CO2 capture performance of calcium-based sorbent doped with manganese salts during calcium looping cycle

Graphical abstract: Comparison of carbonation conversions of Mn-doped and original CaCO3 during long-term cycles for calcination at 850 oC and carbonation at 700 oC. The Mn/Ca molar ratio is 1/100 and 1.5/100 for Mn(NO3)2-doped and MnCO3-doped CaCO3, respectively. Highlights: → We modified CaCO3 with manganese salts including Mn(NO3)2 and MnCO3. → The CO2 capture capacity during multiple cycles is enhanced by modification. → Mn-doped sorbents keep better pore structure during calcium looping cycles. → The improvements of Mn(NO3)2 and MnCO3 on CO2 capture capacity are almost the same. -- Abstract: The effects of manganese salts including Mn(NO3)2 and MnCO3 on CO2 capture performance of calcium-based sorbent during cyclic calcination/carbonation reactions were investigated. Mn(NO3)2 and MnCO3 were added by wet impregnation method. The cyclic CO2 capture capacities of Mn(NO3)2-doped CaCO3, MnCO3-doped CaCO3 and original CaCO3 were studied in a twin fixed-bed reactor and a thermo-gravimetric analyzer (TGA), respectively. The results show that the addition of manganese salts improves the cyclic carbonation conversions of CaCO3 except the previous cycles. When the Mn/Ca molar ratios are 1/100 for Mn(NO3)2-doped CaCO3 and 1.5/100 for MnCO3-doped CaCO3, the highest carbonation conversions are achieved respectively. The carbonation temperature of 700-720 oC is beneficial to CO2 capture of Mn-doped CaCO3. The residual carbonation conversions of Mn(NO3)2-doped and MnCO3-doped CaCO3 are 0.27 and 0.24 respectively after 100 cycles, compared with the conversion of 0.16 for original one after the same number of cycles. Compared with calcined original CaCO3, better pore structure is kept for calcined Mn-doped CaCO3 during calcium looping cycle. The pore volume of calcined MnCO3-doped CaCO3 is 2.4 times as high as that of calcined original CaCO3 after 20 cycles. The pores of calcined MnCO3-doped CaCO3 in the pore size range of 27-142 nm are more abundant relative to clacined original one. That is why modification by manganese salts can improve cyclic CO2 capture capacity of CaCO3.