Application of Extended Permeability to a Thick Palladium Membrane

Abstract

Abstract. Some dense metal membranes are permeable only to hydrogen, useful to produce and purify hydrogen. Conventionally, hydrogen permeation flux through metal membranes is described as the square-root law. The permeability defined in the law is commonly used as a measure of membrane material. However, deviation from the law has been widely reported. We have extended the definition of permeability for precise description. This study applied it to a thick palladium membrane down to 0.01 MPa in absolute pressure. Experimental results showed that hydrogen permeation flux through the palladium membrane 200 µm thick did not obey the square-root law completely. From the permeation behavior, pressure-dependent permeability was evaluated. The resultant permeability was found to decrease and become a constant value, or intrinsic permeability, as pressure approached vacuum.

Hydrogen Permeation Performance Comparison among Palladium and Other Membranes with Different Permeation Laws

“…Square-root permeability is defined by lJ divided by square-root pressure difference, whilst the function representing pressure-dependent permeability is determined by differentiating lJ in terms of the square-root of feed side pressure. To estimate permeation flux, the following formula is useful [9]:…”

“…To confirm the validity of pressure-dependent permeability under wider conditions, a thicker membrane was tested for a wider pressure range, i.e., 200 μm thick and 0.01−1.0 MPa [11]. The pure palladium sheet was cold rolled, purchased from Ishifuku Metal Industry Co., Ltd. (Japan).…”

“…This is why permeance is not adopted for dense metal membranes. We have recently proposed pressure-dependent permeability [9]. By introducing pressure dependence into permeability, permeation behavior can be precisely described.…”

“…Second, the pressure-dependent permeance is applied to various membranes to demonstrate precise description and comparison among them: pure palladium membranes 50 μm and 200 μm thick measured in our group [10,11], a pure palladium membrane described in the power law by Hurlbert and Konecny [6], a pure niobium membrane reported by Zhang et al [7], and a silica membrane without pressure dependence in permeance reported by Tsuru et al [8]. Because original experimental data are from the literature, the experiment is explained as short as possible.…”

Consistent description of hydrogen permeation through metal membrane based on hydrogen chemical potential and its application to alloy design

“…To understand these exceptional cases, Hara et al have recently proposed a concept based on the pressure dependent hydrogen permeability. [17][18][19] It is well known that the gradient of hydrogen concentration, dc/dx, is not always the driving force for hydrogen diffusion. Strictly speaking, the hydrogen diffusion is driven by the gradient of the hydrogen chemical potential, dl/dx.…”