Bench Scale Evaluation of Dense Ceramic Membranes for Production of High Purity Hydrogen from Gasification

Gasification for production of hydrogen and other useful gases, has achieved increasing importance in recent years. The reactions involved in gasification are favored at high temperatures and they are also limited by thermodynamic equilibrium. The development of membranes which can separate these gases under gasifier exit gas condition will significantly improve process efficiency and economics and simultaneously provide for the recovery of valuable gases. The availability of a membrane with adequate hydrogen selectivity and good thermal and mechanical stability is the key for the successful application of membrane technology in hydrogen production and separation. This work introduces a special method of laser based deposition to synthesize Palladium-Platinum (Pd/Pt)-ceramic composite membranes and permeation results of a ceramic membrane, permeable only to hydrogen, provided by Ceramatec Inc. Thin film Pd was deposited on a ceramic substrate by Nd-YAG laser irradiation of PdCl2 coated on γ-alumina substrate. Similarly a Pt thin film was also synthesized from PtCl4 coated γ-alumina substrate. The parameters of the laser beam were optimized, and a new procedure to synthesize metalceramic composite membranes was developed. The characteristics of Pd and Pt coated γ- alumina membranes were studied and compared. Hydrogen permeation experiments were performed in a CO+CO 2+CH4+H2 environment under typical catalytic steam gasifier exit conditions. The Pd-ceramic composite showed good mechanical and thermal stability with a hydrogen permeability flux of 0.061 (mol/m2s). The activation energy of the Pdmembrane was found to be 5.39 (kJ/mol) in a temperature range of 900-1300°F. The ceramic membrane provided by Ceramatec Inc. was tested under the same conditions used to test the Pd membranes. This ceramic membrane showed good thermal and chemical stability and provided the hydrogen permeability flux of 0.0321 (mol/m2 )