The most common commercial process for O
2 separation from N
2 is cryogenic distillation, but the process is expensive and energy intensive. More efficient and effective O
2 separation from the air is needed. One possibility is to use solvent-based absorption coupled with vacuum or thermal regeneration, but solvents with improved O
2 working capacity need to be developed. Cobalt (Co) containing solvents are of particular interest because of their high affinity for O
2. In this presentation, we show screening and theoretical calculations of solvents to solve a Co metal containing complex, salcomine (Co(salen)), and O
2 and N
2 interactions with the systems from quantum mechanical calculations in the gas phase. All possible spin states for the O
2-Co(salen)/solvent systems were considered. The experimental O
2 solubilities in Co(salen) solved in different solvents at room temperature and the theoretical O
2 interactions with the Co(salen)/solvent system were compared. It was found that when the interaction is below -23 kJ/mol, O
2 solubility in the system will be low and is determined by physical absorption. When O
2 interaction with the system is stronger than -30 kJ/mol, at low Co(salen) concentration in solvent, the O
2:Co ratio is 1:1. At higher Co(salen) concentrations in the solvent, the O
2:Co ratio is 0.5. When the O
2 interaction is around -25 kJ/mol, the O
2:Co ratio is about 0.5 independent of the Co(salen) concentration in solvents. In contrast, N
2 interactions with the same systems were found to be much lower, about -16 kJ/mol. Furthermore, the calculations show that by adding ethyl groups on Co(salen), the O
2 interaction could be increased.
The NIST database was screened by specifying some specific sub-structures. Three promising solvents were identified with low vapor pressures. Our molecular modeling calculations further predict that the viscosities for those solvents are low, which was experimentally confirmed. In addition, the quantum mechanical calculations suggest that O2 solubilities in Co(salen) solved in the solvents would be high. We will also discuss the calculation results in the condensed phase.
