Duplex Pd/ceramic/Pd composite membrane for sweep gas-enhanced CO2 capture

Supported, thin-layered Pd membranes are promising tools for pre-combustion carbon capture because they can deliver simultaneously high-pressure CO2 and H-2 streams as needed for sequestration and power generation, respectively. Moreover, the diluent required for the gas turbine fuel can be advantageously added as sweep gas in the membrane separator to boost H-2 permeation. A composite membrane has been prepared with Pd layers on both sides of a porous ceramic tube to eliminate the mass transfer resistance resulting from sweep gas diffusion into the support of conventional Pd/ceramic membranes. The H-2 permeability of the Pd/ceramic/Pd membrane (1.01 x 10(-8) mol m(-1) s(-1) Pa-0.5 at 773 K) is similar to that of a supported single Pd layer membrane but its H-2/N-2 selectivity (18033) is enhanced by an order of magnitude at 773 K and Delta P = 500 kPa. Intriguingly, the selectivity of the double Pd layer membrane improves with increasing pressure difference Delta P while that of Pd/ceramic membranes declines. This unusual pressure dependence originates from the elevated pressure within the ceramic of the double Pd layer membrane. The sweep gas-induced mass transfer resistance grows rapidly with increasing permeate pressure and sweep gas amount attenuating the single gas H-2 flux of the Pd/ceramic membrane by 67% at 1 MPa permeate pressure. This resistance remains significant under CO2 capture conditions albeit concentration polarization on the feed side has an even stronger permeation-retarding effect in that situation. The CO2 capture rate and purity benefit greatly from the enhanced high-pressure H-2 selectivity of Pd/ceramic/Pd membranes which renders them attractive tools for any kind of H-2 separation task.