VaporâLiquid Phase Equilibrium for Separation of Isopropanol from Its

Article Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

pubs.acs.org/jced

Vapor−Liquid Phase Equilibrium for Separation of Isopropanol from Its Aqueous Solution by Choline Chloride-Based Deep Eutectic Solvent Selected by COSMO-SAC Model Haihua Jiang,† Dongmei Xu,*,† Lianzheng Zhang,† Yixin Ma,† Jun Gao,*,† and Yinglong Wang‡ †

College of Chemical and Environmental Engineering, Shandong University of Science and Technology, Qingdao 266590, China College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042, China

‡

J. Chem. Eng. Data Downloaded from pubs.acs.org by UNIV OF SOUTH DAKOTA on 03/28/19. For personal use only.

S Supporting Information *

ABSTRACT: To separate isopropanol from its aqueous solution by distillation, the deep eutectic solvents (DESs) with choline chloride, which were screened using the COSMO-SAC mode, were applied to eliminate the azeotropic point. The charge density distribution over the molecular surface was calculated for isopropanol, water, and DESs to analyze the interactions between different species. Based on the screening results, a DES consisting of choline chloride and triethylene glycol in a molar ratio of 1:3 was selected. To validate the selected DES for the separation of isopropanol from its aqueous solution, the isobaric vapor−liquid equilibrium (VLE) data for the system of isopropanol + water + DES were measured at a pressure of 101.3 kPa. According to the measured VLE data, the azeotropic point of isopropanol and water can be eliminated by the DES at a concentration of 10 wt %. Meanwhile, the thermodynamic consistency of the VLE data was checked by the van Ness test. The non-random two-liquid model was employed to correlate the VLE data, which were in agreement with the measured VLE data. water with ionic liquids have been explored. Zhang et al.21 investigated the effect of ionic liquids on the separation of isopropanol and water. Since most of the ILs are expensive in industry application, it is necessary to find a suitable extractive solvent for the separation of isopropanol and water. In 2003, Abbott et al.22 found that the liquids formed by choline chloride and amide compounds had special solvent properties, and proposed the concept of eutectic mixtures. Later, the researchers discovered that a series of organic salts can form eutectic mixtures with hydrogen bond donors such as carboxylic acids, amides, and alcohols, and the concept of deep eutectic solvents (DESs) was proposed.23,24 Until now, DESs have been applied for the separation of acidic gases,25 alcohols,26 and aromatics.27 Choline chloride-based DESs are biodegradable, less toxic, and easy to synthesize. Gjineci et al.26 explored the separation of azeotropic mixture ethanol and water using the DESs based on choline chloride. Zhang et al.28 determined the vapor− liquid equilibrium data for the system of isopropanol and water by adding glycerol choline chloride as an entrainer. In this work, the DESs based on choline chloride were screened and selected by the COSMO-SAC model to separate the mixture of isopropanol and water. The interactions

1. INTRODUCTION Isopropanol is a basic chemical that is widely used in the industry as a solvent or chemical intermediate. Separation of the aqueous mixture of isopropanol is often required in its production and recovery.1,2 To obtain isopropanol, it is difficult to separate isopropanol from its aqueous solution by traditional distillation, since isopropanol and water can form a minimum boiling point azeotrope. Usually, special distillations3 such as extractive distillation,4−6 azeotropic distillation, salt distillation, pressure-swing distillation, and reactive distillation are considered to separate such azeotropic mixture.7,8 So far, some research work on separation of the mixture of isopropanol and water using various organic solvents including ethylene glycol,9 glycerol,10 and compound solvent11 has been reported in the literatures. Liu et al.12 measured the liquid− liquid equilibrium data for the extraction of isopropanol from its aqueous solution using esters. In contrast to the conventional solvents, ionic liquids (ILs) have been found to be promising solvents for separating the aqueous solution of isopropanol because of their high thermal stability, negligible vapor pressure, and nonvolatile nature.13−16 In recent years, ILs have been applied for the separation of the mixture of isopropanol and water, including 1-ethyl-3-methylimidazole tetrafluoroborate,17 1-butyl-3-methylimidazole tetrafluoroborate,18 1-butyl-3-methylimidazole chloride,19 and 1-butyl-3methylimidazole acetate.20 And, the isobaric or isothermal vapor−liquid equilibrium (VLE) data for isopropanol and © XXXX American Chemical Society

Received: October 6, 2018 Accepted: March 18, 2019

A

DOI: 10.1021/acs.jced.8b00895 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

10−6 Ha, 0.02 Ha nm−1, and 5.0 × 10−13 m for geometry optimization and energy calculations. Then, a COSMO file was generated by inserting the corresponding keywords. The corresponding keywords and necessary parameters were obtained from the reference.41 Detailed step-by-step instructions for the quantum chemical calculations using DMol3 can also be found in Mullins’s work.30 After the COSMO file was generated, the σ-profile of the molecule, which is the distribution of the screening charge density on the surface of the molecule, was finally obtained. When the σ-profiles were generated, the activity coefficient could be calculated from the σ-profiles using the equations that were described in our previous work.34,35 The details about the COSMO-SAC model are presented in the Supporting Information. 2.2. Evaluation Index. The activity coefficient at infinite dilution γ∞ can be used for evaluating the maximum capacity C∞, selectivity S∞, and performance index PI of the targeted DESs.42 S∞ presents the ability of a DES to interact more with one of the components and less with another. Therefore, the selectivity of a DES toward IPA compared with water S∞ IPA,water can be expressed in terms of the ratio of the activity coefficient for water to IPA, which is presented as follows

between the different species were analyzed. Based on the analysis results, a suitable DES was selected, and the isobaric vapor−liquid equilibrium (VLE) data for the system of isopropanol + water + DES were determined to validate the selected DES for the separation of isopropanol from its aqueous solution. Meanwhile, the thermodynamic consistency of the VLE data was checked by the van Ness test. The NRTL model was employed to correlate the VLE data.

2. DESS SCREENING BY COSMO-SAC MODEL The COSMO-SAC model is a continuum solvation model proposed by Lin and Sandler,29 which is a useful tool for the prediction of the thermophysical and chemical properties and phase equilibrium of fluid mixtures.30,31 The calculation of the COSMO-SAC model consists of two steps, viz., the quantum chemical calculation to generate the COSMO file32 and the determination of the activity coefficient from the COSMO file. The detailed calculation of the COSMO-SAC model can be found in the previous publications31,33 and in our previous work.34,35 Table 1 lists the names of hydrogen-bond acceptors Table 1. List of DESs Screened in This Work HBA choline choline choline choline choline choline choline choline choline choline choline choline choline choline choline choline choline choline

chloride chloride chloride chloride chloride chloride chloride chloride chloride chloride chloride chloride chloride chloride chloride chloride chloride chloride

HBD

HBA/HBD

Abbv.

1-methyl urea tetramethyl urea thio urea acetamide glycerol ethylene glycol triethylene glycol malonic acid oxalic acid phenylacetic acid phenylpropionic acid levulinic acid itaconic acid xylitol D-sorbitol D-isosorbide glucose urea

1:2 1:2 1:2 1:2 1:1 1:2 1:3 1:1 1:1 1:1 1:1 1:2 1:1 1:1 1:1 1:2 1:1 1:2

ChCl/MUr ChCl/TMUr ChCl/TUr ChCl/Ac ChCl/Gly ChCl/EG ChCl/TEG ChCl/MA ChCl/OA ChCl/PAC ChCl/PPA ChCl/LA ChCl/IA ChCl/Xy ChCl/Sor ChCl/Iso ChCl/Glu ChCl/Ur

∞ = SIPA,water

∞ γwater ∞ γIPA

(1)

This means that a DES with high selectivity toward IPA has a high value of γ∞ water (low interaction with water) and a low value of γ∞ (high interaction with IPA). C∞ can be used to IPA qualitatively determine the amount of DES required for the distillation process. The capacity of DES for IPA C∞ IPA can be calculated as follows ∞ = C IPA

1 ∞ γIPA

(2)

PI is expressed as the product of selectivity S∞ IPA,water and capacity C∞ IPA, which combines both capacity and selectivity for estimating the overall performance of DES, and is given as follows ∞ ∞ PI = SIPA,water × C IPA

(3)

2.3. DES Ranking from Selectivity and Capacity Screening Results. As shown in Figures 1−3, the results of DES screening are presented in terms of S∞, C∞, and PI at infinite dilution, respectively. In Figure 1, the S∞ values of the DESs for isopropanol follow the order: ChCl/EG > ChCl/ TEG > ChCl/Mur > ChCl/Sor > ChCl/Glu > ChCl/PPA > ChCl/Xy. And, the C∞ values follows the order: ChCl/TEG > ChCl/EG > ChCl/Sor > ChCl/Glu > ChCl/Mur > ChCl/ PPA > ChCl/Xy, as shown in Figure 2. Compared to the other DESs, ChCl/EG and ChCl/TEG have higher values of S∞ and C∞. Based on the results of S∞ and C∞, the PI values of DESs were calculated and followed the order: ChCl/TEG > ChCl/ EG > ChCl/Mur > ChCl/Sor > ChCl/Glu > ChCl/PPA > ChCl/Xy, as shown in Figure 3. Therefore, the DES ChCl/ TEG (mole ratio of 1:3) with a higher value of PI is selected to separate the mixture of isopropanol and water. 2.4. σ-Profile Analysis. To explore the effect of DESs on the separation of IPA and water, the σ-profiles for DESs with high PI values are plotted in Figure 4. For comparison, the σprofiles of water and IPA are also presented in Figure 4. As shown in Figure 4, two vertical dashed lines are the cutoff values for the hydrogen-bond donor (σ < −0.0084 e/Å2) and

(HBA) and hydrogen-bond donors (HBD) of the DESs for screening and the mole ratios of HBA to HBD. The detailed structures of HBA and HBD used in this work are listed in Table 2. 2.1. Calculation Details. Since a single DES is composed of more than one molecule, the electroneutral approach is considered to represent DESs based on the mole composition of their constituents in the COSMO-SAC model. The mathematical adaptation has been detailed in the references.36,37 For quantum chemistry calculations, the DMol3 module incorporating the density functional theory was adopted, which is available in Accelrys’ Materials Studio,31 and applied as in our previous work.33,35,38,39 The first step in quantum chemical calculation is to optimize the geometry of the molecule, then the lowest-energy configuration from density functional theory can be obtained. To perform the geometry optimization, the GGA/VWN-BP functional setting and the DNP v4.0.0 basis set were adopted as proposed by Klamt.40 The convergence criteria for energy, maximum force, and maximum displacement were set at 1.0 × B



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Table 2. Names and Structures of the HBA and HBD

C



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Table 2. continued

Figure 3. Performance of DESs at infinite dilution.

Figure 1. Selectivity of DESs at infinite dilution.

Figure 4. σ-Profiles for water, IPA, and DESs with high PI values. Figure 2. Capacity of DESs at infinite dilution.

0.0084 e/Å2. Also, the further the σ-profile is from the absolute value 0.0084 e/Å2 to the left or the right, the stronger is the hydrogen-bond donator or acceptor ability, respectively. As shown in Figure 4, water has a very broad σ-profile with two pronounced peaks around −0.016 and +0.015 e/Å2, reflecting its excellent ability to act as a donor and an acceptor

acceptor (σ > 0.0084 e/Å2). If the profile lies in the left side of −0.0084 e/Å2, the surface segment has the hydrogen-bond donator ability. Conversely, the surface segment has the hydrogen-bond acceptor ability if it lies in the right side of D



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Ltd.). The conductivity of deionized water is less than 1.0 μS cm−1. The information of the chemicals is listed in Table 4.

of hydrogen bond. The symmetrical shape of water σ-profile indicates a favorable interaction between water and itself, which can explain its high boiling point and surface tension. Compared with water, IPA has even stronger hydrogen-bond donor ability, since the polarization charge density of the latter ranges more widely. Thus, IPA is more likely to form hydrogen bond with DESs. In the meantime, the DESs with high PI values have no σ-profiles in the region of σ < −0.0084 e/Å2, which indicates their weak ability to donate hydrogen bonds. And, DESs with high PI values have σ-profiles in the region of σ > 0.0084 e/Å2, which indicates that these DESs have the ability to accept hydrogen bonds. Thus, the DESs with high PI values are hydrogen-bond acceptors. Compared with the σ-profiles of the DESs with high PI values, the σ-profile of the DES ChCl/TEG extends away from the vertical line of 0.0084 e/Å2, which indicates that the DES has a strong hydrogen-bond acceptor ability. Based on the screening results, the DES ChCl/TEG was selected to break the azeotropic point of the system isopropanol + water. 2.5. Calculation of Interaction Energy. To explore the interactions between DESs with IPA and water, the interaction energy was calculated using the DMol3 module incorporating the density functional theory, which is expressed by the energy difference between the monomer and the complex.38 The interaction energy calculation is presented as follows ΔEinteraction = EAB − EA − E B + E BSSE

(4)

E BSSE = EA − E(A,AB) + E B − E(B,AB)

(5)

Table 4. List of Chemicals Used in This Work name isopropanol choline chloride triethylene glycol water

Table 3. Interaction Energies between DESs and (IPA, Water) ΔE (kJ mol−1)

ChCl/TEG + IPA ChCl/TEG + water ChCl/EG + IPA ChCl/EG + water ChCl/Gly + IPA ChCl/Gly + water

−56.6319 −45.2969 −49.5585 −43.5219 −37.2516 −33.8774

mass fraction purity

CAS

C3H8O C5H14ClNO

67-63-0 67-48-1

0.990 0.990

C6H14O4

112-27-6

0.990

H2O

7732-18-5

supplier Shandong Xiya Chemical CO., Ltd.

Lab made

3.2. Apparatus and Procedures. The selected DES in this work is choline chloride/triethylene glycol (ChCl/TEG), with the molar ratio HBA/HBD of 1:3. The DES was prepared using the method described by Abbott et al.43 To prepare the DES, choline chloride was dried in a vacuum drying oven at 313.15 K for at least 2 days before being used. Then, choline chloride and triethylene glycol in the molar ratio of 1:3 were mixed in a round-bottom flask in an argon protective glovebox. The mixture was stirred at 348.15 K until a clear liquid appeared. After that, the water content in the DES was measured by automatic Karl Fischer moisture analyzer (756 KF Coulometer, Metrohm China Co., Ltd.), which was less than 1000 ppm. For the isobaric VLE measurement, a modified Rose type recirculating equilibrium still was used,44 which was presented in detail in the literatures.45−49 The experiment pressure was maintained by a manometer (Nanjing Hengyuan Automatic Gauge Co., Ltd.), and the pressure fluctuation was controlled within 1 kPa with a two-step automatic control scheme. Meanwhile, a mercury thermometer was used to measure the equilibrium temperature with an accuracy of ±0.1 K. In each experiment, the ternary mixture of isopropanol + water + DES was added into the equilibrium still, which was prepared by an electronic analytical balance (SL512N, Mettler Toledo Instrument Co., Ltd) with an accuracy of ±0.0001 g. To make the contact of the vapor and liquid phases sufficient, the two phases were circulated continuously. When the temperature of vapor phase was kept constant for 3000 s, the equilibrium was set up. The vapor-phase and liquid-phase samples were withdrawn by syringe with the volume about 0.5 mL and discharged into the vials for analysis. The compositions of the samples were determined by gas chromatography (GC). 3.3. Analysis. Analysis of the equilibrium composition of isopropanol and water in the vapor and liquid phases by GC (SP6890, Shandong Rui Hong Chemical Co., Ltd), which were equipped with a packed column (Porapak Q 3 mm × 2 m, Dalian Sanjie Scientific Development Co., Ltd.) and a thermal conductivity detector TCD (Shandong Rui Hong Chemical Co., Ltd). The carrier gas is 99.999% pure hydrogen with a flow rate of 50 mL min−1. The oven temperature was 433.15 K. The injection temperature was fixed at 443.15 K. And, the temperature of TCD detector was held at 443.15 K. Before sample analysis, the peak areas of GC were calibrated by four different standard samples that covered the whole composition range. When analyzing the samples, each sample was analyzed three times. The mean value was adopted when the deviation (mole fraction) was not more than 0.001. The uncertainty of mole fraction is 0.006. The detailed calculation

where EAB is the energy of the complex of AB in the A, B basis set, EA is the energy of A in the A basis set, EB is the energy of B in the B basis set, E(A,AB) is the energy of A in the A, B basis set, and E(B,AB) is the energy of B in the A, B basis set. The calculated interaction energies are given in Table 3.

system

chemical formula

As shown in Table 3, the DESs have strong interactions with isopropanol and water, which can weaken the hydrogen bond formed by isopropanol and water. At the same time, compared with ChCl/EG and ChCl/Gly, the values of interaction energy for (ChCl/TEG and IPA) and (ChCl/TEG and water) shows biggest difference. Therefore, ChCl/TEG was chosen as the suitable DES for separation of isopropanol from its aqueous solution.

3. EXPERIMENTAL SECTION 3.1. Chemicals. The chemicals used in this work were purchased from Shandong Xiya Chemical Co., Ltd. with the purities of 99.0 wt %. All chemicals were used without further purification. And, deionized water was used in this work, which was made in our laboratory by an ultrapure water machine (Chengdu Down’s Corning Technology Development Co., E



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of uncertainty is presented in the Supporting Information. The mass fraction of the DES samples was determined by calculating the mass difference of the samples before and after the vaporization of the solvents at 373.15 K in a vacuum drying oven (DZF- 6050, Shanghai Yiheng, China) until a constant weight was reached. The mass fraction uncertainty of DES (w3) is 0.014.

4. RESULTS AND DISCUSSION 4.1. Validation of Apparatus. The isobaric VLE data for the binary system isopropanol and water at pressure of 101.3 kPa were determined to verify the reliability of the equilibrium still and are listed in Table 5. For comparison, the reference Table 5. Isobaric VLE for Temperature T, Liquid Phase Mole Fraction x, Vapor Phase Mole Fraction y, and Activity Coefficient γ for Isopropanol (1) + Water (2) at Pressure 101.3 kPaa T/K

x1

y1

γ1

γ2

367.10 365.32 360.25 357.23 356.72 356.32 355.29 354.96 354.59 354.44 354.28 354.01 353.87 353.79 353.62 353.51 353.49 353.31 353.46 353.78 353.91 354.32 354.67

0.0201 0.0252 0.0404 0.0513 0.0648 0.0789 0.1092 0.1253 0.2432 0.2507 0.3024 0.3792 0.4212 0.4323 0.5521 0.5707 0.6203 0.6709 0.7368 0.8268 0.8711 0.9012 0.9492

0.2512 0.3023 0.4212 0.4518 0.4866 0.5043 0.5011 0.5219 0.5391 0.5432 0.5473 0.5516 0.5635 0.5781 0.6144 0.6304 0.6427 0.6731 0.7132 0.7933 0.8312 0.8925 0.9382

0.1261 0.1230 0.1169 0.1230 0.1414 0.1635 0.2187 0.2378 0.4402 0.4476 0.5325 0.6553 0.7085 0.7066 0.8432 0.8458 0.9010 0.9237 0.9632 0.9844 0.9950 0.9746 0.9903

1.0722 1.0714 1.0482 0.9725 1.0032 1.0073 0.9290 0.9395 0.8308 0.8249 0.7700 0.6843 0.6518 0.6592 0.5434 0.5384 0.5144 0.4838 0.4437 0.4104 0.3759 0.4600 0.4172

Figure 5. Comparison of the isobaric VLE data for the system of isopropanol (1) + water (2) at 101.3 kPa: (●) this work; (△) ref 20; (◊) ref 50; (○) ref 51; x, liquid phase mole fraction; y, vapor phase mole fraction.

The relative volatility α12 of isopropanol (1) to water (2) is calculated as follows α12 =

y1 /x1 y2 /x 2

(6)

where x (DES free) and y are the mole fractions of the components in the liquid phase and vapor phase, respectively. The values of the relative volatility α12 are listed in Table 6. The x−α diagram for the binary system isopropanol + water is presented in Figure 7. As shown in Figure 6, the content of isopropanol increases in the vapor phase with increasing concentration of the DES. And, the relative volatility of isopropanol to water increases with increasing content of the DES, as shown in Figure 7. The azeotropic point of the system moves and is eliminated with increasing amount of the DES ChCl/TEG (mole ratio of 1:3), which is salting-out effect. For comparison, the VLE data for isopropanol and water with the DES (choline chloride−glycerol, molar ratio 1:2) from the reference by Zhang et al.28 are presented in Figure 8. As shown in Figure 8, the azeotropic point of the system isopropanol and water is eliminated by the DES ChCl/TEG (mole ratio of 1:3) used in this work with the weight percent of 10, whereas in Zhang et al.’s work,28 the azeotropic point can be eliminated by the DES (choline chloride−glycerol, molar ratio 1:2) with the weight percent of 20. As shown in Table 3, compared with ChCl/Gly, the interaction energy difference between (ChCl/TEG + IPA) and (ChCl/TEG + water) is bigger than that between (ChCl/Gly + IPA) and (ChCl/Gly + water), which indicates that ChCl/TEG has greater interaction with isopropanol. Thereby, the relative volatility of isopropanol to water could be changed. 4.3. Correlation of VLE Data. The vapor−liquid phase equilibrium can be expressed as follows

a

Standard uncertainties u are u(x1) = u(y1) = 0.006, u(T) = 0.1 K, u(P) = 2 kPa.

data20,50,51 are plotted in Figure 5. As shown in Figure 5, the measured VLE data are consistent with the literature data, indicating that the apparatus is reliable. Moreover, the system of isopropanol and water formed an azeotrope at x1 ≈ 0.874 (mass fraction) at pressure of 101.3 kPa. 4.2. VLE Data for System Isopropanol + Water + DES. The isobaric VLE data for the system of isopropanol (1) + water (2) + DES (3) were determined at 101.3 kPa by keeping the mass fraction of DES nearly constant at 0.03, 0.05, 0.1, and 0.15, respectively, which are listed in Table 6. From Table 6, with the addition of DES, the activity coefficient of isopropanol increases and that of water decreases. The x−y diagram for the system is presented in Figure 6. As shown in Figure 6, the VLE data for the system without the DES show a deviation compared with those with the DES. Similar results can be observed from the literature.20

ij ViL(P − Pis) yz v s s jj zz yi ϕî P = xiγϕ P exp jj zz i i i RT (7) k { L s v ̂ where the Poynting factor exp[Vi (P − Pi )/RT], ϕi , and φsi associated with nonideality are all close to 1, since the pressure is low, xi and yi represent the mole fractions of component i in

F



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Table 6. Isobaric Binary VLE Data for Temperature T, Liquid Phase Mass Fraction w, Liquid Phase Mole Fraction (DES Free Basis) x′, Vapor Phase Mole Fraction y, Activity Coefficient γ, Relative Volatility α, and Absolute Deviation between Experimental and Calculated Values of Temperature, ΔT, Vapor Phase Mole Fraction, Δy, for Isopropanol (1) + Water (2) + ChCl/TEG (Mole Ratio r of 1:3) (3) at Pressure 101.3 kPaa w3

T/K

x1′

γ1

γ2

α12

ΔT/K

Δy1

1.0024 0.9862 0.9764 0.8874 0.5119 0.3649 0.3406 0.2757 0.2744 0.2187 0.2031 0.1762

0.4996 0.4871 0.4718 0.5112 0.9668 1.5492 1.7889 2.8286 3.7696 6.7211 8.8792 11.0051

0.7857 0.8554 0.8675 1.1509 2.9818 4.8953 5.3859 7.5456 10.3957 10.4684 11.5802 11.6170

0.20 0.13 0.12 0.21 0.02 0.01 0.12 0.01 0.14 0.02 0.23 0.11 0.08

0.0011 0.0023 0.0020 0.0034 0.0021 0.0035 0.0071 0.0034 0.0014 0.0053 0.0024 0.0035 0.0065

About 0.05 1.0374 1.0104 0.9120 0.8655 0.6814 0.6502 0.6207 0.5854 0.5314 0.5228 0.4881 0.4889 0.4298

0.5118 0.4961 0.5113 0.5276 0.7233 0.7820 0.8425 1.0086 1.2569 1.4692 1.8205 2.2198 3.4600

0.7707 0.8224 1.1188 1.2436 2.1086 2.3080 2.5181 3.2202 4.0916 5.4316 6.6921 9.3975 10.1780

0.12 0.22 0.20 0.32 0.01 0.02 0.14 0.01 0.24 0.21 0.23 0.11 0.23 0.02

0.0012 0.0045 0.00324 0.0023 0.0043 0.0012 0.0053 0.0024 0.0063 0.0024 0.0034 0.0022 0.0012 0.0009

About 0.10 1.0528 0.9229 0.6662 0.5905 0.5695 0.5736 0.5532 0.5272 0.4537 0.3397 0.3696

0.5639 0.5362 0.8432 1.0979 1.3601 1.4206 1.6620 1.9918 2.8477 5.1236 5.4454

1.2181 1.4438 2.6745 3.2313 3.6695 3.6701 4.0494 4.5075 5.6056 6.8864 6.9482

0.03 0.12 0.02 0.01 0.08 0.12 0.23 0.14 0.02 0.06 0.08 0.16

0.0022 0.0013 0.0051 0.0063 0.0017 0.0013 0.0068 0.0027 0.0011 0.0034 0.0028 0.0015

About 0.15 1.0633 1.0002 0.7639 0.6579 0.6064 0.5606 0.5381 0.4460 0.3554 0.3344

0.5776 0.5665 0.7365 1.3169 2.0703 2.5225 3.0648 4.1323 5.8328 6.6134

1.6799 1.7430 2.7352 3.9384 4.5323 4.8550 5.0668 5.5615 6.0940 6.4516

0.13 0.14 0.12 0.23 0.24 0.13 0.11 0.04 0.08 0.12 0.14

0.0084 0.0016 0.0025 0.0016 0.0094 0.0004 0.0019 0.0013 0.0084 0.0011 0.0056

y1 About 0.03

0.0305 0.0302 0.0312 0.0322 0.0306 0.0312 0.0302 0.0305 0.0296 0.0292 0.0304 0.0313 0.0317

354.77 354.25 353.73 353.54 354.62 356.29 357.24 360.41 364.12 368.87 371.71 372.73 374.34

0.9161 0.8356 0.7498 0.6305 0.2853 0.1831 0.1584 0.1068 0.0597 0.0384 0.0192 0.0059 0.0000

0.8956 0.8130 0.7222 0.6626 0.5434 0.5232 0.5034 0.4743 0.3976 0.2948 0.1848 0.0645 0.0000

0.0505 0.0503 0.0508 0.0509 0.0498 0.0501 0.0503 0.0502 0.0508 0.0499 0.0510 0.0524 0.0519 0.0499

355.50 354.78 353.88 353.62 354.57 354.96 355.31 356.84 358.41 360.21 362.11 364.76 369.03 374.96

0.8982 0.8486 0.6787 0.6236 0.4312 0.3986 0.3697 0.2973 0.2247 0.1548 0.1145 0.0631 0.0294 0.0000

0.8718 0.8217 0.7026 0.6732 0.6151 0.6047 0.5962 0.5767 0.5425 0.4987 0.4639 0.3876 0.2357 0.0000

0.1003 0.1015 0.1005 0.1000 0.1001 0.1098 0.1007 0.1018 0.1012 0.1009 0.1031 0.1032

356.91 354.62 356.21 358.03 360.32 360.98 362.56 364.32 367.11 371.21 373.25 375.81

0.9714 0.8516 0.4322 0.3213 0.2697 0.2585 0.2270 0.1937 0.1348 0.0484 0.0101 0.0000

0.9764 0.8923 0.6706 0.6047 0.5754 0.5613 0.5432 0.5199 0.4662 0.2594 0.0662 0.0000

0.1509 0.1501 0.1500 0.1503 0.1530 0.1518 0.1497 0.1531 0.1503 0.1504 0.1510

357.34 356.32 356.23 361.78 366.72 368.34 370.46 372.01 373.67 374.59 376.25

0.9868 0.9374 0.5945 0.3489 0.2219 0.1721 0.1335 0.0718 0.0182 0.0099 0.0000

0.9921 0.9631 0.8004 0.6785 0.5638 0.5023 0.4384 0.3008 0.1015 0.0606 0.0000

Standard uncertainties u are u(x1′) = u(y1) = 0.006, u(w3) = 0.0014, u(r) = 0.0014, u(T) = 0.10 K, u(P) = 2 kPa.

a

G



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Figure 6. x1′−y diagram for the system of isopropanol (1) + water (2) + ChCl/TEG (3) at 101.3 kPa: (★) 3 wt %; (●) 5 wt %; (▲) 10 wt %; (■) 15 wt % DES; (□) DES free basis; solid line, correlated by the NRTL model; x′, liquid phase mole fraction (DES free basis); y, vapor phase mole fraction.

Figure 8. Comparison of the isobaric VLE data for the system of isopropanol (1) + water (2) + DES (3) at 101.3 kPa: (■) 10 wt %, this work; (●) 10 wt %, ref 28; (▲) 20 wt %, ref 28; x′, liquid phase mole fraction (DESs free basis); y, vapor phase mole fraction.

obtained directly from the Aspen databank53 and are listed in Table 7. Since the NRTL model is adopted to correlate the VLE data for the systems containing DESs,54 in this work, the NRTL model was used to correlate the VLE data for the system isopropanol + water + ChCl/TEG. The parameters of the NRTL model were regressed from the VLE data by minimizing the following objective function N

F=

∑ {(γ1cal − γ1exp)i2 + (γ2cal − γ2exp)i2 }

(10)

i=1

γcal i

γexp i

where and are the calculated and experimental activity coefficients of the component i. The regressed parameters are listed in Table 8. The root-mean-square deviation (RMSD) for the temperature (T) and the mole fraction of the vapor phase (y1) are expressed as follows N ji zy RMSD(Ti ) = jjjj ∑ (Tical − Ti exp)2 /N zzzz j i=1 z k {

Figure 7. Relative volatility α12 for the system of isopropanol (1) + water (2) + ChCl/TEG (3) at 101.3 kPa: (○) 3 wt %; (●)5 wt %; (▲) 10 wt %; and (■) 15 wt % DES; solid line, correlated by the NRTL model; x′, liquid phase mole fraction (DESs free basis).

0.5

(11)

ij N yz RMSD(yi ) = jjjj ∑ (yi cal − yi exp )2 /N zzzz j i=1 z (12) k { The values of RMSD (y1) and RMSD (T) are listed in Table 9, which are less than 0.02 and 0.21 K, respectively. 4.4. Thermodynamic Consistency Test. To confirm the quality of the measured VLE data, the thermodynamic consistency for all experimental data was checked by the van Ness test, which is presented as follows 0.5

Psi

the liquid phase and vapor phase, respectively, and is the saturation vapor pressure of the pure component i, which can be estimated by the extended Antoine expression.52 Considering the nonideality of the liquid phase, eq 7 can be simplified as yP = xiγiPis i

(8)

The saturation vapor pressure of pure component was calculated by the extended Antoine equation, which is given as follows

Δy =

C 2i ln(Pis/kPa) = C1i + + C4iT + C5i ln T T + C 3i + C6iT

C 7i

forC8i ≤ T /K ≤ C9i

1 N

N

∑ Δyi = i=1

1 N

N

∑ 100|yi cal

− yi exp |

(13)

i=1

ycal i

where N is the number of experimental data, stands for the calculated mole fraction of the component i in the vapor phase, and yexp stands for the experimental mole fraction of the i component i in the vapor phase. The details about the van Ness test are presented in the Supporting Information.

(9)

where C1i to C9i are the parameters for each component i and C8i and C9i are the limits of the temperature range that were H



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Table 7. Parameters of the Extended Antoine Equationa component

C1i

C2i

C3i

C4i

C5i

C6i (×106)

C7i

C8i/K

C9i/K

isopropanol water

103.81 66.74

−9040.00 −7258.20

0 0

0 0

−12.68 −7.30

5.54 4.17

2.00 2.00

185.26 273.16

508.30 647.10

a

The parameters were taken from Aspen property databank.

■

Table 8. Regressed Binary Energy Parameters and Nonrandom Factors of the NRTL Model for the System Isopropanol (1) + Water (2) + ChCl/TEG (Mole Ratio of 1:3) (3)a

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.8b00895.

NRTL parameters i−j

Δgij (J mol−1)

Δgji (J mol−1)

aij

1−2 1−3 2−3

6892.81 −6523.43 −5324.64

71.12 −1950.10 −19217.34

0.3 0.3 0.3

COSMO-SAC model used in this work and calculation for the uncertainty of composition (PDF)

■

τi,j = Δgi,j/RT, Δgi,j = gi,j − gi,i.

AUTHOR INFORMATION

Corresponding Authors

a

*E-mail: [email protected] (D.X.). *E-mail: [email protected] (J.G.).

Table 9. Root-Mean-Square Deviation (RMSD) for the Equilibrium Temperature (T) and Mole Fractions of the Vapor Phase (y1) for the System Isopropanol (1) + Water (2) + ChCl/TEG (Mole Ratio of 1:3) (3)

ORCID

Dongmei Xu: 0000-0002-5770-0513 Jun Gao: 0000-0003-1145-9565 Yinglong Wang: 0000-0002-3043-0891

RMSD DES

w3 (%)

y1

T/K

Funding

ChCl/TEG (mole ratio of 1:3)

3 5 10 15

0.001 0.002 0.002 0.002

0.21 0.17 0.20 0.20

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

The authors declare no competing financial interest.

If Δy is less than 1, the measured VLE data can be considered as thermodynamically consistent. By the van Ness test, the values of Δy are 0.183, 0.157, 0.162, and 0.126 for the system of (isopropanol + water + DES) at the DES concentrations of 0.03, 0.05, 0.1, and 0.15 (mass fraction). All values of Δy are less than 1, which indicates that the measured VLE data are thermodynamically consistent.

■

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5. CONCLUSIONS For the separation of azeotrope isopropanol and water, the DESs based on choline chloride were screened and selected by the COSMO-SAC model. The selectivity, capacity, and performance index were evaluated, and the charge density distribution over the molecular surface was calculated for isopropanol, water, and DESs to analyze the interactions between different species. The DES consisting of choline chloride and triethylene glycol in a molar ratio of 1:3 was selected. And, the isobaric vapor−liquid equilibrium data for the system of isopropanol + water + DES were determined to validate the selected DES for the separation of isopropanol from its aqueous solution. The measured VLE data show that the azeotropic point of isopropanol and water can be eliminated by the DES ChCl/TEG (mole ratio of 1:3) at concentration of 10 wt %. Meanwhile, the thermodynamic consistency of the VLE data was validated by the van Ness test. The measured VLE data were correlated by the NRTL model, and the correlated results agreed well with the experimental VLE data. I



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