Palladium/Copper Alloy Composite Membranes for High Temperature Hydrogen Separation [report]

J. Douglas Way, Paul M. Thoen
2006 unpublished
OBJECTIVES The specific objectives that we have pursued during the last year are: • To identify the structural changes that electrolessly deposited palladium alloy films on porous supports undergo when exposed to gas mixtures at a range of temperature and pressure conditions with the purpose of determining the effect of non-metallic impurities such as carbon, and • To determine the permeation properties and physical and mechanical resistances of these membranes when exposed to gaseous mixtures
more » ... o gaseous mixtures containing such gases as CO, CO 2 , H 2 O and H 2 S at different compositions, ACCOMPLISHMENTS TO DATE Sequential layers of palladium and copper metals were electrolessly deposited on porous Al 2 O 3 and ZrO 2 ceramic micro and ultrafilters. The composite membranes thus made were annealed and tested at temperatures ranging from 250 to 500 °C, under very high feed pressures (up to 450 psig) using pure gases and gaseous mixtures containing H 2 , CO, CO 2 , H 2 O and H 2 S, with the purpose of determining the effects these variables had on the H 2 permeation rate, selectivity and percent recovery. The inhibition caused by CO/CO 2 gases on a 7 µm thick Pd-Cu composite membrane was less than 17% over a wide range of compositions at 350 °C for CO concentrations up to 8 mole %. The sum of the CO and CO 2 compositions was held constant at 28 mole %. H 2 S caused a strong inhibition of the H 2 flux of the same Pd-Cu composite membrane, which is accentuated at levels of 100 ppm or higher. The membrane was exposed to 50 ppm three times without permanent damage. At higher H 2 S levels, above 100 ppm the membrane suffered some physical degradation and its performances was severely affected. The use of sweep gases improved the hydrogen flux and recovery of a Pd-Cu composite membrane. Recently, we have been able to dramatically reduce the thickness of these Pd alloy membranes to approximately one micron. This is significant because at this thickness, it is the cost of the porous support that controls the materials cost of a composite Pd alloy membrane, not the palladium inventory. Very recent results show that the productivity of our membranes is very high, essentially meeting the DOE pure hydrogen flux target value set by the DOE Hydrogen Program. These results were obtained at 365 °C and a differential pressure of 20 psig when a 1.3-micron-thick Pd 95 Cu 5 (composition given in mass %) alloy film was coated on a Pall Corporation Membralox ® T1-70 tubular ceramic substrate. This is significant because at this thickness, it is the cost of the porous support that controls the materials cost of a composite Pd alloy
doi:10.2172/898816 fatcat:vuvdqbp3ffdqlmlwpvkgyedpoi