Separation of azeotropic mixture (2, 2, 3, 3-Tetrafluoro-1-propanol + water) by extractive distillation: Entrainers selection and vapour-liquid equilibrium measurements

doi:10.1016/j.jct.2019.06.026

The Journal of Chemical Thermodynamics

Volume 138, November 2019, Pages 205-210

https://doi.org/10.1016/j.jct.2019.06.026 Get rights and content

Highlights

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The appropriate entrainers were screened using the COSMO-SAC model.
•
The VLE data for TFP + NMP/NMF/DMF were measured at 101.3 kPa.
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The VLE data were correlated by the NRTL, Wilson and UNIQUAC models.
•
The interaction mechanism and effect of the entrainers were explored.

Abstract

For separating the azeotrope of 2, 2, 3, 3-tetrafluoro-1-propanol (TFP) and water by extractive distillation, N-methyl pyrrolidone (NMP), N-methyl formamide (NMF) and N, N-dimethyl formamide (DMF) were selected as entrainers using the COSMO-SAC model based on solvent capacity. And the charge density surface of entrainers and each component in the azeotrope system were calculated. The vapour-liquid equilibrium (VLE) data for the mixtures (TFP + NMP), (TFP + NMF) and (TFP + DMF) were measured by a modified Rose-type recirculating still at the pressure 101.3 kPa. The thermodynamic consistency for the VLE data was validated using the Herington and van Ness methods. The VLE data were correlated with NRTL, Wilson and UNIQUAC models, and the interaction parameters of thermodynamic models were fitted. Meanwhile, the effect of the entrainers on the VLE for TFP and water was explored. Compared with NMF and DMF, NMP was adopted as the suitable entrainer for separation of the azeotropic mixture TFP and water by extractive distillation.

Introduction

2,2,3,3-Tetrafluoro-1-propanol (TFP) is usually utilized in preparation of coatings and pesticide [1], and can be used as a cleaning solvent [2]. During the production and application of TFP, a mixture of TFP and water is usually obtained. However, TFP and water can form an azeotropic mixture with the composition of TFP 72.5 (wt%) and water 27.5 (wt%) at temperature of 365.65 K [3], which is difficult to recover TFP by ordinary distillation. Usually, in order to separate the azeotropic mixtures, special distillation technologies are applied, such as extractive distillation [4], [5], [6], [7], azeotropic distillation [8] and pressure swing distillation [9], [10]. In this work, for separating TFP and water, the extractive distillation was adopted. Based on solvent capacity [11], the potential entrainers N-methyl pyrrolidone (NMP), N-methyl formamide (NMF) and N, N-dimethyl formamide (DMF) were selected using the conductor-like screening segment activity coefficient (COSMO-SAC) model [12].

For separation the azeotrope TFP and water by extractive distillation, the vapour-liquid equilibrium (VLE) data for the mixtures TFP and entrainers are required. Until now, few literatures have reported the VLE data for the systems contained TFP. Gao et al. [13] reported the VLE data for the system TFP + 2,2,3,3,4,4,5,5-octafluoro- 1-pentanol at different pressure. Shi et al. [14] reported the VLE data for all the mixtures (TFP + water), (TFP + chloroform) and (TFP + p-xylene). For all the three binary mixtures (TFP + NMP), (TFP + NMF) and (TFP + DMF), the isobaric VLE data have not been retrieved from the NIST database.

Therefore, the VLE data for all three mixtures (TFP + NMP), (TFP + NMF), and (TFP + DMF) were determined at pressure 101.3 kPa using a recirculating type equilibrium still. The consistency test of Herington and van Ness methods were employed to check the thermodynamic consistency for the measured VLE data. Meanwhile, the NRTL [15], Wilson [16] and UNIQUAC [17] models were used to correlate the measured VLE data. Accordingly, the corresponding interaction parameters for all the three models were correlated. And based on the regressed parameters of the UNIQUAC model, the effect of the entrainers on the VLE for the azeotrope TFP + water were explored by the Flash 2 module in Aspen Plus [18].

Section snippets

Solvent capacity

For selection of the entrainers, solvent capacity (SP) was applied [19], which is defined as follows: $SP = \frac{1}{γ_{AC}^{\infty}}$ where $γ_{AC}^{\infty}$ is the infinite activity coefficient of component TFP in entrainer C. To calculate the infinite dilution activity coefficient, the COSMO-SAC model was employed [20], [21]. The detailed computation steps can be found in the previous work [22], [23], [24].

The calculated results of SP are presented in Fig. 1, As shown in Fig. 1, the order of the solvent capacity for the

Materials

The chemicals TFP, NMP, NMF and DMF were commercial grade. The information of all the chemicals is presented in Table 1, including the CAS No., suppliers, mass fraction, and boiling temperature. The purities of the chemicals were checked by gas chromatography (GC).

Equilibrium measurements

The modified Rose-type recirculating still was employed to determine the VLE data, where a manometer assembly with an accuracy of ±0.1 kPa was connected to the system to measure the equilibrium pressure. A mercury thermometer with an

Experimental results

The VLE data for the binary mixtures (TFP + NMP), (TFP + NMF) and (TFP + DMF) were measured at 101.3 kPa, which is presented in Table 3, Table 4, Table 5 and the graphically for all the three binary mixtures are shown in Fig. 3, Fig. 4, Fig. 5.

The vapour-liquid relationship is presented by the following equation: ${\hat{ϕ}}_{i} y_{i} p = x_{i} γ_{i} ϕ_{i}^{s} p_{i}^{s} exp [\frac{v_{i}^{L} (p - p_{i}^{s})}{RT}]$

Since the VLE measurement was performed at pressure 101.3 kPa, the vapour phase can be assumed as ideal gas, Eq. (2) can be simplified as follows [38]: $y_{i} p= x$

Conclusions

In this work, three entrainers NMP, NMF and DMF were selected based on solvent capacity calculated by the COSMO-SAC model. Meanwhile, the interaction mechanism between entrainers and the components in the azeotroic mixture was explored by the σ-profiles. Then, the isobaric VLE data for (TFP + NMP), (TFP + NMF) and (TFP + DMF) binary mixtures were determined under the pressure of 101.3 kPa by the modified Rose-type recirculating still. The Herington and van Ness methods were employed to check

Acknowledgements

This work was supported by Shandong Provincial Key Research & Development Project (2018GGX107001), National Natural Science Foundation of China (21878178) and Project of Shandong Province Higher Educational Science and Technology Program (J18KA072).

Declaration of Competing Interest

The authors declare no competing financial interest.

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Separation of azeotropic mixture (2, 2, 3, 3-Tetrafluoro-1-propanol + water) by extractive distillation: Entrainers selection and vapour-liquid equilibrium measurements

Highlights

Abstract

Introduction

Section snippets

Solvent capacity

Materials

Equilibrium measurements

Experimental results

Conclusions

Acknowledgements

Declaration of Competing Interest

Sep. Purif. Technol.

Fluid Phase Equilibr.

J. Chem. Thermodyn.

Fuel

Fluid Phase Equilibr.

J. Chem. Thermodyn.

Fluid Phase Equilibr.

J. Chem. Thermodyn.

Fluid Phase Equilibr.

Biomacromolecules

Sep. Purif. Technol.

J. Membr. Sci.

Fluid Phase Equilibr.

J. Mol. Liq.

J. Chem. Thermodyn.

Fluid Phase Equilibr.

Fluid Phase Equilibr.

Fluid Phase Equilibr.

Fluid Phase Equilibr.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

Separation of azeotropic mixture (2, 2, 3, 3-Tetrafluoro-1-propanol + water) by extractive distillation: Entrainers selection and vapour-liquid equilibrium measurements