Characteristics of the reversible reaction between CO2(g) and calcined dolomite

The noncatalytic gas-solid reaction between calcined dolomite and CO2(g) has been studied in an electrobalance reactor as a function of temperature, pressure, and reactive gas composition. Multicycle tests consisting of as many as ten complete calcination-carbonation cycles were carried out to obtain information on sorbent durability. Surface area, pore volume, and pore size distribution measurements were made to supplement the reaction studies. This reaction is of interest both as a model for studying the importance of structural property changes in gas-solid reactions, and as the basis for a possible process for the high temperature separation of CO2 from gas streams. Calcined dolomite is a superior sorbent to calcined CaCO3 in that larger fractional conversions of CaO and improved multicycle durability are possible. With CaO obtained from CaCO3, the first-cycle fractional recarbonation was limited to about 0.80, a value which decreased by 15 to 20% in each subsequent cycle. In contrast, the first-cycle fractional recarbonation of CaO in calcined dolomite was typically 0.90 to 0.95, and this value decreased by only 1 to 2% in each subsequent cycle. These advantages are attributed to the "excess" pore volume created by the original decomposition of MgCO3 in dolomite, and by a reduction in the rate of CaCO3 sintering in the presence of MgO.