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Untersuchungen zur gasinduzierten Phasentrennung bzw. zum Aussalzen mit nahekritischen Gasen wurden an verschiedenen wässrigen Lösungen (auch mit ionischem Fluid) durchgeführt. Ziel war der Nachweis und die Charakterisierung von Hochdruckmehrphasengleichgewichten, die sich für eine technische Anwendung eignen. Kriterien hierfür sind Auftreten des Flüssig/flüssig-Phasenzerfalls bei relativ niedrigem Druck, seine Existenz über einen weiten Druck- und Zusammensetzungsbereich und damit verbunden eine druckinduzierte Änderung der Zusammensetzung der koexistierenden Flüssigphasen. Die eingesetzten ionischen Fluide zeigen zwar das gewünschte Phasenverhalten, erfüllen die Kriterien aber nur teilweise. Im Vorgriff auf eine mögliche Anwendung wurde die Verteilung eines hochmolekularen, amphiprotischen Naturstoffs auf die koexistierenden Flüssigphasen untersucht und durch Einstellung des pH-Werts gezielt verändert. -------------------------------------------------------------------------------------------------------------------------------------
Investigations on gas-induced phase split, i.e., salting out by a nearcritical gas, were carried out for several aqueous solutions (including an ionic liquid). The research aimed to verify and characterize high-pressure multiphase equilibria that might be suitable for technical applications. The respective criteria are occurrence at relatively low pressures and the existence of the phase equilibrium phenomenon over a significant region of both composition and pressure, which is related to a pressure-induced significant alteration of the compositions of the coexisting liquid phases. The employed ionic liquids revealed the expected phase behavior but without full compliance of all criteria. In anticipation of an application, the partitioning of an amphiprotic, high-molecular biomolecule to the coexisting liquid phases was successfully administered via a pH variation.
The solubility of a single gas as well as the simultaneous solubility of several gases in an ionic liquid is of great interest in many areas of chemical engineering, particularly in heterogeneous catalysis. One of the most interesting features involved in the study of the simultaneous solubility of several gases in a pure ionic liquid is the difference between experimental data and predictions for the simultaneous solubility (based on experimental data for the solubility of the single gases). The well soluble gas might act as a cosolvent or as an antisolvent for a sparsely soluble second gas. New experimental results and a correlation are presented for the simultaneous solubility of hydrogen (i.e., a sparsely soluble gas) and carbon dioxide (a well soluble gas) in the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([hmim][Tf2N]) at temperatures between 293 K and 373 K and pressures up to about 9.2 MPa. The experimental results reveal that carbon dioxide acts as a cosolvent for hydrogen in that particular ionic liquid. A correlation shows that the cosolvency effect can be modeled by considering interaction parameters between hydrogen and carbon dioxide in liquid [hmim][Tf2N]. The correlation can also be used to quantify that cosolvency effect: one mole of carbon dioxide in 1000 g of [hmim][Tf2N] increases the solubility of (small amounts of) hydrogen by about 20%.
In the last two decades, the solubility of gases in ionic liquids has attracted a lot of attention. While at the beginning most publications dealt with the solubility of a single gas in a pure ionic liquid, recently the interest starts to shift to the – from an application-oriented point of view – more challenging area of the simultaneous solubility of several gases in an ionic liquid and/or the solubility of a single gas in solvent mixtures with ionic liquids. The current state of information on experimental data (and the phenomena encountered) in such systems is summarized and discussed.