Preparation, testing and modelling of a hydrogen selective Pd/YSZ/SS composite membrane

A palladium selective tubular membrane has been prepared to separate and purify hydrogen. The membrane consists of a composite material, formed by different layers: a stainless steel support (thickness of 1.9 mm), an yttria-stabilized zirconia interphase (thickness of 50 μm) prepared by Atmospheric Plasma Spraying and a palladium layer (thickness of 27.7 μm) prepared by Electroless Plating. The permeation properties of the membrane have been tested at different operating conditions: retentate pressure (1-5 bar), temperature (350-450 °C) and hydrogen molar fraction of feed gas (0.7-1). At 400 °C, a permeability of 1.1 × 10⁻⁸ mol/(s m Pa^0.5) and a complete selectivity to hydrogen were obtained. The complete retention of nitrogen was maintained for all tested experiment conditions, with both single and mixtures of gases, ensuring 100% purity in the hydrogen permeate flux.A rigorous model considering all the resistances involved in the hydrogen transport has been applied for evaluating the relative importance of the different resistances, concluding that the transport through the palladium layer is the controlling one. In the same way, a model considering the axial variations of hydrogen concentration because of the cylindrical geometry of the experimental device has been applied to the fitting of the experimental data. The best fitting results have been obtained considering Sieverts’-law dependences of the permeation on the hydrogen partial pressure.