Metal doped silica membrane reactor: Operational effects of reaction and permeation for the water gas shift reaction

In this work, we investigate the performance of metal (Cobalt) doped silica membranes in a membrane reactor (MR) configuration for the low temperature water gas shift (WGS) reaction. The membranes were hydrostable and showed activated transport even after 2 weeks exposure to steam. High CO conversions resulted in the H-2 and CO partial pressures in the reaction chamber moving in opposite directions, thus favouring H-2/CO separation to treble (5-15) from 150 to 250 degrees C. On the other hand, the separation of H-2/CO2 remained relatively low (2-4) as the driving force for diffusion or partial pressure of these gases remained equal in the reaction chamber irrespective of the extent of conversion. Below approximately 40% CO conversion, the MR is ineffective as the H-2 driving force for permeation was so low that H-2/CO selectivity was below unity. Operating under equilibrium limited conversion (space velocities 7500 h(-1)) conditions, very high conversions in excess of 95% were observed and there were no significant advantages of the MR performance over the packed bed reactor (PBR). However, for higher throughputs (space velocities 38000 and 75000h(-1)) conversion is affected by the reaction rate, and relatively enough H-2 is removed from the reactor through the membrane. Increasing temperature to 250 degrees C as a function of the space velocity (75000h(-1)) allowed for the CO conversion in the MR to shift up to 12% as compared to the PBR. (C) 2007 Elsevier B.V. All rights reserved.