Isobaric Vapor–Liquid Equilibrium for 2-Butanone + Ethanol System

Dec 29, 2017 - tion entrainers to separate the 2-butanone + ethanol binary azeotropic ... icance because the mixture of alcohol with 2-butanone is a v...
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Isobaric Vapor−Liquid Equilibrium for 2‑Butanone + Ethanol System Containing Different Ionic Liquids at 101.3 kPa Wenxiu Li, Xue Chen, Haiying Yin, Linhao Li, and Tao Zhang* Liaoning Provincial Key Laboratory of Chemical Separation Technology, Shenyang University of Chemical Technology, Shenyang 110142, China ABSTRACT: In this work, ionic liquids (ILs) were selected as extractive distillation entrainers to separate the 2-butanone + ethanol binary azeotropic mixture because of their remarkable molecular designability, high selectivity, low volatility, and other excellent characteristics. The isobaric vapor−liquid equilibrium (VLE) data for the ternary systems of 2-butanone + ethanol + acetate-based ILs (1-ethyl-3methylimidazolium acetate [EMIM][OAC], 1-butyl-3-methylimidazolium acetate [BMIM][OAC], and 1-hexyl-3-methylimidazolium acetate [HMIM][OAC]) were measured at 101.3 kPa in an all-glass dynamic recirculating still. The addition of ILs can significantly enhance relative volatility of 2-butanone to ethanol, and the azeotropy of the 2-butanone + ethanol binary mixture is eventually eliminated by increasing the IL content to a certain value. The separation efficiency of the three ILs follows the order [EMIM][OAC] > [BMIM][OAC] > [HMIM][OAC]. Additionally, the binary and ternary VLE data are well-correlated with the nonrandom twoliquid model.

1. INTRODUCTION Ethanol is an important organic solvent which is widely utilized in modern chemical industry. 2-Butanone is used as solvent, dispersant, and cleaner agent for resin adhesives, TiO2 powders, and refrigeration pipelines, respectively.1−3 The separation of the 2-butanone + ethanol mixture is of great practical significance because the mixture of alcohol with 2-butanone is a very common product, for example as an extractant in foodstuffs and food ingredient industries.1−3 2-Butanone and ethanol can form an azeotrope at atmospheric pressure, so it is impossible to completely recover them from their mixture by conventional distillation. At present, extraction and extractive distillation have been adopted to separate the 2-butanone + ethanol azeotropic system.2−5 Compared with the simple extraction, the extractive distillation coupled with the distillation process has the advantages of higher separation efficiency, less use of extractant, lower equipment costs, etc. and has been widely used for the separation of close-boiling or azeotropic mixtures.6−8 In extractive distillation, the decisive step is to choose an effective entrainer. Organic solvents and solid salts are traditional entrainers in extractive distillation. In recent years, ionic liquids (ILs) have attracted considerable attention because of their potential application as entrainers to separate azeotropic mixtures. ILs are chemicals that consist entirely of ions, organic cations, and inorganic or organic anions.9,10 They exhibit many excellent physical and chemical characteristics such as negligibly low vapor pressure, low corrosiveness, high chemical and thermal stability, and good designability.11−14 The separation of the 2-butanone + ethanol binary azeotropic mixture has been studied using organic solvent entrainers such as 2,2,4-trimethylpentane and butyl propionate.3,4 The azeotropic phenomenon of the 2-butanone + ethanol binary mixture can © XXXX American Chemical Society

be completely eliminated by 2,2,4-trimethylpentane. Due to the high volatility of 2,2,4-trimethylpentane, the purification of 2-butanone or ethanol from the ternary mixture containing 2,2,4-trimethylpentane was difficult. The vapor liquid equilibrium (VLE) data of the 2-butanone + ethanol + butyl propionate ternary system can be predicted by the binary interaction parameters of 2-butanone + ethanol, ethanol + butyl propionate, and 2-butanone + butyl propionate binary systems. The azeotropic phenomenon of the 2-butanone + ethanol binary mixture was eliminated when the mole fraction of butyl propionate reached 0.70. There are few reports on the separation of the 2-butanone + ethanol binary system using ILs as extractive distillation entrainers. The extractive distillation process for the ethanol and 2-butanone azeotrope was simulated through Aspen Plus process simulation software by using IL (1,3-dimethylimidazolium dimethylphosphate [DMIM] DMP) extraction solvent, and [DMIM] DMP showed excellent separation efficiency in the extractive distillation simulation of the binary system.5 However, for other ketone−alcohol systems, ILs have been widely used to separate the azeotropic mixtures and have shown excellent separation abilities.15−20 By adding ILs (1-ethyl-3-methylimidazolium tetrafluoroborate [EMIM][BF4], 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4], and 1-octyl-3-methylimidazolium tetrafluoroborate [OMIM][BF4]), the relative volatility of 2-butanone to methanol was significantly enhanced, and the azeotropic phenomenon of the methanol + 2-butanone binary azeotropic mixture was eliminated when the mole fraction of [OMIM] [BF4] reached 0.1.15 The ternary VLE data of Received: September 1, 2017 Accepted: December 29, 2017

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DOI: 10.1021/acs.jced.7b00783 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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acetone + 2-propanol + ILs (1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIM][NTf2] and 1-ethyl3-methylimidazolium bis(trifluoromethylsulfonyl)imide [EMIM][NTf2]) were correlated by Döker et al. using Wilson, NRTL and UNIQUAC models, respectively. The research indicated that error (1.45%) was minimized when using the NRTL equation.16 The separation effects of the two ILs (1-ethyl3-methylimidazolium bromine [EMIM][Br] and 1-butyl-3methylimidazolium bromine [BMIM][Br]) on the acetone + methanol binary mixture were studied through VLE measurements by this research group. The two ILs showed excellent separation efficiency.17 Acetate-based ILs have been widely investigated as potential entrainers to separate azeotropic systems such as alcohol−water, ester−alcohol, and ketone−alcohol systems.21−25 These acetatebased ILs showed advantages of stable physical properties and separation performance,23−25 high separation efficiency,21,22 and mature method of synthesis.26−28 In addition, the pollution and the corrosion produced by inorganic anions (such as BF4−, SO42−, and Cl−) are avoided by using the acetate-based ILs as entrainers.29 In this work, three acetate-based ILs (1-ethyl-3-methylimidazolium acetate [EMIM][OAC], 1-butyl-3-methylimidazolium acetate [BMIM][OAC], and 1-hexyl-3-methylimidazolium acetate [HMIM][OAC]) were studied as potential entrainers for the separation of the 2-butanone-ethanol binary azeotropic system. The VLE experiments for the ternary systems of 2-butanone + ethanol + ILs were operated at 101.3 kPa. The influence of alkyl chain length on the separation of the binary system was discussed. The experimental data were correlated by the nonrandom twoliquid (NRTL) model.

Table 2. Experimental VLE Data for Liquid-Phase Mole Fraction of 2-Butanone x1, Gas-Phase Mole Fraction of 2-Butanone y1, and Temperature T for 2-Butanone + Ethanol (2) System at 101.3 kPaa x1

y1

T/K

x1

y1

T/K

0.000 0.029 0.063 0.094 0.139 0.180 0.237 0.332 0.429 0.470

0.000 0.050 0.101 0.143 0.196 0.241 0.297 0.374 0.445 0.476

351.45 350.78 350.21 349.79 349.25 348.85 348.31 347.79 347.54 347.50

0.544 0.638 0.744 0.815 0.852 0.906 0.945 0.974 1.000

0.527 0.589 0.676 0.747 0.785 0.849 0.903 0.951 1.000

347.51 347.72 348.35 349.08 349.63 350.59 351.34 351.89 352.72

a

Standard uncertainty u(x1) = u(y1) = 0.001, u(T) = 0.01 K, u(P) = 0.1 kPa.

2. EXPERIMENTAL SECTION 2.1. Materials. The chemicals used in this work were 2-butanone (Sinopharm Group, minimum wt 99.5%), ethanol (Sinopharm Group, minimum wt 99.5%), and ILs (Yulu Group, minimum wt 98.0%). Prior to use, the ILs were dried in a vacuum drying oven at 333 K and 2 kPa for approximately 48 h to remove the volatile components. Purities of the two organic solvents were analyzed by gas chromatography. Purities of the three ILs were checked by liquid chromatography. The water content in ILs was less than 0.005 (mass fraction) determined by Karl Fischer titration. Overviews of the chemicals used in this study are summarized in Table 1. 2.2. Apparatus and Procedure. The isobaric VLE experiments were operated in an all-glass dynamic recirculating still (NGW, Wertheim, Germany), and the detailed description of this apparatus is available in previous literature.30 The system pressure was measured by a manometer with an uncertainty of 0.1 kPa and kept constant by a pressure controller at 101.3 kPa (MKS, America). The equilibrium temperature was measured by a standard mercury thermometer (WNG_01 Xinwang china)

Figure 1. y−x diagram for the binary system of 2-butanone (1) + ethanol (2) at 101.3 kPa: ●, experimental data in this work; △, from ref 1; ○, from ref 4; solid line, correlated using the NRTL model.

with the uncertainty of 0.01 K. The thermometer was calibrated by Shitong instrument testing company (China) using the standard testing equipment. Each solution was gravimetrically prepared with the help of a digital balance (CAV264C OHAUS America), and the standard uncertainty was 0.0001 g. The equilibrium apparatus was mainly composed of six parts: a vapor−liquid equilibrium chamber, a temperature measurement chamber, a heating rod, a spherical condenser, a vapor phase sampling point, and a liquid phase sampling point. The vapor was separated from the liquid in the vapor−liquid equilibrium chamber and condensed in the spherical condenser. The smaller the vaporization of vapor, the closer the operating conditions to the

Table 1. Names, Sources, and Water Content of the Chemicals Studied chemical name

CASRN

source

mass fraction of water

2-butanone ethanol [EMIM][OAC]b [BMIM][OAC]c [HMIM][OAC]df

78-93-3 64-17-5 143314-17-4 284049-75-8 888320-05-6

Sinopharm Group Sinopharm Group Yulu Group Yulu Group Yulu Group

none none [BMIM][OAC] > [HMIM][OAC]. These results further confirm the conclusions that all of the three ILs show excellent separation effect on the binary azeotropic system, and the separation efficiency of the three ILs follows this order: [EMIM][OAC] > [BMIM][OAC] > [HMIM][OAC]. The activity coefficients of 2-butanone (γ1) and ethanol (γ2) in the ternary systems with different ILs are calculated and plotted in Figures 11−13 to describe the nonideal properties of the solution. It can be seen that the values of γ1 increase while that of γ2 decrease with the increase in IL content. The results indicate that the attractive force between IL and 2-butanone is less than that between IL and ethanol and that the increase in IL content can lead to an increase in α12 value because the value of α12 is proportional to the ratio of γ1/γ2 according to eq 7. The separation effects of the three ILs on the 2-butanone + ethanol binary azeotropic mixture should be related to the G

DOI: 10.1021/acs.jced.7b00783 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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Table 6. Estimated Values of Binary Interaction Parameters Δgij and Δgji, Nonrandomness Factors αij in the NRTL Model, and Conrresponding Average Relative Deviation ARD component i

component j

αij

2-butanone 2-butanone ethanol 2-butanone ethanol 2-butanone

ethanol [EMIM][OAC] [EMIM][OAC] [BMIM][OAC] [BMIM][OAC] [HMIM][OAC]

0.300 0.098 0.115 0.124 0.119 0.115

Δgij (J/mol) 930 10000 −8778 8500 −9231 11121 ethanol

Antoine parameters 2-butanone ethanolb

b

A

B

C

temperature range (K)

7.2087 8.2133

1368.21 1652.05

236.51 231.48

257.15−376.15 270.15−369.15

1037 −5715 −10521 −5687 −9825 −5968 [HMIM][OAC]

ARD (%) 0.71 1.35 1.21 1.22 0.125

−6867

relative volatility and activity coefficient further confirm these conclusions. The minimum mole fractions of [EMIM][OAC], [BMIM][OAC], and [HMIM][OAC] needed to break the azeotropic phenomenon of 2-butanone−ethanol binary azeotropic system are 0.036, 0.043, and 0.045, respectively. All the data correlated with the NRTL model are in good agreement with the experimental data.

Table 7. Antoine Parameters A, B, and C of 2-Butanone and Ethanola component

Δgji (J/mol)

■

a Antoine equation: lg(P/mmHg) = A − B/(t/°C + C). bParameters were obtained from ref 31.

AUTHOR INFORMATION

Corresponding Author

*Tel.: +86 024 89381082; E-mail: [email protected].

hydrogen bond and the steric effect between them. The azeotropy of ethanol and 2-butanone mixture is attributed to the formation of hydrogen bond between the carbonyl group of 2-butanone and the hydroxyl group of ethanol, where 2-butanone and ethanol are hydrogen bond acceptor and donator, respectively. Anions of the three ILs can also act as acceptors to form hydrogen bonds with the hydroxyl groups of ethanol. The strength of hydrogen bonds between the anions of the ILs and the hydroxyl group of ethanol is stronger than that between the carbonyl group of 2-butanone and the hydroxyl group of ethanol. When the ILs are added to the 2-butanone−ethanol binary mixture, the hydrogen bonds between 2-butanone and ethanol are broken due to the formation of the stronger hydrogen bonds between ethanol and the anions of the ILs. Hence, the azeotropy of the 2-butanone + ethanol binary system can be completely eliminated when the IL content is increased to a specific value. According to the experiments, the separation efficiency of the three ILs follows this order: [EMIM][OAC] > [BMIM][OAC] > [HMIM][OAC]. The shorter the alkyl chain length on the cation of IL, the higher the separation efficiency. On one hand, the increase in alkyl chain length weakens the hydrogen bond between IL and ethanol because of increasing the hydrophobicity of the IL. On the other hand, the binding probability of the hydrogen bond donor and acceptor is decreased with the increase in alkyl chain length due to the steric hindrance. Similar results have also been reported in other ternary systems.29,32 The separation efficiency of [EMIM][OAC] is higher than those of [BMIM][OAC] and [HMIM][OAC]. Moreover, [EMIM][OAC] possesses stable physical properties and separation performance and mature method of synthesis. [EMIM][OAC] does not cause pollution and corrosion of inorganic anions such as BF4−, SO42−, and Cl−. [EMIM][OAC] should be further studied as a potential entrainer for the separation of the 2-butanone and ethanol system.

ORCID

Wenxiu Li: 0000-0002-4749-7259 Tao Zhang: 0000-0002-4637-7482 Funding

This work is financially supported by the National Science Foundation of China (Project 21576166), the Program for Liaoning Excellent Talents in University (Project LR2012013), and the Liaoning Province Science Foundation of China (Project 2014020140). Notes

The authors declare no competing financial interest.

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ABBREVIATIONS xi, mole fraction of component i in the liquid phase xi′, liquid-phase mole fraction of component i excluding IL yi, mole fraction of component i in the vapor phase T, equilibrium temperature Δgij, binary energy parameter of the NRTL model yicalcd, mole fraction of component i in the vapor phase calculated with the NRTL model P, total pressure in the equilibrium system Pi0, saturated vapor pressure of component i at equilibrium temperature α12, relative volatility of component 1 to component 2 αij, nonrandomness parameter of NRTL model γi, activity coefficient of component i γiexptl, activity coefficient of component i by experiment γicalcd, activity coefficient of component i by the NRTL model REFERENCES

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4. CONCLUSIONS In this work, the isobaric VLE data for ternary systems of 2-butanone + ethanol + IL ([EMIM][OAC], [BMIM][OAC], or [HMIM][OAC]) were obtained at 101.3 kPa. All three ILs show excellent separation effects on the 2-butanone−ethanol binary azeotropic system. The shorter the alkyl side chain length, the higher the separation efficiency of IL. The change rules of H

DOI: 10.1021/acs.jced.7b00783 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.jced.7b00783 J. Chem. Eng. Data XXXX, XXX, XXX−XXX