Selection of deep eutectic solvents for <scp> CO ₂ </scp> separation processes by thermodynamic analysis

Abstract To mitigate global warming, it is crucial to reduce CO 2 emissions from the combustion of fossil fuels. CO 2 separation plays a key role in this process. Deep eutectic solvents (DESs) have demonstrated significant advantages and are considered promising liquid absorbents. In this study, DESs were chosen as absorbents for CO 2 separation from various CO 2 streams, including flue gas, lime kiln gas, bio‐syngas, and biogas by thermodynamic analysis. Based on the criteria of the amount of absorbents required and energy use, several DESs including N,N‐dimethylethanolammonium chloride/urea (1:1), choline chloride/urea (2:3), choline chloride/urea (2:5) were selected for the four CO 2 streams. Meanwhile, choline chloride/lactic acid (1:5) was selected for flue gas, tetrabutylammonium bromide/lactic acid (1:3) was selected for lime kiln gas, and N,N‐dimethylethanolammonium chloride/urea (1:1) was selected for bio‐syngas and biogas. It is revealed that the selected DESs exhibit a lower amount of absorbents required and lower energy use than those of other DESs and their aqueous solutions. The relationship among the absorption pressure, the energy use, the physical properties, and the critical properties of DESs are established for the four CO 2 streams. It is shown that the absorption pressure of the DESs can be fitted with the physical properties, which are density and heat capacity, with average relative deviations lower than 5%, while the energy use can be fitted with the critical properties, which are critical temperature and critical pressure, with average relative deviations below 1%. It suggests that the selected DESs have potential for further applications.