Liquid–liquid equilibrium behavior of tetrabutylammonium bromide, benzene, and water mixture

Tetrabutylammonium bromide (QBr) is a weak organic salt and used as a phase-transfer catalyst in phase-transfer catalytic reaction producing the desired product of benzyl bromide in the organic phase. The distribution of QBr between the organic phase (benzene is the organic phase solvent) and the aqueous phase is the important factor influencing benzyl bromide yield. In this study, the liquid–liquid equilibrium of benzene, water, and QBr ternary mixture were measured at 318.15, 328.15, and 338.15 K, respectively. The experimental results exhibited that the solubility of QBr is very large in this heterogeneous liquid mixture and the amount of aqueous phase increases whenever more QBr was added at constant temperature. The concentration of QBr in aqueous phase decreased with the increasing temperature. The organic phase composition did not vary obviously since the solubilities of water and QBr in benzene are very low. An empirical parameter was introduced to represent the degree of dissociation of QBr in solvent while the experimental data were correlated since it is very difficult to measure the degree of dissociation of QBr attributed to the partial dissociation of a weak organic salt. Finally, the experimental data were correlated with the NRTL model of Renon and Prausnitz taking account ion–molecule and molecule–molecule interactions.