Sigmoid Correlations for Gas Solubility and Enthalpy Change of Chemical Absorption of CO₂

Knowledge of the relationship between gas solubility and enthalpy change of chemical absorption of CO₂ is very important for exploring energy-efficient absorbents for CO₂ capture. To this end, equations that can directly correlate gas solubility with absorption enthalpy were derived through combining the van’t Hoff equation with the reaction equilibrium thermodynamic model (RETM). Two typical reaction mechanisms for chemical absorption of CO₂ (1:1 and 1:2) were considered for RETM. The variations of gas solubility with enthalpy change were found to be distinctively sigmoid functions, regardless of the investigated temperature and pressure or assumed reaction forms between CO₂ and the absorbent molecule. Theoretically calculated variation curves of gas solubility vs enthalpy change agreed well with experimental results reported in literature. On the basis of the trade-off relationship between gas solubility and enthalpy change, criterions for evaluating energy-efficient chemical absorbents for CO₂ capture were proposed.