Quantum chemical studies of solvents for CO2 capture

The interactions of CO₂ with thirty-six solvent molecules (cyclohexane, carbon tetrachloride, pentane, thiophene, formic acid, vinyl acetate, 1,4-dioxane, water, methanol, imidazole, dimethyl sulfoxide, etc.) were probed at the MP2/6–311++G(d,p) level of theory. The solvent molecules were bound to either oxygen or carbon atom of CO₂. The investigated solvents exhibited a relatively weak interaction with CO₂. All the interaction energy (E_int) values for the interaction of CO₂ with the investigated solvents were negative and in the range of −3.36 (1,2,3-triazole/CO₂ complex) to −0.33 kcal/mol (carbon tetrachloride/CO₂ complex). A high negative value of E_int reflects the stronger interaction between the solvent molecule and CO₂. The molecular electrostatic potential (MESP) minimum (V_min-X) values of the investigated solvents were in the range of −81.51 (dimethyl sulfoxide) to −3.33 kcal/mol (cyclohexane). A high negative V_min-X value of the solvent molecule is ascribed to its more electron-rich character. V_min-X displayed a good correlation with E_int, indicating that V_min-X can be used as a measure of the interaction strength between CO₂ and the solvents. The MESP analyses also showed that the CO₂ usually becomes electron-rich as a result of the interaction with the solvent molecules. The QTAIM results imply a noncovalent character for the interaction of CO₂ with solvent molecules.