Separation of the MethanolâEthanolâWater Mixture Using Ionic Liquid

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Separation of the Methanol-Ethanol-Water Mixture Using Ionic Liquid Yichun Dong, Chengna Dai, and Zhigang Lei Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b01617 • Publication Date (Web): 25 Jul 2018 Downloaded from http://pubs.acs.org on July 28, 2018

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Industrial & Engineering Chemistry Research

Separation of the Methanol-Ethanol-Water Mixture Using Ionic Liquid Yichun Dong, Chengna Dai, and Zhigang Lei* State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Box 266, Beijing 100029, China

ABSTRACT: Vapor pressure data for the binary systems (water/methanol/ethanol + 1-ethyl-3-methylimidazolium acetate ([EMIM]+[Ac]-)) and the ternary systems (methanol + water + [EMIM]+[Ac]-, ethanol + water + [EMIM]+[Ac]-, and methanol + ethanol + [EMIM]+[Ac]-) were measured by a modified equilibrium still. For the above systems, the maximum average relative deviation between experimental data and the UNIFAC-Lei model predicted values was 7%, confirming the prediction accuracy of UNIFAC-Lei model. Thus, this model was further used to predict the isobaric vapor-liquid equilibrium (VLE) data at 101.3 kPa for the methanol + water + [EMIM]+[Ac]-, ethanol + water + [EMIM]+[Ac]-, and methanol + ethanol + [EMIM]+[Ac]- systems at a fixed mole fraction of ionic liquid (IL) (xIL = 0.2). It was demonstrated that the IL [EMIM]+[Ac]- was an appropriate entrainer to separate the methanol-ethanol-water mixture. On this basis, the extractive distillation process was simulated using the rigorous equilibrium (EQ) stage model. The results showed that the entrainer consumption, the heat duty of total reboilers, and the heat duty of total condensers decrease by 25%, 6%, and 6%, respectively, when [EMIM]+[Ac]- replaces the conventional entrainer ethylene glycol (EG). Furthermore, the σ-profiles and excess enthalpies obtained by COSMO-RS model provided theoretical insights into the separation mechanism at the molecular level.

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Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1. INTRODUCTION Ethanol is often used as a solvent in fine chemical, pharmaceutical and other industries, but in the solvent circulation process some methanol and water are mixed with ethanol. Thus, to reuse ethanol, it should be separated from the methanol and water mixture. In general, the separation process is the key factor influencing the enterprise production cost and economic benefits. At present, there are four methods mainly for the separation of alcohol-water systems: membrane separation,1 azeotropic distillation,2 molecular sieve adsorption,3 and extractive distillation.4,5 Among these methods, extractive distillation brings a lot of advantages, such as easy operation, low investment, and high separation capacity, which lead to its wide application in industry. Thus, extractive distillation was selected in this work to separate the methanol-ethanol-water mixture. Recently, ionic liquids (ILs) have been widely used to separate alcohol-water systems by extractive distillation because of their unique advantages, such as thermal and chemical stabilities, salt effect, nonvolatility, high separation ability, easy regeneration, and being present in the liquid state around room temperature. So far, a lot of ILs (e.g., [EMIM]+[Ac]-, [BMIM]+[Ac]-, [EMIM]+[Cl]-, [BMIM]+[Cl]-, [HMIM]+[Cl]-, [EMIM]+[BF4]-, [BMIM]+[BF4]-, [EMIM]+[EtSO4]-, [BMIM]+[MeSO4]-, [EMIM]+[TfO]-, and [EMIM]+[DCA]-) were used to separate the ethanol and water mixture by some researchers.6–12 Among the investigated ILs, the mole fraction of [EMIM]+[Ac]- for breaking the ethanol and water azeotrope was one of the least ILs. Moreover, [EMIM]+[Ac]- might be a promising entrainer to be applied in industry because of its low toxicity (EC50 = 16800 µM),13 low melting point (228.15 K),14 low viscosity (17.88 mPa s at 343.15 K),15 and

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biodegradability.16 Therefore, [EMIM]+[Ac]- might be a promising entrainer to be used to separate the methanol + ethanol + water mixture. In chemical engineering, phase equilibrium data are crucial to process analysis and design. Experimental data are often not sufficient to cover all the desired conditions (such as temperature, pressure, and composition). Therefore, thermodynamic models are widely used to predict and calculate the missing phase equilibrium data. Nowadays, activity coefficient models (such as the NRTL,17 UNIQUAC,18 and UNIFAC19 models) and equations of state are available. Among the models, the UNIFAC model is the most widely used thermodynamic model. In 2009, Lei et al20 extended the UNIFAC model to ILs, and thus the UNIFAC-Lei model was established. This model, based on the original UNIFAC model for conventional solvents, was extended to calculate the activity coefficients of the systems containing ILs, and this model has been widely used in the community of chemical engineering thermodynamics.21–24 In this work, the UNIFAC-Lei model was extended to the methanol-ethanol-water-IL quaternary system. This model can be used not only to predict the influence of IL on the separation of ethanol and water azeotrope containing some methanol, but also to solve the actual factory requirements with low consumption of time, materials, and human resources. To verify the accuracy of UNIFAC-Lei model, the vapor pressure data of the IL + water/ethanol/methanol binary systems and the IL + water + methanol, IL + water + ethanol, and IL + methanol + ethanol ternary systems were measured. This work comprises the following four parts: (1) the vapor pressure data were measured at different temperatures and concentrations for the binary systems (water/methanol/ethanol +

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[EMIM]+[Ac]-) and the ternary systems (methanol + water + [EMIM]+[Ac]-, ethanol + water + [EMIM]+[Ac]-, and methanol + ethanol + [EMIM]+[Ac]-), and the effect of [EMIM]+[Ac]was investigated based on the data of these systems; (2) the experimental data and predicted values by the UNIFAC-Lei model were compared to verify the accuracy of UNIFAC-Lei model. The popular UNIFAC-Lei model was selected in this work because it has been widely applied for the systems containing ILs by many authors; (3) the isobaric VLE data at 101.3 kPa for ternary systems (methanol + water + [EMIM]+[Ac]-, ethanol + water + [EMIM]+[Ac]-, and methanol + ethanol + [EMIM]+[Ac]-) were predicted by the UNIFAC-Lei model to investigate the effect of IL; and (4) the rigorous equilibrium (EQ) stage model of extractive distillation process was established to evaluate how much energy and materials consumption could be saved when [EMIM]+[Ac]- as entrainer replaces the conventional entrainer ethylene glycol (EG). 2. EXPERIMENTAL 2.1. Materials. All the chemicals used in this work are listed in Table 1. Methanol, ethanol, and [EMIM]+[Ac]- were purchased from Beijing MREDA Scientific Ltd., Beijing J & K Scientific Ltd., and Shanghai Cheng Jie Chemical Co. Ltd., respectively. Deionized water was prepared from a Milli-Q reverse osmosis purification system in our university. Before the experiments, the IL [EMIM]+[Ac]- was put into a vacuum rotary evaporator at 353 K for 12 h to remove traces of water and volatile solvent. After pretreated, the water content in the IL [EMIM]+[Ac]- was less than 500 ppm as determined by a Karl Fischer titration (KLS701). The other chemicals were used without further purification because no significant impurities were determined by gas chromatograph (GC 4000A).

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2.2. Apparatus and Procedure. The vapor pressure data were measured in a modified equilibrium still, and the details of the still can be found in our previous work.25 To test the reliability of experimental apparatus, the vapor pressure data of pure component (i.e., methanol, ethanol, and water) and ethanol + water were measured and compared with the calculated values by Antoine equation and the literature data,26 respectively. The parameters of Antoine equation27,28 are listed in Table 2. As shown in Figure 1, the experimental vapor pressures agree well with the calculated values. The average relative deviation (ARD) was calculated by ARD =

1 N

1

Pexp -Pcal

N

Pexp

∑

(1)

where Pexp represents the experimental vapor pressure, Pcal represents the calculated vapor pressure; and N represents the number of data points. The ARDs of vapor pressures for methanol, ethanol, water, and ethanol-water mixture are 2%, 4%, 4%, and 1%, respectively. This means that the experimental apparatus and method used in this work are reliable.

3. COMPUTATIONAL SECTION 3.1. UNIFAC-Lei Model. The UNIFAC model, an efficient thermodynamic model, was applied for calculating the activity coefficient. The UNIFAC-Lei model, based on the original UNIFAC model for conventional solvents, was extended to calculate the activity coefficient of the systems containing ILs. This model has been widely used in the community of chemical engineering thermodynamics.29–32 In the UNIFAC-Lei model, ILs are divided into several groups, while the skeleton of cation and anion are treated as an electrically neutral groups.33 In this work, the UNIFAC-Lei model was used to predict the VLE of the systems 5



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containing IL. In this model, [EMIM]+[Ac]- was divided into three groups, i.e., CH3, CH2, and [MIM][Ac], as shown in Figure 2. The group assignment of other components is given in Table 3. The activity coefficient in UNIFAC-Lei model can be calculated by ln γi = ln γiC + ln γiR

(2)

where ln γiC , a function of Rk and Qk, represents the combinatorial contribution, which is related to the different groups with the difference in size and shape; and ln γiR containing group binary interaction parameters ( αmn and αnm ), represents the residual contribution, which is related to the interaction between different functional groups. In this work, six groups were concerned: CH3, CH2, OH, H2O, DOH, and [MIM][Ac]. The group parameters (Rk and Qk) of these groups are listed in Table 4. The interaction parameters between water and [MIM][Ac] groups and between OH and [MIM][Ac] groups were obtained by correlating the experimental data from previous publications,34,35 and the results are given in Supporting Information Tables S1 and S2. Other interaction parameters come from the literatures.36,37 The objective function (OF) was the minimized total ARD:

 1 OF = min   N

N

∑ 1

γi,cal -γi,exp   γi,exp 

(3)

where γ i ,exp and γ i ,cal represent the activity coefficients of component i in the liquid phase obtained from experiment and UNIFAC-Lei model, respectively. N is the number of data points. All the UNIFAC-Lei group interaction parameters concerned in this work are listed in Table 5, and the current UNIFAC-Lei parameter matrix for ILs is illustrated in Figure 3.

3.2. COSMO-RS Model. The COSMO-RS model is an efficient tool applied for predicting the thermodynamic properties and phase behavior of pure components and 6


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mixtures.49–56 The polarization charge densities (σ-profiles) of pure components and the excess enthalpies of mixtures in this work were calculated by the COSMOthermX software (version C30_1301) based on the COSMO-RS model. In this work, methanol, ethanol, and water could be found in the TZVP-C30–1301 databank. However, the COSMO files of [EMIM]+ and [Ac]- were generated by Gaussian 09 software, and these files were added into the COSMOthermX package. Then, the thermodynamic properties of pure components or mixtures were computed. The σ-profiles of methanol, ethanol, water, [EMIM]+, and [Ac]-, as well as the excess enthalpies of the methanol-[EMIM]+[Ac]-, ethanol-[EMIM]+[Ac]-, and water-[EMIM]+[Ac]- systems, were calculated using the COSMO-RS model, which provided some theoretical insights into the separation mechanism at the molecular level.

3.3. Process Simulation. The rigorous equilibrium (EQ) stage model RadFrac in Aspen Plus software (version 8.4) was used to simulate the separation process of methanol, ethanol, and water mixture by extractive distillation using EG or [EMIM]+[Ac]- as entrainer.57–60 The relevant UNIFAC-Lei model parameters were input into the Aspen Plus software. In the simulation, methanol, ethanol, water, and EG were added from APV84.PURE28 databank, while the IL [EMIM]+[Ac]- was added from NISTV84.NIST-TRC databank.

4. RESULTS AND DISCUSSION 4.1. Analysis of Vapor Pressure of Binary Systems. The vapor pressure data of the three binary systems, i.e., methanol + [EMIM]+[Ac]-, ethanol + [EMIM]+[Ac]-, and water + [EMIM]+[Ac]-, were measured at varying temperatures from 323.15 to 353.15 K. The experimental data and predicted values by UNIFAC-Lei model are given in Supporting

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Information Tables S3, S4, and S5. The vapor pressure of methanol + [EMIM]+[Ac]- binary system is shown in Figure 4, and the others are shown in Supporting Information Figures S1 and S2. To analyze the influence of IL on the vapor pressure data of methanol, ethanol, or water, the activity coefficients of the solvents were estimated using the following equation:

γ1=

Py1ϕ1 P1S x1

(4)

where P and P1S represent the total pressure of the system and the saturated vapor pressure calculated by Antoine equation of component 1; x1 and y1 represent the mole fractions of component 1 in the liquid and vapor phases, respectively; φ1 represents the fugacity coefficient of component 1. In this work, the vapor phase is assumed to be completely composed of methanol, ethanol, or water because [EMIM]+[Ac]- is non-volatile; thus, y1=1. φ1 is also considered as 1 because of the low pressure. Therefore, equation (4) can be simplified as

γ1=

P P1S x1

(5)

The experimental and calculated activity coefficients of methanol, ethanol, and water at varying temperatures from 323.15 to 353.15 K are shown in Supporting Information Figure S3. As shown in Figure S3, all the systems show negative deviations from Raoult’s law (γ1 < 1), indicating that the interactions between [EMIM]+[Ac]- and the solvents are strong. The γ1 of water is lower than that of methanol (or ethanol), indicating that the interaction between [EMIM]+[Ac]- and water are stronger than that between [EMIM]+[Ac]- and methanol (or ethanol); thus, the affinity between [EMIM]+[Ac]- and the solvent follows the order: water >

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ethanol ≈ methanol. Moreover, the ARDs of vapor pressures for these three binary systems are 6%, 6%, and 7%, respectively. This reveals that the values predicted by UNIFAC-Lei model agree well with experimental data, confirming the accuracy of UNIFAC-Lei model for predicting the vapor pressure of these three binary systems.

4.2. Analysis of Vapor Pressure of Ternary Systems. The vapor pressure data of the three ternary systems, i.e., methanol + water + [EMIM]+[Ac]-, ethanol + water + [EMIM]+[Ac]-, and methanol + ethanol + [EMIM]+[Ac]-, were measured at a fixed mole fraction of [EMIM]+[Ac]- (x = 0.2) at varying temperatures from 323.15 to 358.15 K. The experimental data and predicted values by UNIFAC-Lei model are given in Supporting Information Figures S4-S6 and Tables S6-S8. The ARDs of vapor pressures for these three ternary systems are 5%, 6%, and 5%, respectively. This indicates that the UNIFAC-Lei model could be used to predict the VLE data of these three ternary systems.

4.3. Analysis of Isobaric VLE Data of Ternary Systems. To investigate the effect of IL on the separation performance of the methanol, ethanol, and water mixture, the isobaric VLE data at 101.3 kPa for these ternary systems, i.e., methanol + water + [EMIM]+[Ac]-, ethanol + water + [EMIM]+[Ac]-, and methanol + ethanol + [EMIM]+[Ac]- were predicted by the UNIFAC-Lei model at a fixed mole fraction of [EMIM]+[Ac]- (x = 0.2). For more details, please see Supporting Information Tables S9, S10, and S11, along with the experimental data coming from literature. The xi´-yi´ (on an entrainer-free basis) curves are shown in Figures 5, 6, and 7. As shown in Figure 5, [EMIM]+[Ac]- doesn’t have an obvious effect on the VLE of methanol and water. Moreover, the IL exhibits a salting-out effect for methanol in the water-rich region, but

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exhibits a salting-in effect in the methanol-rich region. On the contrary, as shown in Figure 6, the IL has an obvious effect on the VLE of ethanol and water because the IL can break the ethanol and water azeotrope. The IL also exhibits a salting-out effect for ethanol in the water-rich region. Figure 7 shows that the VLE of methanol and ethanol system changes only a little after the addition of [EMIM]+[Ac]- into the mixture. This indicates that [EMIM]+[Ac]exhibits a similar salting effect on both methanol and ethanol. That is, the affinity between [EMIM]+[Ac]- and the solvent follows the order: water > ethanol ≈ methanol. This means that both methanol and ethanol in the ethanol-methanol-water mixture can be obtained as light components at the top of extractive distillation column when [EMIM]+[Ac]- is used as entrainer.

4.4. Analysis of Residue Curve Maps. The residue curve maps (RCMs), which describe the composition of liquid phase in a batch distillation as time goes by, are crucial graphical tools to analyze and design the distillation processes.66,67 For extractive distillation, in the RCM the pure solvent composition is a stable node, and the minimum-boiling azeotropic point is an unstable node. If no distillation boundaries exist in the RCM, all the three pure components can be obtained as products.68 In the methanol, ethanol, and water mixture, ethanol and water can form a minimum-boiling azeotropic mixture. Thus, we like to decide whether [EMIM]+[Ac]- is an appropriate entrainer to separate ethanol and water. Figure 8 shows the RCM of water (1) + ethanol (2) + [EMIM]+[Ac]- (3) ternary system as calculated by the UNIFAC-Lei model. In the RCM, the direction of residual curves is from the azeotrope of ethanol and water to [EMIM]+[Ac]- as the distillation time goes by, and the rest of the vertices are saddle points.

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This indicates that no matter what the initial composition of liquid phase is, [EMIM]+[Ac]will be obtained as a bottom product in the distillation process. Moreover, in the RCM, there are no distillation boundaries so that only one distillation region exists. That is, the three pure components, i.e., ethanol, water, and [EMIM]+[Ac]-, can be obtained in an extractive distillation process. Therefore, the IL [EMIM]+[Ac]- is indeed a suitable entrainer for the separation of ethanol and water by extractive distillation.

4.5. Analysis of σ-Profiles. σ-Profiles, calculated by the COSMO-RS model, could be used to explore the separation mechanism for the methanol-ethanol-water-[EMIM]+[Ac]system at the molecular level.69–71 The σ-profiles are divided into three parts: hydrogen bond donor region (σ < -0.0082 e/Å2), nonpolar surface region (-0.0082 e/Å2 < σ < 0.0082 e/Å2), and hydrogen bond acceptor region (σ > 0.0082 e/Å2).72,73 The σ-profiles of methanol, ethanol, water, [EMIM]+, and [Ac]- are shown in Figure 9. The σ-profiles of methanol, ethanol, and water all cover a wide range. The main peaks of σ-profiles of methanol and ethanol are in the nonpolar surface region, while the main peaks of σ-profiles of water are in both the hydrogen bond donor and acceptor regions. This indicates that water has either stronger hydrogen bond donator or acceptor ability than methanol and ethanol. For [EMIM]+ cation, the main σ-profile peaks are in the nonpolar surface region, and only a few parts are in the hydrogen bond donor region, indicating that the cation [EMIM]+ has a weak hydrogen bond donor ability. Meanwhile, the [Ac]- anion has a strong peak in the hydrogen bond acceptor region, indicating that [Ac]- has a strong hydrogen bond acceptor ability. Thus, the interaction between [Ac]- and water is stronger than that between [Ac]- and methanol (or ethanol) because of the formation of strong hydrogen bonds between [Ac]- and water, resulting in the

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improvement of relative volatility of alcohols to water.

4.6. Analysis of Excess Enthalpy. Herein, the excess enthalpy (HE) as an important thermodynamic property was used to analyze the molecular interactions in solution, which is E composed of three parts: electrostatic misfit interaction energy ( H MF ), H-bond interaction E E energy ( H HB ), and van der Waals interaction energy ( H vdW ). The HE can be calculated by

E E E H E = H MF + H HB +H vdW

(4)

The excess enthalpies (the detailed calculation procedure is given in Supporting Information) of the methanol - [EMIM]+[Ac]-, ethanol - [EMIM]+[Ac]-, and water [EMIM]+[Ac]- systems were calculated by the COSMO-RS model. As shown in Figure 10, E E for all the three systems, H HB has the dominant contribution to the HE, H MF has the E secondary contribution, and H vdW has negligible contribution. In addition, HE of the water -

[EMIM]+[Ac]- system is larger than that of the methanol - [EMIM]+[Ac]- system or the ethanol - [EMIM]+[Ac]- system, indicating that the intermolecular interaction between water and [EMIM]+[Ac]- is stronger than between methanol (or ethanol) and [EMIM]+[Ac]-. Thus, the affinity between [EMIM]+[Ac]- and the solvent follows the order: water > ethanol ≈ methanol, which is consistent with the predicted VLE data as mentioned above. The relative volatility of methanol (or ethanol) to water will be improved with the addition of [EMIM]+[Ac]-. Thus, [EMIM]+[Ac]- is a good extrainer for the separation of methanol-ethanol-water mixture by extractive distillation.

4.7. Process Simulation & Design. 4.7.1. Flow Sheet. The separation process for the methanol-ethanol-water mixture using [EMIM]+[Ac]- or pure EG as entrainer was simulated with Aspen Plus software (version 8.4)

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using the rigorous EQ stage model RadFrac. As shown in Figure 11, the separation process consists of an extractive distillation column (EDC), a distillation column (DC), and a solvent recovery equipment (SRE). Figure 11a shows the flow sheet of extractive distillation process using the conventional entrainer EG. The feed (17.29 wt% methanol + 75.19 wt% ethanol + 7.52 wt% water coming from the industrial value) enters into the EDC at the middle stage, and the entrainer EG is added at the top of EDC. The methanol and ethanol mixture obtained at the top of EDC are introduced into the DC, in which methanol and ethanol are produced at the top and bottom, respectively. The entrainer EG containing some water at the bottom of EDC is introduced into the SRE, namely a distillation column. In the SRE, water is obtained at the top, while the entrainer EG is obtained at the bottom. Then the dried entrainer is recycled into the top of EDC after cooling. Meanwhile, Figure 11b shows the flow sheet of extractive distillation process using [EMIM]+[Ac]- as entrainer. The EDC and DC in Figure 11b are the same as those in Figure 11a, whereas the SRE is different. Because the IL [EMIM]+[Ac]- is non-volatile, the SRE is just a simple flash drum (under vacuum condition) which replaces the conventional distillation column shown in Figure 11a to remove water from [EMIM]+[Ac]-. The EDC needs a little fresh entrainer to make up the minor loss of entrainer in the whole process. 4.7.2. Simulation Results. In the simulation, the constraints for the optimized specifications are given as follows: (1) mass purity > 99% for methanol at the top of DC, (2) mass purity > 99.9% for ethanol at the bottom of DC, and (3) mass purity > 99.5% for entrainer at the bottom of SRE. The operating conditions are listed in Table 6. The simulation results for pure [EMIM]+[Ac]- and pure EG are given in Table 7. It can

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be seen that the entrainer flow rate is 75 kg·h−1 for pure [EMIM]+[Ac]-, down from 100 kg·h−1 for pure EG. Moreover, when [EMIM]+[Ac]- replaces EG as entrainer, the total heat duties (the sums of heat duties of EDC, DC, and SRE or flash drum) of reboilers and condensers decrease by 6% and 6%, respectively. In this regard, the entrainer [EMIM]+[Ac]is more promising for saving entrainer amount and energy consumption than EG. The mole composition profiles of methanol, ethanol, water, and entrainer in the liquid and vapor phases along EDC are shown in Figure 12. The condenser is stage 1, while the reboiler is stage 25. As shown in Figure 12a, there are two abrupt changes of liquid mole fractions because the feed and entrainer streams are fed at the stages 7 and 3, respectively. As shown in Figure 12b, in the vapor phase, the mole fractions of water increase from the top to bottom of EDC, while the mole fractions of methanol and ethanol decrease along this direction, but the mole fractions of EG or [EMIM]+[Ac]- are almost negligible because of their high boiling points. Moreover, the mole fractions of ethanol in the vapor phase are higher in the case of [EMIM]+[Ac]- as entrainer than in the case of EG. It is evident that [EMIM]+[Ac]- improves the relative volatility of ethanol to water, thus intensifying the separation process.

5. CONCLUSIONS To the best of our knowledge, this is the first work to measure the vapor pressure data for the binary systems (water/methanol/ethanol + [EMIM]+[Ac]-) and the ternary systems (methanol + water + [EMIM]+[Ac]-, ethanol + water + [EMIM]+[Ac]-, and methanol + ethanol + [EMIM]+[Ac]-) over a wide concentration range. The experimental data showed that the vapor pressure decreases rapidly with the increase of [EMIM]+[Ac]- concentration

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because of the strong interaction between [EMIM]+[Ac]- and methanol/ethanol/water. The popular UNIFAC-Lei model was extended to the binary and ternary systems investigated in this work. The separation process of methanol-ethanol-water mixture was simulated by the Aspen Plus software (version 8.4) with the rigorous EQ stage model. The simulation results showed that [EMIM]+[Ac]- as entrainer is more promising for saving the entrainer amount and energy consumption than EG. The entrainer amount, the heat duty of total reboilers, and the heat duty of total condensers decrease by 25%, 6%, and 6%, respectively. Furthermore, the σ-profiles and excess enthalpies were obtained by the COSMO-RS model, providing theoretical insights into the separation mechanism at the molecular level. The intermolecular interaction between water and [EMIM]+[Ac]- is stronger than that between methanol (or ethanol) and [EMIM]+[Ac]- because of the stronger H-bond formation in the former. It is worth mentioning that the devices are simplified when [EMIM]+[Ac]- is used as entrainer.

■ ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the website. VLE data of the ternary system (ethanol (1) + water (2) + [BMIM]+[Ac]-); vapor pressure data of the binary systems (methanol/ethanol/water + [EMIM]+[Ac]-) and ternary systems (methanol + water + [EMIM]+[Ac]-, ethanol + water + [EMIM]+[Ac]-, and methanol + ethanol + [EMIM]+[Ac]-). (word file)

■ AUTHOR INFORMATION Corresponding Author *Tel.: +86-1064433695. E-mail: [email protected].

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ORCID Zhigang Lei: 0000-0001-7838-7207

Notes The authors declare no competing financial interest.

■ ACKNOWLEDGMENTS This work is financially supported by the National Natural Science Foundation (No. 21476009) and the National Key R&D Plan of China (No. 2018YFB0604702).

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23



Table Captions

Table 1. Chemical Properties of the Materials Used in This Work

Table 2. Antoine Coefficients A, B, and C

Table 3. UNIFAC-Lei Group Assignment

Table 4. UNIFAC-Lei Group Volume (Rk) and Surface Area (Qk)

Table 5. UNIFAC-Lei Interaction Parameters amn /K and anm /K

Table 6. Optimized Specifications and Operating Conditions for the Separation of Methanol, Ethanol, and Water Using Different Entrainers

Table 7. Comparison of the Process Simulation Results Between [EMIM]+[AC]- and EG as Entrainers

24


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Table 1. Chemical Properties of the Materials Used in This Work Materials

CAS RN

Sources

Methanol Ethanol

67-56-1 64-17-5

MREDA J&K

Water

7732-18-5

Our university

[EMIM]+[Ac]-

143314-17-4

Cheng Jie

Mass fraction purity

Purification methods

Analysis methods

≥ 99.9%a ≥ 99.9%a electric resistivity ≥ 10 MΩ•cm

None None

-

None

CREATE RM-320b

Vacuum drying

Karl-Fischer titration

≥ 99%

a

Provided by supplier. The instrument on water purification system.

b

25



Page 26 of 46

Table 2. Antoine Coefficients A, B, and C

a b

Components

A

B

C

T range/K

Reference

Methanolla Ethanolb Waterb

16.5725 7.237103 7.196213

-3626.55 1592.864 1730.63

-34.29 -46.966 -39.724

257~364 293.15-366.15 274.15-373.15

[16] [17] [17]

ln(Ps/kPa) = A + B/[(T/K) + C]. log10(Ps/kPa) = A - B/[(T/K) + C].

26


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Table 3. UNIFAC-Lei Group Assignment Compounds

Structural groups

Methanol Ethanol Water EG [EMIM]+[Ac]-

1 CH3, 1 OH 1 CH3, 1 CH2, 1 OH 1 H2O 1 DOH 1 CH3, 1 CH2, 1 [MIM][Ac]

27



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Table 4. UNIFAC-Lei Group Volume (Rk) and Surface Area (Qk) Groups

Rk

Qk

CH3

0.9011

0.8480

CH2

0.6744

0.5400

OH

1.0000

1.2000

H2O

0.9200

1.4000

DOH

2.4088

2.2480

[MIM][Ac]

6.8459

4.3335

28


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Table 5. UNIFAC-Lei Interaction Parameters amn /K and anm /K m

n CH3

CH2

OH

H2O

DOH

[MIM][Ac]

CH3

0

0

986.50

1318.00

3025.00

371.56

CH2

0

0

986.50

1318.00

3025.00

371.56

OH

156.40

156.40

0

353.50

-318.90

-656.81

H2O

300.00

300.00

-229.10

0

12.72

-659.06

DOH

139.90

139.90

267.60

-137.40

0

-

[MIM][Ac]

667.48

667.48

-239.17

-434.15

-

0

29



Page 30 of 46

Table 6. Optimized Specifications and Operating Conditions for the Separation of Methanol, Ethanol, and Water Using Different Entrainers Contents Columns

Streams

Entrainers Extractive distillation column Pressure (atm) Total stages Feed stage Entrainer feed stage Mass reflux ratio Distillate rate (kg/h) Distillation column Pressure (atm) Total stages Feed stage Mass reflux ratio Bottoms rate (kg/h) Solvent recovery equipment Pressure (atm) Temperature (℃) Total stages Feed stage Mass reflux ratio Bottom rate (kg/h) Feed stream Temperature (℃) Pressure (atm) Component flow rate (kg/h) Water Methanol Ethanol Entrainer stream Temperature (℃) Pressure (atm) Component flow rate (kg/h) EG [EMIM]+[Ac]-

EG

[EMIM]+[AC]-

1 25 15 3 1.3 92.48

1 25 15 3 1.3 92.48

1 38 21 13.3 75.10

1 38 21 13.3 75.10

1 5 3 1 100.00

0.01 200 -

25 1

25 1

7.52 17.29 75.19

7.52 17.29 75.19

25 1

25 1

100 -

75

30


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Table 7. Comparison of the Process Simulation Results Between [EMIM]+[AC]- and EG as Entrainers Contents Streams

Entrainers Top stream of EDC

Bottom stream of EDC

Top stream of DC Bottom stream of DC Top stream of SRE Recycled entrainer stream Heat duty

EDC DC SRE Heat exchanger (cooler1)

Heat exchanger (cooler2)

Total heat duty

Temperature (℃) Composition (mass faction) Water Methanol Ethanol Entrainer Temperature (℃) Composition (mass faction) Water Methanol Ethanol Entrainer Temperature (℃) Mass purity of methanol Temperature (℃) Mass purity of ethanol Temperature (℃) Mass purity of Water Temperature (℃) Mass purity of EG Condenser (kW) Reboiler (kW) Condenser (kW) Reboiler (kW) Condenser (kW) Reboiler (kW) Inlet temperature (℃) Outlet temperature (℃) Condenser (kW) Inlet temperature (℃) Outlet temperature (℃) Condenser (kW) Condenser (kW) Reboiler (kW)

31


EG

IL

74.13

73.22

0.001 0.187 0.812 0.000 146.85

0.000 0.187 0.813 0.000 190.55

0.070 0.000 0.000 0.930 64.58 0.994 78.29 0.999 99.55 0.938 191.26 0.996 -53.29 66.60 -75.89 76.00 -9.23 12.53 191.26 25.00 -12.23 -150.64 155.13

0.091 0.000 0.000 0.909 64.58 0.994 78.30 0.999 100.00 0.996 200.00 0.995 -53.26 62.73 -75.90 76.00 6.40 200.00 25.00 -6.98 200.00 95.00 -5.65 -141.79 145.13


Figure Captions Figure 1. Vapor pressure data of (a) water, ethanol, or methanol and (b) the ethanol (1) + water (2) mixture.

Figure 2. Group assignment for [EMIM]+[Ac]-.

Figure 3. Current UNIFAC-Lei parameter matrix for ILs (■, previously published parameters;37–41 ■, previously published parameters by our group;33,36,42–48 ■, new parameters (this work); □, no parameters available).

Figure 4. Vapor pressures of the methanol (1) + [EMIM]+[Ac]- (2) binary mixture at different temperatures (Solid lines, predicted values by the UNIFAC-Lei model; scattered points, experimental data).

Figure 5. Isobaric VLE data for the methanol (1) + water (2) + [EMIM]+[Ac]- (3) system at 101.3 kPa (■, experimental data from literature;61 ●, experimental data from literature;62 dashed line, predicted results by the UNIFAC-Lei model with x3 = 0; solid line, predicted results by the UNIFAC-Lei model with x3 = 0.2).

Figure 6. Isobaric VLE data for the ethanol (1) + water (2) + [EMIM]+[Ac]- (3) system at 101.3 kPa (■, experimental data from literature;63 ●, experimental data from literature;64 ▲, experimental data from literature;65 dashed line, predicted results by the UNIFAC-Lei model

32


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with x3 = 0; solid line, predicted results by the UNIFAC-Lei model with x3 = 0.2).

Figure 7. Isobaric VLE data for the methanol (1) + ethanol (2) + [EMIM]+[Ac]- (3) system at 101.3 kPa (■, experimental data from literature;61 dashed line, predicted results by the UNIFAC-Lei model with x3 = 0; solid line, predicted results by the UNIFAC-Lei model with x3 = 0.2).

Figure 8. RCM for the ternary system of ethanol + water + [EMIM]+[Ac]- at 101.3 kPa (○, azeotropic point).

Figure 9. σ-Profiles for methanol, ethanol, water, EMIM+, and Ac-.

Figure 10. Excess enthalpies of (a) methanol (1) + [EMIM]+[Ac]- (2), (b) ethanol (1) + [EMIM]+[Ac]- (2), and (c) water (1) + [EMIM]+[Ac]- (2) at T = 298.15 K.

Figure 11. Process flowsheet for the separation of the methanol, ethanol, and water mixture by extractive distillation using (a) EG and (b) [EMIM]+[Ac]- as entrainers.

Figure 12. Composition profiles along EDC ((a) mole fraction in the liquid phase; (b) mole fraction in the vapor phase; solid lines, [EMIM]+[Ac]- as the entrainer; dashed lines, EG as the entrainer; ● and ○, methanol; ▼ and ▽, ethanol; ◆ and ◇, water; ▲ and ∆, entrainer).

33



100

(a)

80

P /kPa

60

40 ■ Water ▲ Ethanol ● Methanol — Calculated values

20

0 290

300

310

320

330

340

350

360

370

380

T /K

80 (b)

70

60 P /kPa

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 46

T = 343.15 K

50 ■ Experimental data

40

— Literature values

30 0.0

0.2

0.4

0.6

0.8

1.0

x1

Figure 1. Vapor pressure data of (a) water, ethanol, or methanol and (b) the ethanol (1) + water (2) mixture.

34


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Figure 2. Group assignment for [EMIM]+[Ac]-.

35


8

[MIM][MeSO 4] [MIM][EtSO 4]

35 36

group;33,36,42–48 ■, new parameters (this work); □, no parameters available).

36

ACS Paragon Plus Environment [R1R2R3R4P][TS] [R1R2R3R4P][MeSO 4]

69 70 71

[R1R2R3R4P][Cl] [R1R2R3R4P][FAP] [R1R2R3R4S][Tf2N]

73 74 75

72 [R1R2R3R4P][(C8H 17)2PO 2]

[R1R2R3R4][TS] [R1R2R3R4P][BF 4]

68

[Quin][Tf2N] [R1R2R3R4][Tf 2N] 67

[OCH2MIM][Tf 2N] 65 66

[N-C3OHPY][FAP] [(OCH2)2IM][Tf 2N]

62 64

[N-C3OHPY][Tf2N]

61 63

[MPYR][TfO] [MPYR][SCN]

60

[MPY][TOS] [MPYR][Tf 2N]

57 59

[MPY][SCN]

56 58

[MPY][TfO] [MPY][C2H 5OC2H 4SO4]

55

[MPY][BF4] [MPY][Tf 2N] 54

[MPIP][SCN] 53

52

[MIM][TOS] 49

[MIM][Ac]

[MIM][TFA] 48

[MPIP][Tf 2N]

[MIM][TCB] 47

51

[MIM][SCN] 46

50

[MIM][PF 6] [MIM][SbF 6] 45

43 44

[MIM][NO 3] [MIM][OcSO 4]

42

[MIM][DMPO 4] [MIM][MDEGSO 4]

41

39 40

[MIM][Cl] [MIM][DEPO 4]

38

37 [MIM][CH 3OC2C2H 4SO4]

[MIM][TFO] [MIM][MeSO 3]

34

32 33

[MIM][Tf 2N] [MIM][BOB]

31

Thiophene [MIM][BF 4]

30

28 29

DMF NMP

27

H 2S N2O

26

24 25

H2 SO2

23

O2 CO2

22

CH4

20 21

CO2 C2H 4

19

17 18

CHF 2 CHF 3

16

CF 2

13 CHF

CH 2O

12

15

HCOO

11

14

CHO CCOO

10

CH2CO

H2O ACOH

7 9

OH CH 3OH

6

4 5

ACH ACCH 2

3

CH2 C=C

2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 1

Industrial & Engineering Chemistry Research Page 36 of 46

28 29

26 27

24 25

22 23

20 21

18 19

16 17

14 15

12 13

10 11

8 9

6 7

4 5

2 3

1

Figure 3. Current UNIFAC-Lei parameter matrix for ILs (■, previously published parameters;37–41 ■, previously published parameters by our

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


P /kPa

Page 37 of 46

100

x1=0.1

90

x1=0.2

80

x1=0.3

70

x1=0.4

60

x1=0.5

50 40 30 20 10 0 320

330

340

350

360

T /K

Figure 4. Vapor pressures of the methanol (1) + [EMIM]+[Ac]- (2) binary mixture at different temperatures (Solid lines, predicted values by the UNIFAC-Lei model; scattered points, experimental data).

37



1.0

0.8

0.6 y1'

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 46

0.4

0.2

0.0 0.0

0.2

0.4

x1'

0.6

0.8

1.0

Figure 5. Isobaric VLE data for the methanol (1) + water (2) + [EMIM]+[Ac]- (3) system at 101.3 kPa (■, experimental data from literature;61 ●, experimental data from literature;62 dashed line, predicted results by the UNIFAC-Lei model with x3 = 0; solid line, predicted results by the UNIFAC-Lei model with x3 = 0.2).

38


Page 39 of 46

1.0

0.8

0.6 y1'

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.4

0.2

0.0 0.0

0.2

0.4

0.6

0.8

1.0

x1 '

Figure 6. Isobaric VLE data for the ethanol (1) + water (2) + [EMIM]+[Ac]- (3) system at 101.3 kPa (■, experimental data from literature;63 ●, experimental data from literature;64 ▲, experimental data from literature;65 dashed line, predicted results by the UNIFAC-Lei model with x3 = 0; solid line, predicted results by the UNIFAC-Lei model with x3 = 0.2).

39



1.0

0.8

0.6 y1'

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 40 of 46

0.4

0.2

0.0 0.0

0.2

0.4

0.6

0.8

1.0

x1 '

Figure 7. Isobaric VLE data for the methanol (1) + ethanol (2) + [EMIM]+[Ac]- (3) system at 101.3 kPa (■, experimental data from literature;61 dashed line, predicted results by the UNIFAC-Lei model with x3 = 0; solid line, predicted results by the UNIFAC-Lei model with x3 = 0.2).

40


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Ethanol 0.00 1.00

0.25

0.75

0.50

0.50

0.75

[EMIM]+[Ac]-

1.00 0.00

0.25

0.25

0.50

0.75

0.00 Water 1.00

Figure 8. RCM for the ternary system of ethanol + water + [EMIM]+[Ac]- at 101.3 kPa (○, azeotropic point).

41



20 H2O Methanol Ethanol + EMIM Ac

15

P (σ)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 42 of 46

10

5

0 -0.03

-0.02

-0.01

0.00

0.01

0.02

2

σ (e/Å )

Figure 9. σ-Profiles for methanol, ethanol, water, EMIM+, and Ac-.

42


0.03

Page 43 of 46

2

(a)

HE (vdW)

0

HE (misfit)

HE (kJ•mol-1)

-2 -4

HE (H-bond) -6

HE

-8 -10 -12 0.0

0.2

0.4

0.6

0.8

1.0

x1 2

HE (vdW)

(b)

HE (kJ•mol-1)

0 -2

HE (misfit)

-4

HE (H-bond)

-6

HE

-8 -10 -12 0.0

0.2

0.4

0.6

0.8

1.0

x1 2

(c)

HE (vdW)

0 -2

HE (kJ•mol-1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


HE (misfit)

-4 -6

HE (H-bond)

-8 -10 -12 0.0

HE 0.2

0.4

0.6

0.8

1.0

x1

Figure 10. Excess enthalpies of (a) methanol (1) + [EMIM]+[Ac]- (2), (b) ethanol (1) + [EMIM]+[Ac]- (2), and (c) water (1) + [EMIM]+[Ac]- (2) at T = 298.15 K.

43



Page 44 of 46

(a) Methanol Make up

DC

Entrainer

Water

EDC Ethanol

Feed

SRC

Pump

Cooler 1

(b) Methanol Make up

DC

Entrainer

Cooler 2

EDC Ethanol

Feed

Water

Flush drum

Pump

Cooler 1

Figure 11. Process flowsheet for the separation of the methanol, ethanol, and water mixture by extractive distillation using (a) EG and (b) [EMIM]+[Ac]- as entrainers. 44


Page 45 of 46

1.0 (a)

0.8

x

0.6

0.4

0.2

0.0

0

2

4

6

8

10 12 14 16 18 20 22 24 26 Stage no.

1.0 (b)

0.8

0.6 y

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.4

0.2

0.0

0

2

4

6

8

10 12 14 16 18 20 22 24 26 Stage no.

Figure 12. Composition profiles along EDC ((a) mole fraction in the liquid phase; (b) mole fraction in the vapor phase; solid lines, [EMIM]+[Ac]- as the entrainer; dashed lines, EG as the entrainer; ● and ○, methanol; ▼ and ▽, ethanol; ◆ and ◇, water; ▲ and ∆, entrainer).

45



Page 46 of 46

Table of Content (TOC) Graphic:

A

S

A+B+C

DC

EDC B Flush drum

Cooler

46


C

Separation of the MethanolâEthanolâWater Mixture Using Ionic Liquid

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