Abstract
Hydrogen selective membranes are interesting candidates to be applied in hydrogen and energy technology. In water gas shift membrane reactors, for example, the membranes can be used to achieve CO2 capture in pre-combustion decarbonisation cycles for large-scale power generation or hydrogen production. Pd and many Pd-alloys, such as Pd-23%Ag have high solubility (S) and diffusivity (D) of hydrogen, and show great promise as membranes for hydrogen separation, membranes are relatively thick (20 μm or more) and hence too expensive for these large-scale applications. For economically viable membranes a 5 to 10-fold reduction in thickness is necessary. In the last two decades, substantial research efforts have been devoted to reduce membrane cost by developing methods to deposit thin Pd and Pd-alloy layers on porous ceramics or stainless steel supports. For direct deposition on porous supports, by electroless plating, chemical vapor deposition, physical vapor deposition, and sputtering, a lower thickness limit apparently exists for which a dense and pinhole free layer can be obtained. Differently from the direct deposition, SINTEF has developed a novel, so-called two-step process, enabling production of very thin defect-free Pd-alloy films on macroporous supports. In the European FP6 project CACHET (Carbon Dioxide Capture and Hydrogen Production from Gaseous Fuels), the application of these membranes in Pd membrane reactors for CO2 capture is being evaluated. In the current overview, we report the preparation, transport properties, and long-term stability of tubular supported Pd-23%Ag membranes. For these highly selective Pd-23%Ag composite membranes, a H2 flux reaching ~ 1223 mL·cm-2·min-1 at 25 bar differential pressure has been obtained. Based on long-term test over 100 days, the life-time of the supported membranes was estimated to 2-3 years. In a mixture of 50% H2+50% N2 a maximum H2 flux of 230 mL·min-1·cm-2 and separation factor of 1400 were achieved at 26 bar. The