Dense inorganic membranes for production of hydrogen from methane and coal with carbon dioxide sequestration

Principles and strategies for design and operation of catalysts associated with both dense oxygen transport membranes and dense hydrogen transport membranes are discussed. Dense ceramic oxygen transport membranes function through the diffusion of oxygen anions, O-2-. A key catalytic step is the adsorption and dissociation of molecular oxygen, and the associated transfer of four electrons. In dense hydrogen transport membranes, whether ceramic or metallic, molecular hydrogen must be catalytically dissociated on the retentate-side membrane surface to allow transport of hydrogen through the bulk membrane in a dissociated form. Dissociated hydrogen must be re-combined and desorbed from the permeate side membrane surface. Strategies are discussed for increasing resistance of catalysts to poisons. By separating oxygen from the other components of air, oxygen transport membranes allow a potential efficient means for production of synthesis gas (H-2 + CO) from natural gas or coal, without diluting the product with nitrogen. Further reaction of CO with steam over water-gas shift catalysts produces additional hydrogen plus CO2. Extraction of hydrogen from water-gas shift reactors through dense hydrogen transport membranes, while retaining CO2 at operating pressures of coal gasifiers (e.g. 1000 psi or 69 bar) produces essentially pure hydrogen in the permeate and CO2 at high pressure and high concentration, which is ideal for efficient sequestration Of CO2- Process flow scenarios for integration of both oxygen transport membranes and hydrogen transport membranes with coal gasifiers, natural gas syngas reactors, water-gas shift reactors and systems for sequestration Of CO2 are discussed. (c) 2006 Elsevier B.V. All rights reserved.