Experimental and predicted vapor–liquid equilibrium for binary systems with diethanolamine, m-cresol and p-cresol at 20.0 kPa

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Highlights

Abstract

Isobaric vapour–liquid equilibrium (VLE) data for two binary systems of p-Cresol (PC) + diethanolamine (DEA) and m-Cresol (MC) + DEA were measured at 20.0 kPa. The Herington area method was used to check the binary VLE data, and the results showed good thermodynamic consistency. Meanwhile, the Wilson, NRTL, UNIQUAC models and the chemistry theory proposed by Dolezalek were used to correlate the VLE data. The binary energy interaction parameters for activity models, and reaction equilibrium constants for chemistry theory were obtained. With help of the parameters obtained in this work, the NRTL model was used to predict the VLE data of the two binary systems at the pressure of 8.33 kPa. The predictive results were compared with the literature’s data. At same time, the excess Gibbs free energy for the two binary systems, and infinite dilution activity coefficients for MC and PC in DEA were estimated. The calculated results showed that the DEA had slightly stronger interaction with PC than MC.

Introduction

M-cresol (MC) and P-cresol (PC) are very important organic materials. MC can be used to synthetize spices, cosmetics, and pharmaceutical products et al. [1]. Furthermore, p-Cresol is mainly adopted in disinfectants and fumigants, in the production of explosives, antioxidants and synthetic resins, et al. [2]. MC and PC are presenting in coal tar and products of chemical synthesis. However, separating these two compounds is difficult because the molecular structure difference and the boiling temperature deference of the two materials are extremely small. At present, the commonly separation methods include crystallization [3], adsorption [4], alkylation reaction [5], et al. Ningoo [6] had proposed the use of extractive distillation with using alkanolamine as entrainer to separate PC and MC, however, Zaretskii et al. [7] believed that this method required more experimental data to verify; At the same time, alkanolamine and cresols are very complex systems. Supplementing the relevant VLE data of the system can provide basic data for the verification and development of new solution theory.

In our work, the VLE data for two binary systems of MC + DEA and PC + DEA at 20.0 kPa were determined by a modified Othmer Still. The thermodynamic consistency of binary VLE data was examined by using Herington area [8] method. Meanwhile, the binary VLE data were correlated using the Wilson [9], NRTL [10], and UNIQUAC [11] models. The VLE data for the two binary systems at 8.33 kPa were predicted by NRTL model, and the results were compared with literatures data [6]. The excess Gibbs free energy gE for these two binary systems were calculated. In addition, the chemistry theory [12] was used to explain the VLE behavior. The reaction equilibrium constants were obtained by fitting the activity coefficient data of the two binary systems. Then, the reaction thermodynamic parameters were predicted.

Section snippets

Materials and analysis method

In our experimental work, the chemicals of MC, PC and DEA were used to perform the measurement. The MC (≥99.0% wt) was supplied by Sinopharm Chemical Regent Co. Ltd., and the PC (≥99.0% wt) and DEA (≥99.0% wt) were purchased from Aladdin Regent Co. Ltd.. No further purification was conducted for these reagents. Table 1 showed the initial mass fractions and some relevant detailed information on those chemicals.

In addition, the measurement of the normal boiling point, boiling point at 20.0 kPa

Experimental results for binary systems

VLE data contained two binary systems, namely, MC and DEA, and PC and DEA. Fig. 3, Fig. 4 show the measured VLE data of these systems, and the values are listed in Table 3, Table 4. The vapour-liquid equilibrium can be calculated by the following expression [6], [13],yip=γixipiswhere the pis can be calculated by Eq. (3),lnpis/kPa=A+BT/K+C+ElnT/K+FT/KGwhere A, B C, E, F, G are the equation parameters. Table 5 shows the equation parameters [40] of these chemicals.

We used Eqs. (2), (3) to

Conclusions

In this work, the binary VLE data for two binary systems of MC + DEA and PC + DEA were measured at 20.0 kPa. The VLE values of two binary systems passed the thermodynamic consistency. In the two systems, the excess Gibbs free energy suggested the interaction between PC and DEA was slightly stronger than that of MC and DEA. The Wilson, NRTL, and UNIQUAC models were used to correlate the binary VLE data, and we obtained the binary interaction energy parameters involved in these models.

At the same

Acknowledgments

This research was funded by the National Natural Science Foundation of China (21706017) and the Nature Science Foundation of Jiangsu Province for financial support under Project BK 20150262.

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