Selective Separation of Methacrylic Acid and Acetic Acid from

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Selective separation of methacrylic acid and acetic acid from aqueous solution using carboxyl-functionalized ionic liquids Yinge Bai, Ruiyi Yan, Wenhui Tu, Jianguo Qian, Hongshuai Gao, Xiangping Zhang, and Suojiang Zhang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b03516 • Publication Date (Web): 07 Nov 2017 Downloaded from http://pubs.acs.org on November 12, 2017

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ACS Sustainable Chemistry & Engineering

Selective separation of methacrylic acid and acetic acid from aqueous solution using carboxyl-functionalized ionic liquids Yinge Bai†,‡, Ruiyi Yan†, Wenhui Tu†,‡, Jianguo Qian†,‡, Hongshuai Gao†, Xiangping Zhang*,†,‡, †

Suojiang Zhang*, ,‡ †

Key Laboratory of Green Process and Engineering, State Key Laboratory of Multiphase Complex Systems, Beijing Key Laboratory of ILs Clean Process, Institute of Process Engineering, Chinese Academy of Sciences, 1 North 2nd Street, Zhongguancun, Haidian District, 100190 Beijing, P. R. China ‡ School of Chemistry and Chemical Engineering, University of Chinese Academy of Sciences, 100049 Beijing, P. R. China Corresponding authors’ email address: *Xiangping Zhang: [email protected] *Suojiang Zhang: [email protected] Abstract Five

kinds

of

carboxyl-functionalized

tricaprylmethylammonium

succinate

quaternary

([A336]Suc),

ammonium

ionic

liquids

tricaprylmethylammonium

(ILs),

aspartate

([A336]Asp), tricaprylmethylammonium glutamate ([A336]Glu), tricaprylmethylammonium trifluoroacetate ([A336]TFA), and tricaprylmethylammonium phthalate ([A336]Pha) with strong hydrophobicity and hydrogen bond basicity were used to separate methacrylic acid (MAA) and acetic acid (HAc) from the aqueous solution. [A336]Suc shows the better extraction performance than the other ILs because of the stronger hydrogen bonding basicity. Even though HAc shows the antagonistic effect on the extraction of MAA, the selectivity of MAA to HAc is achieved 54.70 for [A336]Suc at the optimized extraction conditions. The molecular mechanism of the extraction by IL is revealed by combining FT-IR and quantum chemical calculations. The results indicate that multiple hydrogen bonds are presented in the IL-acid complex which plays an important role in the acid extraction. Meanwhile, the computational studies demonstrate that the preferential extraction of MAA to HAc by [A336]Suc originated from the difference in the 1

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strength of the hydrogen bonding interaction between carboxylate group of ILs and acid.

Keywords: Ionic liquid, carboxyl group, extraction, methacrylic acid, acetic acid

Introduction Carboxylic acids are the well-known type of organic acids, which are widely used in chemical and food industry 1. The recovery of carboxylic acid from aqueous solution, especially selective recover the desired acid from the acid mixture, is commonly encountered in the chemical industry, such as the carboxylic acid separation from the downstream and wastewater of carboxylic acid production process. The conventional separation method is distillation. However, carboxylic acid and water is both polar substance and the interaction of the acid with water molecule is strong 2. On the other hand, the stable hydrogen bonded dimer is easy formed between two carboxylic acids since it contains both hydrogen bond acceptor group (the carbonyl C=O) and hydrogen bond donor group (the hydroxyl OH) in the molecule. 3. Thus, it is difficult to recover carboxylic acid from dilute aqueous solution by distillation, which is a high energy consumption process. Solvent extraction is another competitive route to recover carboxylic acid from aqueous solution 4-5. In the extraction process, the most important are the extractant and the conventional solvents for extraction of carboxylic acid are toluene, heptane, etc. These solvents have the drawbacks of the low extraction capacity and selectivity. Hence it is urgent to search highly efficient extractant to extract carboxylic acids from aqueous solution. Ionic liquids (ILs) are a subset of liquid substances composed entirely of ions with melting points below 373 K 6. The negligible volatility and diversity make ILs as environmentally benign solvents to substitute the conventional solvents 7. The properties of ILs (i.e. thermophysical properties, hydrophobicity, and solution behavior) are tunable by adjusting the structure of the cation and anion since ILs are composed of a large organic cation and organic/inorganic anion. This makes ILs as designable solvents suitable for separating many kinds of compound mixtures by liquid-liquid extraction, such as olefin/paraffin 8, alkanol/alkane 2


9-10

, alkanol/water

11

, and

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carboxylic acid/water

12

. Recently, there is growing attention using the green and designable

solvents ILs in extraction process to recover carboxylic acid from aqueous solution. For example, imidazolium-based ILs with hexafluorophosphate anion ([PF6] － ) are used as extractant to recover several carboxylic acid (acetic, glycolic, propionic, lactic, pyruvic, and butyric acid) from fermentation broth

13

. However, the extraction ability of these ILs is very low. Afterward,

the quaternary ammonium ILs

12, 14

are used to extract carboxylic acid from aqueous solutions,

which shows better extract ability than imidazolium-based IL. For the separation of carboxylic acid and water, the designed IL should have both hydrophobicity and strong interaction with the acid. In our previous work, it is found that the hydrogen bonding interaction plays an important role in the extraction of carboxylic acid from aqueous solution

15

. The IL with anion of [PF6]－

shows lower hydrogen bonding ability than the ILs with chlorine, acetate anion 15-16. The most of the imidazolium-based ILs with chlorine and acetate anion is hydrophilic and not suitable for extraction carboxylic acid from aqueous solution. Quaternary ammonium ILs with these anions can still keep the hydrophobicity because of the long carbon chain in the cation. Therefore, there is an improvement of quaternary ammonium ILs by tune the anion of the IL for carboxylic acid extraction. In this work, five kinds of quaternary ammonium ILs with strong hydrogen bond basicity were used to extraction carboxylic acid from aqueous solution. Two kinds of carboxylic acid, acetic acid (HAc) and methacrylic acid (MAA), are used as the model acid for the extraction experiment. HAc is an important chemical reagent to the production of cellulose acetate and polyvinyl acetate 17. In the food industry, HAc is used as an acidity regulator and vinegar. MAA is widely used in polymer industries. In the oxidation of methacrolein to production MAA process, the main by-product is HAc 18. After recovering of MAA, the wastewater also contains a low concentration of MAA and HAc. Thus, the extraction performances of ILs for carboxylic acid were evaluated by extraction MAA and HAc from the single acid aqueous solution, respectively. Then the selective extraction of MAA from the two acid mixtures aqueous solution was performed by using IL extractant. The effect of HAc concentration, contact time, IL 3



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concentration, organic/aqueous (O/A) phase ratio and extraction temperature on the extraction of MAA were studied. The molecular mechanism of the IL extraction was explored by quantum chemical calculation and FT-IR. After the extraction, the recovery of acids from the organic phase was studied.

Experimental section Materials Tricaprylmethylammonium chloride (Aliquat® 336, [A336]Cl) was purchased from Sigma-Aldrich. Succinic acid (99.5% purity), aspartic acid (99% purity), trifluoroacetic acid (99% purity), glutamic acid (99% purity), phthalic acid (99% purity), 1-chlorooctane (99% purity), and trioctylamine (95% purity, TOA) were supplied by Aladdin Industrial Corporation (China). Ethanol (99.5% purity) and HAc (99.5% purity) were purchased from Xilong Chemical Co., Ltd (China). MAA (99% purity) was purchased from Alfa Aesar (China). All chemicals were commercially available and used as received. Synthesis and character of ILs ILs were prepared from the neutralization of acids (provide anion of ILs) with tricaprylmethylammonium hydroxide ([A336]OH). [A336]OH was prepared from [A336]Cl by the anion-exchange method. The prepared ILs was also characterized by their 1H-NMR (600MHz, DMSO-d6) and FT-IR spectra. The thermal stability of the prepared ILs was tested by thermogravimetric analysis (TGA). The water content was measured by Karl-Fischer titration method. The density and viscosity of the obtained ILs were measured by density and viscosity meter (DMA 5000-AMVn, Anton Paar). Chloride content of the prepared IL was determined by turbidimetry method. All of the details can be found in Supporting Information. The Kamlet-Taft empirical polarity parameters, hydrogen bond basicity (β) of ILs, were measured by solvatochromic method

19

. The β parameter was determined from the ultraviolet

absorption spectroscopic shift of both N, N-diethyl-4-nitroaniline (DENA) and 4-nitroaniline 4


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(NA) using Eq. (1) 20: (1)

β =0.3696ν DENA -0.3571ν NA + 0.9429

where νNA and νDENA is the wave number where the maximum absorption of NA and DENA dye in the sample was found. The measurement was repeated five times to guarantee that the standard deviation was within 0.6%. Extraction procedures The carboxylic acids aqueous solution and IL extractant were mixed though magnetic stirrer for 4 h, firstly. Then the mixture was allowed to settle for at least 4 h to get two phases. The extraction temperature was controlled by water bath (accuracy ±0.10 K). Samples were taken from each phase and the amount of acid in each phase was analyzed by gas chromatography. The effectiveness of the ILs extractant was analyzed by determining the partition coefficient (P) and selectivity (S). The partition coefficient P is defined as Eq. (2): P=

[HA]O [HA]W

(2)

where, [HA]O is the concentration of carboxylic acid in the organic phase (mol/L), [HA]W is the concentration of carboxylic acid in the aqueous phase (mol/L). The selectivity S of carboxylic acid is defined as Eq. (3) S=

PHA(I)

(3)

PHA(II)

where, PHA(I) and PHA(II) is the partition coefficient of carboxylic acid HA(I) and HA(II), respectively. All of the measurements were repeated at least three times and the uncertainties of the results were with 5%. Computational methods The initial structure of MAA, HAc and IL ion pairs was prepared using Gaussview. The optimization was realized by DFT method via Gaussian 09 program

21

. The geometry of the

acids, IL ion pairs and the complex of IL with acid was optimized under B3LYP/6-31G(d,p) level. 5



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The optimized structures were confirmed to achieve the minima on the potential surface energy and no imaginary frequency exists via frequency analysis. The interaction energy between ILs and MAA was also calculated at the same level and the energy was corrected for the basis set superposition error (BSSE) by the counterpoise method 22. To evaluate the solvation effect on the interaction of IL and acid, the interaction energies of IL with acid were calculated at the same level with polarizable continuum model (PCM). The wavefunction analyses in this work were used by Multiwfn 3.3.9, which is a powerful multifunctional wavefunction analysis program

23

. The color mapped isosurface graphs of

electrostatic potential were rendered by VMD 1.9.2 program

24

. The wavefunction used in this

work was produced at the same level as the geometry optimization.

Results and discussion Extraction of MAA and HAc by IL Based on the previous work of our group, ILs with strong hydrogen bond basicity will have good extraction performance for recovery of acid from dilute aqueous solution

15

. The most

commonly used ILs in the extraction of aqueous solution is fluoro-anion ([PF6]－ and [NTf2]－) ILs on account of the strong hydrophobicity. However, the hydrogen bond basicity of these ILs is too weak to extract carboxylic acid from aqueous solution 16. ILs with carboxylic acid and amino acid anions will have strong hydrogen bond basicity 16, 25. The problem of ILs with these kinds of anion is that the ILs are usually hydrophilicity and easy dissolve in the water phase. Thus, in this work cation of tricaprylmethylammonium ([A336]+) is introduced into ILs to address this problem. The cation has long carbon chain (C8-C10) and will enhance the hydrophobicity of IL. Five kinds of carboxyl-functionalized anion (i.e. succinate, aspartate, glutamate, trifluoroacetate, and phthalate) are selected. These anions contain strong electronegativity atoms (two oxygen atoms in carboxylate), which will exhibit strong hydrogen bond basicity. Meanwhile, the long-chain structure of the cation is also important to the strong hydrogen bond basicity. This is because the hydrogen bond basicity of IL could be enhanced by reducing the interaction of cation 6


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and anion

26-27

. As expected, the carboxyl-functionalized ILs exhibit strong hydrogen bond

basicity, with the β value over 1 (Table 1). For [A336]Suc, the β value is even achieved 1.57, which is very high in the reported β value of ILs 16. However, these ILs are too viscous to handle in the extraction experiment (Table S1). Therefore, diluent is used to reduce the viscosity of these ILs. Consider the solubility of the IL and the hydrophobicity, 1-chlorooctane is selected as a diluent to dilute the IL. The added of 1-chlorooctane has dramatically reduced the viscosity of IL. For example, the 0.15 mol/L of [A336]Suc in 1-chlorooctane has a viscosity of 1.61 mPa·s and the viscosity of pure [A336]Suc is 1429.9 mPa·s at 298.15 K. The viscosities of IL/1-chlorooctane mixture are seen in Supporting Information (Table S2). On the other hand, the added of 1-chlorooctane can also reduce the loss of IL into water. Even the [A336]-based ILs show the strong hydrophobicity, there are some losses when contact with water. For example, the solubility of [A336]Suc in water is 1010.66 mg/L. For [A336]Asp, the solubility is even achieved 31988.06 mg/L. However, when the IL with dilute is contacted with water, the losses of IL dramatically decrease, such as, for 0.15 mol/L [A336]Suc in 1-chlorooctane, the equilibrium concentration is 110.44 mg/L IL in water (Supporting Information Table S1). The partition coefficients of MAA and HAc are measured to evaluate the extraction ability of ILs. First of all, the pure diluent 1-chlorooctane shows very low extraction ability and has partition coefficient of 1.27 for MAA and 0.011 for HAc. This indicates that acid is mainly extracted by IL and 1-chlorooctane just acts as diluent. For the five ILs, the partition coefficient of acid is followed as: [A336]Suc > [A336]Asp > [A336]Glu > [A336]TFA > [A336]Pha, which is agreement with the β value of these ILs (Table 1). [A336]Suc shows best extraction performance with highest partition coefficient of 17.40, 0.34 for MAA and HAc, respectively, since it has the strongest hydrogen bond basicity. The strong hydrogen bond interaction could easy to drag the acid away from the aqueous solution. The extraction ability of [A336]Suc is almost 3 times than TOA, which is commonly used as reactive extraction solvents for the recovery of dilute carboxylic acid from aqueous solution. In addition, the extraction performance of IL for MAA is much higher than that for HAc. For example, the partition coefficient of MAA 7



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by [A336]Suc is 50.18 times higher than that of HAc. This may be attributed to the stronger specific interaction between IL with MAA than with HAc and the higher hydrophobicity of MAA than HAc. Anyway, from the extraction at different concentration of acid in aqueous solution, the selective separation of MAA and HAc is possible by using [A336]Suc as extractant (Supporting Information, Fig. S8). Table 1. The partition coefficients of MAA and HAc for IL in single acid solutions (Extraction conditions: extraction time is 120 min, extraction temperature is 298.15 K, volume ratio of extractant to feed is 1:1, extractant is 0.15 mol/L IL in 1-chlorooctane, feed: 0.12 mol/L MAA and 0.83 mol/L HAc in aqueous solution) and β value of IL. Partition coefficient

βa

Solvent

a

MAA

HAc

[A336]Suc

17.40

0.34

1.57

[A336]Asp

13.18

0.31

1.44

[A336]Glu

8.71

0.28

1.39

[A336]TFA

7.40

0.18

1.31

[A336]Pha

3.78

0.15

1.04b

TOA

6.53

0.11

1.08

1-Chlorooctane

1.27

0.011

0.44

data obtained at 298.15 K. b data obtained at 313.15 K.

Selective separation of MAA and HAc From the above analysis [A336]Suc shows best extraction ability than other ILs. The partition coefficient of MAA is higher than that of HAc in the single acid extraction. This suggests the possible selective separation of MAA and HAc in the two acid mixture aqueous solutions. However, the presence of HAc in aqueous solution shows the antagonistic effect on the extraction of MAA (Fig. S9 in Supporting Information). In the aqueous solution of the two acid mixtures, the partition coefficients have decreased for both of MAA and HAc. Even though the presence of HAc hindered the extraction of MAA, the partition coefficient of MAA still can 8


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reach 7.20 for [A336]Suc at the high HAc concentration (0.83 mol/L). Thus, the recovery of MAA from the two acid aqueous solutions with 0.12 mol/L MAA and 0.83 mol/L HAc was studied. Based on the optimized extraction conditions (Supporting Information), the selectivity of MAA to HAc is achieved 54.70 for [A336]Suc. It is almost two times higher than the extraction by TOA (Table 2). This indicates that [A336]Suc has the strong selective separation performance. Table 2. The partition coefficient of MAA and HAc and the selectivity of MAA to HAc at the optimized conditions: extraction temperature is 288.15 K, contact time is 10 min, volume ratio of extractant to feed is 1:4, extractant is 0.10 mol/L [A336]Suc in 1-chlorooctane, and feed is 0.12 mol/L MAA and 0.83 mol/L HAc mixtures in aqueous solution. Extractant

PMAA

PHAc

SMAA/HAc

[A336]Suc

5.47

0.10

54.70

TOA

4.70

0.17

27.65

FT-IR analysis The interaction of [A336]Suc with MAA was investigated by FT-IR spectroscopy. As shown in Fig. 1, bands present at 915.11 cm-1 for MAA and HAc at non-polar solvent is assigned to the out of plane deformation vibration of OH…O group. This confirms that carboxylic acids (MAA and HAc) in 1-chlorooctane exist as dimer 28. For the pure [A336]Suc in 1-chlorooctane, the out of plane deformation vibration of OH … O group is also existed, which indicates the intermolecular hydrogen bonding interaction is presented in [A336]Suc phase. This may be the reason for the high viscosity of the IL 29. Fig. 1d shows the FT-IR spectrum of [A336]Suc where the absorption peak at 1735.12 cm-1 can be assigned to the C＝O stretching vibration for the succinate anion

28

. The band shifts from 1735.12 cm-1 to 1711.19 cm-1 and 1716.93 cm-1 when

[A336]Suc upon contact with MAA and HAc, respectively. The bathochromic shift can be attributed to the hydrogen bonding interaction of acid with the anion of [A336]Suc 2. The lower wavenumber of the C＝O stretching vibration in [A336]Suc + MAA indicates the stronger 9



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hydrogen bonding interaction of MAA with [A336]Suc than that of HAc. This may be the reason for the more extraction of MAA than HAc using [A336]Suc as extractant. The another evident for the hydrogen bonding interaction between acid and [A336]Suc is the peak shift associated with －COO－ asymmetric stretching vibration of [A336]Suc from 1580.24 cm-1 to 1559.74 cm-1 and 1560.01 cm-1, respectively, upon contact with MAA and HAc. e d

e

c d

b

c

a

b

a 1800

1700

1600

1500

1400

1300

1200

975

950

925

900

875

850

Wavenumber (cm-1) Figure 1. FT-IR spectra of MAA, HAc, [A336]Suc, and the mixture of [A336]Suc and MAA or HAc in the diluent 1-chlorooctane. (a) MAA; (b) [A336]Suc + HAc; (c) [A336]Suc + MAA; (d) [A336]Suc; (e) HAc.

Molecular mechanism of the extraction by IL Charge distribution To depth understand the interaction sites of acid and IL, the charge distribution of acids and ILs was studied. Three types of atomic charge, namely ADCH charge 30, CHELPG charge 31 and MK charge 32 were calculated to study charge distribution of acids and ILs. The calculated results are given in Table 3. Table 3. Atomic and the functional group's charges of MAA, HAc, and [A336]Suc. The atomic numbering used is shown in Supporting Information (Fig. S14-S16). Molecule MAA

Atom/Group

ADCH Charge

CHELPG Charge

MK Charge

C1 C2

-0.196 -0.043

-0.356 0.062

-0.487 0.124

10


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HAc

[A336]Suc

H3 H4 C5 O6 O7 H8 Carboxyl Alkenyl C1 O2 O3 H4 Carboxyl C87 O88 O89 C90 O91 O92 H93 Carboxyl

0.113 0.135 0.306 -0.360 -0.348 0.333 -0.069 -0.294 0.304 -0.371 -0.375 0.347 -0.094 0.298 -0.424 -0.460 0.255 -0.406 -0.503 0.464 -0.191

0.167 0.158 0.710 -0.562 -0.632 0.431 -0.052 -0.239 0.799 -0.590 -0.642 0.431 -0.002 0.815 -0.737 -0.821 0.745 -0.605 -0.632 0.413 -0.079

0.211 0.208 0.692 -0.556 -0.627 0.435 -0.057 -0.363 0.802 -0.585 -0.628 0.426 0.015 0.805 -0.725 -0.812 0.679 -0.581 -0.608 0.412 -0.097

Even the atomic charges derived from three methods differ from each other, some conclusions obtained from the calculated results can be summarized as follows: (1) For MAA, the most negative charges are focused around oxygen atoms (O6 and O7). All the hydrogens have positive charge. H8, bonded with electronegative atom O7, has the most positive charge (0.333, 0.431 and 0.435 of ADCH, CHELPG and MK charge, respectively). Carboxyl group and alkenyl (C1=C2) act as electron withdrawing group in MAA. (2) HAc shows analogous charge distribution to MAA. (3) For IL, all of the oxygen atoms in anion have negative charge. For example, The oxygen atoms O88, O89, O91 and O92 in [A336]Suc have charges of -0.424, -0.460, -0.406 and -0.503 for ADCH charge, respectively. In general, the values and signs of atoms or groups in molecule are obtained through the atomic charge calculation. Then the calculated results can be used to predict the electrostatic interaction between atoms or fragments. From the above analysis, the hydrogen atom in carboxyl group of carboxylic acid has large positive charge. The oxygen atoms in the anion of IL are a negative charge. Thus the strong electrostatic interaction between hydrogen atom in carboxyl 11



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group of carboxylic acid with the oxygen atoms in succinate is possible. However, the strength of the interaction is unable to be determined, since there is no consensus between ADCH, CHELPG and MK method for the compare of H8 in MAA and H4 in HAc. Electrostatic potential The atomic charge is a useful tool to describe the electron distribution of molecule. However, the problem of atomic charge is that the definition is arbitrarily and there is no rigorous physical basis. The different definitions introduce different results. Besides the atomic charge distribution, electrostatic potential, which is a real physical property, on molecular surface can also be used to understand and predict intermolecular interaction

33-34

. As shown in the

electrostatic potential mapped vdW surface of MAA (Fig. 2a, 2b), there is a small portion vdW surface with large negative value of electrostatic potential, e.g. the electrostatic potential value below -20 kcal/mol only accounts for 11.79% of the overall vdW surface; they attribute to the surface close to the oxygen of the carboxyl group. There is also only a tiny part (2.69%) of the vdW surface with electrostatic potential value larger than 35 kcal/mol. They all are from the hydrogen in carboxyl group. Most part (80.40%) of the vdW surface of MAA has low electrostatic potential value (i.e. within -15 to 15 kcal/mol). The global minima and maxima of electrostatic potential on the surface are -33.45 and 50.43 kcal/mol, and correspond to the oxygen and hydrogen in carboxyl group, respectively. The electrostatic potential of HAc is similar to MAA (Fig. 2c, 2d). For HAc, the area of vdW surface has large negative value (i.e. < -20 kcal/mol) and large positive value (i.e. > 35 kcal/mol) of electrostatic potential are 16.15 Å2 and 3.73 Å2, respectively. The value is close to that for MAA, which is 15.22 Å2 and 3.48 Å2, respectively. And the global minima and maxima of electrostatic potential of the acetic, which are -33.90 and 50.73 kcal/mol, are also close to MAA, respectively. However, HAc is less 2 carbons than MAA in the alkyl group bonded to the carboxyl group. This makes the surface of HAc (69.27 Å2) with a low electrostatic potential value lower than that of MAA (103.87 Å2). This indicates MAA will have more hydrophobicity than HAc.

12


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Figure 2. Electrostatic potential mapped vdW surface of (a) MAA, (c) HAc, (e) [A336]Suc. Surface local minima and maxima of electrostatic potential are represented as magenta and green spheres and labeled by magenta and green texts, respectively. The unit is in kcal/mol. There are many extrema for [A336]Suc surface (18 minima and 37 maxima). For clarity, the local surface minima larger than -30 kcal/mol and maxima less than 12 kcal/mol are discarded. Surface area in each electrostatic potential range on the vdW surface of (b) MAA, (d) HAc, (f) [A336]Suc.

The electrostatic potential was also calculated for [A336]Suc (Fig 2e). The vdW surface of the cation ([A336]+) is shown the positive electrostatic potential. The negative electrostatic potentials are concentrating on the anion of [A336]Suc. The lone pair of each oxygen atom leads 13



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to electrostatic potential minimum on the vdW surface, such as the electrostatic potential minimum near O88 is -50.27 kcal/mol, the minimum value near O91 is -47.71 kcal/mol and the minimum value near O92 is -32.59 kcal/mol. The value of the most negative one is -52.71 kcal/mol, which is near O89. It is also the global surface minimum of [A336]Suc. The electrostatic potentials near O88 and O89 are different to each other. This can be explained by the effect of the cation of IL since O88 is more close to the cation of IL than O89 (Seen in the next section) in the optimized structure of [A336]Suc. Even though the most parts of the anion show negative electrostatic potential, the global maximum of electrostatic potential (35.91 kcal/mol) is on the surface of anion. It stems from the positive charge of H93. The surface areas in each electrostatic potential range on the vdW surface are also counted (Fig. 2f). From the statistical data, we find that the most part of the surface shows low electrostatic potential (almost 76% of the overall surface), which is mostly attributed to the long alkyl chain in cation. This suggests the hydrophobicity of IL is mainly from the cation. Meanwhile, the vdW surface has large positive value of electrostatic potential is extremely small, the electrostatic potential > 36 kcal/mol only has 0.08% of the overall surface. Nevertheless, the vdW surface with large negative value of electrostatic potential (i.e. < -32 kcal/mol) accounts for 7.19% of the overall vdW surface. This suggests that the probabilities of the acid molecule interact with oxygen atoms are higher than with hydrogen atom. The interaction between acid and IL To gain better insights into the nature of selective separation of MAA and HAc by IL, the structures of IL/acid complex were optimized. From the above analysis, the hydrogen bonding interaction may exist between IL and acid. Hydrogen bond is formed between the donor group (X－H) and acceptor (Y). Normally, acceptor Y is an electronegative atom, such as O, N and halide. X is N or O atom and also can be less electronegative atoms (such as C, S, Si or a halogen) 35-36

. The distance between the hydrogen atom in X－H and the acceptor atom Y and the

corresponding angle ∠X－H…Y are used commonly criterion for a hydrogen bond. In a 14


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hydrogen bond (X－H…Y), the distance of H…Y is less than the sum of their van der Waals radii, the angle is larger than 90°

37

. From the calculation results (Fig. 3), multiple hydrogen

bonding interactions are occurring between acid and IL. For example, Fig. 3a shows the interactions of [A336]Suc with HAc. The distance of H97 (hydrogen atom in carboxyl group of HAc) and O89 (an oxygen atom in the carboxylate group of [A336]Suc) is 1.48 Å, which is longer than the covalent bond length of O－H (0.96 Å) and shorter than the sum of van der Waals atomic radii of O and H (2.72 Å) 37. And the angle ∠O96－H97…O89 is 178.71° (Table 4). This is within the accepted criteria of the O－H…O hydrogen bond. Besides the hydrogen bond with carboxylate group in anion, HAc also forms another two but weaker hydrogen bond with the cation of [A336]Suc, which is C7－H12…O95 (2.33 Å, 150.18°) and C31－H34…O95 (2.65 Å, 119.26°). Similarly, there are also triple hydrogen bonds in the [A336]Suc + MAA complex, which is O100－H101…O89 (1.47 Å, 178.66°), C7－H12…O99 (2.35 Å, 154.26°) and C31－H34…O99 (2.63 Å, 118.07°). Topology analysis based on atoms in molecules (AIM) theory

38

was performed to obtain

more insight into the intermolecular interaction between IL and acid. In this work, we will only consider the properties such as electron density (ρBCP), Laplacian of electron density (▽2ρBCP) and energy density (HBCP) at bond critical points (BCP). The parameters of ρBCP and ▽2ρBCP are used to characterize the bonding interactions present. The ρBCP value within 0.002 - 0.04 a.u. and 0.02 - 0.15 a.u. for ▽2ρBCP are criteria for hydrogen bonding interaction

39

. For [A336]Suc +

MAA complex, three BCPs are found between O89 and H101, O99 and H12, O99 and H34. The

ρBCP and ▽2ρBCP of these BCPs are presented in Table 4. From the calculation results, hydrogen bonds exist in C7－H12…O99 and C31－H34…O99 since the ρBCP and ▽2ρBCP value is within the criterion. As for O100－H101…O89, the ρBCP value (0.082 a.u.) are higher than the proposed upper limit for hydrogen bond criteria. Nevertheless, the interaction between O89 and H101 is still identified as hydrogen bond since the other criteria are agreed, such as the ▽2ρBCP value (0.145 a.u.) is within the criterion, bond distance and bond angle are within the hydrogen bond criteria. In addition, the HBCP at BCP of H101…O89 is negative (-0.0232 a.u.), which indicates 15



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that the hydrogen bond O100－H101…O89 has covalent character

Page 16 of 26

40

. Thus the bond O100－

H101…O89 stronger than the other two hydrogen bond (C7－H12…O99 and C31－H34…O99), which have both positive HBCP and ▽2ρBCP 41. Moreover, the potential energy density at critical point, V(rBCP), is used to evaluate the strength of the hydrogen bond between H…O

42

. The

V(rBCP) value of H101…O89 (-0.083 a.u.) is much higher than that of H12…O99 and H34…O99, which confirms the stronger hydrogen bonding interaction of O100－H101…O89 than C7－ H12…O99 and C31－H34…O99. Just like [A336]Suc + MAA complex, [A336]Suc + HAc complex also has one strong hydrogen bond (O96－H97…O89) and two weak hydrogen bond (C7－H12…O95 and C31－H34…O95). This indicates that the hydrogen bonding interaction between acid and carboxylate group of IL dominates the interaction between acid and IL. Compared the V(rBCP) value of H101…O89 ([A336]Suc + MAA complex) with the value of H97…O89 ([A336]Suc + HAc complex), the former (-0.083 a.u.) is higher than the latter (-0.077 a.u.), which means the stronger hydrogen bonding interaction of MAA with carboxylate group than HAc with carboxylate group. The results imply the important role of IL’ carboxylate group for the selective separation of MAA and HAc from aqueous solution. Based on the geometries and topology analysis of the IL-acid complex, we can conclude that (1) the interaction between IL and acid belongs hydrogen bonding; (2) there are multiple hydrogen bonds between IL and acid; (3) the hydrogen bond between carboxylate functional group of IL with acid has covalent character and much stronger than hydrogen bonds between cation of IL with acid. However, the overall interaction strengths between different IL and acid are still not clear. Therefore, the interaction energy of IL with acid in gas phase is calculated to evaluate the strength of the interaction (Table 4). The interaction energies follow as: [A336]Suc + MAA (-21.96 kcal/mol) > [A336]Suc + HAc (-21.21 kcal/mol). This is agreement with the partition coefficient values obtained from extraction experiment. Since the dilute solvent 1-chlorooctane is used, it is necessary to investigate the effect of solvation on the interaction of IL with acid. In the solvent, the interaction strength of IL with acid is weakened, such as the interaction energy of [A336]Suc + MAA complex is varied from -21.96 kcal/mol in gas phase to 16


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-17.46 kcal/mol in solvent (Table 4). However, the order of the interaction strength of different IL + acid complex is not changed. Combining the results of gas phase calculation and PCM calculation, the correlation between the IL + acid hydrogen bonding interaction and the extraction of MAA and HAc by IL is well. This indicates the hydrogen bonding interaction plays an important role in the extraction of MAA from the two acid aqueous solutions.

a

O88

C87 O89

C31 H34

1.48 Å H97

2.65 Å C7

O96

2.33 Å C94

H12 O95

17



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Page 18 of 26

b C31 O89

H34

1.47 Å H101

2.63 Å O100 C7

2.35 Å O99 C98

H12

Figure 3. Optimized structures showing the interactions of IL with acid: (a) [A336]Suc + HAc, (b) [A336]Suc + MAA. Evident hydrogen bonds are highlighted by green dot lines; the H…O distance is also marked. For clarity, only parts of side chain of the IL cation are displayed in the figure. The complete optimized structures are shown in Supporting Information (Fig. S17-S18).

18


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Table 4. Bond atoms, bond angles, electron density ρBCP, Laplacian of electron density ▽2ρBCP, energy density HBCP, and potential energy density V(rBCP) at the BCP from AIM analysis and interaction energy of IL with acid in gas phase (∆EG) and in solvent (∆ES).

Complex

[A336]Suc/MAA

[A336]Suc/HAc

Bond

ρBCP × 102

▽2ρBCP × 102

HBCP × 103

V(rBCP) × 103

∆EG

∆ES

Angles (°)

(a. u.)

(a. u.)

(a.u.)

(a.u.)

(kcal/mol)a

(kcal/mol)b

O100－H101…O89

178.66

8.22

14.51

-23.15

-82.57

C7－H12…O99

154.26

1.20

3.75

0.43

-8.52

-21.96

-17.46

C31－H34…O99

118.07

0.75

2.87

1.19

-4.81

O96－H97…O89

178.71

7.88

14.99

-19.73

-76.92

C7－H12…O95

150.18

1.25

3.96

0.48

-8.95

-21.21

-17.08

C31－H34…O95

119.26

0.72

2.74

1.16

-4.53

Bond Atoms

a: The interaction energy is corrected for the basis set superposition error (BSSE) by the counterpoise method 22. b: The solvent is 1-chlorooctane and the calculation is based on PCM solvation model 43.

19



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The recovery of acid After the extraction process, acids in the aqueous solution are extracted into the organic phase. It is also important to recover acids from the organic phase. The commonly used method is distillation and back extraction. Since the high boiling point of MAA and HAc, reduced pressure distillation seems a good choice. However, a majority of the organic phase is the dilute solvent (1-chlorooctane), the solute MAA and HAc just account for 0.9 wt% and 1.3 wt%. It is difficult to recover MAA and HAc from the organic phase by reduced pressure distillation. Actually, the solvent 1-chlorooctane and acid are coming out together under a reduced pressure distillation at 3.9 kPa and 343.15 K. On the other hand, MAA is a heat sensitive matter. It is easy polymerized under high temperature. In the reduced pressure distillation process, the polymerization of MAA occurs in the mixture after a long distillation time. Another suitable method is back extraction. The back extraction procedure can be operated at low experimental condition such as at room temperature, atmospheric pressure etc. MAA is not easy to polymerize at this condition and the monomer of MAA is obtained. Thus the back extraction is a competitive method for the recovery of MAA from the organic phase. The extraction of acid from aqueous solution is strongly affected by the pH of the solution

44-45

. As mentioned above, the extraction of MAA and HAc from aqueous

solution is mainly because of the hydrogen bonding interaction between the hydrogen atom in hydroxyl group of carboxylic acid and an oxygen atom in anion of IL. In other words, the un-dissociated forms of the carboxylic acid are favorable for IL extraction process. The content of the un-dissociated acid is strongly depending on the pH of the aqueous solution. When the pH of the aqueous solution is higher than the pKA value of the acid, the un-dissociated portion of acid in the aqueous medium is decreased dramatically. Such as, HAc with pKA value of 4.75, the un-dissociated portion of HAc in the aqueous medium is 35.99 % with pH of the aqueous solution is 5, and un-dissociated portion of HAc in the aqueous medium is 0.56 % with pH of the aqueous solution is 7 5. Thus, the hydrogen bonding interaction will be interrupted with the pH > pKA and then the carboxylic acid is released from the organic phase. Deionized water with sodium hydroxide adjust pH is used 20


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as stripping solvent to recover acids from the organic phase by back extraction. The pH of the stripping agent is adjusted to 12.85 for the sufficient stripping of the acids. The amount of the stripping agent is added by the 1:1 (v/v) ratio to the organic phase. And the back extraction efficiency of MAA and HAc for the 3 stages is shown in Table 5. Table 5. Back extraction efficiency of MAA and HAc for 3 stages stripping. Extraction conditions: initial mass fraction of acid in the organic phase is 0.9 % of MAA and 1.3 % of HAc, temperature is 298.15 K, pH of the stripping agent is 12.85, volume ratio is 1:1, and stripping time is 30 min. Eback a (%) Stages HAc

MAA

1

74.10

0.31

2

97.86

4.44

3

100

91.73

a: Eback means back extraction efficiency. It is calculated according to Eback = 1 − mO ci macid , where ci is the concentration of acid in the organic phase after i stage of back extraction, mO is the mass of organic phase, macid is the initial mass of acid in the aqueous solution.

From Table 5, HAc has removed from organic phase ahead of MAA. In the first two stages, the back extraction efficiency of HAc is achieved 97.86 % and the back extraction efficiency of MAA is just 4.44 %. After removing of HAc from the IL phase, there is a dramatic increase of MAA distribution into the aqueous phase, which introduces the high back extraction efficiency of MAA in the third stage of back extraction (Eback is 91.73 %). This indicates that the back extraction with pH shift is an effective method to recover acid from organic phase.

Conclusions ILs with carboxyl-functionalized anion shows strong hydrogen bond basicity was used as extractant to extract MAA and HAc from aqueous solution. The long carbon side chain of cation and strong electronegativity oxygen atoms in anion contributes the high hydrophobicity and hydrogen bond basicity of ILs, which is expected to provide high extraction ability for MAA. Firstly, the single acid aqueous solution is employed to 21



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evaluate the extraction ability of ILs. The results show that the partition coefficients of MAA are higher than that of HAc for both of ILs. [A336]Suc exhibits the best extraction performance, which is obtained 17.40 for the partition coefficient of MAA. Then, selective separation of MAA and HAc were employed by [A336]Suc. At the optimized extraction conditions, the selectivity of MAA to HAc is achieved 54.70 for [A336]Suc. In order to give insight on the interaction of IL with acid, atomic charge, electrostatic potential and topology analysis were performed. The results show that multiple hydrogen bonds are presented in IL-acid complex and the hydrogen bond between acid and carboxylate group of IL dominates the interaction between acid and IL. Meanwhile, FT-IR confirmed the hydrogen bonding interaction of IL with acid. The strength of interaction between IL and acid follows as: [A336]Suc + MAA

> [A336]Suc + HAc. This is

agreement with the partition coefficient values obtained from extraction experiment, which imply the important role of hydrogen bonding interaction between carboxylate group and acid in the selective extraction of MAA from the two acids aqueous solution. In addition, MAA is recovered from organic phase by back extraction method after extraction process. The back extraction experiment shows that 97.86 % of HAc can be recovered in two-stage process and 91.73 % of MAA is recovered in three stage back extraction.

Supporting Information Synthesis and characterization of ILs, Extraction experiment, Atomic charges, Optimized structure of [A336]Suc-MAA and [A336]Suc-HAc (PDF).

Corresponding authors *Xiangping Zhang. Tel./fax: +86 10 82544875. E-mail addresses: [email protected] *Suojiang Zhang. Tel./fax: +86 10 82544875. E-mail addresses: [email protected]

Acknowledgements This work was supported by National Key Research and Development Program of 22


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China (2017YFA0206803); the National Natural Science Fund for Distinguished Young Scholars (21425625), and National Natural Science Foundation of China (21676277, 51574215, 21436010).

References 1.

Lopez-Garzon, C. S.; Straathof, A. J. Recovery of carboxylic acids produced by fermentation.

Biotechnol. Adv. 2014, 32 (5), 873-904. DOI: 10.1016/j.biotechadv.2014.04.002 2.

Reichardt, C., Welton, T. Solvents and Solvent Effects in Organic Chemistry, 4th ed.; Wiley-VCH Verlag

GmbH & Co. KGaA: Weinheim, 2011. 3.

Wade, L. G. Organic Chemistry; Pearson Education: Boston, 2013.

4.

Henczka, M.; Djas, M. Reactive extraction of acetic acid and propionic acid using supercritical carbon

dioxide. J. Supercrit. Fluid. 2016, 110, 154-160. DOI: 10.1016/j.supflu.2015.11.018 5.

Marti, M. E.; Gurkan, T. Selective recovery of pyruvic acid from two and three acid aqueous solutions

by reactive extraction. Sep. Purif. Technol. 2015, 156, 148-157. DOI: 10.1016/j.seppur.2015.09.067 6.

Chen, S.; Zhang, S.; Liu, X.; Wang, J.; Wang, J.; Dong, K.; Sun, J.; Xu, B. Ionic liquid clusters:

Structure, formation mechanism, and effect on the behavior of ionic liquids. Phys. Chem. Chem. Phys. 2014, 16 (13), 5893-5906. DOI: 10.1039/c3cp53116c 7.

Rogers, R. D.; Seddon, K. R. Ionic liquids--solvents of the future? Science 2003, 302 (5646), 792-793.

DOI: 10.1126/science.1090313 8.

Li, R.; Xing, H.; Yang, Q.; Zhao, X.; Su, B.; Bao, Z.; Yang, Y.; Ren, Q. Selective extraction of 1-hexene

against n-hexane in ionic liquids with or without silver salt. Ind. Eng. Chem. Res. 2012, 51 (25), 8588-8597. DOI: 10.1021/ie3001452 9.

Kamiński, K.; Krawczyk, M.; Augustyniak, J.; Weatherley, L. R.; Petera, J. Electrically induced

liquid–liquid extraction from organic mixtures with the use of ionic liquids. Chem. Eng. J. 2014, 235, 109-123. DOI: 10.1016/j.cej.2013.09.019 10. González, B.; Corderí, S. Capacity of two 1-butyl-1-methylpyrrolidinium-based ionic liquids for the extraction of ethanol from its mixtures with heptane and hexane. Fluid Phase Equilibr. 2013, 354, 89-94. DOI: 10.1016/j.fluid.2013.06.018 11. Stoffers, M.; Górak, A. Continuous multi-stage extraction of n-butanol from aqueous solutions with 1-hexyl-3-methylimidazolium

tetracyanoborate.

Sep.

Purif.

Technol.

2013,

120,

415-422.

DOI:

10.1016/j.seppur.2013.10.016 12. Blahušiak, M.; Schlosser, Š.; Marták, J. Extraction of butyric acid with a solvent containing ammonium ionic liquid. Sep. Purif. Technol. 2013, 119, 102-111. DOI: 10.1016/j.seppur.2013.09.005 13. Matsumoto, M.; Mochiduki, K.; Fukunishi, K.; Kondo, K. Extraction of organic acids using imidazolium-based ionic liquids and their toxicity to Lactobacillus rhamnosus. Sep. Purif. Technol. 2004, 40 (1), 97-101. DOI: 10.1016/j.seppur.2004.01.009 14. Keshav, A.; Chand, S.; Wasewar, K. L. Recovery of propionic acid from aqueous phase by reactive extraction using quarternary amine (Aliquat 336) in various diluents. Chem. Eng. J. 2009, 152 (1), 95-102. DOI: 10.1016/j.cej.2009.03.037 15. Bai, Y.; Yan, R.; Huo, F.; Qian, J.; Zhang, X.; Zhang, S. Recovery of methacrylic acid from dilute aqueous solutions by ionic liquids though hydrogen bonding interaction. Sep. Purif. Technol. 2017, 184, 23



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

354-364. DOI: 10.1016/j.seppur.2017.05.013 16. Ab Rani, M. A.; Brant, A.; Crowhurst, L.; Dolan, A.; Lui, M.; Hassan, N. H.; Hallett, J. P.; Hunt, P. A.; Niedermeyer, H.; Perez-Arlandis, J. M.; Schrems, M.; Welton, T.; Wilding, R. Understanding the polarity of ionic liquids. Phys. Chem. Chem. Phys. 2011, 13 (37), 16831-16840. DOI: 10.1039/c1cp21262a 17. Xu, Z.; et al. Acetic and propionic acids. In Comprehensive Biotechnology, 2nd ed.; Murray, M.-Y., Ed.; Academic Press: Burlington, 2011. 18. Zhou, L.; Wang, L.; Zhang, S.; Yan, R.; Diao, Y. Effect of vanadyl species in Keggin-type heteropoly catalysts in selective oxidation of methacrolein to methacrylic acid. J. Catal. 2015, 329, 431-440. DOI: 10.1016/j.jcat.2015.05.031 19. Mellein, B. R.; Aki, S. N. V. K.; Ladewski, R. L.; Brennecke, J. F. Solvatochromic studies of ionic liquid/organic mixtures. J. Phys. Chem. B 2007, 111 (1), 131-138. DOI: 10.1021/jp0653353 20. Kamlet, M. J.; Taft, R. W. The solvatochromic comparison method. I. The β-scale of solvent hydrogen-bond acceptor (HBA) basicities. J. Am. Chem. Soc. 1976, 98 (2), 377-383. DOI: 10.1021/ja00418a009 21. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A. Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Keith, T.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, revision D.01; Gaussian, Inc.: Wallingford CT, 2013. 22. Boys, S. F.; Bernardi, F. The calculation of small molecular interactions by the differences of separate total energies. Some procedures with reduced errors. Mol. Phys. 1970, 19 (4), 553-566. DOI: 10.1080/00268977000101561 23. Lu, T.; Chen, F. Multiwfn: A multifunctional wavefunction analyzer. J. Comput. Chem. 2012, 33 (5), 580-592. DOI: 10.1002/jcc.22885 24. Humphrey, W.; Dalke, A.; Schulten, K. VMD: Visual molecular dynamics. J. Mol. Graph. Model. 1996, 14 (1), 33-38. DOI: 10.1016/0263-7855(96)00018-5 25. Xie, Y.; Xing, H.; Yang, Q.; Bao, Z.; Su, B.; Ren, Q. Aqueous biphasic system containing long chain anion-functionalized ionic liquids for high-performance extraction. ACS Sustain. Chem. Eng. 2015, 3 (12), 3365-3372. DOI: 10.1021/acssuschemeng.5b01068 26. Xu, D.; Yang, Q.; Su, B.; Bao, Z.; Ren, Q.; Xing, H. Enhancing the basicity of ionic liquids by tuning the cation-anion interaction strength and via the anion-tethered strategy. J. Phys. Chem. B 2014, 118 (4), 1071-1079. DOI: 10.1021/jp4096503 27. Yang, Q.; Xu, D.; Zhang, J.; Zhu, Y.; Zhang, Z.; Qian, C.; Ren, Q.; Xing, H. Long-chain fatty acid-based phosphonium ionic liquids with strong hydrogen-bond basicity and good lipophilicity: Synthesis, characterization, and application in extraction. ACS Sustain. Chem. Eng. 2015, 3 (2), 309-316. DOI: 10.1021/sc5006796 28. Socrates, G. Infrared Characteristic Group Frequencies; John Wiley & Sons, Inc.: Chichester, 1980. 29. Zhang, X.; Huo, F.; Liu, X.; Dong, K.; He, H.; Yao, X.; Zhang, S. Influence of microstructure and 24


Page 24 of 26

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interaction on viscosity of ionic liquids. Ind. Eng. Chem. Res. 2015, 54 (13), 3505-3514. DOI: 10.1021/acs.iecr.5b00415 30. Lu, T.; Chen, F. W. Atomic dipole moment corrected Hirshfeld population method. J. Theor. Comput. Chem. 2012, 11 (1), 163-183. DOI: 10.1142/S0219633612500113 31. Breneman, C. M.; Wiberg, K. B. Determining atom-centered monopoles from molecular electrostatic potentials. The need for high sampling density in formamide conformational analysis. J. Comput. Chem. 1990, 11 (3), 361-373. DOI: 10.1002/jcc.540110311 32. Besler, B. H.; Merz, K. M.; Kollman, P. A. Atomic charges derived from semiempirical methods. J. Comput. Chem. 1990, 11 (4), 431-439. DOI: 10.1002/jcc.540110404 33. Murray, J. S.; Politzer, P. The electrostatic potential: An overview. Wiley Interdiscip. Rev.-Comput. Mol. Sci. 2011, 1 (2), 153-163. DOI: 10.1002/wcms.19 34. Murray, J. S.; et al. Electrostatic potentials: Chemical applications. In Encyclopedia of Computational Chemistry; Schleyer, P. V. R., Ed.; John Wiley & Sons, Inc.: Chichester, 2002. 35. Desiraju, G. R. A bond by any other name. Angew. Chem.-Int. Edit. 2011, 50 (1), 52-59. DOI: 10.1002/anie.201002960 36. Dong, K.; Zhang, S.; Wang, D.; Yao, X. Hydrogen bonds in imidazolium ionic liquids. J. Phys. Chem. A 2006, 110 (31), 9775-9782. DOI: 10.1021/jp054054c 37. Bondi, A. van der Waals volumes and radii. J. Phys. Chem. 1964, 68 (3), 441-451. DOI: 10.1021/j100785a001 38. Bader, R. F. W. Atoms in Molecules: A Quantum Theory; Clarendon Press: Oxford, 1994. 39. Lipkowski, P.; Grabowski, S. J.; Robinson, T. L.; Leszczynski, J. Properties of the C−H···H dihydrogen bond: An ab initio and topological analysis. J. Phys. Chem. A 2004, 108 (49), 10865-10872. DOI: 10.1021/jp048562i 40. Jenkins, S.; Morrison, I. The chemical character of the intermolecular bonds of seven phases of ice as revealed by ab initio calculation of electron densities. Chem. Phys. Lett. 2000, 317 (1), 97-102. DOI: 10.1016/S0009-2614(99)01306-8 41. Rozas, I.; Alkorta, I.; Elguero, J. Behavior of ylides containing N, O, and C atoms as hydrogen bond acceptors. J. Am. Chem. Soc. 2000, 122 (45), 11154-11161. DOI: 10.1021/ja0017864 42. Espinosa, E.; Molins, E.; Lecomte, C. Hydrogen bond strengths revealed by topological analyses of experimentally observed electron densities. Chem. Phys. Lett. 1998, 285 (3), 170-173. DOI: 10.1016/S0009-2614(98)00036-0 43. Cances, E.; Mennucci, B.; Tomasi, J. A new integral equation formalism for the polarizable continuum model: Theoretical background and applications to isotropic and anisotropic dielectrics. J. Chem. Phys. 1997, 107 (8), 3032-3041. DOI: 10.1063/1.474659 44. Gorden, J.; Zeiner, T.; Sadowski, G.; Brandenbusch, C. Recovery of cis,cis-muconic acid from organic phase after reactive extraction. Sep. Purif. Technol. 2016, 169, 1-8. DOI: 10.1016/j.seppur.2016.05.032 45. Keshav, A.; Wasewar, K. L.; Chand, S. Extraction of propionic acid from model solutions: Effect of pH, salts, substrate, and temperature. AIChE J. 2009, 55 (7), 1705-1711. DOI: 10.1002/aic.11780

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Abstract graphic

Synopsis: The development of green and highly efficient extractant to separate carboxylic acid is necessary for chemical engineering.

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Selective Separation of Methacrylic Acid and Acetic Acid from

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