CO₂ capture from post combustion flue gas: A sorbent stability study

The long term stability of an amine adsorbent for CO ₂ capture from post combustion flue gas via high temperature (∼105 °C) vacuum swing adsorption (VSA) was studied. The adsorbent was prepared by loading branched polyethyleneimine (PEI) into SBA15 type mesoporous silica. In these experiments, VSA conditions were simulated by a partial pressure swing in a combined thermogravietric analyser/differential thermal analyser (TGA/DTA). Under conditions that were deliberately chosen to accentuate any deterioration in performance, the reversible CO ₂ capacity of the adsorbent was observed to diminish over time when water was absent from the simulated flue gas. When the simulated flue gas was humidifed to the extent of only 1%, this deterioration in adsorption capacity was substantially diminished. FTIR spectrometry of samples taken before and after the TGA/DTA analyses suggest that the loss of CO ₂ capacity was due to the transformation of amines into ureas and that the formation of ureas is suppressed in the presence of water. Thus, the results demonstrate that a small partial pressure of water can inhibit urea formation and so preserve the working capacity of the sorbent.