Performance of non-aqueous amine hybrid solvents mixtures for CO₂ capture: A study using a molecular-based model

We present here results regarding the chemisorption of CO₂ in non-aqueous hybrid solvents of mixtures of amines and physical solvents such as glycols or glymes as alternatives to aqueous amines for CO₂ capture and separation, using the molecular-based equation of state, soft-SAFT, as a modelling tool. The reactive nature of the CO₂ absorption process in non-aqueous amines was implicitly considered through the formation of CO₂-amine physical aggregates bounded by strong and localised intermolecular interactions, with the effect of non-aqueous solvents on the reactivity included in these interactions. With such a modelling framework, only VLE data on the absorption of CO₂ in amine solvents is required, without any need for additional information such as speciation reactions or equilibrium constants, thus decreasing the number of adjustable parameters needed to accurately model the absorption process. Subsequently, the developed models were used to examine the CO₂ capture performance of these hybrid solvents in terms of absorption cyclic capacity and heat of regeneration as key performance indicators using a simple and short-cut estimation method. Results show that for the same total amine mass concentration, non-aqueous amine solvents possess a 30-40% decrease in total heat of regeneration compared to their aqueous counterparts at the expense of a 10-50% reduction in cyclic capacity. These results validate the reliability of the molecular modelling approach as an attractive and valuable tool for the screening of chemical solvents and process modelling.