(672h) a New Experimental Technique for the Study of Gas Permeation of Binary Mixture

It is well known that the gas permeation follows the mechanisms of ‘sorption-diffusion’ in microporous inorganic membranes and ‘solution-diffusion’ in polymeric membranes. ^1,2 However, the traditional experimental technologies for investigating those diffusion/permeation processes, such as diffusion cell, are costly, difficult to operate (e.g. using GC or MS for the composition analysis of permeate), and prone to experimental errors (e.g. the use of helium as the sweeping gas as down-stream, which may cause back-diffusion to upstream).

In this study, we proposed and validated a new experimental technique for effective study of such processes. Binary gas permeation (Helium and CO₂) were measured on a Carbon Molecular Sieve Membrane (CMSM) derived from Kapton polyimide at 700. The transient permeation time lag and steady state permeation fluxes were measured for the binary mixture as well as for each pure gas component.

It was found that the proposed method, which can readily condense the CO₂ component into solid phase via a physical/nondestructive method, offers the good advantages over the traditional methods, by revealing the ‘true’ permeation behavior of each component in the binary mixture. The method can provide us with deep insight into the gas permeation processes together with the Maxwell-Stefan theory. The figure below shows the permeation data of one set of He-CO₂ mixture.

 

Figure 1. The pressure of binary permeated side against time by using a new method.

Key words: Time lag; adsorption; diffusion; permeation; gas mixture

1. Koresh, J. E.; Soffer, A., Mechanism of permeation through molecular-sieve carbon membrane. Part 1.-The effect of adsorption and the dependence on pressure. Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases 1986, 82 (7), 2057-2063.

2. W.J. Koros, et al, Polymeric membrane materials for solution-diffusion based permeation separations, Progress in Polymer Science, 13, 1988, 339-401