Is the color of Ionic Liquids a problem?
Colored materials are quite often perceived as being impure. In fact, most Ionic Liquids are colorless liquids. However, they tend to become colored especially during prolonged thermal treatment. The good news is that the color persistently stays in the Ionic Liquid and cannot be extracted in any organic product or solvent. Currently no one has managed to isolate the colorant because the quantities are just too low. It is assumed that oligomers of the imidazole or even radical ions might cause the color. For commercial applications the color is usually not a problem, since products are not affected. BASF has been running a pilot plant for an extractive distillation process for 3 months continuously. The color of the Ionic Liquid changed to black, but the performance stayed constant without the need for any purge. During the entire run the product was colorless clear and fully inline with the required specification. For this application it would have been a waste of money to start with
