Permeation of hydrogen through palladium/alumina composite membranes

In this study, the Pd/alumina composite membranes for hydrogen separation w ere 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 mu m 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 mechan ism. It also showed that the selectivity coefficient of H-2/N-2 in the comp osite membranes reaches to infinite. The exponential dependency of the hydr ogen 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 r esults are within 8.8-9.3 kJ/mol. Additionally, the transport behavior of h ydrogen through the bulk Pd layer of Pd/alumina composite membranes were an alyzed based on the resistance model. Consequently, the hydrogen flux throu gh 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 P d film (15 mum) was observed to be proportional to the difference in the sq uare root of the hydrogen pressure on either side of the film, in accordanc e with Sievert's law.