Measurement of (vapor + liquid) equilibrium for the systems {methanol + dimethyl carbonate} and {methanol + dimethyl carbonate + tetramethylammonium bicarbonate} at p = (34.43, 67.74) kPa

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Abstract

Isobaric (vapor + liquid) equilibrium (VLE) data for the binary system (methanol + dimethyl carbonate) and the ternary system (methanol + dimethyl carbonate + tetramethylammonium bicarbonate) have been measured at p = (34.43, 67.74) kPa using a modified Rose–Williams still. The experimental data for the binary system were well correlated by Wilson, NRTL, and UNIQUAC activity-coefficient models at the two reduced pressures. All the experimental results of the binary system passed the thermodynamic consistency test by the area test of Redlich–Kister and the point test of Van Ness et al. The experimental results of ternary system show that the salt tetramethylammonium bicarbonate has a salting-in effect on methanol. And this effect enhances when the salt concentration increases.

Highlights

VLE data for the binary system and the ternary system were measured. ► Methanol, dimethyl carbonate, and tetramethylammonium bicarbonate were studied. ► Isobaric experimental data were measured at p = (34.43, 67.74) kPa. ► VLE data of binary system were correlated with the Wilson, NRTL, and UNIQUAC models. ► The salt effect of TMAB on the VLE of {methanol + DMC} system was investigated.

Introduction

This work originates from an industrial project whose product is the electronic grade tetramethylammonium hydroxide (TMAH). TMAH, an organic base as strong as KOH, is widely used in developing and washing processes of semiconductor production [1], [2]. Recently, semiconductors have been integrated more densely, and this progress requires a higher purity of TMAH. The electronic grade TMAH was obtained through electrolysis of the tetramethylammonium bicarbonate (TMAB) in an electrolytic cell with a cation exchange membrane [3], [4]. In the process of synthesizing the organic salt TMAB, trimethylamine gas and dimethyl carbonate (DMC) were raw materials and purified methanol was used as the solvent. In order to obtain higher yield of TMAB, dimethyl carbonate should be excessive. While the electrolysis process had a strict requirement with the amount of methanol and DMC. Simultaneously, considering that TMAB is prone to break down at about 403.15 K, vacuum distillation was designed to rectifying the mixture containing methanol, DMC, and TMAB. Therefore, the understanding of chemical–physical properties of DMC + methanol + TMAB mixture at reduced pressures needs to be studied in order to enhance the ability to separate the TMAB-based mixture.

(Vapor + liquid) equilibrium (VLE) for the binary system (methanol + dimethyl carbonate) [5], [6], [7], [8], [9], [10] has been widely studied at atmospheric or pressurized conditions. But few literatures involve the binary system (methanol + DMC) at reduced pressures. Fukano et al. [11] measured the boiling point data of the mixture (methanol + DMC) from 40.00 kPa to 93.32 kPa. Matsuda et al. [12] have reported the VLE data for the system (methanol + DMC) at p = (66.66, 93.32) kPa recently, while the integral VLE data of the binary system (methanol + DMC) at reduced pressures still have been limited. On the other hand, the VLE data for the ternary system containing methanol and DMC mainly focused on the effect of the third component, usually an effective extraction agent (aniline [13] and dimethyl oxalate [14]) to enhance the relative volatility between methanol and dimethyl carbonate. A few literatures [13], [14], [15] involve the salt effect of methanol and DMC system. While no isobaric VLE data are available for the ternary system (methanol + DMC + TMAB) at reduced pressures.

The objective of this work is to obtain the (vapor + liquid) equilibrium data for the binary system (methanol + DMC) and the ternary system (methanol + DMC + TMAB) at p = (34.43, 67.74) kPa. The VLE data for the binary system (methanol + DMC) obtained were correlated with Wilson, NRTL, and UNIQUAC activity coefficient models.

Section snippets

Chemicals

Methanol (⩾0.998 mass fraction, HPLC grade, Merck) and dimethyl carbonate (⩾0.990 mass fraction), were supplied by Tianjin Guangfu Technology Development Co. Ltd., China. Methanol was used without further purification. Dimethyl carbonate was dried over molecular sieves (Guangfu, type 0.3 nm). The purity of the DMC and methanol were 0.998 mass fraction and 0.995 mass fraction by GC. All products were degassed ultrasonically. Tetramethylammonium bicarbonate (TMAB) was prepared in our own

Binary system

Isobaric (vapor + liquid) equilibrium data for the binary system (methanol + DMC) have been measured at p = (34.43, 67.74) kPa. The experimental VLE data and the results are listed in TABLE 3, TABLE 7. The experimental binary VLE data were tested for thermodynamic consistency using the area test of Redlich–Kister [20], [21] and the point test of Van Ness et al. [22], modified by Fredenslund et al. [23], which have been described by Gmehling and Onken [24]. The results of thermodynamic consistency test

Conclusions

In this paper, isobaric (vapor + liquid) equilibrium data for the binary system (methanol + dimethyl carbonate) and the ternary system (methanol + dimethyl carbonate + tetramethylammonium bicarbonate) have been measured at p = (34.43, 67.74) kPa. The experimental data of binary system were well correlated by the Wilson, NRTL, and UNIQUAC activity coefficient models at the two reduced pressures. And the NRTL activity coefficient model shows slightly better results than the other two models with the

Acknowledgments

This work has been supported by the Programme of Introducing Talents of Discipline to Universities (No. B060006). And we would like to express our sincere appreciation to the anonymous reviewers for their insightful comments, which have greatly aided us in improving the quality of the paper.

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