Extraction of 1,3-propanediol from aqueous solutions using different ionic liquid-based aqueous two-phase systems

Abstract

The separation of 1,3-propanediol from water is challenging because of its high polarity and high boiling point. Thus far, extraction has not been considered a potential separation method because of the extremely low solubility of 1,3-propanediol in organic solvents. However, aqueous two-phase systems could be used to overcome this limitation. Hence, the aim of the present study was to investigate the ability of water miscible ionic liquids to build aqueous two-phase systems for the separation of 1,3-propanediol. Different ionic liquids were tested using 1-butyl-3-methylimidazolium trifluoromethansulfonate as the initial ionic liquid, and the type of anion (dicyanamide, thiocyanate, methysulfate) and structure of the cation (1-butyl-3-methylmorpholinium, 1-butyl-3-methylpyrrolidinium, 1-ethyl-3-methylimidazolium, 1-methoxyethyl-3-methylimidazolium) were independently varied. All investigated ionic liquids showed the ability to form two phases by adding a mixture of K2HPO4 and KH2PO4; however, the phase forming strength differs. An increase in the polarity of the ionic liquid leads to smaller miscibility gaps of the resulting aqueous two-phase systems. Additionally, the performance of the aqueous two-phase systems in the extraction of 1,3-propanediol was investigated. The results indicated that all of the aqueous two-phase systems are suitable for the extraction of 1,3-propanediol and the distribution coefficient of 1,3-propanediol depends on the polarity or hydrogen-bond accepting strength of the cation and anion.