Experimental and modeling studies on the low-temperature water-gas shift reaction in a dense Pd-Ag packed-bed membrane reactor

In this work, an experimental and modeling study is described, focusing on the performance of a Pd-Ag membrane reactor recently proposed and suitable for the production of ultra-pure hydrogen. A packed-bed membrane reactor (MR) with a "finger-like" membrane configuration has been used for carrying out the water-gas shift reaction (WGS) in the region of low temperature operation using a simulated reformate feed. The experiments were performed under a broad range of operating conditions of temperature (200-300 degrees C) and space velocity (1200-10,800 L-N kg(cat)(-1) h(-1)); the effect of feed pressure (1-2 bar) was also analyzed, as well as the operating mode at the permeate side: vacuum (30 mbar) or sweep gas (1.0 bar; nitrogen at 1 L-N min(-1)). A one-dimensional, isothermal and steady-state model is proposed, which assumes axially dispersed plug flow pattern and pressure drop in the retentate side and plug flow with constant pressure in the permeate side. An innovative composed kinetic model was also used to describe the catalytic activity of the catalyst for the WGS reaction. In general, the simulation results showed a good agreement to the experimental data, in terms of carbon monoxide conversion and hydrogen recovery (and also outlet retentate composition) using only two fitting parameters related to the decline of H-2 permeability due to the presence of CO. Both simulation and experimental runs showed that the MR achieves high performances, for some operating conditions clearly above the maximum limit for conventional packed bed reactors. The performance reached is particularly relevant when hydrogen is recovered via sweep gas mode (a high sweep flow rate was employed), because a lower partial pressure could be reached than using vacuum pumping. In the first case, almost complete CO conversion and H-2 recovery could be reached. (C) 2011 Elsevier Ltd. All rights reserved.