Phase Behavior of Supercritical CO2 Microemulsions with Surfactant

Article pubs.acs.org/jced

Phase Behavior of Supercritical CO2 Microemulsions with Surfactant Ls-36 and Selective Solubilization of Propane-1,3-diol Wen Yu, Dan Zhou, Jian-zhong Yin,* and Jin-ji Gao State Key Laboratory of Fine Chemicals, School of Chemical Machinery, Dalian University of Technology, Dalian 116024, P. R. China ABSTRACT: Supercritical carbon dioxide (scCO2) microemulsion systems were formed in a custom-made volumevariable optical phase equilibrium cell, by employing Ls-36 (dodecyl(poly(ethylene-methylethylene glycol)) ether) as a surfactant, ethanol (EtOH) as a cosolvent, and propane-1,3diol (1,3-PDO) as a disperse phase in the CO2 continuous phase. The phase behaviors of the ternary system of Ls-36 + CO2 + EtOH, quaternary system of Ls-36 + CO2 + EtOH + H2O, and quinary system of Ls-36 + CO2 + EtOH + 1,3-PDO + H2O were investigated in the temperature range of 303.05 K to 323.25 K and pressure range of 7.81 MPa to 18.99 MPa were studied. Thermodynamically stable microemulsion can be formed by controlling the operating pressure and temperature to selectively extract the 1,3-PDO from its dilute aqueous solution. It was found that a higher concentration of Ls-36 was more beneficial to the solubilization of 1,3-PDO. The results may provide useful thermodynamics data for industrial design and a feasible basis and practical guidance for selectively extracting 1,3-PDO from fermentation broth efficiently in industry.

1. INTRODUCTION Supercritical carbon dioxide (scCO2) is one of the most attractive green solvents because it is readily available, inexpensive, nontoxic, nonflammable and has a moderate critical temperature and pressure (304.25 K and 7.38 MPa). As an alternative to organic solvents, the applications of scCO2 have been studied in many fields, such as material synthesis,1−3 chemical reactions,4−7 and extraction8−11 and so on. However, it is known that scCO2 is a poor solvent for the polar substances such as protein, metal ions, and polymers, and so forth, which will greatly limit its applications. One effective way to overcome this shortcoming is to add a suitable surfactant into scCO2 to form scCO2 microemulsion, whose polar core can solubilize the problem by solubilizing these insoluble substances within the polar core in the microemulsion. scCO2 microemulsions are thermodynamically stable systems made of water, CO2, a surfactant, and occasionally a cosurfactant. Choosing suitable surfactants soluble in scCO2 is the prerequisite to form the stable water-in-CO2 (W/C) microemulsions. However, it was found that only a few readily available commercial surfactants can be dissolved in CO2.12 During the last two decades, a number of research groups13−17 have made great efforts to synthesize special surfactants that can be dissolved in CO2 to form scCO2 microemulsion, which expanded the applications of scCO2 microemulsion to some new fields such as extraction of high-molecular-weight biomolecules or hydrophilic molecules,18−20 acting as media for chemical reactions21−23 and preparation of nanomaterials.24−27 In particularly, a nonfluorous and nonsilicon nonionic surfactant, Ls-36 was found to be soluble in scCO2 without © 2013 American Chemical Society

cosolvent and to form W/C microemulsion which can be used to solubilize water at easily accessible conditions.28 However, to the best of our knowledge, selective extraction of the polyalcohol from dilute aqueous solutions using scCO2 microemulsion with Ls-36 as a surfactant has not been reported so far. Propane-1,3-diol (1,3-PDO) is an important chemical widely applied in plastic industry and pharmaceutics. 1,3-PDO is typically produced through fermentation process. However, the separation and purification of 1,3-PDO from the dilute aqueous solutions obtained from fermentation broth have presently become a challenging problem in industry. As a new efficient extraction method, scCO2 microemulsion extraction might become an excellent way for extracting polyalcohols from dilute aqueous solutions. In this work, scCO2 microemulsion systems, including the ternary system Ls-36 + CO2 + EtOH, the quartenary system Ls-36 + CO2 + EtOH + H2O, and the quinary system Ls-36 + CO2 + EtOH + H2O + 1,3-PDO were prepared by using Ls-36 as a surfactant and ethanol as a cosolvent. The phase behaviors of these systems were studied at different concentrations of 1,3-PDO in aqueous solution to obtain the suitable conditions for selectively solubilizing 1,3PDO from dilute aqueous solutions. The results reported here will provide useful information for the separation and purification of 1,3-PDO in bioprocess. Received: December 21, 2012 Accepted: February 14, 2013 Published: February 21, 2013 814

dx.doi.org/10.1021/je301356r | J. Chem. Eng. Data 2013, 58, 814−820

Journal of Chemical & Engineering Data

Article

2. EXPERIMENTAL SECTION 2.1. Materials. Surfactant Ls-36 was purchased from Shanghai Owen Chemicals Co. Ltd., China. The structure of the Ls-36 is shown in Figure 1. Absolute ethyl alcohol was

Table 2. Cloud-Point Pressures of the Ls-36 + CO2 + EtOH Ternary Systema T/K

P/MPa

m = 0.454 303.47 9.30 306.75 9.99 309.46 11.12 312.27 12.10 314.80 12.97 317.60 13.92 320.41 14.64

Figure 1. Structure of surfactant Ls-36.

T/K

P/MPa

m = 0.681 304.41 11.39 306.75 12.23 309.56 12.67 312.27 13.59 314.89 14.60 317.89 15.50 320.60 15.77

T/K

P/MPa

m = 1.362 302.64 13.64 305.45 14.12 308.35 14.65 311.18 15.90 314.19 16.66 316.92 17.55 319.62 18.33

a

m is the concentration of Ls-36 ethanol solution. Standard uncertainties u are u(T) = ± 0.01 K, u(m) = ± 0.005 mol·kg−1, and the combined expanded uncertainty Uc is Uc(P) = ± 0.04 MPa (level of confidence = 0.95, where k = 2).

provided by Shenyang Xin Xing Chemical Reagent Company of China. 1,3-PDO was supplied by Dalian Wei Xin Chemical Company of China. All of the chemicals are of AR grade and were used as received. CO2 (purity ⩾ 99.0 %) was supplied by Dalian Guang Ming Gas Corporation of China. Double-distilled water was prepared in this laboratory. The specifications of the used chemicals are given in Table 1. 2.2. Apparatus and Procedures. The microemulsions were prepared in a custom-made volume-variable optical phase equilibrium cell. The apparatus for phase behavior measurement was similar to that in our previous reports.16,20 The apparatus consists mainly of a high-pressure view cell (net volume is 53.79 mL) with two optical quartz windows. The maximum operating pressure and temperature of this cell is 30 MPa and 353.15 K, respectively. The optical cell was heated by water bath. In a typical experiment, the designated amount of surfactant and water were introduced to the cell, and a magnetic stir bar was placed into the cell. Then the cell was sealed and heated to the designed temperature in the water bath. The temperature was measured using a thermocouple with an accuracy of ± 0.1 K. The air in the cell was repetitively replaced with CO2. Then, CO2 was charged into the cell very slowly using a high-performance liquid chromatography (HPLC) pump and the pressure of the system was measured using a pressure transducer (DG1300-BZ-A-2-40) with an accuracy of ± 0.01 MPa. For the cloud-point pressure measurement, the pump was stopped once an optical transparent single phase solution was obtained. Then, the stirring was stopped, and the system was allowed to stand for a long time to ensure the stability of the microemulsion system before observing the phase behavior. Subsequently, the pressure of the system was gradually decreased by controlling the variable-volume piston (volume range 0 mL to 1.5 mL) until the cloud point appeared. The experiment was repeated for three times, and the average of the cloud point pressures was recorded. The results were shown in Tables 2 to 4, with the combined expanded uncertanity within ± 0.04 MPa (level of confidence = 0.95, where k = 2).

3. RESULTS AND DISCUSSION 3.1. Effects of Ethanol Content on the Phase Behavior of the Ls-36 + CO2 + EtOH System. Choosing an appropriate surfactant is the key to the formation of stable W/C microemulsions. A low-cost nonfluorous and nonsilicone surfactant Ls-36 was previously reported to have high solubility in scCO2 by Liu et al.28 It was therefore used to form a stable scCO2 microemulsion and to solubilize a certain amount of water. Nevertheless, the reported operating pressure was as high as 23.13 MPa while the W0 (water-to-surfactant molar ratio) value was lower than 5, which is evidently unfavorable to the industrial applications. On the other hand, ethanol was reported to be able to significantly reduce the system pressure when it was used as a cosolvent in W/C microemulsion, which can be attributed to its good solubility in CO2 and improvement of the polarity of the whole phase.29,30 Therefore, in this study, we used ethanol as cosolvent and measured cloudpoint pressures of different systems in the presence of ethanol. The phase behavior of the ternary system Ls-36 + CO2 + EtOH was investigated at a fixed Ls-36 amount of (0.716 g), while varying the amount of ethanol. In the experiment, different amounts of ethanol (0.79 g, 1.58 g, and 2.37 g, which correspond to 0.454 mol·kg−1, 0.681 mol·kg−1, and 1.362 mol·kg−1, respectively) were added. The experimental cloudpoint pressure data of Ls-36 + CO2 system with or without ethanol at all operation conditions are shown in Table 2. The cloud-point curves for the ternary system Ls-36 + CO2 + EtOH with different ethanol concentrations are shown in Figure 2. A single phase was observed at each condition above the solid lines. It can be seen that the cloud-point pressures of the ternary system Ls-36 + CO2 + EtOH decreased as the ethanol concentration increased, which is consistent with other reports.29,31 For example, at 308.20 K, the cloud point pressure is about 10.82 MPa with the presence of 2.37 g of EtOH in the system, while it was 14.50 MPa without EtOH at the same

Table 1. Source and Purity of Chemicals chemical name

abbreviation

source

mole fraction purity

purification method

dodecyl(poly(ethylenemethylethylene glycol)) ether absolute ethyl alcohol

Ls-36

Shanghai Owen Chemicals Co. Ltd., China

≥ 0.995

none

EtOH

≥ 0.995

none

propane-1,3-diol carbon dioxide

1,3-PDO CO2

Shenyang Xin Xing Chemical Reagent Company of China Dalian Wei Xin Chemical Company of China Dalian Guang Ming Gas Corporation of China

≥ 0.990 ≥ 0.990

none none

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Table 3. Cloud-Point Pressures of the Ls-36 + CO2 + EtOH + H2O System with Ls-36 Ethanol Solution Molarity m = 0.227 mol·kg−1a W0

T/K

P/MPa

5.6

303.66 306.56 309.37 311.90 314.55 317.32 320.41 303.57 306.37 309.27 312.55 315.17 316.58 319.76 303.75 306.75 309.27 311.99 314.70 317.60 320.32 303.94 306.65 309.27 311.90 314.61 317.42 320.13 303.66 306.28 309.18 311.99 314.70 317.14 320.04

7.81 8.63 9.58 10.49 11.29 12.30 13.21 8.90 9.66 10.45 11.28 12.19 12.97 13.81 9.34 9.90 10.59 11.42 12.47 13.17 13.83 9.63 9.76 10.74 11.57 12.53 13.27 14.01 9.93 10.63 11.30 11.95 12.75 13.54 14.62

7.8

10.0

12.2

14.4

Table 4. Cloud-Point Pressures of the Ls-36 + CO2 + EtOH + 1,3-PDO + H2O Quinary Systema T/K 0.681b 303.94 306.75 309.37 312.27 314.89 317.70 320.32 323.22 0.681c 303.57 306.47 309.37 311.80 314.70 317.60 320.13 322.94 0.681d 304.03 306.56 309.46 312.18 314.70 317.42 320.41 323.22

P/MPa 11.74 12.31 13.06 13.93 14.93 16.05 17.01 17.85 11.79 12.48 13.26 14.25 15.55 16.43 17.26 18.09 11.55 12.09 12.98 13.97 15.03 16.01 16.79 17.61

T/K 0.454b 303.85 306.56 309.37 311.80 314.61 317.51 320.23 323.04 0.454c 303.94 306.47 309.27 311.90 314.7 317.51 320.32 322.94 0.454d 303.85 306.37 309.37 311.71 314.61 317.42 320.13 323.03

P/MPa 10.41 11.17 12.21 13.03 13.84 14.77 15.57 16.41 10.23 10.83 11.85 12.85 13.78 14.76 15.61 16.23 9.98 10.96 11.67 12.78 13.82 14.74 15.37 16.07

T/K 0.227b 303.85 306.56 309.18 311.99 314.42 317.23 320.32 322.94 0.227c 303.85 306.75 309.56 311.61 314.52 317.32 320.23 322.94 0.227d 303.94 306.47 309.27 312.08 314.80 317.70 320.23 323.03

P/MPa 9.06 9.94 10.59 11.52 12.29 13.09 14.02 14.79 8.83 9.74 10.59 11.28 12.08 12.80 13.69 14.49 8.62 9.55 10.36 11.36 12.39 13.18 13.88 14.58

a

m is the concentration of Ls-36 ethanol solution. Standard uncertainties u are u(T) = ± 0.01 K, u(m) = ± 0.005 mol·kg−1, and the combined expanded uncertainty Uc is Uc(P) = ± 0.04 MPa (level of confidence = 0.95, where k = 2). b0.025 mass fraction 1,3-PDO dilute aqueous solution was added. c0.050 mass fraction 1,3-PDO dilute aqueous solution was added. d0.075 mass fraction 1,3-PDO dilute aqueous solution was added.

a

W0 is the water-to-Ls-36 molar ratio. Standard uncertainties u are u(T) = ± 0.01 K, u(W0) = ± 0.05, u(m) = ± 0.005 mol·kg−1, and the combined expanded uncertainty Uc is Uc(P) = ± 0.04 MPa (level of confidence = 0.95, where k = 2).

temperature.28 The reason for the decrease of the cloud-point pressure in presence of EtOH is that EtOH can increase the bulk density of the mixture and the polarity of scCO2, which are favorable to promote the solubility of Ls-36 in scCO2. Moreover, the attractive polar interactions between Ls-36 and ethanol and the hydrogen bonding among the head groups (EO and PO) in Ls-36 and the OH group in the ethanol are strong and beneficial to decreasing the cloud-point pressure. 3.2. Phase Behavior of the Ls-36 + CO2 + EtOH + H2O System. It is known that the water concentration is one of the most important variables affecting the cloud point pressures of the system and the size of the reverse micelle, both of which determine the solubilization capability of the W/C microemulsion for polar substances. It is therefore of importance to investigate the effect of the amount of water on the phase behavior of Ls-36 + CO2 + EtOH + H2O microemulsion system. To determine the suitable amount of water, several experiments were carried out at a fixed Ls-36 and ethanol while

Figure 2. Cloud-point curves for the Ls-36 + CO2 + EtOH ternary system with different Ls-36 ethanol solution concentrations. Ls-36 ethanol solution concentration: red ●, 0.454 mol·kg−1; blue ▲, 0.681 mol·kg−1; green ▼, 1.362 mol·kg−1; ■, without EtOH (Ls-36 + CO2 system).

varying the amount of water. A key property of reverse micelles is water-to-Ls-36 molar ratio, W0 ([H2O]/[Ls-36]), which shows the number of water molecules that can be held by a surfactant molecule. The effect of water concentration on the phase transition pressure of the Ls-36 + CO2 + EtOH + H2O system was investigated at different W0 values, with the 816



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standard uncertainty u is u(W0) = ± 0.05. The results are listed in Table 3. The cloud-point pressure curves of microemulsion with various W0 values in the presence of scCO2 are shown in Figure 3. A transparent single phase could be observed in the

The P−T phase diagrams of the quinary Ls-36 + CO2 + EtOH + 1,3-PDO + H 2 O system at different Ls-36 concentrations and 1,3-PDO concentrations are shown in Figure 4. Figure 4 also shows the dependence of the cloud

Figure 3. Relationships between the cloud-point pressures and the W0 value for the Ls-36 + CO2 + EtOH + H2O quaternary system at 0.227 mol·kg−1 Ls-36 EtOH solution. W0 value: ■, 5.6; red ●, 7.8; blue ▲, 10.0; green ▼, 12.2; pink ◀, 14.4.

region above the solid lines at each condition, while a phase separation occurred at conditions below the lines, as indicated by a new liquid phase adhered to the surfaces of the windows and inner wall of the cell. As can be seen in Figure 3, the solid lines show that the cloud point pressures increased greatly from 7.81 MPa to 9.93 MPa as the W0 increased from 5.6 to 14.4 at 303.66 K. This result indicates enhanced solubilization of water in the system, which is consistent with the results obtained in AOT + CO2 + decane reverse micelle system.32 According to Koper et al.,33 the hydrodynamic radius of the droplets can be calculated as follows: 3ν W0 + δ rh = as (1)

Figure 4. Cloud-point pressures for the Ls-36 + CO2 + EtOH + 1,3PDO + H2O system with at different concentrations of Ls-36 ethanol solution. Ls-36 EtOH solution concentration: blue ▲, 0.227 mol·kg−1; red ●, 0.454 mol·kg−1; ■, 0.681 mol·kg−1. 1,3-PDO aqueous solution concentration: a, 0.025 mass fraction; b, 0.050 mass fraction; c, 0.075 mass fraction.

point pressure on the molar amount of Ls-36 at each fixed concentration of 1,3-PDO. The cloud-point pressures increased linearly with the Ls-36 concentration (Figure 4a−c). This will provide a convenient way for predicting the cloud-point pressures through the concentration of Ls-36 and thus can simplify greatly the operation in the measurement. The more Ls-36 is added, the higher cloud-point pressure the system has. It is due to that more CO2 is needed to dissolve more Ls-36 molecules. Meanwhile, a higher pressure is also needed to form a stable microemulsion. To the contrary, the decrease in the Ls36 concentration is unfavorable to the formation of micelle and thus will decrease the cloud-point pressure. The phase behaviors of the Ls-36 + CO2 + EtOH + H2O + 1,3-PDO system and the Ls-36 + CO2 + EtOH + H2O system were studied in an effort to use scCO2 microemulsion for the extraction of 1,3-PDO from dilute aqueous solution. The cloud point pressures of the Ls-36 + CO2 + EtOH + H2O + 1,3-PDO system and the Ls-36 + CO2 + EtOH + H2O system were measured as a function of the concentrations of the surfactant Ls-36 and 1,3-PDO. To reveal the selectively dissolving power of the W/C microemulsion, the cloud point pressures of Ls-36 + CO2 + EtOH + H2O system with 0.957 mol·L−1 EtOH at W0 = 7.8 were compared with that of the Ls-36 + CO2 + EtOH + H2O + 1,3-PDO system at the same compositions but various concentrations of 1,3-PDO aqueous solutions (from 0.025 to 0.075 mass fraction). The concentration of Ls-36 varies from 0.01 mol·L−1 to 0.03 mol·L−1. As can be seen from Figure 5 (1), (2), (3), a transparent phase solution was formed above the solid line at each investigated condition. The cloud-point pressures of the quinary system Ls-36 + CO2 + EtOH + H2O + 1,3-PDO were lower than those of the quaternary system Ls-36

where v is the molecular volume of the water (3.0 × 10−29 m3), as is the area occupied by one surfactant molecule at the interface between the water core and the surfactant monolayer, and δ is the thickness of the surfactant monolayer. According to the eq 1, the value of rh is proportional to the W0 value, that is, the size of the micellar core increases with the increase of W0 at a constant concentration of the surfactant. Nevertheless, considering the limited solubilization capability of the scCO2 microemulsion of water and the increasing tendency of the cloud point pressure with W0, the optimum W0 is determined to be 7.8 (0.0755 mL of H2O) for the quaternary microemulsion system of Ls-36 + CO2 + EtOH + H2O. 3.3. Phase Behavior of the Ls-36 + CO2 + EtOH + 1,3PDO + H2O System. To simulate the real fermentation broth and identify the influence of the concentration of 1,3-PDO on the phase behavior of the Ls-36 + CO2 + EtOH + 1,3-PDO/ H2O system, various concentrations of 1,3-PDO dilute aqueous solutions (0.025, 0.050, and 0.075 mass fraction) were prepared as a model system. To study whether the Ls-36 + CO2 + EtOH microemulsion system can selectively solubilize 1,3-PDO from its dilute solution or not, the phase behaviors of the quaternary Ls-36 + CO2 + EtOH + H2O system and the quinary Ls-36 + CO2 + EtOH + 1,3-PDO + H2O system were investigated at temperature range from 303.05 K to 323.25 K by fixing the water amount (0.0755 mL) while varying the concentrations of 1,3-PDO (0.025, 0.050, and 0.075 mass fraction). 817



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Figure 5. Selective solubilization of different mass concentrations of 1,3-PDO aqueous solution in Ls-36 + CO2 + EtOH + 1,3-PDO + H2O system. ■, Ls-36 + CO2 + EtOH + 1,3-PDO + H2O system; red ●, Ls-36 + CO2 + EtOH + H2O system. Ls-36 ethanol solution concentration: a, 0.227 mol·kg−1; b, 0.454 mol·kg−1; c, 0.681 mol·kg−1. 1,3-PDO aqueous solution concentration: (1) 0.025 mass fraction; (2) 0.050 mass fraction; (3) 0.075 mass fraction.

+ CO2 + EtOH + H2O at the same Ls-36 concentration and temperature, demonstrating that 1,3-PDO can be solubilized easier than water at the same conditions. Thus, the Ls-36 + CO2 + EtOH + H2O + 1,3-PDO system can selectively extract 1,3-PDO from water at appropriate operating pressures. A scheme diagram is given to illustrate the selective dissolving power of the quinary microemulsion for 1,3-PDO (Scheme 1). Moreover, it is obvious that the difference of the cloud-point pressures between the two systems became more prominent with an increase of the Ls-36 concentration at a constant W0 value. In other words, at higher Ls-36 concentrations, the increment of cloud-point pressure in the Ls-36 + CO2 + EtOH + H2O system is much more than that in the Ls-36 + CO2 + EtOH + H2O + 1,3-PDO system. This behavior may indicate that a higher Ls-36 concentration is favorable to separate 1,3PDO from water. Furthermore, the lower cloud-point pressure of the Ls-36 + CO2 + EtOH + H2O + 1,3-PDO system implies

Scheme 1. Schematic Diagrams to Illustrate the Structures of Reverse Micelle. a, Ls-36 + CO2 + EtOH System; b, Ls-36 + CO2 + EtOH + H2O System; c, Ls-36 + CO2 + EtOH + 1,3PDO + H2O System

that this system possess a greater ability to decrease interfacial tension between water and scCO2. In other words, the Ls-36 + CO2 + EtOH + H2O + 1,3-PDO system more easily forms a microemulsion than the Ls-36 + CO2 + EtOH + H2O system. 818



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(10) Pourmortazavi, S. M.; Hajimirsadeghi, S. S.; Kohsari, I.; Hosseini, S. G. Orthogonal Array Design for the Optimization of Supercritical Carbon Dioxide Extraction of Different Metals from a Solid Matrix with Cyanex 301 as a Ligand. J. Chem. Eng. Data 2004, 49, 1530−1534. (11) Ruiz-Rodriguez, A.; Fornari, T.; Hernández, E. J.; Señorans, F. J.; Reglero, G. Thermodynamic modeling of dealcoholization of beverages using supercritical CO2: Application to wine samples. J. Supercrit. Fluids 2010, 52, 183−188. (12) Consani, K. A.; Smith, R. D. Observations of the solubility of surfactants and related molecules in carbon dioxide at 50 °C. J. Supercrit. Fluids 1990, 3, 51−65. (13) Gale, R. W.; Fulton, J. L.; Smith, R. D. Organized molecular assemblies in the gas phase: reverse micelles and microemulsions in supercritical fluids. J. Am. Chem. Soc. 1987, 109, 920−921. (14) Eastoe, J.; Downer, A.; Paul, A.; Steytler, D. C.; Rumsey, E.; Penfold, J.; Heenan, R. K. Fluoro-surfactants at air/water and water/ CO2 interfaces. Phys. Chem. Chem. Phys. 2000, 2, 5235−5242. (15) Zhang, J.; Liu, J.; Gao, L.; Zhang, X.; Hou, Z.; Han, B.; Wang, J.; Dong, B.; Rong, L.; Zhao, H. Small-angle X-ray scattering study on correlation length and density fluctuations in a supercritical CO2-water mixture. Fluid Phase Equilib. 2002, 198, 251−256. (16) Zhou, D.; Yu, W.; Xu, Q.-Q.; Yin, J.-Z. Solubilization of Polyalcohol in Supercritical CO2 Microemulsion. Acta Phys.-Chim. Sin. 2011, 27, 1300−1304. (17) Mohamed, A.; Sagisaka, M.; Hollamby, M.; Rogers, S. E.; Heenan, R. K.; Dyer, R.; Eastoe, J. Hybrid CO2-philic Surfactants with Low Fluorine Content. Langmuir 2012, 28, 6299−6306. (18) Johnston, K. P.; Harrison, K. L.; Clarke, M. J.; Howdle, S. M.; Heitz, M. P.; Bright, F. V.; Carlier, C.; Randolph, T. W. Water in carbon dioxide microemulsions: An environment for hydrophiles including proteins. Science 1996, 271, 624−626. (19) Yin, J.-Z.; Wang, A.-Q.; Wei, W.; Liu, Y.; Shi, W.-H. Analysis of the operation conditions for supercritical fluid extraction of seed oil. Sep. Purif. Technol. 2005, 43, 163−167. (20) Zhou, D.; Yu, W.; Yin, J.-Z. Selective Solubilization of Propane1,3-diol from Dilute Aqueous Solution Using Supercritical CO2 Microemulsion. J. Chem. Eng. Data 2012, 57, 1787−1793. (21) Bunker, C. E.; Rollins, H. W.; Gord, J. R.; Sun, Y.-P. Efficient Photodimerization Reaction of Anthracene in Supercritical Carbon Dioxide. J. Org. Chem. 1997, 62, 7324−7329. (22) Ohde, H.; Ohde, M.; Bailey, F.; Kim, H.; Wai, C. M. Water-inCO2 Microemulsions as Nanoreactors for Synthesizing CdS and ZnS Nanoparticles in Supercritical CO2. Nano Lett. 2002, 2, 721−724. (23) Yin, J.-Z.; Tan, C.-S. Solubility of hydrogen in toluene for the ternary system H2 + CO2 + toluene from 305 to 343 K and 1.2 to 10.5 MPa. Fluid Phase Equilib. 2006, 242, 111−117. (24) Ji, M.; Chen, X.; Wai, C. M.; Fulton, J. L. Synthesizing and Dispersing Silver Nanoparticles in a Water-in-Supercritical Carbon Dioxide Microemulsion. J. Am. Chem. Soc. 1999, 121, 2631−2632. (25) Zhang, J.; Liu, Z.; Han, B.; Jiang, T.; Wu, W.; Chen, J.; Li, Z.; Liu, D. Preparation of Polystyrene-Encapsulated Silver Nanorods and Nanofibers by Combination of Reverse Micelles, Gas Antisolvent, and Ultrasound Techniques. J. Phys. Chem. B 2004, 108, 2200−2204. (26) Shimizu, R.; Nibe, A.; Sawada, K.; Enokida, Y.; Yamamoto, I. Preparation of hydrophobic platinum catalysts using a water-in-CO2 microemulsion. J. Supercrit. Fluids 2008, 44, 109−114. (27) Xu, Q.-Q.; Zhang, C.-J.; Zhang, X.-Z.; Yin, J.-Z.; Liu, Y. Controlled synthesis of Ag nanowires and nanoparticles in mesoporous silica using supercritical carbon dioxide and co-solvent. J. Supercrit. Fluids 2012, 62, 184−189. (28) Liu, J. C.; Han, B. X.; Wang, Z. W.; Zhang, J. L.; Li, G. Z.; Yang, G. Y. Solubility of Ls-36 and Ls-45 surfactants in supercritical CO2 and loading water in the CO2/water/surfactant systems. Langmuir 2002, 18, 3086−3089. (29) Chennamsetty, N.; Bock, H.; Scanu, L. F.; Siperstein, F. R.; Gubbins, K. E. Cosurfactant and cosolvent effects on surfactant selfassembly in supercritical carbon dioxide. J. Chem. Phys. 2005, 122, 094710.

4. CONCLUSION The phase behavior of a scCO2 microemulsion of the quaternary Ls-36 + CO2 + EtOH + H2O system and the quinary Ls-36 + CO2 + EtOH + 1,3-PDO + H2O system were investigated in the volume-variable high-pressure view cell at a temperature range of 303.05 K to 323.25 K and at pressures of 7.81 MPa to 18.99 MPa. The W/C microemulsion was stabilized by the nonfluorous and nonsilicon nonionic surfactant Ls-36 and cosolvent ethanol. At each experimental condition, a transparent phase solution was observed, including both water and 1,3-PDO can be dissolved in the microemulsion. Moreover, at appropriate temperatures and pressures, 1,3-PDO can be easier to dissolve in the polar core of scCO2 microemulsion than water, which made it possible to the aim to selectively extract 1,3-PDO from dilute aqueous solution using scCO2 microemulsion. More intriguing, the cloud-point pressure difference of the two systems became more prominent with increasing the concentration of Ls-36 at a constant W0 value, implying a higher concentration of Ls-36 would be beneficial to separate 1,3-PDO from its dilute aqueous solution. The results obtained in this work might be useful to biotechnology industrial applications.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel./Fax: +86-411-84986274. Funding

The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (20976026, 20976028). Notes

The authors declare no competing financial interest.

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REFERENCES

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Phase Behavior of Supercritical CO2 Microemulsions with Surfactant

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