High Temperature Carbonation of Ca(OH)2

Steam hydration is reported to be an effective method for reactivating spent sorbents in calcium looping applications; however, uncertainties remain regarding the optimal method of returning the hydrated sorbent to the CO2 capture loop. Carbonation conversions were found to be higher when Ca(OH)(2) was directly carbonated at high temperatures compared to conversions reached when Ca(OH)(2) was dehydrated prior to carbonation. This observation can lead to improved hydration based reactivation techniques for calcium looping applications. Upon heating in CO2, calcium hydroxide remained stable at temperatures > 450 degrees C and the extent of carbonation was controlled by temperature only. The carbonation mechanism of Ca(OH)(2) at high temperatures appears to be more complex than the expected simple mechanism comprising the dehydration reaction of Ca(OH)(2) and the subsequent carbonation of the resulting CaO. An alternate mechanism was proposed, involving the formation of liquid like layers of water on the surface of Ca(OH)(2).