Hydrothermal stability of cobalt silica membranes in a water gas shift membrane reactor

Abstract

Cobalt silica membranes were fabricated using sol–gel techniques for separation of H 2 in a membrane reactor set up for the low temperature (up to 300 °C) water gas shift (WGS) reaction. Single dry gas testing prior to reaction showed He/N 2 and H 2/CO 2 selectivities increasing from 75–400 to 45–160 as the temperature increased from 100 to 250 °C, respectively. During reaction the membrane delivered a H 2 permeation purity of 89–95% at high conversions, with the higher water ratio conversion providing superior membrane operational performance. Characterisation of bulk gels indicated that the cobalt silica was hydrophilic and exposure to steam at 200 °C resulted in the densification of the film matrix. The cobalt doping allowed for the membrane structural microporosity to be maintained as H 2 selectivity was not affected by steam exposure, though the flux decreased due to pore collapse of the film matrix. A total of 8 thermal cycle testing were carried out from room temperature to 300 °C, and the membrane displayed good hydrothermal stability, maintaining a high H 2 selectivity for over 200 h of operation.