Separation of Hydrophobic Compounds Differing in a

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Separation of Hydrophobic Compounds Differing in Monounsaturated Double Bond Using Hydrophilic Ionic Liquid-water Mixtures as Extractants Yifeng Cao, Luwei Ge, Xinyan Dong, Qiwei Yang, Zongbi Bao, Huabin Xing, and Qilong Ren ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b03827 • Publication Date (Web): 01 Jan 2018 Downloaded from http://pubs.acs.org on January 1, 2018

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ACS Sustainable Chemistry & Engineering

Separation of Hydrophobic Compounds Differing in Monounsaturated Double Bond Using Hydrophilic Ionic Liquidwater Mixtures as Extractants

Yifeng Cao,†,§ Luwei Ge,† Xinyan Dong,‡ Qiwei Yang,† ,* Zongbi Bao,† Huabin Xing †,* and Qilong Ren†

Key Laboratory of Biomass Chemical Engineering of Ministry of Education, College of Chemical and Biological Engineering, Zhejiang University, 38 Zheda Road, Hangzhou 310027, China ‡ Ningbo Institute of Technology, Zhejiang University, 1 Xuefu Road, Ningbo 315100, China †

Corresponding Author: * Q. Yang: E-mail: [email protected]. Phone: +86-571-8795-2375. Fax: +86-571-8795-2375. H. Xing: E-mail: [email protected]. Phone: +86-571-8795-2375. Fax: +86-571-8795-2375. § Present address: Department of Materials and Interfaces, Weizmann Institute of Science, 234 Herzl Street, Rehovot 761000, Israel

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ABSTRACT Effective separation of analogues structurally differing in monounsaturated double bond remains challenging. In this study, hydrophilic ionic liquid (IL)-water mixtures were investigated as extractants for the extractive separation of hydrophobic analogues capsaicin and dihydrocapsaicin. A useful ‘diluent-swing’ effect was introduced to the IL-based extraction and the recovery of solute for recycling the extractant. The extractive separation is carried out at high IL concentrations where water behaves as cosolvent, and back-extraction of solute from IL-water mixture is performed at low IL concentrations where water acts as anti-solvent. The influences of IL structures (cations, anions and substituent groups) and concentration, as well as the analogues concentration on the separation efficiency were fully investigated. The selectivities of capsaicin to dihydrocapsaicin higher than 2.0 was achieved by a number of IL-water mixtures, mainly due to the enhanced dipolarity/polarizability by introducing water to the extractant. Interestingly, a synergistic effect on the distribution

coefficients

and

enhanced

selectivities

were

attained

by

N-

ethylpyridinium bromide ([EPy]Br) - water mixtures. This work shed light on developing feasible and effective large-scale separation method for compounds structurally different in monounsaturated carbon-carbon double bond.

KEYWORDS:

Ionic

liquids,

Hydrophobic

bioactive

extractants, Separation, Capsaicin.

2


compounds,

Aqueous

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■ INTRODUCTION The separation and purification of value-added natural bioactive compounds using environment-friendly techniques has been challenging but of great importance for both academia and industry.1-3 During the past two decades, ionic liquids (ILs) have been widely investigated as substituents for volatile organic solvents (VOCs) in isolating value-added natural products.4-6 This is mainly due to their unique properties, including negligible volatile pressure, high dissolution ability to compounds through various interactions, and high cohesive energy leading to ease of forming biphasic system with other solvents.7-9 Importantly, the in-depth theoretical and experimental investigation of the physicochemical properties of ILs enable rational design of taskspecific ILs for high performance separation processes and further understanding of the separation mechanisms.10-13 Hydrophilic ILs show superiority in hydrophobic bioactive compounds separation due to the fact that the hydrophobic compounds could be separated from hydrophilic ILs more easily than from hydrophobic ILs.14 However, high viscosity, high cost and the difficulties in purification/dehydration have been the major concerns associate with using hydrophilic ILs as separation media. It is also observed that small amount of water in ILs results in obviously reduced extraction ability.15 To overcome these problems, hydrophilic IL-water mixtures have been investigated as feasible extractants in certain applications.3,16,17 Using water as diluent not only reduces the viscosity and avoids the time-consuming IL dehydration/purification process, but also finely tunes the physical and chemical properties in a wide range by changing IL to water ratios.18,19 For instance, enhanced dipolarity/polarizability was reported for ILwater mixtures than for corresponding ILs,3 and additionally, changing the molar fraction of ILs in IL-water mixtures impacts more on the hydrogen-bonding acidity than varying structures of commonly used ILs.19 More interestingly, enhanced solubility and extraction ability to bioactive compounds were observed using amphiphilic IL-water mixtures.17,20,21 All such properties make IL-water mixtures as promising separation media for bioactive compounds. Bioactive analogues with structures differing in the saturation of acyl groups exist 3



wildly in nature. An example is capsaicin (CAPS) and dihydrocapsaicin (DHCAPS) (Figure 1), which make up around 80 ~ 95% of the total capsaicinoids content in Capsicum sp. plants.22 A recent study indicates that more pronounced cytotoxic responses for dihydrocapsaicin than capsaicin were observed.23 However, the separation process is quite challenging due to the similar physical and chemical properties caused by the structural similarity. Liquid chromatography,24 simulated moving bed chromatography (methanol/water = 75/25, v/v, Sinochrom ODS-BP),25 and high-speed counter-current chromatography (ethyl acetate/methanol/water/acetic acid = 20/20/20/20/2 (v/v/v/v/v))26 have been investigated for this separation purpose. Aiming at developing efficient and easily large-scaled separation process, we established a liquid-liquid extraction method using IL-water mixture as extractant (namely, extraction solvent) for the separation of value-added compound capsaicin from dihydrocapsaicin, which has not been reported so far. By utilizing the green solvent water as diluent, this method exhibits certain advantages, such as appropriate distribution behavior of solutes, relatively high selectivity and extraction capacity. In addition, the back-extraction of capsaicin and regeneration of IL could be achieved by lowered IL contents. In conclusion, effectively performing extractive separation at high IL concentration and back-extraction at low IL concentration by changing water content in the extractant, namely “diluent-swing” effect, was achieved. Our findings suggest that the use of hydrophilic IL-water mixtures as extractant is an effective method for the separation of saturated and unsaturated compounds.

■ EXPERIMENTAL SECTION Materials. The ILs with different cation and anion structures (Figure 2) used in this study were purchased from Lanzhou Greenchem. ILS (LICP, CAS, China) with purities > 98%. The IL names and abbreviations are as follows: 1-ethyl-3methylimidazolium bromide ([EMIm]Br), 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl), 1-ethyl-3-methylimidazolium dicyanamide ([EMIm]N(CN)2), 1-ethyl-3methylimidazolium ethylsulfate ([EMIm]EtSO4), 1-ethyl-3-methylimidazolium nitrate ([EMIm]NO3), 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIm]BF4), 1-ethyl4


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3-methylimidazolium perchlorate

triocyanate

([EMIm]ClO4),

([HOEMIm]Cl),

([EMIm]SCN),

1-ethyl-3-methylimidazolium

1-hydroxyethyl-3-methylimidazolium

N-ethylpyridinium

bromide

([EPy]Br),

chloride N-ethyl-N-

methylpyrrolidinium bromide ([EMPyr]Br), N-ethyl-N-methylpiperidinium bromide ([EMPip]Br), 1-butylpyridinium bromide ([BPy]Br) and 1-octylpyridinium bromide ([OPy]Br). Choline chloride ([Cho]Cl) with a purity of 99% was purchased from Aladdin Chemicals Co. Ltd (Shanghai, China). The capsaicinoids sample, containing 66.7 wt.% capsaicin and 30.8 wt.% dihydrocapsaicin, was purchased from Hangzhou Great Forest Biomedical Ltd (China). The capsaicin and dihydrocapsaicin standard samples (99.8 wt.%) were purchased from Chengdu Must Bio-Technology co., Ltd (China). Liquid-liquid Extraction Procedure. Liquid-liquid extraction experiments were carried out as the procedure described in our previous work.27 Capsaicinoids-ethyl acetate solution (feed solution) and IL-water mixture (extractant) were prepared separately. Then, equal volume of both solutions were transferred to a conical flask, which was shaken at 200 rpm and maintained at a constant temperature (± 0.1 °C) by an oven oscillator for 2 h until phase equilibrium was attained. After that, the flask was settled at the same temperature for another 2 h until phase separation completed. Samples from each phase were taken by syringes and diluted with methanol for HPLC analysis. The distribution coefficient (D) of solute (capsaicin or dihydrocapsaicin) was calculated according to Equation 1, D=Cext/Craf

(1)

where Cext and Craf are the concentration (mg·mL-1) of solute in the extraction and raffinate phases, respectively. The extraction phase and raffinate phase are the IL-rich phase and ethyl acetate-rich phase after equilibrium, respectively. The selectivity of capsaicin to dihydrocapsaicin (Scaps/dhcas) was calculated according to Equation 2, Scaps/dhcas =Dcaps/Ddhcaps

(2)

where Dcaps and Ddhcaps are the distribution coefficients of capsaicin and dihydrocapsaicin, respectively. HPLC Analysis. The concentrations of capsaicin and dihydrocapsaicin in each sample were analyzed by a Waters HPLC system equipped with a 1525 HPLC pump, 5



a column oven, a 717 plus autosampler and a 2487 dual absorbance detector. A Waters X-Bridge C18 column (4.6 mm I.D. × 150 mm length; particle size 5 µm) was used for the separation of capsaicin and dihydrocapsaicin. The mobile phase was a mixture of methanol/water (70/30, v/v) and the flow rate was 1 mL·min-1. The column temperature was maintained at 30 °C. The wavelength of UV detector was set at 280 nm.

■ RESULTS AND DISCUSSION Previous solubility studies show capsaicin and dihydrocapsaicin dissolve in strong polar solvents, such as butyl ether, isopropyl ether, ethyl acetate, acetone and ethanol, but poorly dissolve in water and weak to non-polar solvents.28, 29 Ethers are highly flammable solvents, while acetone and ethanol cannot form biphasic systems with water and ionic liquids due to the miscibilities. Considering the safety and ability of forming biphasic systems with IL-water mixtures, ethyl acetate was chosen as solvent for capsaicinoids. The biphasic system consisting of ethyl acetate, IL and water, with known mutual miscibilities,30 was employed. The influence of IL structure and concentration, and capsaicinoids concentration on the separation results, as well as IL recycling were fully studied. Influence of IL structure on the separation. A number of ILs with different cations, alkyl chain lengths on cation and anions were screened for the separation of capsaicin and dihydrocapsaicin. To evaluate the separation efficiency, distribution coefficients of capsaicin and dihydrocapsaicin between biphasic systems, together with the selectivities of capsaicin to dihydrocapsaicin were calculated according to Equations 1 and 2, and presented in Table S1, Figures 3, 4 and 5. Higher distribution coefficients for capsaicin than those of dihydrocapsaicin were observed for all the studied extractants, giving rise to selectivities of capsaicin to dihydrocapsaicin range between 1.0 and 2.1. Particularly, selectivities over 2.0 were obtained by a series of ILs, such as [EMIm]Cl, [EPy]Br and [EMPyr]Br. It is worth noticing that, extractive separation of saturated and monounsaturated compounds is rather difficult. For example, the selectivities of capsaicin to dihydrocapsaicin using complex organic 6


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systems were 1.0 ~ 1.5, and the selectivities of fatty acids methyl oleate (C18:1) to methyl stearate (C18:0) were close to or lower than 2.0 by using IL/co-solvents as extractants.26,31 Therefore, the selectivities we obtained are comparable or even higher than the reported values, indicating that the structural difference between capsaicin and dihydrocapsaicin could be distinguished and effective separation could be achieved by IL-water mixtures. Four types of commonly used cations, [EMPyr]+, [EPy]+, [EMIm]+ and [EMPip]+, were selected to investigate their impact on the separation efficiency. Results in Figure 3 clearly show that the studied cations influence more on the distribution coefficients than on the selectivity: the distribution coefficient of capsaicin varies from 0.029 to 0.10; in contrast, the selectivity of capsaicin to dihydrocapsaicin slightly changes within the range of 1.8 to 2.1. Higher distribution coefficients were achieved by [EPy]+ and [EMIm]+, indicating that the aromatic cations are able to establish stronger interactions with solutes through π- π interactions. For ILs with cations [HOEMIm]+ and [Cho]+, distribution coefficients below the detection limit (< 0.001) were observed (Table S1). Strong hydrogen-bonding interaction between anion (Cl-) and these cations bearing hydroxyl group weakens the interaction strength between the extractant and solutes, resulting in such low distribution coefficient.32,33 Cation substituent alkyl group with different chain lengths was also studied. Enhanced distribution coefficients and decreased selectivity of capsaicin to dihydrocapsaicin were observed as increasing the alkyl chain length (Figure 4). The same enhanced distribution coefficients with increasing the length of alkyl chain was also observed for hydrophobic α-tocopherol, which was attributed to the misfit interaction or electrostatic interaction between α-tocopherol and ILs.34 Besides the stronger interaction between solutes and ILs, long alkyl chain also causes higher mutual solubilities of the biphasic system,30 thereby renders low separation efficiency – the distribution coefficients and selectivity values approach 1. A series of anions, Br-, Cl-, ClO4-, EtSO4-, N(CN)2-, NO3- and SCN-, were selected to investigate how the anions influence the separation of capsaicin and dihydrocapsaicin. The distribution coefficients of capsaicin and dihydrocapsaicin follow a similar 7



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increasing trend of Cl- ˂ NO3- ˂ Br- ˂ BF4- ˂ EtSO4- ˂ ClO4- ˂ SCN- ˂ N(CN)2-, while selectivity of capsaicin to dihydrocapsaicin manifests a reverse trend to the ratio of distribution coefficients (Figure 5). The anions mainly determine the hydrogenbonding basicity (hydrogen-bonding accepting ability, β) of ILs,35 and influence the separation results mainly through two aspects, mutual solubility of the biphasic system and interaction strength between IL and solutes. It is seen from Figure 5 that anions with lower hydrogen-bonding basicity, such as ClO4-, SCN- and N(CN)2-, exhibit higher distribution coefficients but lower selectivity, which is mainly caused by the elevated mutual solubilities of the biphasic system.30 To reduce IL loss and facilitate the separation of capsaicin from dihydrocapsaicin, anions with higher hydrogen-bonding basicity (such as Cl-, NO3- and Br-) are preferred. Taking into account the obtained results, it is clear that ILs with aromatic cation, short cationic alkyl chain, and anions of high hydrogen-bonding basicity are preferred for the efficient separation of capsaicin and dihydrocapsaicin. Effect of IL concentration in the extractant. The concentration of IL plays a dominant role in determining the physical and chemical properties of IL-water mixtures, such as viscosity, dipolarity/polarizability (π*), and hydrogen-bonding basicity, consequently determines the separation efficiency.18,19 Herein, we studied how the molar percentage of [EPy]Br (x[EPy]Br) in the extractant affects the separation of capsaicin and dihydrocapsaicin. The results presented in Figure 6 show that the distribution behavior of capsaicin and dihydrocapsaicin is sensitive to [EPy]Br concentrations. Remarkably, a maximum distribution coefficient was observed when x[EPy]Br was 41%. When x[EPy]Br increased from 10% to 41%, the distribution coefficients of capsaicin increases from 0.012 to a maximum value 0.21, and afterwards shows a decreasing trend afterwards as x[EPy]Br increases from 41% to 46% (90 wt.%). The same behavior was observed for dihydrocapsaicin. This is probably caused

by

the

fact

that

increasing

IL

concentration

causes

increased

polarity/polarizability (π*) and decreased hydrogen-bonding basicity (β),3 which have competitive effects on dissolving capsaicin/dihydrocapsaicin into IL-water mixtures. It is expected that the mixed IL and water caused much higher values of distribution 8


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coefficients than those obtained using pure water or IL ([EPy]Br) as extractant, suggesting the synergistic effect of IL and water on the distribution behavior of capsaicin and dihydrocapsaicin. On the one hand, increasing IL concentration decreased polarity/polarizability (π*) and increased hydrogen-bonding basicity (β),3 which probably have competitive effects on dissolving capsaicin/dihydrocapsaicin into IL-water mixtures and thus lead to the presence of a maximum value of the distribution coefficients. On the other hand, at low IL concentrations, the multiple interactions between IL and capsaicin/dihydrocapsaicin enhance as IL concentration increases and bring about an increasing trend in distribution coefficients of capsaicin and dihydrocapasicin, while at high IL concentrations the less hydrated cations and anions probably result in increased interaction between them which competitively reduce the IL-solute interaction strength and thus decrease the distribution coefficients. Synergistic effect of IL and IL-cosolvent mixtures on the distribution behavior of solutes has also been observed. For instance, a synergistic effect was observed for the extraction of organic acids by ILs;36,37 and maximum values of distribution coefficients for tocopherol analogues were observed as xIL in extractant increases, where [BMIm]Cl-cosolvent (acetonitrile/dimethyl formamide/dimethyl sulfoxide) mixture was used as extractant.27 The selectivity of capsaicin to dihydrocapsaicin follows a slightly decreasing trend from 2.1 to 1.9 as x[EPy]Br increases from 10 % to 46% (Figure 6). This also indicates that using water as extractant favors the separation of capsaicin from dihydrocapsaicin. Considering the facts that the structural difference of capsaicin and dihydrocapsaicin lying on carbon-carbon double bond and decreased dipolarity/polarizability (π*) of IL-aqueous solution was observed as IL content increases,3 it is inferred that the dipolarity/polarizability of IL-aqueous solution is a major factor determining the separation of capsaicin and dihydrocapsaicin. It is worth noticing that, the obvious change of distribution coefficient against IL concentration (“diluent-swing” effect) facilitates back-extraction and IL recycling: after selectively separating capsaicin and dihydrocapsaicin at high IL concentrations, back-extraction of capsaicin from IL-rich phase under low/diluted IL concentrations, 9



thereby makes it possible for the regeneration of IL. Details on the regeneration of IL are illustrated later. Effect of initial solutes concentration. As the extraction capacity is strongly correlated to solvent consumption, high extraction capacity is crucial for potential industrial application. For this reason, initial concentration of capsaicinoids in the ethyl acetate phase ranging from (10.3 ~ 95.2) mg·mL-1 was investigated at xIL= 30% and the results are shown in Figure 7. As the total solute concentration in the ethyl acetate solution increases, roughly linear decrease in the distribution coefficients for capsaicin and dihydrocapsaicin were observed. In contrast, the selectivity coefficient of capsaicin to dihydrocapsaicin within the studied capsaicinoids concentration range remains almost constant (0.19 ± 0.1). The respective concentrations of capsaicin and dihydrocapsaicin in the extraction phase (IL-rich phase) versus those in the raffinate phase (ethyl acetate-rich phase) after equilibrium were plotted in Figure 7 (b). It is seen that the concentrations in the extraction phase increase as enhancement in the raffinate phase, and no saturation was formed throughout the experiments. These results reveal that high extraction capacity is obtained by using IL-water mixture as extractant in spite of low solubility of capsaicin in water. Back-extraction of capsaicin and recycling of IL-water mixture. Due to the requirements of green process and the high cost of ILs, back-extraction of capsaicin from the IL-rich phase (extraction phase) and IL regeneration are crucial for sustainable and economic applications. As ILs are slightly volatile, solutes with high boiling points could not be recovered by distillation, which has limited potential application of ILs in industry. The way of back-extraction of solute from the IL-rich phase, however, has been proved to be feasible for IL recycling.38 Herein, we take advantage of the fact that the distribution behavior of capsaicin and dihydrocapsaicin are sensitive to IL concentration in the extractant (Figure 6), and use ethyl acetate for back-extraction of capsaicin from diluted IL-rich phase. After that, the regeneration of IL could be performed by concentrating the diluted IL aqueous solution. Due to the 10


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non-volatility of ILs, techniques such as vacuum membrane distillation (VMD) and short path vacuum distillation have been proved to be feasible for this purpose.39-41 An example of detailed procedures is as follows. After liquid-liquid extraction (for instance, using x[EPy] = 40%), the IL-rich phase will be diluted by water until x[EPy] = 10%, then the diluted solution reaches equilibrium with equal volume of ethyl acetate, by which means more than 98% of the solutes (capsaicin and dihydrocapsaicin) will be back-extracted to the ethyl acetate-rich phase (distribution coefficients for capsaicin and dihydrocapsaicin are 0.012 and 0.0058 (Table S1)). The regenerated diluted IL-water mixture will be reused by vacuum distillation until desired IL concentration (x[EPy] = 40%) is reached. To evaluate the feasibility of this liquid-liquid extractive separation process for a practical application, fractional extraction is preferred due to the fact that products with high purity and recovery could be obtained theoretically by rational designing the ratios of feed phase (F), extraction solvent (ES) and scrubbing solvent (SS) as well as the numbers of the extraction and scrubbing stages.31,42 Figure 8 illustrates the purity and recovery of target compound, capsaicin, in the extraction phase versus flow ratio ES/(F+SS) and the number of the extraction stage under fixed number of scrubbing stage and flow rates of F and SS. The purity of capsaicin in the extraction phase ranges from 79.8% ~ 98.8%, and the recovery ranges from 9.1% ~ 100%. When ES:F:SS=1:14:0.8 with 18 stages in the extraction section and 6 stages in the scrubbing section, the relative purity of capsaicin increases from 68.4% in the feed solution to 91.1% in the extraction solution, together with a recovery of 91.2%. Figure 9 shows the whole process of extractive separation of capsaicin from dihydrocapsaicin using IL-water as extractant, including fractional extraction, backextraction of capsaicin from diluted IL-water mixture (liquid-liquid extraction) and concentrating of IL-water mixture (water evaporation) for extractant recycling. As a matter of fact, in addition to IL-water mixture (10#), water (11#) an ethyl acetate (regenerate from 4# and 8# by distillation) could also be further reused, which thereby reduces the solvent consumptions and cost. 11



■ CONCLUSIONS In conclusion, we established a feasible method for the effective separation of capsaicin and dihydrocapsaicin using hydrophilic IL-water as extractant. By means of the “diluent-swing” effect, the extractive separation at high IL concentrations where water behaves as cosolvent, and back-extraction for IL recycling at low IL concentrations, where water acts as anti-solvent, could be achieved. The results show that the distribution behaviors of capsaicin and dihydrocapsaicin are influenced by the mutual solubilities of the biphasic system, as well as the complex interactions between the biphasic systems and solutes. The separation selectivity of capsaicin to dihydrocapsaicin is improved by increasing the dipolarity/polarizability of the extractant. Using IL-water mixtures as extractants, proper distribution coefficients together with improved selectivities of capsaicin to dihydrocapsaicin were acquired. In addition, back-extraction of solute and IL recycling could be achieved. This work provides a promising strategy for large-scale separation of bioactive compounds structurally differ in carbon-carbon double bond.

■ Supporting Information Distribution coefficients of capsaicin and dihydrocapsaicin as well as selectivities of capsaicin to dihydrocapsaicin obtained with different IL-water mixtures.

■ AUTHOR INFORMATION Corresponding Author

* Q. Yang: E-mail: [email protected]. Phone: +86-571-8795-2375. Fax: +86-5718795-2375. H. Xing: E-mail: [email protected]. Phone: +86-571-8795-2375. Fax: +86-571-8795-2375. Notes

The authors declare no competing financial interest.

■ ACKNOWLEDGEMENTS 12


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This work was supported by the National Natural Science Foundation of China (No. 21476192, 21725603 and 21306168) and National Program for Support of Topnotch Young Professionals (to H. X.).

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Figure 1. Chemical structures of capsaicin and dihydrocapsaicin. 63x57mm (600 x 600 DPI)



Figure 2. Chemical structures of the cations and anions used in this study. 52x18mm (600 x 600 DPI)


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Figure 3. Effect of cation core structure on the liquid-liquid extractive separation of capsaicin and dihydrocapsaicin. The initial capsaicinoids concentration in the feed solution was 10 mg·mL-1. The initial molar percentage of IL in IL-water mixture was 30%. The initial volume ratio of extractant to feed solution was 1:1. The temperature was 303.2 K. 83x59mm (300 x 300 DPI)



Figure 4. Effect of alkyl chain length attached to cation on the liquid-liquid extractive separation of capsaicin and dihydrocapsaicin. The initial capsaicinoids concentration in the feed solution was 4 mg·mL-1. The initial molar percentage of IL in IL-water mixture was 10%. The initial volume ratio of extractant to feed solution was 1:1. The temperature was 303.2 K. 84x59mm (300 x 300 DPI)


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Figure 5. Effect of anion on the liquid-liquid extractive separation of capsaicin and dihydrocapsaicin. Cation [EMIm]+ was used. The initial capsaicinoids concentration in the feed solution was 10 mg·mL-1. The initial molar percentage of IL in IL-water mixture was 30%. The initial volume ratio of extractant to feed solution was 1:1. The temperature was 303.2 K. 84x59mm (300 x 300 DPI)



Figure 6. Effect of anion on the liquid-liquid extractive separation of capsaicin and dihydrocapsaicin. Cation [EMIm]+ was used. The initial capsaicinoids concentration in the feed solution was 10 mg·mL-1. The initial molar percentage of IL in IL-water mixture was 30%. The initial volume ratio of extractant to feed solution was 1:1. The temperature was 303.2 K. 84x59mm (300 x 300 DPI)


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Figure 7. Effect of the initial concentration of solutes in the feed solution on the liquid-liquid extractive separation of capsaicin and dihydrocapsaicin: (a) distribution coefficients of capsaicin and dihydrocapsaicin and (b) the concentrations of capsaicin and dihydrocapsaicin in the extraction phase versus those in the raffinate phase after equilibrium. The initial molar percentage of [EPy]Br in the [EPy]Br-water mixture was 30%. The initial volume ratio of extractant to feed solution was 1:1. The temperature was 303.2 K. 84x130mm (300 x 300 DPI)



Figure 8. Purity (a) and recovery (b) of capcaisin in the extraction phase versus the number of extraction stages (Next) and flow ratio of ES/(F+SS), where ES, F and SS represent flow rates of extraction solvent, feed and scrubbing solvent, respectively. The extract was 35 mol% [EPy]Br aqueous solution. The number of scrubbing stages was fixed to 6. The flow ratio of F:SS:ES was of 1:0.8:ES, and ES ranges from 0.6 to 2. 152x71mm (300 x 300 DPI)


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Figure 9. Flowchart of the extractive separation of capsaicin and dihydrocapsaicin, back-extraction of capsaicin and recycling of IL-water mixture. 1. IL-water mixture (extractant); 2. ethyl acetate (scrubbing solvent); 3. ethyl acetate dissolving capsaicin and dihydrocapsaicin (feed); 4. dihydrocapsaicin-rich ethyl acetate phase; 5. capsaicin-rich IL-water phase; 6. water; 7. ethyl acetate; 8. capsaicin-rich ethyl acetate phase; 9. diluted IL-water mixture; 10. IL-water mixture for reuse; 11. water for reuse. 139x78mm (300 x 300 DPI)



TOC Synopsis: The IL-water involved liquid-liquid extraction for the separation of analogues is feasible as a substituent for high VOCs consumption methods. 120x66mm (300 x 300 DPI)


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Separation of Hydrophobic Compounds Differing in a

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