Efficient Liquid–Liquid Extraction of Benzene from Its Mixture with Cyclohexane by Utilizing Hyperbranched Polymeric Ammoniums Salts

A novel hyperbranched polymeric quaternary ammonium salt (HPQAS) with benzene rings in the structure (PVBC-TMA) was synthesized by self-condensing vinyl polymerization followed with quaternary amination reaction. Meanwhile, a hyperbranched polyamidoamine (PAMAM) was separately neutralized with different acids to produce the HPQASs without benzene rings. These HPQASs were dissolved in DMSO and used to extract benzene from its mixture with cyclohexane. The liquid–liquid equilibrium (LLE) data indicate that the HPQAS/DMSO mixture showed a higher selectivity coefficient (19.92) than DMSO (<15). PVBC-TMA having benzene rings showed higher extraction performance than the PAMAM salts without benzene rings, especially when the composition of benzene/cyclohexane is close to the azeotrope state. The cation−π and π–π interactions between the ammonium ion and the benzene ring in the HPQAS with benzene in the benzene/cyclohexane mixture were thought to be the mass transfer impetus for extracting benzene from its mixture with cyclohexane by utilizing the HPQASs. This was the first example of applying the hyperbranched polymeric ammonium in the separation of benzene/cyclohexane.