Minimising the regeneration heat duty of post-combustion CO2 capture by wet chemical absorption: The misguided focus on low heat of absorption solvents

An ideal solvent for CO2 capture by chemical absorption has to meet a number of requirements, such as high CO2 capacity, high rate of reaction, low costs, low corrosive behaviour, low degradation and low vapour pressure; above all, it has to show a low regeneration heat duty. This heat can be approximated as the sum of three terms: the sensible heat to raise the solvent from absorber to desorber temperature, the heat of evaporation required to produce the stripping steam in the reboiler, and the heat necessary to desorb the CO2 from the solution (heat of absorption).Many solvent screening studies focus almost exclusively on solvents that show a low heat of absorption. In these studies, the strong dependence of the three contributors to the overall regeneration heat duty on the chosen process parameters and on one another are often neglected.This work explains why the focus on solvents with a low heat of absorption, without considering the overall process, is not sufficient in quantifying the energy performance of alternative solvents. By using thermodynamic interrelations and underpinned by process simulations it is shown that operating parameters of the process, in particular the desorber pressure, must be taken into consideration in the evaluation of new solvents.