Miscibility of tetrafluoroborate ionic liquids with dihydroxy alcohols

In this paper, we have carried out a study on miscibility of ([bmim]+, [hmim]+, [omim]+)[BF4]− ionic liquids and dihydroxy alcohols: vicinal (1,2-diol) — C2(1,2)(OH)2 to C6(1,2)(OH)2, terminal (1,ω-diol) — C2(1,2)(OH)2 to C5(1,5)(OH)2 and butanediol isomers. Phase diagrams were determined at atmospheric pressure over the temperature range (270 to 340) K using the cloud-point method. LLE data for all 18 binary systems determined show the same behavior, representing phase diagrams with the upper critical solution temperature (UCST). With increasing chain length in C-3 position of the imidazolium cation, the UCST shifts toward higher temperatures for the systems with ethane-1,2-diol. Contrary, for the systems of longer diols with hydroxyl group in 1,2-position (propane-1,2-diol, butane-1,2-diol, pentane-1,2-diol and hexane-1,2-diol) improvement of miscibility was observed. The influence of different characteristics of alcohols and ILs, including cation alkyl chain length, alcohol chain length, and relative position of both OH groups in diol was also studied.