Elsevier

Fluid Phase Equilibria

Volume 275, Issue 1, 15 January 2009, Pages 27-32
Fluid Phase Equilibria

Vapor–liquid equilibria for water + acetic acid + (N,N-dimethylformamide or dimethyl sulfoxide) at 13.33 kPa

https://doi.org/10.1016/j.fluid.2008.09.010Get rights and content

Abstract

Isobaric vapor–liquid equilibrium (VLE) data of the systems acetic acid + N,N-dimethylformamide (DMF), acetic acid + dimethyl sulfoxide (DMSO), DMSO + water, water + acetic acid + DMF, and water + acetic acid + DMSO have been measured at 13.33 kPa by using an improved Rose equilibrium still. The association of acetic acid in vapor phase has been considered, and the nonideality of vapor phase was accounted for using the Hayden–O’Connell (HOC) method. The experimental binary data have been correlated by the NRTL, Wilson and van Laar models. The NRTL model parameters obtained from the binary data have been used to predict the ternary VLE data. The ternary predicted values obtained in this way agree well with the experimental values.

Introduction

Acetic acid is an important compound, and is widely used in the petroleum and dyestuff industries, and also in fiber synthesis, acrylic spinning, and polyester leather synthesis. The separation of acetic acid from aqueous solutions is industrially important. Because of the closeness of their boiling points and the deviation from ideal solution behavior, acetic acid cannot be easily removed from its mixtures with water by distillation. Extractive distillation is an attractive process for the separation of acetic acid from water.

Several solvents [1], [2], [3], [4], such as dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N-methyl pyrrolidone, and N-methyl acetamide, have been used as solvents for the separation of acetic acid and water. DMSO and DMF are good solvents for the separation of acetic acid, but they have a high normal boiling point, and DMSO easily decomposes at high temperature. Therefore, it is necessary to study the VLE of the systems water + acetic acid + (DMF or DMSO) at reduced pressure. Many VLE data of the systems water + acetic acid [5] or DMF [5] or DMSO [6], [7], [8]) have been reported. Unfortunately, little work has been done on VLE of the systems acetic acid + (DMF or DMSO), only isothermal VLE data of the systems acetic acid + (DMF or DMSO) are reported [9], [10]. In this article, the VLE data of the systems acetic acid + DMF, acetic acid + DMSO, DMSO + water, water + acetic acid + DMF, and water + acetic acid + DMSO were measured at 13.33 kPa. NRTL models parameters of the systems water + acetic acid, DMSO + water, DMF + water, acetic acid + DMF, and acetic acid + DMSO were obtained, and based to predict the VLE data of the ternary system water + acetic acid + (DMF or DMSO).

The nonideality in the vapor phase is accounted for by using the Hayden–O’Connell (HOC) method in combination with the chemical theory [11], [12], [13] to account for association between components. The liquid-phase nonideality is considered by the nonrandom two-liquids model (NRTL) [14], the Wilson model [15], and the van Laar equation [16]. The NRTL model was used to predict the VLE data of the ternary systems.

Section snippets

Materials

DMSO (99.7 mass%) was purchased from Wuxi Haishuo Biological Company, DMF (≥99.5 mass%) from Rugao Jinling Reagent Company, and acetic acid (≥99.5 mass%) from Hangzhou Chemical Reagent Company. All samples were purified by distillation. The water sample was distilled twice. The purity of the samples was checked by measuring boiling points and further confirmed by gas chromatography. Good agreement between the measured boiling points and literature values [17] is obtained as shown in Table 1.

Apparatus and procedure

The

Experimental data

To test the equilibria apparatus and experimental procedure, VLE data of the system water + acetic acid was measured at 101.33 kPa as shown in Fig. 2. It is found that the experimental data of this work agree well with the literature data [22], [29].

Experimental VLE data of the binary systems DMSO + water, acetic acid + DMSO, and acetic acid + DMF have been measured at 13.33 kPa. The results were reported in Table 2 and Fig. 3, Fig. 4, Fig. 5. The systems acetic acid + (DMSO or DMF) show a maximum

Conclusions

The VLE data of the systems acetic acid + DMSO, DMSO + water, acid + DMF, water + acetic acid + DMSO and water + acetic acid + DMF were measured at 13.33 kPa by using an improved Rose equilibrium still. The thermodynamic consistency test was passed for the measured binary systems. Parameters of NRTL model for the binary systems were obtained. The VLE data of the ternary systems water + acetic acid + (DMSO or DMF) at 13.33 kPa were predicted by using binary NRTL parameters. Ternary predicted values agree well with

Acknowledgment

Thanks are due to Yangfang Li for her helpful assistance in the computation work. This research was supported by the National Natural Science Foundation of China (NO. 20804038).

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