New insights into the functional group influence on CO2 absorption heat and CO2 equilibrium solubility by piperazine derivatives

Piperazine (PZ) derivatives which have been widely used in CO 2 capture technology exhibit stable physicochemical properties, such as resistance to thermal degradation and low regeneration energy consumption. Both two parameters of CO 2 absorbents, low CO 2 absorption heat (ΔH abs ) and large CO 2 equilibrium solubility (α e ), are important to CO 2 capture performance. However, the influence of functional group types of PZ derivatives on their CO 2 capture performance remained unclear. This research aimed to study the functional group influence on the ΔH abs and α e by PZ derivatives with two amines using experimental and quantum chemical methods. The results indicated that PZ derivatives with the ethyl side chain had larger ΔH abs and α e than those with the methyl side chain. The presence of the hydroxy group in PZ derivatives reduced the ΔH abs and the α e . The presence of cyclic methyl side chains on the N atom of PZ derivatives decreased the ΔH abs and increased α e at the same time. The findings show that PZ derivatives with cyclic methyl side chains, steric hindrance effect, and no hydroxy group are favorable for CO 2 capture. Among the eight PZ derivatives, TEDA with lower ΔH abs (48.99 kJ/mol) and higher α e (0.917 mol CO 2 /mol amine) is an excellent absorbent. The results of this study are very important for screening efficient and low-energy consumption absorbents for CO 2 capture.