2-Propanol Dehydration via Extractive Distillation Using a Renewable

Article pubs.acs.org/jced

2‑Propanol Dehydration via Extractive Distillation Using a Renewable Glycerol−Choline Chloride Deep Eutectic Solvent: Vapor−Liquid Equilibrium Lianzhong Zhang,* Zheng Zhang, Dongping Shen, and Mingyang Lan Zhejiang Province Key Laboratory of Biofuel, College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China ABSTRACT: A renewable deep eutectic solvent, glycerol−choline chloride (molar ratio 2:1), was tested as an entrainer for dehydration of 2-propanol by extractive distillation. Isobaric vapor−liquid equilibrium data for the quaternary system water + 2-propanol + glycerol + choline chloride were measured at 100 kPa. With the addition of the deep eutectic solvent, the azeotrope of water + 2-propanol can be removed at a solvent mass fraction of 0.142, which is much smaller than the minimum solvent mass fraction of 0.229 for glycerol alone. With regard to the relatively low viscosity as compared with glycerol, the deep eutectic solvent may have better performance when used as entrainer for 2-propanol dehydration. The NRTL equation was used for the modeling of the quaternary vapor−liquid equilibrium data. Binary parameters of water + 2-propanol, water + glycerol, and 2-propanol + glycerol were fixed as the same for the system water + 2-propanol + glycerol and were taken from the literature. The correlation appeared to be in good agreement with the experimental results. Mean absolute deviations were 0.15 K for equilibrium temperature and 0.0035 for 2-propanol mole fraction in the vapor phase, respectively.

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INTRODUCTION

Table 1. Chemical Samples Used in This Study

2-Propanol is a basic chemical widely used in the industry as solvent or as chemical intermediate. Separation of the aqueous mixture of 2-propanol is often demanded in its production and recovery. The mixture of water + 2-propanol forms a minimum boiling point azeotrope. Therefore, 2-propanol dehydration can not be achieved by conventional distillation. At the present stage, extractive distillation is considered as a promising technique, especially for large-scale application. Extractive distillation uses a solvent, frequently termed as entrainer, which interacts with the components to be separated and alters their nonideality to a different extent and, therefore, removes the azeotrope or increases the relative volatility. In recent years, various solvents have been reported to be feasible separation agents for the dehydration of 2-propanol, including a number of ionic liquids (ILs),1 ethylene glycol,2 and glycerol.3 Deep eutectic solvents (DESs) are mixtures composed of hydrogen bond donors and hydrogen bond acceptors that together have much lower melting point.4−6 The mixtures are sometimes referred to as low transition temperature mixtures (LTTMs),7 because they may show a glass transition temperature instead of a eutectic melting point. DESs (or LTTMs) are regarded as promising alternative to ILs because they show many similar properties, but they are generally inexpensive and ́ can be prepared in a easier way. As reported by Rodriguez et al.,8 the azeotrope of water + ethanol can be removed by malic acid/choline chloride 1:1, glycolic acid/choline chloride 3:1, and glycolic acid/choline chloride 1:1, while lactic acid/ choline chloride 2:1 can only move the azeotrope to the pure ethanol side. These results were related to a solvent mole fraction of 0.2. For water + 2-propanol, the azeotrope cannot be © 2017 American Chemical Society

chemical name

source

2-propanol

Sinopharm Chemical Reagent Co. Ltd. glycerol Sinopharm Chemical Reagent Co. Ltd. choline chloride J&K Scientific Ltd.

mass fraction purity

purification method

0.997

none

0.99

none

0.98

none

broken by both glycolic acid/choline chloride 3:1 and lactic acid−choline chloride 2:1, at solvent mole fractions up to 0.1.9 In the present work a glycerol−choline chloride 2:1 deep eutectic solvent was consider for use in 2-propanol dehydration by extractive distillation. The DES is renewable, because both glycerol and choline chloride are nontoxic and environment compatible. The DES can be prepared with 100% atom economy, through simple mixing of the two components, which are both inexpensive. As compared with glycerol alone, the viscosity of the DES is relatively low.10 This is favorable for application in extractive distillation. To test the entrainer performance of the DES, isobaric data were measured for vapor−liquid equilibrium (VLE) of the quaternary system water +2-propanol + glycerol + choline chloride. To the best of our knowledge, these data are not available in the literature.

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EXPERIMENTAL SECTION Materials. 2-propanol (mass fraction purity 0.997) and glycerol (mass fraction purity 0.99) were supplied by Sinopharm Received: October 28, 2016 Accepted: January 13, 2017 Published: January 25, 2017 872

DOI: 10.1021/acs.jced.6b00912 J. Chem. Eng. Data 2017, 62, 872−877

Journal of Chemical & Engineering Data

Article

Table 2. Experimental Vapor−Liquid Equilibrium Data for Temperature T, Liquid-Phase Mole Fraction on Solvent-Free Basis x′, Liquid-Phase Mass Fraction w, Vapor-Phase Mole Fraction y, and Calculated Results for Activity Coefficient γ and Relative Volatility α, for the Quaternary System Water (1) + 2-Propanol (2) + Glycerol (3) + Choline Chloride (4) at p = 100 kPaa

a

x′2

wsb

T/K

0.0998 0.0993 0.1008 0.0997 0.1004 0.1002 0.0996 0.1002

0.8054 0.7032 0.6018 0.5056 0.4018 0.3004 0.2007 0.1008

370.05 363.17 359.54 357.86 356.85 356.35 356.15 356.04

0.1996 0.2003 0.2002 0.1992 0.2001 0.2006 0.2010 0.2000

0.8029 0.7013 0.6009 0.5015 0.4011 0.3024 0.2004 0.1008

364.44 359.37 357.15 356.04 355.44 355.11 354.94 354.90

0.3937 0.4027 0.3999 0.4002 0.4009 0.3985 0.4007 0.3999

0.8010 0.7030 0.6026 0.5021 0.4021 0.3058 0.2008 0.1023

361.86 358.49 356.93 355.99 355.32 354.81 354.40 354.08

0.5871 0.6003 0.6004 0.6004 0.6003 0.6003 0.6002 0.6002

0.7928 0.7013 0.6033 0.5006 0.4041 0.3033 0.2010 0.1019

361.03 358.73 357.50 356.60 355.90 355.21 354.54 353.86

0.8019 0.8012 0.8000 0.8008 0.8011 0.8013 0.8016 0.8006

0.8077 0.7035 0.6027 0.5043 0.4037 0.3012 0.1978 0.1033

361.74 359.25 358.19 357.47 356.81 356.11 355.33 354.48

0.9452 0.9502 0.9500 0.9506 0.9501 0.9502 0.9496 0.9496

0.8040 0.7008 0.5998 0.4999 0.4038 0.3020 0.2010 0.1008

361.65 359.57 358.70 358.13 357.62 357.08 356.38 355.55

y1 x′2 = 0.1 0.3226 0.3502 0.3736 0.4023 0.4292 0.4536 0.4711 0.4945 x′2 = 0.2 0.2115 0.2500 0.2906 0.3294 0.3657 0.3995 0.4295 0.4541 x′2 = 0.4 0.1205 0.1528 0.1978 0.2393 0.2792 0.3175 0.3581 0.3950 x′2 = 0.6 0.0739 0.0953 0.1251 0.1582 0.1938 0.2304 0.2697 0.3126 x′2 = 0.8 0.0282 0.0423 0.0597 0.0779 0.0990 0.1241 0.1536 0.1880 x′2 = 0.95 0.0074 0.0103 0.0149 0.0201 0.0267 0.0329 0.0425 0.0546

y2

γ1

γ2

α21

0.6774 0.6498 0.6264 0.5977 0.5708 0.5464 0.5289 0.5055

0.73 0.82 0.89 0.95 0.99 1.02 1.03 1.06

7.09 7.06 6.79 6.46 6.00 5.61 5.32 4.94

19.0 16.8 15.0 13.4 11.9 10.8 10.2 9.18

0.7884 0.7499 0.7094 0.6706 0.6343 0.6005 0.5705 0.5459

0.72 0.81 0.89 0.96 1.02 1.08 1.12 1.15

5.46 4.95 4.44 4.01 3.61 3.29 3.01 2.81

15.0 12.0 9.75 8.19 6.94 5.99 5.28 4.81

0.8795 0.8471 0.8022 0.7607 0.7208 0.6825 0.6419 0.6050

0.68 0.77 0.89 1.00 1.10 1.19 1.30 1.39

3.90 3.23 2.76 2.41 2.15 1.96 1.77 1.62

11.3 8.22 6.09 4.76 3.86 3.25 2.68 2.30

0.9260 0.9047 0.8749 0.8418 0.8062 0.7696 0.7303 0.6874

0.70 0.78 0.89 1.02 1.17 1.31 1.48 1.68

3.12 2.52 2.12 1.84 1.64 1.49 1.36 1.25

8.81 6.32 4.65 3.54 2.77 2.22 1.80 1.46

0.9717 0.9577 0.9403 0.9221 0.9010 0.8758 0.8464 0.8120

0.65 0.75 0.89 1.03 1.20 1.41 1.67 1.99

2.80 2.15 1.78 1.55 1.38 1.26 1.16 1.09

8.51 5.63 3.94 2.95 2.26 1.75 1.36 1.08

0.9926 0.9897 0.9850 0.9799 0.9732 0.9670 0.9575 0.9454

0.66 0.77 0.91 1.08 1.29 1.47 1.77 2.20

2.58 1.96 1.61 1.40 1.26 1.15 1.08 1.03

7.73 5.03 3.48 2.53 1.91 1.54 1.20 0.92

u(T) = 0.08 K, u(p) = 0.05 kPa, ur(x2′) = 0.01, u(ws) = 0.003, ur(y1) = 0.01, ur(y2) = 0.01. bws = w3 + w4, w3/w4 = 1.319.

Chemical Reagent Co. Ltd. Choline chloride (mass fraction purity 0.98) was supplied by J&K Scientific Ltd. They were

used without further purification. Water was double distilled. The chemical sample descriptions are presented in Table 1. 873



Article

Liquid-phase compositions were calculated through a procedure based on mass balance.11,13 Standard uncertainties were estimated to be 0.08 K for temperature, 0.05 kPa for pressure, and 0.003 for the liquid-phase solvent mass fraction. Relative standard uncertainties for water and 2-propanol mole fractions in the vapor-phase and for 2-propanol mole fraction in the liquid-phase were estimated to be 0.01.

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RESULTS AND DISCUSSION The isobaric VLE data are presented in Table 2. For the quaternary system water (1) + 2-propanol (2) + glycerol (3) + choline chloride (4), reported data include mole fraction of 2-propanol in the liquid phase on a solvent-free basis (x′2), solvent mass fraction in the liquid phase (ws = w3 + w4), mole fraction of water in the vapor phase (y1), mole fraction of 2-propanol in the vapor phase (y2), and equilibrium temperature (T). The experimental data were measured at p = 100 kPa. There are six data sets reported at x′2 = 0.1, 0.2, 0.4, 0.6, 0.8 and 0.95, respectively. Calculated results are also presented in Table 2 for the activity coefficients of water (γ1) and 2-propanol (γ2), and the relative volatility of 2-propanol to water (a21). Ideal gas assumption was applied in the calculation of the activity coefficients. The vapor pressures were calculated by parameters available in the literature.14 The effect of the deep eutectic solvent on the volatile binary pair is illustrated in Figures 1 to 4. The trend of relative volatility of 2-propanol to water, α21, can be observed in Figure 1, with varying solvent mole fraction, xs. At all of the six 2-propanol mole fractions, enhancement of α21 can be observed by the addition of the deep eutectic solvent. Mechanism for the effect of solvent on α21 can be described by the effect on activity coefficients. With the ideal gas assumption, relative volatility of the volatile binary pair can be described as an product of a ratio of activity coefficients and a ratio of vapor pressures, that is, sat α21 = (γ2/γ1)(psat 2 /p1 ). The ratio of vapor pressures changes very little, from 1.956 to 1.966, in the experimental temperature range. Therefore, the effect of solvent on α21 is mainly related with its effect on the activity coefficients. With the increase of xs, as shown in Figure 2, the activity coefficient of water decreases, while the activity coefficients of 2-propanol increases. Both of these opposite trends lead to the increase of α21.

Figure 1. Experimental and calculated relative volatility of 2-propanol to water, α21, in relation with solvent mole fraction, xs = x3 + x4 (x3/x4 = 2), for the saturated mixture water (1) + 2-propanol (2) + glycerol (3) + choline chloride (4) at p = 100 kPa: ○, x′2 = 0.1; ●, x′2 = 0.2; □, x′2 = 0.4; ■, x′2 = 0.6; ◊, x′2 = 0.8; ⧫, x′2 = 0.95; Lines were calculated by NRTL parameters in Table 3: solid line, x′2 = 0.1, 0.2, 0.4, 0.6, 0.8, and 0.95, respectively; dashed line, x′2 = 1.

By Karl Fischer titration, water mass fraction for 2-propanol, glycerol, and choline chloride was typically 4.8 × 10−4, 7.6 × 10−4, and 10.3 × 10−4 respectively. Apparatus and Procedure. VLE data were measured by use of an ebulliometer.11,12 The experimental procedure was the same as that for water + 2-propanol + glycerol,3 except that a deep eutectic solvent prepared by mixing glycerol and choline chloride (molar ratio 2:1 or mass ratio 1.319:1) was used instead of glycerol. For the measurement of the quaternary system water (1) + 2-propanol (2) + glycerol (3) + choline chloride (4), mass fraction of the solvent, ws = w3 + w4, was changed from approximately 0.8 to 0.1, while the 2-propanol mole fraction on a solvent-free basis, x′2 = x2/(x1 + x2), was kept almost unchanged. When equilibrium was established, the vapor phase was sampled by a syringe. The glycerol mass fraction in the vapor phase was determined by gas chromatograph (Fuli 9790J). The water mass fraction was measured by Karl Fischer titration (SF-3 Titrator, Zibo Zifen Instrument, Ltd.). Consequently, water and 2-propanol mole fractions can be calculated.

Figure 2. Experimental and calculated activity coefficients of (a) water, γ1, and (b) 2-propanol, γ2, in relation with solvent mole fraction, xs = x3 + x4 (x3/x4 = 2), for the saturated mixture water (1) + 2-propanol (2) + glycerol (3) + choline chloride (4) at p = 100 kPa: ○, x′2 = 0.1; ●, x′2 = 0.2; □, x′2 = 0.4; ■, x′2 = 0.6; ◊, x′2 = 0.8; ⧫, x′2 = 0.95. Lines were calculated by NRTL parameters in Table 3: solid line, x′2 = 0.1, 0.2, 0.4, 0.6, 0.8, and 0.95, respectively; dashed line, x′2 = 1. 874



Article

Figure 3. Experimental and calculated activity coefficients of (a) water, γ1, and (b) 2-propanol, γ2, in relation with 2-propanol mole fraction on solvent-free basis, x′2, for the saturated mixture water (1) + 2-propanol (2) + glycerol (3) + choline chloride (4) at p = 100 kPa: ○, ws = 0.8; ●, ws = 0.7; □, ws = 0.6; ■, ws = 0.5; ◊, ws = 0.3; ⧫, ws = 0.1. Lines were calculated by NRTL with parameters in Table 3: solid lines, ws = 0.8, 0.7, 0.6, 0.5, 0.3, and 0.1, respectively; dashed line, ws = 0. ws = w3 + w4, w3/w4 = 1.319.

rapid decrease of γ2, α21 decreases rapidly with increasing x′2 at all given ws, as shown in Figure 4 The quaternary experimental data were correlated using the NRTL equation.15 Binary parameters for water + 2-propanol, water + glycerol, and 2-propanol + glycerol have been reported in the literature.3 These parameters were used in the modeling and were kept unchanged. Binary parameters for water + choline chloride, 2-propanol + choline chloride, and glycerol + choline chloride were regarded as temperature-independent and were optimized using the following objective function

F=

1 N

⎛ γ ∑ ⎜⎜ 1,cal γ − N ⎝ 1,exp

⎞2 ⎟ + 1 1 ⎟⎠ N

⎛ γ ∑ ⎜⎜ 2,cal γ − N ⎝ 2,exp

⎞2 ⎟ 1 ⎟⎠

(1)

where N is the number of data points. It was found that the correlation was insensitive to the choice of the nonrandomness factors, which were therefore set as 0.3. The result of the binary parameters are listed in Table 3. Using the binary parameters in Table 3, quaternary VLE data were calculated. As can be observed in Figures 1 to 4, the calculated results are in good agreement with the experimental values. The Mean absolute deviations were 0.15 K for equilibrium temperature and 0.0035 for vapor phase mole fraction of 2-propanol, respectively. The NRTL model and the parameters proposed in Table 3 appear to be adequate for modeling the VLE behavior and, therefore, can be used for the design of extractive distillation column using the deep eutectic mixture as solvent.

Figure 4. Experimental and calculated relative volatility of 2-propanol to water, α21, in relation with 2-propanol mole fraction on solvent-free basis, x′2, for the saturated mixture water (1) + 2-propanol (2) + glycerol (3) + choline chloride (4) at p = 100 kPa: ○, ws = 0.8; ●, ws = 0.7; □, ws = 0.6; ■, ws = 0.5; ◊, ws = 0.3; ⧫, ws = 0.1. Lines were calculated by NRTL with parameters in Table 3: solid lines, ws = 0.8, 0.7, 0.6, 0.5, 0.3, and 0.1, respectively; dashed line, ws = 0. ws = w3 + w4, w3/w4 = 1.319.

In Figure 3, the trend of activity coefficients can be observed with varying x′2 at various fixed ws. With the increase of x′2, γ2 decreases rapidly at all given ws, while γ1 increases at ws = 0.1 to 0.3 and tends to change much less at higher solvent mass fractions, especially at the 2-propanol-rich end. Because of the

Table 3. Estimated Values of Binary Parameters in the NRTL Equationa component i

component j

aij

bij/K

aji

bji/K

cij

water 2-propanol glycerol water water 2-propanol

choline chloride choline chloride choline chloride 2-propanol glycerol glycerol

0 0 0 5.3852 0 0

−2136.88 −1205.84 −2929.25 −1005.06 617.62 259.42

0 0 0 −2.5041 0 0

−857.92 640.92 1393.98 850.87 −499.09 402.30

0.3 0.3 0.3 0.3 0.3 0.3

τij = Δgij/RT = aij + bij/T; Gij = exp(−cijτij). The binary parameters of water + 2-propanol, water + glycerol, 2-propanol + glycerol were taken from ref 3. a

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Figure 5. Calculated results of (a) activity coefficients of water, γ1, (b) activity coefficients of 2-propanol, γ2, and (c) relative volatility of 2-propanol to water, α21, in relation with solvent mass fraction, ws, at x′2 = 1 and p = 100 kPa: solid line, for the system water (1) + 2-propanol (2) + glycerol (3) + choline chloride (4) in this work, w3/w4 = 1.319, ws = w3 + w4; dashed line, for the system water (1) + 2-propanol (2) + glycerol (3) reported in ref 3, ws = w3.

Funding

Effect of the deep eutectic mixture, as a solvent for extractive distillation, on the binary pair of water +2-propanol was compared with that of glycerol alone.3 Activity coefficients were calculated for the quaternary mixture water (1) + 2-propanol (2) + glycerol (3) + choline chloride (4) and the ternary mixture water (1) + 2-propanol (2) + glycerol (3) at x′2 = 1 and p = 100 kPa. Results were presented in Figure 5a and 5b, in relation with solvent mass fraction, ws. When the DES is added, the activity coefficient of water decreases more rapidly as compared with that when glycerol is added. Meanwhile, the activity coefficient of 2-propanol increases more rapidly with the addition of DES. As a result, the relative volatility increases more significantly when the DES is added. Therefore, breaking the azeotrope of water +2-propanol require less DES (ws = 0.142 or xs = 0.084) than glycerol (ws = 0.229 or xs = 0.162).3 This result can be observed in Figure 5c. It can be expected that the extractive distillation process would require less amount of solvent when using the DES instead of glycerol alone. It should be noted that the DES is also less viscous than glycerol.10 Therefore, the DES may have better performance when used in the process of 2-propanol dehydration by extractive distillation.

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CONCLUSIONS

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AUTHOR INFORMATION

The authors wish to acknowledge the financial support by the National Natural Science Foundation of China (21476205). Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Pereiro, A. B.; Araújo, J. M. M.; Esperança, J. M. S. S.; Marrucho, I. M.; Rebelo, L. P. N. Ionic liquids in separations of azeotropic systems − A review. J. Chem. Thermodyn. 2012, 46, 2−28. (2) Zhang, L.; Wang, X.; Zhu, X.; Shen, D. Experimental measurement and modeling of vapor−liquid equilibrium for the ternary systems water + ethanol + ethylene glycol, water + 2-propanol + ethylene glycol, and water + 1-propanol + ethylene glycol. J. Chem. Eng. Data 2016, 61, 2596−2604. (3) Zhang, L.; Zhang, W.; Yang, B. Experimental measurement and modeling of ternary vapor−liquid equilibrium for water + 2-propanol + glycerol. J. Chem. Eng. Data 2014, 59, 3825−3830. (4) Abbott, A. P.; Capper, G.; Davies, D. L.; Rasheed, R. K.; Tambyrajah, V. Novel solvent properties of choline chloride/urea mixtures. Chem. Commun. 2003, 70−71. (5) Zhang, Q. H.; Vigier, K. D.; Royer, S.; Jérôme, F. Deep eutectic solvents: syntheses, properties and applications. Chem. Soc. Rev. 2012, 41, 7108−7146. (6) Smith, E. L.; Abbott, A. P.; Ryder, K. S. Deep eutectic solvents (DESs) and their applications. Chem. Rev. 2014, 114, 11060−11082. (7) Francisco, M.; van den Bruinhorst, A.; Kroon, M. C. Lowtransition-temperature mixtures (LTTMs): a new generation of designer solvents. Angew. Chem., Int. Ed. 2013, 52, 3074−3085. (8) Rodríguez, N. R.; González, A. S. B.; Tijssen, P. M. A.; Kroon, M. C. Low transition temperature mixtures (LTTMs) as novel entrainers in extractive distillation. Fluid Phase Equilib. 2015, 385, 72−78. (9) Rodríguez, N. R.; Kroon, M. C. Isopropanol dehydration via extractive distillation using low transition temperature mixtures as entrainers. J. Chem. Thermodyn. 2015, 85, 216−221. (10) Abbott, A. P.; Harris, R. C.; Ryder, K. S.; D’Agostino, C.; Gladden, L. F.; Mantle, M. D. Glycerol eutectics as sustainable solvent systems. Green Chem. 2011, 13, 82−90. (11) Zhang, L.-Z.; Deng, D.-S.; Han, J.-Z.; Ji, D.-X.; Ji, J.-B. Isobaric vapor-liquid equilibria for water + 2-propanol + 1-butyl-3-methylimidazolium tetrafluoroborate. J. Chem. Eng. Data 2007, 52, 199−205. (12) Zhang, L.; Han, J.; Deng, D.; Ji, J. Selection of ionic liquids as entrainers for separation of water and 2-propanol. Fluid Phase Equilib. 2007, 255, 179−185. (13) Zhang, L.; Yuan, X.; Qiao, B.; Qi, R.; Ji, J. Isobaric vapor-liquid equilibria for water + ethanol + ethyl acetate + 1-butyl-3-

A renewable glycerol−choline chloride deep eutectic solvent was tested as an entrainer for 2-propanol dehydration by extractive distillation. Quaternary VLE data were measured at 100 kPa for the system water + 2-propanol + glycerol + choline chloride. The experimental results were successfully correlated by the NRTL equation. Results showed that the azeotrope of water + 2-propanol can be removed with the addition of the deep eutectic solvent at a solvent mass fraction of 0.142. The glycerol−choline chloride deep eutectic solvent is potentially effective entrainer for dehydration of 2-propanol by extractive distillation.

Corresponding Author

*E-mail: [email protected]. Tel.: +86 571 88320892. ORCID

Lianzhong Zhang: 0000-0001-6596-8248 876



Article

methylimidazolium acetate at low water mole fractions. J. Chem. Eng. Data 2008, 53, 1595−1601. (14) Reid, R. C.; Prausnitz, J. M.; Poling, B. E. The Properties of Gases and Liquids, 4th ed.; McGraw-Hill: New York, 1987; Appendix A. (15) Renon, H.; Prausnitz, J. M. Local compositions in thermodynamic excess functions for liquid mixtures. AIChE J. 1968, 14, 135−144.

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2-Propanol Dehydration via Extractive Distillation Using a Renewable

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