On the influence of steam on the CO2 chemisorption capacity of a hydrotalcite-based adsorbent for SEWGS applications

Hydrotalcite-based adsorbents have shown great potential for use in sorption-enhanced water-gas-shift applications. A combination of thermogravimetric experiments and breakthrough experiments have been carried out to elucidate the effect of steam on the CO2 cyclic sorption capacity on a K-promoted hydrotalcite-based adsorbent. Different TGA cycles have been designed to study the mass change on sorbents exposed to different sequences of different CO2/H2O/N2 mixtures. Because the complex sorption/desorption and replacement phenomena cannot be explained by TGA experiments only, additional information from breakthrough experiments in a packed bed reactor was used to correlate the observed total mass change in the TGA cycles to the phenomena prevailing on the sorbent. A mechanism has been developed which is able to describe the cyclic working capacity, for both CO2 and H2O under different experimental conditions. It was found that at least four different adsorption sites participate in the sorption/desorption of CO2 and H2O. Two adsorption sites can be regenerated with N2, whereas the other adsorption sites require the presence of H2O or CO2 to be desorbed. Regeneration of the adsorbent with steam leads to a significant increase in the CO2 cyclic working capacity from 0.3 to 0.53 mmol/g compared to a dry regeneration with N2 using the same cycle times.