(86h) Ionic Liquids for Separation of Aromatics and Aliphatics: Extraction and Regeneration of Solvent Using CO2

Ionic liquids have been shown to be effective extraction solvents for the extraction of aromatic compounds from aliphatic compounds, as many ionic liquids are nearly insoluble in the raffinate phase and have good selectivity towards aromatics. One of the most important steps in an extraction process is regeneration of the solvent, which is usually accomplished by distillation or stripping. These methods often require high temperatures and high energy consumption, leading to a desire for a greener alternative. It has been shown that near supercritical CO₂ can be used as an antisolvent gas to induce a liquid-liquid phase split in some mixtures of ionic liquids and organic compounds. Previous work has shown the organic-rich liquid phase contains negligible ionic liquid, making the gas antisolvent process a very effective separation technique, as CO₂can be removed easily by lowering pressure.

Solubility has been measured in mixtures of ionic liquids and aromatic compounds, where a liquid+vapor to liquid+liquid+vapor phase transition is observed, demonstrating the ability of CO₂ to regenerate the ionic liquid. To be an energy efficient process, a low phase transition pressure with a low composition of CO₂ in the liquid phases is desired. Additionally, the ionic liquid must have high selectivity and capacity for the aromatic in the liquid-liquid extraction process. Various ionic liquids have been tested both for extraction and regeneration with CO₂ by measuring ternary liquid-liquid equilibrium of ionic liquid, aromatic, and heptane and high pressure phase behavior of ionic liquid, aromatic, CO₂ systems. Properties such as excess enthalpy and excess volume have also been studied to gain insight into the underlying thermodynamics to help guide process optimization.