LIQUID EXPULSION PERMPOROMETRY FOR CHARACTERIZATION OF POROUS MEMBRANES

The processes in a liquid pre-wetted porous membrane are described for the situation when a gradually increasing pressure difference of an i nert gas is imposed across the membrane (liquid expulsion permporometr y). The description takes into account the compressible nature of the gas and the distribution of the pore sizes. By comparing the experimen tally obtained dependence of the gas flowrate through the membrane ver sus the imposed pressure difference (wet curve) it is possible to eval uate the distribution of the fractional membrane porosity (pore-volume distribution) with the pore size. At the same time the ratio of poros ity and tortuosity of transport pores (geometric membrane parameter, p si) is determined. This parameter can be used together with the mean i ntegral pore radius [r] and the mean integral square of pore radii [r2 ] (determined by analysis of the gas flowrate dependence versus deltap for a dry membrane - dry curve) for the prediction of diffusion and/o r viscous flow for any gas or gas mixture under any temperature and pr essure condition. The simulated pore-size distributions are compared w ith the results of the traditional method; it appears that the traditi onal approach leads to systematic deviations in the obtained pore-size distributions.