Supported perfluorotributylamine liquid membrane for H₂/O₂ separation

Photocatalytic water splitting is the cleanest method to produce H₂, but often requires the removal of O₂, which is simultaneously generated. To achieve this separation, use was made of supported liquid membranes formed from perfluorotributylamine (PFTBA) imbued in porous alumina supports. The PFTBA membranes were subject to single and mixed H₂/O₂ gas permeance tests at room temperature and showed a sieving transport behavior. The membranes had an average H₂/O₂ selectivity of 140 with a H₂ permeability of 4500 barrers. The performance of the membrane showed only a slight dependence with increases of temperature and gas flow rate, but these increases reduced the lifetime of the membranes because of enhanced volatilization of the perfluoro compound. Studies showed that at small support pore sizes, the membrane displayed longer lifetime because of reduced vapor pressure of the liquid inside the porous support. A partial pressure analysis revealed that the selectivity improved when the partial pressure of the gases was reduced. Additionally, it was shown that separation at humid conditions reduced the stability of the membrane, but did not affect its permeance. The diffusivity and solubility of the gases across the membrane were obtained by the time-lag technique. It was found that H₂ has higher solubility and diffusivity than O₂ giving rise to a higher overall permeance for the smaller sized gas.