Permeation of compressed and supercritical fluids through porous membranes

For the permeation of compressed and supercritical fluids through porous membranes, the investigation on major influence factors and process modeling is essential. The permeance of helium, nitrogen and carbon dioxide at various temperature, pressure and pressure difference was measured at first. A new model equation was developed by modifying the two-term dusty-gas model. The variation of viscosity with pressure, especially in the near-critical region where the possible abnormal change of viscosity with pressure may exist, was considered in the model development. The results of experimental measurement and theoretical analyses show that the permeation of helium in porous membrane agrees well with the two-term dusty-gas model due to its minor change of viscosity with pressure. Whereas, the influence of viscosity change on nitrogen permeation is not negligible in the pressure range of investigation. In the near-critical region, the permeation of carbon dioxide is obviously increased due to its phase transition in membrane pores. However, the modified model is in good agreement with the measured permeance of CO at both low-pressure and high-pressure regions.