Pd/Al₂O₃ Composite Membranes for the Production of Pure Hydrogen

Abstract

In recent years, the application of high-temperature membrane reactors, especially for the catalytic dehydrogenation of hydrocarbons, has received growing attention. It is well known that membranes have the potential to surpass the equilibrium conversion by selective removal of one of the reaction products, usually hydrogen. Palladium-based membranes have the potential to separate hydrogen from gas streams due to the unique permeation properties of palladium metal to hydrogen. However, thin films of the metal are required in order to obtain the necessary flux; this is usually achieved by deposition onto a porous substrate. Because of its simplicity and low cost, electroless plating was used in this work to deposit paladium as a thin film onto a porous Al₂O₃ substrate. The prepared membranes were characterized by SEM method. Their thickness was found to be 9 μm. Permeation experiments were performed at 573–648 K temperature range. Hydrogen fluxes approximately 0.35 mol m⁻² s and hydrogen/nitrogen selectivities of 5,500 were obtained. Measurements of the temperature coefficient for hydrogen permeation through the final repaired membrane gave a value of 10.25 kJ mol⁻¹ in good agreement with previous reports. The pressure exponent value of 0.5 was obtained. The prepared membranes could be used in the membrane reactor in order to perform dehydrogenation of methylcyclohexane reaction, which was investigated in a fixed bed catalytic reactor previously.

Keywords:

• electroless plating
• methylcyclohexane dehydrogenation
• Pd/Al₂O₃ membrane