(442e) Theoretical Investigations of Air Separation Using Cobalt-Containing Complexes and Solvents
AIChE Annual Meeting
2021
2021 Annual Meeting
Computational Molecular Science and Engineering Forum
Practical Applications of Computational Chemistry and Molecular Simulation III
Tuesday, November 16, 2021 - 1:30pm to 1:50pm
The most common commercial process for O2 separation from N2 is cryogenic distillation, but the process is expensive and energy intensive. More efficient and effective O2 separation from the air is needed. One possibility is to use solvent-based absorption coupled with vacuum or thermal regeneration, but solvents with improved O2 working capacity need to be developed. Cobalt (Co) containing solvents are of particular interest because of their high affinity for O2. In this presentation, we show screening and theoretical calculations of solvents to solve a Co metal containing complex, salcomine (Co(salen)), and O2 and N2 interactions with the systems from quantum mechanical calculations in the gas phase. All possible spin states for the O2-Co(salen)/solvent systems were considered. The experimental O2 solubilities in Co(salen) solved in different solvents at room temperature and the theoretical O2 interactions with the Co(salen)/solvent system were compared. It was found that when the interaction is below -23 kJ/mol, O2 solubility in the system will be low and is determined by physical absorption. When O2 interaction with the system is stronger than -30 kJ/mol, at low Co(salen) concentration in solvent, the O2:Co ratio is 1:1. At higher Co(salen) concentrations in the solvent, the O2:Co ratio is 0.5. When the O2 interaction is around -25 kJ/mol, the O2:Co ratio is about 0.5 independent of the Co(salen) concentration in solvents. In contrast, N2 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 O2 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.