Towards an energy-efficient carbon capture: Catalysts for a low energy carbonate absorption process

Worldwide implementation of carbon taxes and policies have prompted the utilisation of carbon dioxide capture for large and small emitters. However, the current technology has yet to be economically attractive and viable, with the cost of the process, the sorbent, and its regeneration being relatively high. In this work, we show that magnesium or calcium salts can be used as potential catalysts for the decarboxylation of metal bicarbonates (Na and K), as CO2 carriers, at low temperatures (50 - 60 degrees C). The nature and concentrations of the catalyst and CO2 carrier (slurry vs dissolved) were examined in detail to establish performance and specificity. C-13 NMR was used to validate the catalyzed decarboxylation of (NaHCO3)-C-13, and revealed a plausible intermediate (MgHCO3+ center dot 5H(2)O). Kinetic laws were established for the reaction, displaying high decarboxylation rate constants when the temperature is increased above 60 degrees C and/or when the bicarbonate concentration is increased to similar to 3 M. Furthermore, the apparent activation energies were also determined. The decarboxylation rate constant can reach 2,360,000 mol(-1).min(-1) for a slurry of potassium bicarbonate at 47 degrees C. For a loading used in a potassium carbonate absorption process (30 w%), the rate constant was 1,030,000 mol(-1).min(-1) at 54 degrees C, which is half the current regeneration temperature of 120 degrees C. Magnesium carbonate was identified as an excellent decarboxylation catalyst for the promoted potassium carbonate absorption process, imparting energy and cost savings without an increase in toxicity and corrosivity.