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 (he 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 atlributed 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.