Composite palladium membranes: Synthesis, separation and reaction

Dense Pd membranes were prepared by the electroless plating on the porous stainless steel (PSS) supports with a 0.5 mum grade. The Pd/PSS membranes with the thickness between 19 and 28 mum exhibited no He permeation at room temperature up to 3 atm pressure, indicating that the Pd membranes were dense. At 350°C the H2 permeance up to 8 m3/(m 2 h atm0.5) was obtained with a H2/N 2 selectivity coefficient of 5000 at a pressure difference of 1 atm. The experimental results indicated that the H2 permeation through the membrane followed the Sievert's law. The fluxes of gases other than H 2 were quantitatively described as a combination of Knudsen diffusion and viscous flow through the grain boundary created in the Pd layer at high temperatures.; The activation energy of the H2 permeation through the Pd/PSS membrane was determined to be 16.4 kJ/mol. The intermetallic diffusion between the components of the PSS support and the Pd layer appeared to occur at temperatures greater than 550°C for the Pd/PSS membranes, causing the reduction of the H2 permeation. On the other hand, the Pd/Al2O 3/PSS membranes exhibited no reduction of the H2 permeation up to 600°C, indicating that the intermediate Al2O3 layer could prevent the intermetallic diffusion.; The Pd/oxidized PSS membranes (the Pd membranes were prepared on the oxidized PSS supports) improved the membrane performance in terms of their thermal and long-term H2 permeation stability. No significant change in the H2 flux was observed after the membrane had exposed to temperatures between 350 and 450°C for over 6000 hours. Furthermore, the thermal swing experiments between 350°C and 450°C also showed no H2 flux reduction.; The Pd/PSS membrane was used to separate H2 at 350°C from the H2/CO2 mixtures with three concentrations of H 2 (75, 50, and 25%). The separation factor of H2/CO 2 exhibited a maximum with respect to the pressure difference for all three mixtures due to the different dependencies of pressure on the H 2 and CO2 permeation.; A one-dimensional model for the dehydrogenation of ethylbenzene to styrene was developed for the Pd membrane and conventional fixed-bed reactors. The simulation results showed that the Pd membrane reactor was superior to the fixed-bed reactor.; The dehydrogenation of ethylbenzene to styrene was investigated experimentally in both the Pd membrane and fixed-bed reactors. As the result of the removal of H2 from the reaction zone, the membrane reactor gave about 10% higher ethylbenzene conversion than that of the fixed-bed reactor.