High-pressure phase behaviour of poly(d -lactic acid), trichloromethane, and carbon dioxide ternary mixture systems

J. Chem. Thermodynamics 90 (2015) 216–223

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High-pressure phase behaviour of poly(D-lactic acid), trichloromethane, and carbon dioxide ternary mixture systems Taehyun Im a, JungMin Gwon a, Soo Hyun Kim b, Hun Yong Shin c, Hwayong Kim a,⇑ a Brain Korea 21 Program in Chemical Engineering, School of Chemical and Biological Engineering, and Institute of Chemical Processes, Seoul National University, 559 Gwanangno, Gwanak-gu, Seoul 151-744, Republic of Korea b Korea Institute of Science and Technology, 39-1 Hawolgok-dong, Seongbuk-gu, Seoul 136-791, Republic of Korea c Department of Chemical and Biological Engineering, Seoul National University of Science and Technology, 172, Gongneung 2-dong, Nowon-gu, Seoul 139-743, Republic of Korea

a r t i c l e

i n f o

Article history: Received 16 March 2015 Received in revised form 22 June 2015 Accepted 23 June 2015 Available online 3 July 2015 Keywords: Poly(D-lactic acid) Supercritical carbon dioxide (Polymer + solvent + gas) ternary systems The hybrid equation of state for (CO2 + polymer) system Biodegradable polymer

a b s t r a c t The high pressure phase behaviour of poly(D-lactic acid) (Mw = 359,000), trichloromethane, and carbon dioxide ternary mixture systems is presented in this study. Cloud and bubble point pressures were measured using a variable volume view cell at temperatures (313.15 to 363.15) K and pressures up to 33.6 MPa. The hybrid equation of state for the polymer-carbon dioxide system was used to correlate the experimental results. The van der Waals one-fluid mixing rule with three adjustable binary interaction parameters was used for all correlations. The binary parameters were optimised using the simplex method algorithm. Ó 2015 Published by Elsevier Ltd.

1. Introduction Poly(D-lactic acid) (PDLA) is a biodegradable plastic polymer. PDLA is a representative polymer produced from bio-based resources [1], and is used in packaging and biomedical application, such as flexible film packaging, cold drink cups, implants and biocompatible sutures. The general method to obtain PDLA is by lactide ring-opening polymerization with metal catalysts, such as Sn(II), in the melt, solution, or as a suspension [2]. Supercritical fluids (SCFs) are commonly employed to synthesize and develop PDLA. A SCF is a fluid above its critical pressure and temperature. Studying processes with SCFs has occurred because of its wide range of applications, such as (liquid + solid) extraction, impregnation [3], tailoring of chemical characteristics of materials [4]. Carbon dioxide is the most widely used SCF because of its low critical temperature (304.12 K) [5], non-flammability, non-toxicity and inexpensiveness [6]. Thus, CO2 is the most studied and common SCF. In this study, trichloromethane was used as the solvent to dissolve PDLA because CO2 cannot dissolve easily the high molar mass polymer. The solubility

⇑ Corresponding author. Tel.: +82 2 880 7406; fax: +82 2 888 6695. E-mail address: [email protected] (H. Kim). http://dx.doi.org/10.1016/j.jct.2015.06.033 0021-9614/Ó 2015 Published by Elsevier Ltd.

of the polymer in CO2 was increased by adding trichloromethane. Proper thermodynamic models for (PDLA + solvent + CO2) are needed to determine the best operating conditions for various PDLA processes. In this study, the phase behaviour of PDLA, trichloromethane, and carbon dioxide ternary mixture systems is presented. Experimental values were obtained using a variable volume view cell at temperatures (313.15 to 363.15) K and pressures up to 33.6 MPa. We correlated the experimental results with the hybrid equation of state [7] using the van der Waals one-fluid mixing rule with three binary interaction parameters.

2. Experimental 2.1. Materials PDLA (M = 359,000; polydispersity, 1.7) was synthesized by the Korea Institute of Science and Technology and was used without further purification. PDLA polydispersity and molar mass were measured by gel permeation chromatography. Trichloromethane (minimum purity, 99.9 mol%) was supplied by Sigma–Aldrich (St Louis, MO, USA). Carbon dioxide was purchased from Korea Industrial Gases (Seoul, Korea), and its minimum purity was 99.999 mol%. Table 1 lists the properties of the pure components.

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T. Im et al. / J. Chem. Thermodynamics 90 (2015) 216–223 TABLE 1 The properties of pure components. Material

Molar mass

Poly(D-lactic acid)

359,000

Molecular structure

O O

CH

H

119.377

Cl

Carbon dioxide

44.01

C

Cl O@C@O

1.686

C CH3

Trichloromethane

Polydispersity

n 0.999

Cl

0.99999

2.2. Apparatus and procedure The experimental results were obtained using a high pressure apparatus equipped with a variable volume view cell, which has been described previously [8–11]. The apparatus consisted of a view cell equipped with a pressure generator (model 62-6-10; High Pressure Equipment Co., Erie, PA, USA), a camera (model CVC5520; Veltek International, Inc., Shrewsbury, MA, USA), a borescope (Model R100-038-00-50; Olympus Corp., Tokyo, Japan), a sapphire window, and a monitor. Temperature and pressure were determined by a PRT type thermometer (model 5622-32SR; accuracy, ±0.045 K; Hart Scientific, Inc., Everett, WA, USA) and a pressure transducer (model TJE/Redlion PAXS0000; accuracy, 0.1%; Honeywell International Inc., Morristown, NJ, USA). Their values were displayed by a temperature indicator (model 1502; Hart Scientific) and a pressure indicator (model PAXP0000; Red Lion Controls Inc., York, PA, USA). The thermometer and pressure transducer were calibrated by the national calibration laboratory of the Republic of Korea, the Korea Testing Laboratory. A magnetic stirring bar was used to agitate the mixture in the cell. The advantages of this equipment are the short measurement time and suitability at very high pressures. Figure 1 shows a diagram of a typical variable volume view cell. The phase behaviour measurement for the (PDLA + trichloromethane + CO2) ternary system was conducted using the following procedures. First, a predetermined mass of

PDLA was inserted into the variable volume view cell to an accuracy of ±0.001 g with a pair of tweezers. The trichloromethane was added to the cell to an accuracy of ±0.001 g with a syringe. The cell was purged three times with CO2 at room temperature to eliminate air and chemical impurities, and a predetermined quantity of CO2 was fed into the cell. A high pressure bomb was used to inject CO2 into the cell to an accuracy of ±0.01 g. Total weight of the three components was 8 g per experiment. When cell temperature reached the desired value, a high-pressure generator was turned on to increase cell pressure until a single phase was formed. After reaching a single homogeneous phase, system pressure was decreased by a pressure generator until a phase transition was observed. At this point, the pressure was recorded as the cloud or bubble point pressure. Then, the temperature of the mixture was increased at intervals of 10 K, and cell pressure was increased to reach a homogeneous phase again. This procedure was continued until the phase transition pressure differed by <±0.04 bar, and the experimental results were obtained by averaging the last three pressures.

3. Thermodynamic models The hybrid equation of state was applied to the (polymer + CO2) system using the van der Waals one-fluid mixing rule to correlate the experimental results. The pure parameters of all components are needed to correlate conventional thermodynamic models, such as the Peng–Robinson equation of state (PR-EOS) and the perturbed-chain statistical associating fluid theory in the (PDLA + trichloromethane + CO2) system; however, that of PDLA is not available. This is the main reason for using the hybrid equation of state. The major advantage of this equation of state is that it does not require polymer properties, such as critical temperature, critical pressure, and acentric factor, but does require molar mass and the estimated pure polymer parameters from the experimental values. The compressibility factor of the hybrid EOS is expressed as the sum of three terms.

Z ¼ Z PR þ Z assoc þ Z chain :

ð1Þ

The first two terms are used for trichloromethane and pure CO2, and the first and third terms are used for the polymers. The compressibility factor from the PR-EOS [12] is determined by the following cubic equation.

Z 3PR  ð1  BÞZ 2PR þ ðA  3B2  2BÞZ PR  ðAB  B2  B3 Þ ¼ 0;

ð2Þ

where

A¼

aP R2 T 2

ð3Þ

;

TABLE 2 The parameters of the materials for the hybrid equation of state.

FIGURE 1. Schematic diagram of the variable volume view cell (VVVC) apparatus: (1) camera; (2) light source; (3) borescope; (4) thermocouple; (5) magnetic stirrer; (6) air bath; (7) view cell; (8) digital thermometer; (9) digital pressure indicator; (10) digital pressure transducer; (11) pressure gauge; (12) hand pump; (13) monitor.

Material

Parameters of macromolecule

Poly(D-lactic acid)

a0i /(J  m3) b0/(cm3  mol1) C M

Material

Trichloromethane Carbon dioxide

13.4593 0.11492 0.00122 2296.25

Critical constants TC/K

PC/MPa

x

536.50 [14] 304.12 [5]

5.500 [14] 7.374 [5]

0.229 [14] 0.225 [5]

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T. Im et al. / J. Chem. Thermodynamics 90 (2015) 216–223

TABLE 3 Experimental values for the {PDLA(1) + Trichloromethane(2) + CO2(3) system}.a Mass fractionb

T/K

P/MPa

Transitionc

w0 2 0.700 w0 3 0.300

363.15 353.15 343.15 333.15 323.15 313.15

9.012 8.242 7.389 6.597 5.815 5.135

BP BP BP BP BP BP

w0 2 0.649 w0 3 0.351

363.15 353.15 343.15 333.15 323.15 313.15

11.784 8.792 7.903 6.975 6.105 5.282

CP BP BP BP BP BP

w0 2 0.598 w0 3 0.402

363.15 353.15 343.15 333.15 323.15 313.15

18.875 15.353 11.496 7.540 6.520 5.668

CP CP CP CP BP BP

w0 2 0.550 w0 3 0.450

363.15 353.15 343.15 333.15 323.15 313.15

26.581 22.861 19.160 15.251 11.075 6.666

CP CP CP CP CP CP

w0 2 0.501 w0 3 0.499

363.15 353.15 343.15 333.15 323.15 313.15

32.286 28.485 24.625 20.650 16.310 11.685

CP CP CP CP CP CP

w0 2 0.693 w0 3 0.307

363.15 353.15 343.15 333.15 323.15 313.15

8.835 7.997 7.321 6.474 5.658 5.031

BP BP BP BP BP BP

w0 2 0.644 w0 3 0.356

363.15 353.15 343.15 333.15 323.15 313.15

13.952 10.521 8.233 7.387 6.551 5.770

CP CP BP BP BP BP

w0 2 0.601 w0 3 0.399

363.15 353.15 343.15 333.15 323.15 313.15

18.250 14.762 11.552 7.690 6.450 5.450

CP CP CP CP BP BP

w0 2 0.564 w0 3 0.436

363.15 353.15 343.15 333.15 323.15 313.15

23.115 20.032 16.452 12.600 8.529 6.231

CP CP CP CP CP BP

w0 2 0.499 w0 3 0.501

363.15 353.15 343.15 333.15 323.15 313.15

33.632 29.977 26.284 22.020 17.775 13.329

CP CP CP CP CP CP

w0 2 0.697 w0 3 0.303

363.15 353.15 343.15 333.15 323.15 313.15

9.168 8.478 7.675 6.814 6.055 5.248

BP BP BP BP BP BP

Polymer mass fraction (w1) = 0.01

Polymer mass fraction (w1) = 0.02

Polymer mass fraction (w1) = 0.03

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T. Im et al. / J. Chem. Thermodynamics 90 (2015) 216–223 TABLE 3 (continued) Mass fractionb

T/K

P/MPa

Transitionc

w 2 0.644 w0 3 0.356

363.15 353.15 343.15 333.15 323.15 313.15

15.818 12.409 8.780 7.562 6.590 5.723

CP CP CP BP BP BP

w0 2 0.603 w0 3 0.397

363.15 353.15 343.15 333.15 323.15 313.15

18.725 15.900 12.307 8.484 7.251 6.359

CP CP CP CP BP BP

w0 2 0.550 w0 3 0.450

363.15 353.15 343.15 333.15 323.15 313.15

26.608 23.190 19.547 15.565 11.298 6.950

CP CP CP CP CP CP

w0 2 0.500 w0 3 0.500

363.15 353.15 343.15 333.15 323.15 313.15

33.241 29.885 26.266 22.165 17.805 13.421

CP CP CP CP CP CP

0

a b c

Standard uncertainties u are u(T) = ±0.080 K, u(P) = ±0.0064 MPa, and u(w) = ±0.0013 [15,16]. w1 (PDLA), w0 2 (trichloromethane) and w0 3 (CO2) are mass fractions; w0 2 and w0 3 are calculated on a polymer-free basis. BP : bubble-point (L–V transition), CP : cloud point (L–L transition).

TABLE 4 Calculation results with the hybrid equation of state. Mass fraction of PDLA

k12

k13

k23

AADP (%)

0.01 0.02 0.03

0.01322 0.01160 0.03966

0.94345 0.50696 0.19035

0.01777 0.01072 0.10442

4.00 4.37 3.18

where q is the density of the associating molecules, XS is the mole fraction of the associating molecules not bonded at site S, and the sum is over all binding sites of the associating molecules. The compressibility factor for the chain connectivity of the polymer is calculated by:

Z chain ¼

X xi ð1  mi Þ

"

g hs ii ðdii Þ

f3 2

þ

ð1  f3 Þ # 2 3 dii f22 f3 ; þ þ ð1  f3 Þ2 2 ð1  f3 Þ4 i

3 dii f2 3dii f2 f3 þ 2 ð1  f3 Þ2 ð1  f3 Þ3

2

B¼

dii f22

bP : RT

ð4Þ

ð10Þ

The mixture parameters used in the PR-EOS were calculated with the van der Waals one-fluid mixing rule:

a¼

XX xi xj aij ; i

ð5Þ

TABLE 5 Comparisons between the experimental and replicated resultsa.

j

X b¼ xi b i ;

ð6Þ

i

aij ¼ ðai aj Þ1=2 ð1  kij Þ:

ð7Þ

The critical properties of the polymer, such as critical temperature (TC), pressure (PC), and the acentric factor (x), are essential to obtain the PR-EOS compressibility factor, but they are scarce, and those of PDLA, which was the polymer used here this work, is not available. The following empirical equation was employed to estimate the van der Waals energy parameter (ai).

ai ¼ a0i expðC i TÞ;

ð8Þ

where a0i and Ci were obtained by fitting the experimental results to obtain the PR-EOS excluded volume (bi) parameter. The second term of equation (1), the compressibility factor for the associating effect, is:

X 1

Z assoc ¼ q

S

X

S





1 @X S ; 2 @q

ð9Þ

a

Polymer mass fraction (w1) = 0.01

Experimental values

Replicates

Mass fractionb

T (K)

P (bar)

Transitionc

P (bar)

Transitionc

w0 2 0.700 w0 3 0.300

363.15 353.15 343.15 333.15 323.15 313.15

90.12 82.42 73.89 65.97 58.15 51.35

BP BP BP BP BP BP

90.15 82.42 73.85 65.94 58.11 51.37

BP BP BP BP BP BP

Polymer mass fraction (w1) = 0.03

Experimental data

Replicates

Mass fractionb

T/K

P (bar)

Transitionc

P (bar)

Transitionc

w0 2 0.550 w0 3 0.450

363.15 353.15 343.15 333.15 323.15 313.15

26.608 23.190 19.547 15.565 11.298 6.950

CP CP CP CP CP CP

26.602 23.185 19.542 15.564 11.297 6.952

CP CP CP CP CP CP

Standard uncertainties u are u(T) = ±0.080 K, u(P) = ±0.0063 MPa and u(w) = ±0.0013 [15,16]. b w1 (PDLA), w0 2 (trichloromethane) and w0 3 (CO2) are mass fractions; w0 2 and w0 3 are calculated on a polymer-free basis. c BP: bubble-point (L–V transition), CP : cloud point (L–L transition).

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350 300

10 P/MPa

250 200 150 100 50 0 310

320

330

340

350

360

370

T/K FIGURE 2. Experimental data and calculated results using the hybrid equation of state for PDLA (mass fraction w1 = 0.01) + trichloromethane + CO2 system. Mass fractions of CO2 in the mixed solvent on a polymer-free basis: j, 0.499; 4, 0.450; ., 0.402; s, 0.351; d, 0.300; Solid lines, the calculations with the hybrid EOS.

400 350 300

10 P/MPa

250 200 150 100 50 0 310

320

330

340

350

360

370

T/K FIGURE 3. Experimental data and calculated results using the hybrid equation of state for PDLA (mass fraction w1 = 0.02) + trichloromethane + CO2 system. Mass fractions of CO2 in the mixed solvent on a polymer-free basis: j, 0.501; 4, 0.436; ., 0.399; s, 0356; d, 0.307; Solid lines, the calculations with the hybrid EOS.

where xi is the mole fraction of polymer i, mi is the number of polymer segments, dii is the effective molecular diameter, and f is the reduced density. The parameter mi is optimised by the experimental results. The parameter gii is the radial distribution function for a pair of polymer segments and is given by the following equation:

g hs ii ðdii Þ ¼

 2 1 3dii f2 dii f22 þ þ 2 ; 2 ð1  f3 Þ2 2 ð1  f3 Þ3 1  f3

ð11Þ

where fk ¼

pNA X q X i mi dkii : 6

ð12Þ

i

The polymer parameters (a0i , Ci, bi, mi), the critical constants (TC, PC, x) for the hybrid EOS, and the binary interaction parameter kij used in the one-fluid mixing rule were estimated using the simplex method algorithm and the experimental data. They are shown in tables 2 and 4.

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T. Im et al. / J. Chem. Thermodynamics 90 (2015) 216–223

4. Results and discussion Table 3 shows the phase separation data for the (PDLA + trichloromethane + CO2) system measured at temperatures (313.15 to 363.15) K and for various initial trichloromethane/CO2 loadings. The measurements were conducted at PDLA mass fractions of 0.01, 0.02, and 0.03, respectively. Two replicates were performed to validate the apparatus and their conditions were chosen randomly. The comparisons between the

experimental and replicated data are shown in table 5. No precipitation of PDLA was generated during the experiment and it could be confirmed visually through VVVC. The bubble point, which is the L–V phase transition, or the cloud point, which is the L–L transition, occurs depending on the mixture composition and temperature. When the temperature and mass fraction of CO2 are relatively low, the bubble points occur dominantly. However, as the temperature and CO2 mass fraction increase, cloud points are observed more frequently than bubble points. This observation is

350 300

10 P/MPa

250 200 150 100 50 0 310

320

330

340

350

360

370

T/K FIGURE 4. Experimental data and calculated results using the hybrid equation of state for PDLA (mass fraction w1 = 0.03) + trichloromethane + CO2 system. Mass fractions of CO2 in the mixed solvent on a polymer-free basis: j, 0.500; 4, 0.450; ., 0.397; s, 0.356; d, 0.303; Solid lines, the calculations with the hybrid EOS.

350 300

10 P/MPa

250 200 150 100 50 0 0.25

0.30

0.35

0.40

0.45

0.50

0.55

Mass fraction of CO2 FIGURE 5. Effect of CO2 mass fraction in a mixed solvent on bubble and cloud point pressures of PDLA (mass fraction w1 = 0.01) at various temperatures: d, 313.15 K; s, 323.15 K; ., 333.15 K; 4, 343.15 K; j, 353.15 K; h, 363.15 K.

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consistent with the study of Bungert et al. [13], which described this phenomenon using the concept of the lower critical solution temperature behaviour of (polymer + solvent + gas) systems. The P–T isopleths for the three different PDLA mass fractions are shown in figures 2–4. Agreement between the experimental and correlated data was relatively unsatisfactory when shifts from the bubble point to the cloud point occurred because the slopes between adjacent points increased dramatically in this region. When the system temperature is close to the critical point of the solvent and relatively far from the hypothetical critical point of the

polymer, the difference in temperature dependence of volume between the solvent and polymer leads to a dramatic increase in phase separation pressure. In this case, the cloud point (L–L transition) occurs. On the other hand, when the system temperature is relatively lower than the above-mentioned temperature, a decrease of the difference of the temperature dependence of the increase in volume between the solvent and the polymer causes a less dramatic increase in phase separation pressure and the bubble point (L–V transition) occurs. So when the above-mentioned temperature is reached, the jumps in the isopleths appeared. In

300

10 P/MPa

250

200

150

100

50 0.25

0.30

0.35

0.40

0.45

0.50

0.55

Mass fraction of CO2 FIGURE 6. Effect of CO2 mass fraction in constant temperature (T = 343.15 K) on the phase separation pressure at various PDLA mass fraction (w1): d, 0.01; s, 0.02; ., 0.03.

350 300

10 P/MPa

250 200 150 100 50 0 0.45

0.50

0.55

0.60

0.65

0.70

0.75

Mass fraction of Trichloromethane FIGURE 7. Effect of trichloromethane mass fraction in a mixed solvent on phase separation pressures of PDLA (mass fraction w1 = 0.03) at various temperatures: d, 313.15 K; s, 323.15 K; ., 333.15 K; 4, 343.15 K; j, 353.15 K; h, 363.15 K.

T. Im et al. / J. Chem. Thermodynamics 90 (2015) 216–223

this region, the differences of slopes between three adjacent points make a cusp in the isopleths, so the hybrid equation of state has difficulty to interpret the experimental data. Figures 5 and 6 present the effect of the CO2 mass ratio, which demonstrates that an increase in the CO2 mass fraction causes a corresponding increase in phase separation pressure. Figure 7 shows that as the trichloromethane mass fraction increases, the phase separation pressure decreases at constant temperature. We conclude from figures 5– 7 that trichloromethane is a good solvent, but CO2 is not. The correlated results for the hybrid EOS were compared with the experimental values in figures 2–4. The objective function (OBF) and the absolute average deviation of pressure (AADP) percent for the correlation are defined by:

  cal  N  exp X P i  Pi  OBF ¼ ;    P exp i i¼1 PN AADPð%Þ ¼

exp i¼1 jðP i

ð13Þ exp  P cal i Þ=P i j  100; N

ð14Þ

where N equals the number of experimental data points, and Pexp and Pcal are the experimental and correlated pressures, respectively. The calculated results, the adjusted binary interaction parameters k12, k13, k23, and the AADP (%) for the (PDLA + trichloromethane + CO2) system with the hybrid EOS are shown in table 4. The AAPD (%) values were 4.00 for wt 1.0%, 4.37 for wt 2.0%, and 3.18 for wt 3.0%. 5. Conclusions The phase behaviour of PDLA, trichloromethane, and carbon dioxide ternary mixture systems were determined from (313.15 to 363.15) K using a variable volume view cell at pressures up to 33.6 MPa. The bubble point or cloud point occurred depending on the mass fraction of PDLA, the CO2/trichloromethane mass ratio,

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and temperature. As the mass fraction of CO2 and PDLA increased, the cloud point occurred quickly, whereas the cloud point occurred slowly when the trichloromethane mass ratio increased. The correlation results were obtained with the hybrid equation of state using the van der Waals one-fluid mixing rule with three adjustable binary interaction parameters. The correlation results indicate an AADP (%) of about 3.18 to 4.37 [AADP (%) = 4.00 (wt 1.0%), 4.37 (wt 2.0%), and 3.18 (wt 3.0%)]. Acknowledgement This work was supported by the Korea government (MEST) (NRF-2012M1A2A2671789). References [1] J. Gwon, S.H. Kim, H.Y. Shin, H. Kim, J. Chem. Eng. Data 59 (2014) 2144–2149. [2] R. Auras, L.-T. Lim, S.E.M. Selke, H. Tsuji, Poly(lactic acid): Synthesis, Structures, Properties, Processing, and Applications, Wiley, 2011. [3] P. Subra, P. Jestin, Powder Technol. 103 (1999) 2–9. [4] P. Pollet, E.A. Davey, E.E. Ureña-Benavides, C.A. Eckert, C.L. Liotta, R. Soc. Chem. 16 (2014) 1034–1055. [5] B.E. Poling, J.M. Prausnitz, J.P. O’Connell, The Properties of Gases and Liquids, fifth ed., McGraw-Hill Book Company, 2000. [6] P. York, Pharm. Sci. Technol. Today 2 (1999) 430–440. [7] H.Y. Shin, J. Wu, Ind. Eng. Chem. Res. 49 (2010) 7678–7684. [8] Z. Lei, C. Dai, B. Chen, Chem. Rev. 114 (2014) 1289–1326. [9] J. Shin, Y.-W. Lee, H. Kim, W. Bae, J. Chem. Eng. Data 51 (2006) 1571–1575. [10] S. Kwon, W. Bae, H. Kim, J. Chem. Eng. Data 50 (2005) 1560–1563. [11] W. Bae, S. Kwon, H.-S. Byun, H. Kim, J. Supercrit. Fluids 30 (2004) 127–137. [12] D.-Y. Peng, D.B. Robinson, Ind. Eng. Chem. Fundam. 15 (1976) 59–64. [13] B. Bungert, G. Sadowski, W. Arlt, Ind. Eng. Chem. Res. 37 (1998) 3208–3220. [14] G. Liessmann, W. Schmidt, S. Reiffarth, Data Compilation of the Saechsische Olefinwerke Boehlen, DETHERM, 1995. [15] Analytical Methods Committee, Analyst 120 (1995) 2303–2308. [16] R.D. Chirico, M. Frenkel, V.V. Diky, K.N. Marsh, R.C. Wilhoit, J. Chem. Eng. Data 48 (2003) 1344–1359.

JCT 15-170