Density functional theory study on the thermodynamics and mechanism of carbon dioxide capture by CaO and CaO regeneration

Reducing CO2 emission is one of the most important events to solve the global climate problem. The carbonation reaction of CaO and the reverse reaction are potential methods for CO2 capture and concentration from dilute flue gases at high temperature. In this paper, the thermodynamics and mechanisms of CO2 capture by CaO and CaO regeneration from CaCO3 were studied and identified in the framework of density functional theory (DFT). In the calculation, the exchange-correlation term was approximated by Perdew-Wang (PW91), a function within the generalized gradient approximation (GGA) family. The reaction energies of carbonation reaction and calcination reaction were calculated to be -147.64 kJ mol(-1) and 180.60 kJ mol(-1), respectively. To study the reaction between CO2 and CaO, the transition states of carbonation and calcination were also analyzed. The results showed that the carbonation of CaO was rather fast, and the activation energy of carbonation reaction was 0 kJ mol(-1), which indicated that the reaction process was not the rate-determining step during the process of CO2 capture. The regeneration of CaO by CaCO3 calcination occurred at higher temperature, with the activation energy of 166.85 kJ mol(-1), and the rate of calcination was controlled by the chemical reaction.