The one-component steady-state permeation of gases through a silicalite-1 zeolite composite membrane as a function of temperature was studied at 190 to 680K for light hydrocarbons, noble gases and inorganic gases (table 29). In general, with increasing temperature, the permeance went through a maximum, followed by a minimum. For gases which were weakly adsorbed, the permeance exhibited only a minimum and, for gases which were strongly adsorbed, only a maximum was observed. The permeance for the various gases, at a feed pressure of 101kPa, spanned 4 orders of magnitude. The lowest permeation was found for i-butane at 300K, with a permeance of 7 x 10−10mol/msPa. The highest value was found for methane, with a permeance of 7 x 10−7mol/m2sPa at about 240K. A comparison of the isobars and temperature dependence of the steady-state permeance, both at 101kPa, showed that - at the temperature where the amount adsorbed vanished - the permeance began to increase. The temperature dependence of the steady-state fluxes through the silicalite-1 membrane could be explained only if two diffusion mechanisms were taken into account. At high occupancies, the mass transport could be described by equilibrium adsorption followed by surface diffusion and, at low occupancies, the mass transport could be described as activated gaseous diffusion. With increasing temperature, the mass-transport mechanism changed from a surface diffusion regime to an activated gaseous diffusion regime. Upon assuming these two diffusivity models, the results agreed well with experimental results for the one-component flux through the silicalite-1 membrane.

Temperature Dependence of One-Component Permeation through a Silicalite-1 Membrane. W.J.W.Bakker, L.J.P.Van Den Broeke, F.Kapteijn, J.A.Moulijn: AIChE Journal, 1997, 43[9], 2203–14

Table 29

Permeation Parameters for Silicalite-1