Aqueous Potassium Bicarbonate/Carbonate Ionic Equilibria at Elevated Pressures and Temperatures

Aqueous bicarbonate/carbonate ionic equilibria play an important role in determining the practicality of various aqueous-alkaline fuel cells and the hot carbonate process for removing carbon dioxide from synthesis gas streams. These equilibria are also of interest to scientists concerned with climate change. In this article, we report measurements of aqueous bicarbonate/carbonate ionic equilibria between 150 and 320 degrees C at the solutions' respective saturation pressures. The aqueous bicarbonate ions are not stable at temperatures above 150 degrees C: the bicarbonate decomposes into carbonate and aqueous CO2. The dissolved CO2 is released from the solution when the reaction vessel is quickly cooled and depressurized, leaving behind stable carbonate ions in a solution with increased pH. A thermodynamic analysis of these findings indicates that the spontaneous and endothermic bicarbonate decomposition reaction proceeds with a positive change in entropy.