Permeation of hydrogen through palladium/alumina composite membranes

In this study, the Pd/alumina composite membranes for hydrogen separation were prepared on a disk-type of alpha -alumina porous support and supported gamma -alumina membrane by electroless-plating technique, respectively. The composite membranes with thickness of palladium layer ranging from 7-15 mum are used in the gas permeation experiment under 600-669 K and 50-220 kPa. The experimental results demonstrated that the hydrogen transport through these composite membranes is mainly controlled by solution-diffusion mechanism. It also showed that the selectivity coefficient of H-2/N-2 in the composite membranes reaches to infinite. The exponential dependency of the hydrogen partial pressure on permeation rate is in the range of 0.627 to 0.688, which is somewhat above that predicted by Sievert's law. Furthermore, the apparent activation energies of hydrogen permeation from the experimental results are within 8.8-9.3 kJ/mol. Additionally, the transport behavior of hydrogen through the bulk Pd layer of Pd/alumina composite membranes were analyzed based on the resistance model. Consequently, the hydrogen flux through a Pd/ alumina composite membrane, with a palladium film of 7 mum thick, deviated from Sievert's law. In addition, the hydrogen flux through thick Pd film (15 mum) was observed to be proportional to the difference in the square root of the hydrogen pressure on either side of the film, in accordance with Sievert's law.