Determination and correlation of liquid–liquid equilibrium data for the dichloromethane + water + N,N-dimethylacetamide + NaCl system

Abstract

The (liquid + liquid) equilibrium (LLE) data for the quaternary system dichloromethane (DCM) + water + N,N-dimethylacetamide (DMAC) + NaCl have been determined at (298.15 and 308.15) K and atmospheric pressure. The experimental data were correlated by using Othmer–Tobias equation, and all the linear correlation coefficients were approximate to 1. Both NRTL and UNIQUAC models were adopted to correlate the LLE data, the model parameters were regressed by nonlinear least-squares method, then the LLE data of the quaternary system were calculated. The comparison between calculated and experimental data shows good agreement. The results show that the enlargement of two-phase region occurred with an increase of salt concentration in initial aqueous phase, and adding salt to the system is beneficial to increase the selectivity of solvent.

Introduction

In industrial applications, especially in the production of medical intermediates, the waste liquor is usually drained off with the different concentrations of DMAC and a small quantity of DCM. Direct emissions would cause significant pollution and loss of DMAC [1]. The study of efficiently separating and recovering DMAC from the waste liquor possesses an important significance on industry and environmentally sustainable development. At present, there is relatively little research on the liquid–liquid equilibrium (LLE) for the system containing salt. Ghalami-Choobar et al. [2] has studied the salt effect on the LLE of water + propionic acid + cyclohexanol system, the salt effect of methyl acetate + methanol + water system has been studied by Huang et al. [3], The LLE data for the quaternary system water + acetic acid + MTBE + NaCl have been determined by Zhang and Wang [4]. However, the research on the LLE data for quaternary system DCM + water + DMAC + NaCl has not been reported in the literature yet.

As a basic work, we have already determined the LLE data for the ternary system DCM + water + DMAC, the LLE data obtained are shown in Table 2 [5]. In order to investigate the salt effect on this system, we have determined the LLE data for the DCM + water + DMAC + NaCl system with different content of NaCl at 298.15 K and 308.15 K, respectively. The experimental data were correlated by using the NRTL and UNIQUAC models, the results indicated that the experimental data agreed well with the calculated LLE data, the above data and calculation methods are helpful for separating and recovering DMAC from waste liquor in industrial applications.