3.5. Heat of regeneration
The TGA and DSC analyses were performed on AC-MEA and AC-DEA samples which had captured CO2 at 70 C and 430 kPa. Under this condition, the samples yielded the highest CO2 adsorption capacities of 198.9 mg CO2/g AC-MEA (4.52 mol/kg) and 216.1 mg CO2/g AC-DEA (4.91 mol/kg). Fig. 8 shows the TGA and the DSC curves during a rise in temperature from 70 to 160 C for the AC-MEA and from 70 to 170 C for the AC-DEA. From the TGA curves, the weight loss due to the temperature rise was 169.2 mg/g AC-MEA and 194.4 mg/g AC-DEA. The weight loss was due to the desorption of CO2 from the adsorbent. The amount of desorbed CO2 was 15% and 10% lower than the amount of adsorbed CO2 estimated from the adsorption isotherms for the AC-MEA and the AC-DEA,
respectively. A possible explanation for the difference between the adsorbed and the desorbed amounts was that some CO2 molecules were released from the adsorbent during sample handling and
storage before the desorption experiments [51].
The DSC curves illustrated that the desorption was an endothermic reaction. The endothermic heat of the spent AC-MEA and AC-DEA was 556.5 and 635.8 J/g sample, respectively,
and Qregen of the spent AC-MEA and AC-DEA was 145 and 144 kJ/mol CO2, respectively. The heat input required to regenerate the spent impregnated AC samples was comparable to the
regeneration heat of zeolite 13X (146 kJ/mol CO2) [24] and was much lower than the heat required to regenerate the rich CO2 30% MEA solution (344.5 kJ/mol CO2) [52].