Separation of dibutyl carbonate/butyl carbamate close-boiling mixture using imidazolium-based ionic liquids

Abstract

An efficient method using commercially available ionic liquids (ILs) as extractants for the separation of a close-boiling mixture containing dibutyl carbonate (DBC) and butyl carbamate (BC) was provided. It was found that 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) displayed the best performance for the separation of DBC and BC, and the purity of the DBC and BC could reach 99.8% and 99.9%, respectively, under the optimum conditions. According to the results of infrared spectroscopy (IR) and thermogravimetric (TG) analyses, the superiority of [BMIM]Cl might be related to the high nucleophilicity (i.e. ability to hydrogen bond) of the Cl⁻, which could be able to interact with the amino in BC to form a eutectic mixture and resulted in easy removal of DBC. Meanwhile, no decomposition of [BMIM]Cl was observed in the heating process, and the obtained results showed that [BMIM]Cl could be successfully reused for ten recycles with DBC purity of 99.5% avoiding any further treatment. Moreover, [BMIM]Cl also exhibited good performance in the separation of a dimethyl carbonate/methanol azeotropic mixture.