Swelling poly(ionic liquid)s for demulsifying oil-in-water emulsion by anion exchange

In this work, poly(ionic liquid)s (PILs) with swelling ability were prepared via the free radical copolymerization of N-vinyl imidazolium ionic liquids and divinylbenzene. Nuclear magnetic resonance and Fourier-transform infrared analyses confirmed the successful synthesis of PILs. The PILs were evaluated as demulsifiers for a model oil-in-water emulsion, where sodium dodecyl sulfate (SDS) was used as a surfactant. The demulsification efficiencies of PILs increased from 18%, 34%, 92% to 99% with the alkyl chain of three-substituents on imidazolium varied from n-octyl, n-hex1yl, n-butyl to n-ethyl, which positively related with the swelling ratios of PILs in the emulsion. The amounts of dodecyl sulfate and Br⁻ in the aqueous phase after demulsification were analyzed by high-pressure liquid chromatography and ion chromatography, respectively. The decreased amount of dodecyl sulfate coincided with the increased amount of Br⁻, indicating that the anion exchange between surfactant SDS and PILs was occurred. The PILs could be recycled by ion exchange with NaBr solution and the demulsification efficiencies did not show significant decline during five times of recycling. Meanwhile, P[VEIm]Br@4 Å zeolite prepared by loading poly(1-vinyl-3-ethylimidazolium bromide) on 4 Å zeolite was used for continuous demulsification in the T type device. The T type device had stable fluxes (1083 L ·m⁻² h⁻¹) for various oil-in-water emulsions with excellent demulsification efficiencies (above 99%).