Separation and reaction using porous and palladium membranes

Aldeeb, AS

Abstract

Two different types of inorganic membranes were prepared in this study,porous-silica/y-alumina membranes and palladium/a-alumina composite membranes.
Porous silica/y-alumina membranes were prepared by dip coating, characterized by gas permeation at elevated temperatures and different pressure differences. This
membrane was then used to investigate the influence of diffusion direction on gas permeation through it. The results obtained showed that a combination of Knudsen and
viscous flow transport mechanisms occurred during the experiments at the working conditions of pressure and temperature with Knudsen flow dominating. The results also
showed that the average pore size of the silica layer coated was 1 nm. The diffusion direction was found to influence the gas permeation through this membrane. Higher
permeation rates were obtained when the diffusion direction was from layers of largest pore size towards layers of the smallest pore size. A maximum difference of 4% was
calculated.
Dense palladium composite membranes were prepared using the electroless plating technique with a-alumina tubes as substrates. The electroless plating technique employed consisted of the conventional two step sensitization-activation method and a hydrazine-based plating bath. Vacuum was used at the initial stages of the procedure to
help improve the palladium film quality and once the pores of the substrate were partially plugged, osmotic pressure was introduced through the osmotic 2M NaCl solution. The palladium film obtained was 7.0 um thick and possessed high selectivity towards hydrogen with a H2/N2 ratio of over 1600.
The electroless plating technique was used to plate
y-alumina tube using a modified activation procedure that employs a chloroform solution in palladium acetate.
The fabricated palladium film appeared not to adhere to the very smooth outer surface of the y-alumina.
The composite palladium membrane obtained was used to investigate the influence of reactive and inert sweep gases on hydrogen flux through such membranes and was used to study their usefulness in propane dehydrogenation. Results obtained showed that inert sweep gas used (N2) improved the hydrogen flux and hydrogen flux improvement was even bigger when a reactive sweep gas (air) was utilized.
The results also showed that the concept of catalytic membrane reactors works.
Propane conversions obtained using a catalytic membrane reactor were higher than those obtained using both fixed bed reactor and certainly higher than equilibrium values
at the same working conditions.

Citation

Aldeeb, A. Separation and reaction using porous and palladium membranes. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Oct 3, 2012
• Award Date: Jan 1, 2007