Hydrogel with Selective Absorption for Separation of Liquid Mixtures

Abstract

Separation of liquid mixtures is crucial in many industries including petrochemicals, mining, leather, food, steel and metal processing. Conventional separation technologies such as distillation and liquid-liquid extraction are limited by high energy consumption, the inability to separate azeotropes (constant boiling mixture) or post treatment after separation. Therefore, there is a dire need to develop an energy efficient methodology to separate liquid mixtures. Absorption is a promising alternative that can separate liquid mixtures by selectively absorbing one phase over the other. In this work, we report a hydrophilic (water-loving) and oleophobic (oil-hating) hydrogel by copolymerizing N-Isopropylacrylamide (NIPAM) with 1H,1H,2H,2H-Heptadecafluorodecyl acrylate (F-acrylate) (F-NIPAM). Our F-NIPAM can selectively absorb polar liquids while repelling non-polar liquids. Utilizing selective absorption, we demonstrate separation of both immiscible oil-water mixtures and miscible polar-non-polar liquid mixtures including heptane-ethanol and methanol-methyl oleate. Our F-NIPAM’s selective absorption can be characterized by the Flory-Huggins polymer-solvent interaction parameter (). The  values of our F-NIPAM with polar liquids are ≤ 0.5 while that with non-polar liquids are greater than 0.5. Guided by the above principles, we also demonstrate separation of miscible polarpolar liquids by increasing the  value for only one phase greater than 0.5. We also show that our F-NIPAM can release the absorbed liquid either by the application of mild heat or by submerging in an aqueous sodium chloride (NaCl) solution. Finally, we engineer an apparatus that allows for continuous separation of liquid mixtures and in situ release of the absorbed liquid from our FNIPAM. Utilizing the apparatus, we successfully demonstrate the separation of oil-water mixtures and simultaneous recovery of the absorbed water.