Elsevier

Fluid Phase Equilibria

Volume 235, Issue 2, 31 August 2005, Pages 182-190
Fluid Phase Equilibria

Thermodynamics of binary mixtures containing N-methyl-2-pyrrolidinone: VLE measurements for systems with ethers—Comparison with the Mod. UNIFAC (Do) and DISQUAC models—Predictions for VLE, GmE, HmE and SLE

https://doi.org/10.1016/j.fluid.2005.06.017Get rights and content

Abstract

Isothermal vapour–liquid equilibrium data, (VLE) have been measured by an ebulliometric method for four binary mixtures of N-methyl-2-pyrrolidinone (NMP) with dipropyl ether at T = 353.15 K and T = 373.15 K, or dibutyl ether at T = 373.15 K, or methyl 1,1-dimethylethyl ether (MTBE) at T = 333.15 K, or methyl 1,1-dimethylpropyl ether (MTAE) at T = 353.15 K, in the pressure range from P = 0 kPa to P = 135 kPa.

The experimental VLE results have been correlated using a three parameter Redlich–Kister expansion. All these systems present positive deviations from Raoult's law.

Binary mixtures of NMP with dipropyl ether, dibutyl ether, MTBE and MTAE have been investigated in the framework of the Modified UNIFAC (Do) and DISQUAC models. The reported new interaction parameters for the NMP-group (Nsingle bondCO) and the ether group (single bondOsingle bond) give much better results than known from literature predictions of the thermodynamic properties, including vapour–liquid equilibrium, excess molar Gibbs energy, molar excess enthalpies and solid–liquid equilibrium. Our experimental data and literature data for binary mixtures containing NMP and ethers were compared to the results of predictions with the Mod. UNIFAC (Do) and DISQUAC models.

Introduction

N-Methyl-2-pyrrolidinone (NMP) is an aprotic and dipolar solvent of high selectivity. It has been used to extract aromatic hydrocarbons from aliphatic hydrocarbons. NMP causes the known specific interactions of a large carbonyl group, or nitrogen atom, or the hydrogen atom of methyl group with a solvent. On the other side the monoethers are aprotic and are considered essentially to be non-associating molecules. The interactions between NMP and ethers are believed to occur via complex formation between the two species.

The molecular structure of the N-methyl-2-pyrrolidinone under study is as follows:The interaction of NMP with ethers was studied by us by the measurements of the excess molar volumes and enthalpies of binary mixtures [1] and solid–liquid equilibrium measurements [2]. Recently, we have studied the interaction of NMP with ketones [3] and 2-alkanols [4]. The thermodynamic description using new interaction parameters of the Mod. UNIFAC (Do) or DISQUAC model were presented.

The present work is the continuation of our studies concerning the physicochemical properties of binary mixtures involving NMP. Up to now, we have reported data on vapour–liquid equilibria (VLE) [3], [4], solid–liquid equilibria [2], [5], [6], [7], [8], excess molar volumes, VmE [1], [9], [10], [11], [12], and excess molar enthalpies, HmE [10], [11], [12], of systems formed by NMP and n-alkanes, cycloalkanes, 1-alkenes, 1-alkynes, benzene, toluene, chlorobenzene, 1,1,1-trichloroethane, dichloromethane, 1-alkanols, ketones and ethers. We showed that, in (NMP + alkanol) solutions, the strong polar interactions between NMP and solvent are more important than the self-association of the alcohol. For this reason the ERAS model [13] was used for the description of some mixtures [4], [12]. The purpose of this paper is to investigate the ability of the Mod. UNIFAC (Do) and DISQUAC models to describe the GmE for (NMP + an ether) mixtures. For a more complete study, we also report VLE (Px) measurements of N-methyl-2-pyrrolidinone with dipropyl ether at T = 353.15 K and T = 373.15 K, or dibutyl ether at T = 373.15 K, or methyl 1,1-dimethylethyl ether, (tert-butyl methyl ether) (MTBE) at T = 333.15 K, or methyl 1,1-dimethylpropyl ether, (tert-amyl methyl ether) (MTAE) at T = 353.15 K, at pressure range from P = 0 kPa to P = 135 kPa by an ebulliometric method. New interaction parameters for (NMP + ether) of the Mod. UNIFAC (Do) and DISQUAC models were determined to describe the thermodynamic properties of these mixtures: VLE, GmE, HmE and SLE.

Section snippets

Materials

The origin of the chemicals (in parentheses are Chemical Abstracts registry numbers, and their mass percent purities) are as follows: NMP (872-50-4, Aldrich Chemical Co., 0.995, anhydrous), dipropyl ether (111-43-3, Aldrich, 99 mol%), dibutyl ether (142-96-1, Aldrich, 99 mol%), dipentyl ether (693-65-2, Fluka AG, 99 mol%), methyl 1,1-dimethylethyl ether (1634-04-46, Aldrich, 99.5 mol%), methyl 1,1-dimethylpropyl ether (994-05-8 Aldrich, 99 mol%). NMP was purified by fractional distillation under low

Results and data reduction

The experimental Px1 data at different temperatures are listed in Table 3, Table 4 and are plotted in Fig. 1, Fig. 2. No data have been found in the literature for comparison. The Px1 measurements were reduced using Barker's method [27] to obtain values γi, the activity coefficient of component i in the liquid state. To this end, it was assumed that GmE is represented by an equation of the Redlich–Kister type:GmERT=x1(1x1)i=0i=kAi(2x11)iwhere GmE is the molar excess Gibbs energy, x1 the

The Mod. UNIFAC (Do) model

There have been several attempts in the literature to correlate and predict thermodynamic excess functions and phase equilibria using either theoretical lattice-type models or other, more empirical, group contribution models. The Mod. UNIFAC (Do) [29], [30], [31] group contribution model based on the local composition concept with temperature-dependent parameters needs four parameters per contact (two for the Gibbs energy and two for the enthalpy) to reproduce GmE and HmE; two heat capacity

The DISQUAC model

The molecules under study, i.e. NMP and ethers, are regarded as possessing four types of groups: (1) type a (CH3, CH2 in NMP and ethers), (2) type c (c-CH2 in NMP), (3) type e (single bondOsingle bond in ethers) and (4) type n (single bondNsingle bondCdouble bondO group in NMP, which is different from the group in the Mod. UNIFAC model). The geometrical parameters, relative volumes ri, total relative surfaces qi, and surface fraction αdi for the compounds considered in this work were calculated on the basis of the group volumes and surfaces

Discussion

The results from the Mod. UNIFAC (Do) and DISQUAC models are compared with the experimental data for VLE, GmE, HmE and SLE in Table 11 and for selected mixtures in Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7. Generally, in the case of the VLE, the prediction is quite satisfactory (σ < 2 kPa). Using the new and available interaction parameters, the models are more or less successful in predicting the phase equilibria. The prediction of GmE is somewhat worse for the (NMP + MTAE) system by

Conclusions

P−x measurements at different temperatures for (NMP + ether) systems are reported. Mixtures of NMP with ethers were investigated in the framework of the Mod. UNIFAC (Do) and DISQUAC models. The corresponding interaction parameters were developed. The Mod. UNIFAC (Do) model offers an agreement of the usual quality using a limited number of adjusted parameters. The discrepancies were mainly due to the steric effects in the investigated ethers, which especially influence the SLE. The DISQUAC model

Acknowledgement

The authors gratefully acknowledge the Warsaw University of Technology for the financial support.

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