Flux, hydrogen

Carbon molecular sieve membranes Resistant to contaminants Intermediate hydrogen flux and selectivity Intermediate hydrogen flux and selectivity High water permeability Pilot-scale testing in low temperature WGS membrane reactor application Need demonstration of long-term stability and durability in practical applications... 

Kamakoti, P., B.D. Morreale, M.V. Ciocco, B.H. Howard, R.P. Killmeyer, A.V. Cugini, and D.S. Sholl, Prediction of hydrogen flux through sulfur-tolerant binary alloy membranes, Science, 307, 569-573,2005. 

Ma, Y.H., P.R Mardilovich, and Y. She, Stability of hydrogen flux through Pd/Porous stainless steel composite membranes, Proceedings of International Conference on Inorganic Membranes, ICIM5, Nagoya, 1998. 

Mardilovich, I.P., E. Engwall, and Y.H. Ma, Dependence of hydrogen flux on the pore size and plating surface topology of asymmetric Pd-porous stainless steel membranes, Desalination, 144, 85-89,2002. 

Roa, F. and J.D. Way, Influence of alloy composition and membrane fabrication on the pressure dependence of the hydrogen flux of palladium-copper membranes, Ind. Eng. Chem. Res., 42(23),... 

Figure 2. Description of the initial and boundary conditions for the hydrogen diffusion problem in the pipeline. The parameter / denotes hydrogen flux and C,(P) is normal interstitial lattice site hydrogen concentration at the inner wall-surface of the pipeline in equilibrium with the hydrogen gas pressure P as it increases to 15 MPa in 1 sec. At time zero, the material is hydrogen free,...

Figure 5. Description of (a) boundary conditions for the elastoplastic problem and (b) initial and boundary conditions for the hydrogen diffusion problem at the blunting crack tip in the MBL formulation. The parameter bCl denotes the crack tip opening displacement in the absence of hydrogen. The parameter C, (P) denotes NILS hydrogen concentration on the crack face in equilibrium with hydrogen gas pressure P. and / is hydrogen flux.

Figure 6. Normalized NILS hydrogen concentration CL / C at steady state vs. normalized distance R/b from the crack tip for the full-field (crack depth wh=0.2) and MBL (domain size L=h-a) solutions under zero hydrogen flux conditions on the OD surface and remote boundary, respectively. The parameter b denotes the crack tip opening displacement for each case. The inset shows the concentrations near the crack tip.

The transport of hydrogen from the entry side to the exit side of the membrane can be described by Pick s laws of diffusion. In the steady state, the hydrogen flux is given hy Pick s first law of diffusion ... 

Assuming that the exiting hydrogen atoms are oxidized sufficiently fast, the concentration of absorbed hydrogen direcdy beneath the exit surface may be taken as zero. Using Faraday s law, the steady-state hydrogen flux across the membrane is described by the steady-state hydrogen permeation current ... 

The cells shown in Figs. 28 and 29 all operate according to the same principles, which have been developed by Arup. The interior of the cell acts as the anode chamber, and a metal oxide cathode placed inside the cell in an alkaline electrolyte acts as the counter electrode. The hydrogen flux across the integrated membrane (coated with palladium on the internal surface) can be measured as the potential drop across a resistor placed between the membrane and the counter electrode. 

The limiting reactant in the reactor is hydrogen. All mass transfer resistances have to be accounted for. The hydrogen flux from the gas to the liquid, to the external pellet surface and inside the pellet are equal, assuming complete wetting of the pellets, as expected under those conditions (Ref. 4). 

By analogy to Figures 3.2 and 3.3, the cathode is represented as being composed of two different layers. It should be noted that for the cathode there is a one-way flux of oxygen from the gas channel to the reaction zone, while for the anode there is a hydrogen flux to the reaction zone and a water flux from the reaction zone to the gas channel, as illustrated in Figure 3.3. 

The performance of the membrane was tested with a mixture of 90% nitrogen and 10% hydrogen at atmospheric pressure and 500 °C. The permeate side of the membrane was set under vacuum. A hydrogen flux of 100 Ndm3 m-2 s-1 was determined at the pressure drop of 1 bar. 

Tong et al. [98] prepared Pd and Pd77Ag23 membranes by applying a similar procedure to that of Franz et al. [93], The membranes introduced on the support by sputtering had a thickness between 500 and 1 000 nm. They were stable against a differential pressure up to 4 bar and were operated at 450 °C for more than 1000 h. A hydrogen flux up to 90 Ndm3 m 2 s 1 and a separation factor of 1 500 for H2/He were determined for these membranes. 

A hydrogen flux between 50 and 90 Ndm3 m 2 s 1 was determined for these membranes on increasing the operating temperature from 350 to 450 °C. The H2/He separation factor was > 2 750. An increased hydrogen flux compared with membranes deposited on porous supports was demonstrated. Addition of steam to the retenate flow (20% H2, 60% He, 20% H20) reduced the hydrogen flux from 90 to 15 Ndm3 m 2 s 1. 

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