Evaluation of reproducible high flux silicalite-1 membranes: gas permeation and separation characterization

The permeation of helium, ethane, propane, n-butane, i-butane through a newly developed silicalite-l membrane was performed using by a batch method and a Wicke-Kallenbach (WK) method. This membrane exhibits high flux properties and maintains a good separation selectivity. A procedure is outlined to interpret measured fluxes and estimate the various contributions of transport modes. The experimental fluxes of helium, ethane, propane and n-butane in the batch method could be divided into different parallel contributions, such as surface diffusion, activated gaseous diffusion and viscous flow. The permeation of helium was mostly governed by activated gaseous diffusion at 303-573 K. For adsorbing gases such as ethane, propane and n-butane, surface diffusion was dominant at temperatures up to 393 K. Their permeation mechanism shifted to activated gaseous diffusion with increasing temperature. In the WIC method, both single component measurements and binary mixture separations using n-butane and i-butane were performed in the temperature range of 303-573 K. The selectivity for n-butane in a 1:1 mixture n-butane/i-butane was about 28 up to 400 K, which was higher than the ideal selectivity calculated from the single component measurements because of the competitive adsorption of the butanes. The selectivity of the membrane for n-butane/i-butane mixtures was highly dependent on feed composition and feed pressure. (C) 2001 Elsevier Science B.V. All rights reserved.