Effect of Asymmetric Membrane Structure on Hydrogen Transport Resistance and Performance of a Catalytic Membrane Reactor for Ethanol Steam Reforming

Abstract

The performance of catalytic membrane reactors (CMRs) depends on the specific details of interactions at different levels between catalytic and separation parts. A clear understanding of decisive factors affecting their operational parameters can be provided via mathematical simulations. In the present paper, main results of numerical studies of ethanol steam reforming, followed by downstream hydrogen permeation through an asymmetric supported membrane, are reported. The membrane module consists of a thin selective layer supported on a substrate with graded porous structure. One-dimensional isothermal reaction–transport model for the CMR has been developed, and its validation has been carried out by using performance data from a lab-scale reactor with a disk-shaped membrane. Simulations demonstrate the model’s capabilities to analyze local concentrations gradients, as required to provide accurate estimates of the relationship between structure–property–performance. It was shown that transport properties of multilayer asymmetric membranes are highly related to the structural properties of each single layer.

An Experimental Performance Study of a Catalytic Membrane Reactor for Ethanol Steam Reforming over a Metal Honeycomb Catalyst

“…Thereby, this value is supposed to be a limit of the membrane permeation, when the diffusion flux through the membrane is no more governed by the driving partial pressure force, but rather by the diffusion through the membrane module. Thus, it was shown earlier [ 14 ] that the asymmetric support contributes up to 70% to the overall resistances across the membrane module.…”

“…Three distinct ranges of the proton conductivity in the temperature dependence in moist atmosphere of hydrogen, corresponding to different mechanisms of predominant proton conduction were revealed. The slope of the high-temperature plot (490–700 °C) results in an activation energy of ≈60 kJ mol −1 [ 14 ]. Generally, if the membrane permeation is limited by the surface reaction, the permeation flux has a linear dependence on the driving partial pressure force.…”

“…In order to quantify the impact of introducing a structural catalyst in the CMR reactor instead of a packed bed [ 7 , 14 ], hydrogen recovery and yield were evaluated through experiments being performed at the same flow rates, of 5 Nl h −1 for the feed gas (ethanol and water mixture in argon) and of 10 Nl h −1 for the Ar sweeping gas ( Figure 13 ). These plots clearly indicate that the reactor operating with the catalytic monolith shows better performance in terms of both hydrogen recovery and the yield with respect to the packed bed catalyst.…”

“…The effective activation energy was calculated according to Sievert’s law for hydrogen permeation flux, (Nml H 2 cm −2 min −1 ), and Sievert’s permeance, (mol m −2 s −1 Pa −0.5 ) [ 14 ]. The hydrogen permeation flux obeys Sievert’s law: where and are the hydrogen partial pressures on opposite sides of the dense layer.…”

“…An overall hydrogen flux was achieved to be about 1.31 Nml cm −2 min −1 . Numerical study of interrelated phenomena of catalytic reaction and permeation through the asymmetric membrane has shown a strong impact of the structural parameters of composite membranes on the reactor performance [ 14 ].…”