Inhibition Effect of CO on Hydrogen Permeation Through a Pd/Al₂O₃ Composite Membrane: A Comprehensive Study on Concentration Polarization and Competitive Adsorption Effect

Abstract

Palladium membranes have been used for hydrogen purification for a long time due to their infinite selectivity and excellent permeation performance. However, a coexisting impurity gas, like CO, will inhibit the hydrogen permeation flux that results from the concentration polarization (CP) and competitive adsorption inhibition effects. This work aims to investigate the two inhibition effects separately and quantitatively under different temperatures and pressures. Therefore, permeation experiments of H₂ (90%)/N₂ (10% to 5%)/CO (0% to 5%) mixtures have been carried out at temperatures ranging from 623 to 698 K and H₂ partial pressure drops from 30 to 100 kPa. The permeation of H₂/N₂ is used to study CP because the competitive adsorption of N₂ can be ignored. Then, the further H₂ flux reduction of xH₂/(1-x-z)N₂/zCO permeation relative to that of xH₂/(1-x)N₂ permeation can be attributed to the competitive adsorption of CO. The experimental results show that the CP effect would be enhanced by increasing temperature and pressure, while the CO competitive adsorption effect would be depressed. Meanwhile, the CO inhibition effect generally becomes smaller when the membrane thickness becomes thicker. Based on the results in this work, operation conditions are suggested to be at a higher temperature and higher pressure for a thicker Pd membrane in consideration of increasing the H₂ permeation flux and reducing the CO adsorption effect. The experimental and calculation methods used in this work can provide a new way for investigating the inhibition effect on hydrogen permeation caused by other nonpermeable gases like CO₂, Ar, or H₂O.

Keywords:

• Palladium membrane
• concentration polarization
• competitive adsorption
• inhibition effect
• Sieverts-Langmuir model

Acknowledgments

This work was financially supported by the National Key Research & Development Program of China (2017YFE0301503, 2017YFE0300303) and the National Natural Science Foundation of China under grant number 21601170.