Capture of CO2 Using Sorbents of Calcium Magnesium Acetate (CMA)

Synthetic sorbents of calcium magnesium acetate (CMA) with differing molar ratios of Ca/Mg were tested in a fluidized bed to determine their capacity to absorb CO2 over several cycles of carbonation, via CaO(s) + CO2(g) ? CaCO3(s), and the reverse calcination. Their performances were compared, at 750 °C, on the basis of moles of CO2 absorbed per mole of CaO present in the sorbent, to those of a U.K. limestone and a dolomite when carbonated in a gas containing 15 mol % CO2 and N2 balance and calcined in pure N2. Three of the CMA sorbents were also carbonated in gases containing 30 and 50 mol % CO2 (N2 balance). All experiments were at atmospheric pressure. It was found that, with a mole fraction of CO2 of 15 mol % during carbonation, the dolomite and CMA 7:3 (7 mol of Ca to 3 mol of Mg) exhibited the highest uptake of CO2 over the 10 cycles of the experiment. It was also found that these sorbents had the highest pore volume using the method of Barrett, Joyner, and Halenda (BJH), which measures the volume in pores <200 nm in diameter, confirming the theory that the fast stage of the carbonation reaction occurs predominantly in pores of this size range. Thus, the materials with the largest BJH volume were also those with the largest capacity to take up CO2. The effect of increasing the concentration of CO2 for carbonation was found to increase the uptake of CO2 for each of the synthetic sorbents tested, an important and interesting result, the reason for which is discussed in this paper.