(231an) Conceptual Process Design for Separation of Rare Gases Using Ionic Liquids | AIChE

(231an) Conceptual Process Design for Separation of Rare Gases Using Ionic Liquids


Liu, X., University of the California
Prausnitz, J. M., University of California, Berkeley

Ionic liquids may provide an absorption-based process to separate krypton and xenon from an oxygen stream taken from air-sepration plant. Because the polarizabilities of krypton and xenon are quite different from that of oxygen, an ionic liquid may be a good solvent for a separation process.

Our calculations with COSMO-RS (COnductor-like Screening Model for Real Solvents) suggest that a carefully selected ionic liquid can preferably dissolve xenon and krypton over  oxygen in a way that the relative volatility of oxygen to krypton and krypton to xenon may be about 3 and 4, respectively.

We developed three different methods to measure solubilities of gases, in particular krypton, xenon, oxygen and other gases in selected ionic liquids at 25 to 80°C and pressures from atmospheric to 5 MPa. Because of the lack of solubility data and the lack of off-the-shelf equipment, experimental equipment was built and calibrated. Equipment was built for using experimental methods based on gas-liquid chromatography, on the inert-gas stripping technique, and on isochoric-synthetic principles. For our purposes, the isochoric-synthetic method was best.

We measured solubilities of krypton, xenon and oxygen in many ionic liquids and found that trihexyltetradecylphosphonium bis (2,4,4-trimethylpentyl) phosphinate [P(14)666][TMPP] shows good selectivity and high capacities for the rare gases. However, this ionic liquid has a very high viscosity. We measured densities and viscosities of [P(14)666][TMPP] at different temperatures with and without promising diluents for reducing viscosity.

Final attention was given towards a process flow diagram for a possible sepration process based on selective absorption at ambient temperature.