High-Flux Palladium Membranes Based on Microsystem Technology

Abstract

Hydrogen-selective Pd membranes can be used to improve the conversion of dehydrogenations, steam reforming, and the water gas shift reaction. The application of these membranes on a large scale is prohibited by the costs of the existing membranes, requiring membranes with a much higher permeability. In this paper we describe the manufacturing of Pd and Pd/Ag membranes using microsystem technology. These membranes exhibit fluxes that can be a factor of 10 higher than the fluxes obtained using porous supports. Despite the thin Pd and Pd/Ag layers applied, these membranes are pinhole-free.

Organic–inorganic hybrid silica membranes with controlled silica network size: Preparation and gas permeation characteristics

“…This coincided well with the calculated weight loss in the case of decomposition of one ethoxy group in hybrid silica polymers. On the other hand, the detection curve of CH 4 (mass number: 16) increased from approximately 500 • C, which is consistent with the second part of weight loss. Under an N 2 atmosphere, a partial pyrolysis of the bridging ethane groups was observed between 480 and 800 • C [29,30].…”

“…For decomposition of the -(CH 2 ) 2 -group, CH 4 and C 2 H 4 can be generated. In the present study, indicators for decomposition were C 2 H 5 OH (mass number: 31) for the ethoxy groups and CH 4 (mass number: 16) for the -(CH 2 ) 2 -group. The detection curve of C 2 H 5 OH (mass number: 31) gradually increased from 200 • C, which was in good agreement with the first part of weight loss, indicating that most unreacted ethoxy groups can be decomposed above 200 • C. A drastic weight loss of approximately 13% between 200 and 300 • C under air atmosphere was due to the combustion of the ethoxy groups.…”

“…Recently, molecular dynamics (MD) simulation revealed that the amorphous silica structure had a large number of pores with a pore size of less than 0.25 nm, through which He (kinetic diameter: 0.26 nm) and H 2 (kinetic diameter: 0.289 nm) molecules cannot permeate [15]. If pore size distribution (PSD) of silica networks can be shifted to larger pore sizes while keeping a sharp PSD, this will lead to a drastic increase in hydrogen permeability that is almost the same as, or even higher than, ultra thin palladium membranes (H 2 permeance: 1 × 10 −5 mol m −2 s −1 Pa −1 ) [16].…”

Non-ideal absorption effects on hydrogen permeation through palladium–silver alloy membranes

“…This observation, along with the high cost of palladium, has motivated continuous efforts to fabricate palladium-alloy membranes of decreasing thickness. Recently, application of microfabrication techniques has enabled repeatable fabrication of free-standing palladium-alloy membranes with a thickness on the order of one micrometer [1][2][3][4][5][6][7][8][9]. As the thickness of palladium-alloy membranes continues to decrease, a natural question which must be addressed is whether there is a fundamental upper limit to the hydrogen permeation rate.…”

Experimental investigation of a microchannel membrane configuration with a 1.4μm Pd/Ag23wt.% membrane—Effects of flow and pressure

“…The n-value depends on the rate-limiting steps in the permeation process. As long as bulk diffusion is the rate-limiting step, the n-value will be approximately equal to 1/2 due to Sievert's law, while it will typically approach 1 as surface or other processes become more and more important [1,[3][4][5][6][7][8]. In this case the value of n may even differ at the two sides of the membrane.…”