Highly Efficient CO₂ Sorbents: Development of Synthetic, Calcium-Rich Dolomites

The reaction of CaO with CO₂ is a promising approach for separating CO₂ from hot flue gases. The main issue associated with the use of naturally occurring CaCO₃, that is, limestone, is the rapid decay of its CO₂ capture capacity over repeated cycles of carbonation and calcination. Interestingly, dolomite, a naturally occurring equimolar mixture of CaCO₃ and MgCO₃, possesses a CO₂ uptake that remains almost constant with cycle number. However, owing to the large quantity of MgCO₃ in dolomite, the total CO₂ uptake is comparatively small. Here, we report the development of a synthetic Ca-rich dolomite using a coprecipitation technique, which shows both a very high and a stable CO₂ uptake over repeated cycles of calcination and carbonation. To obtain such an excellent CO₂ uptake characteristic it was found to be crucial to mix the Ca²⁺ and Mg²⁺ on a molecular level, that is, within the crystalline lattice. For sorbents which were composed of mixtures of microscopic crystals of CaCO₃ and MgCO₃, a decay behavior similar to natural limestone was observed. After 15 cycles, the CO₂ uptake of the best sorbent was 0.51 g CO₂/g sorbent exceeding the CO₂ uptake of limestone by almost 100%