Influence of steam partial pressures in the CO2 capture capacity of K-doped hydrotalcite-based sorbents for their application to SEWGS processes

The performance of three different alkali-promoted hydrotalcite-based materials has been studied under conditions typical of sorption-enhanced WGS process to investigate the influence of steam partial pressure in the feed gas stream in the CO2 capture mechanisms and system efficiency. The sorbents were prepared by calcination and a minimum temperature of 600 degrees C was required to guarantee that all CO2 has been released from the structure. The presence of steam in the feed gas was found to be very beneficial for the capture process efficiency even at very low water content. In order to gain insight into the capture mechanisms involved in the CO2 capture process, XRD analysis were performed and the results showed that under low steam contents in the feed gas formation of K-dawsonite takes place while under high steam contents (35% v/v) reconstruction of hydrotalcite structure and formation of some carbonates are detected and CO2 capture values between 4 mol/kg and 9 mol/kg have been measured for the three sorbents when tested under isothermal conditions (300 degrees C) at P-H2O = 4.5 bar and P-CO2 = 0.34 bar. Under these operating conditions formation of magnesium carbonate is suspected to occur although it could not be demonstrated. (C) 2013 Elsevier Ltd. All rights reserved.