffusion. With increasing temperature the mass-transport mechanism shifts from the surface diffusion regime to the activated gaseous diffusion regime. With these two diffusivities modeling results agree well with experimental results for the one-component flux through the silicalite-l zeolite membrane.