Interfacial permeation phenomena of hydrogen purification and carbon dioxide separation in a non-isothermal palladium membrane tube

Hydrogen can be purified and carbon dioxide can be separated from their gas mixtures in a palladium (Pd) membrane tube. To figure out the hydrogen permeation characteristics in a non-isothermal Pd membrane tube, a numerical method is developed. The influence of the Reynolds numbers at the retentate and permeate sides, the temperatures of feed gas and sweep gas, and the H-2 concentration in the feed gas on the interfacial H-2 permeation and H-2 recovery are analyzed. The results indicate that the minimum H2 partial pressure difference and permeation rate along the membrane surface develops, as a consequence of competition between the membrane permeance and the H-2 partial pressure difference. A dimensionless mass transfer parameter (xi), which is a non-dimensional driving force ratio between H-2 diffusion in the gas phase and H-2 permeation across the membrane, is conducted to aid in illustrating the mass transfer characteristics along the membrane surface. The xi curve is insensitive to the Reynolds numbers, but depends significantly on interfacial temperature and H-2 inlet concentration. When the H-2 inlet concentration is low, all H-2 in the feed gas can be recovered and the minimum distribution no long appears. This also implies that all CO2 is separated. (C) 2016 Elsevier B.V. All rights reserved.