Hydrogen separation at low pressures using thin Pd-Au membranes

MEYER, G.O,; CORNAGLIA, M.L.; BARUJ, A.; BLANCO, M.V.; TARDITI, A.

Zaragoza

Conferencia; 21st World Hydrogen Conference; 2016

The separation of hydrogen using Pd alloy membranes generates great interest due to the varied range of applications for solving industry requirements. In this paper the results of the characterization of a Pd/Au membrane for the selective permeation of hydrogen from a gas mixture and its comparison with the case of pure hydrogen are presented. Hydrogen separation was tested under different conditions of membrane temperature, feeding gas pressure and retentate flow. The results obtained will serve as a basis for the design of hydrogen separation processes from low pressure gas mixtures. A Pd/Au membrane of 10 microns thickness deposited on a porous stainless steel disk was used. In the membrane/substrate interface a ZrO2 thin layer was deposited by dip coating method [1]. The membrane was placed into a modified Swagelok VCR fitting, Figure 1a, and the resulting device was then connected to a closed circulation system, which is presented in Figure 1b. The dependence of the membrane permeate flow with feeding pressure was evaluated under feeding flows of pure hydrogen and of a gas mixture containing H2:N2 + H2O in an approximate ratio 49:1. Measurements were performed by fixing different feeding flows at temperatures between 300°C and 500°C and waiting up to observe equilibrium conditions. In each case the retentate flow was maintained constant and the permeate flow was determined by making the difference between the feeding flow and the retentate flow, for each pressure. During the experiments, the pressure differences between both sides of the membrane ranged from 10 kPa to 600 kPa. In the case of the measurements with impure hydrogen, a reservoir of 150 cm3 (Figure 1b) was initially filled with the gas and an external source of ultrapure hydrogen was used to compensate the permeated flow and to keep unaltered the gas mixture composition. Figure 2a presents the hydrogen permeate flows obtained for the different pressures at 300°C and 400°C.We also performed experiments close to the final application: the reservoir was initially filled at 200 kPa (with the gas mixture or with pure hydrogen as target) and the separation was allowed to proceed until the pressure of the system is reduced to 40 kPa by hydrogen permeation. Under these conditions, as hydrogen permeated through the membrane the gas mixture was enriched in N2 and H2O. The experiments were repeated at different temperatures and the separation time for each temperature and gas composition was determined. The results obtained at 300°C, 400°C and 500°C are plotted in Figure 2.b.