Solubility of Vitamin E Acetate in Supercritical Carbon Dioxide with

Article Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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Solubility of Vitamin E Acetate in Supercritical Carbon Dioxide with Ethanol as Cosolvent Jiangrui Cheng,† Sai Han,† Junying Song,† Weifang Wang,† and Zhen Jiao*,†,‡,§ †

School of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, China Centre for Nanobiotechnology, Joint Research Institute of Southeast University and Monash University, Suzhou 215123, China § Laboratory for Simulation and Modelling of Particulate Systems, Department of Chemical Engineering, Monash University, Melbourne, Victoria 3800, Australia Downloaded via UNIV OF LOUISIANA AT LAFAYETTE on October 29, 2018 at 18:16:57 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

‡

ABSTRACT: Vitamin E acetate (VEA) has been widely used as medicines, nutrients, and cosmetic additives. Solubility data are generally used to aid the design of processes to prepare products that provide the required dosage of the active compound(s). In this study, the static cloud-point method is employed to determine the solubility of VEA in supercritical carbon dioxide (scCO2) with ethanol (0.5, 1.0, and 2.0 mol %) as the cosolvent at temperatures of 313.15, 318.15, 323.15, and 328.15 K, and pressures of 8−15 MPa. The results show that the solubility of VEA in scCO2 can be remarkably enhanced by adding ethanol as the cosolvent. It could also be increased with the enhancing pressure and the decreasing temperature at the constant ethanol concentration. Furthermore, some semiempirical models including Christil-G, K-J, Bartle, MST-S, Reddy, and Pérez are employed to correlate the experimental data. The average absolute relative deviations values of these models range from 2.43 to 6.86%, indicating that these models could well predict the VEA solubility data in scCO2 + ethanol systems of this study.

1. INTRODUCTION A large number of pollution problems associated with chemical manufacturing are derived not only from raw materials and products but also from the materials used in their manufacturing processes, especially the solvents used in the reaction medium, separation, and formulation. The current widely used solvents are organic compounds, especially several volatile organic compounds (VOCs) (e.g., methanol, acetone, cyclohexane), which are flammable, toxic, and environmentally damaging. It is necessary to limit their usage and the developments of the nontoxic and harmless solvents to replace organic compounds become important.1−3 One of the promising green solvents is the supercritical fluids (SCF), especially supercritical carbon dioxide (scCO2).4−12 The scCO2 refers to a carbon dioxide fluid whose temperature and pressure are both above its critical point (Pc = 7.38 MPa, Tc = 304.13 K).13 Supercritical fluids are characterized by having densities like that of a liquid yet having viscosities more similar to those of gases, resulting in the good dissolving capacity and the high mass transfer rate. Moreover, scCO2 is colorless, odorless, nontoxic, and has no residue in the final product. Therefore, it has been widely used in industry.14 VEA can effectively inhibit lipid peroxidation and therefore it can be used as an antioxidant.15−17 VEA is a type of derivative of vitamin E as it eliminates free radicals in the body and © XXXX American Chemical Society

reduces the damage of ultraviolet rays to the human body. VEA has been widely used as an additive in various medicines, nutrients, and cosmetic preparations that provide appropriate dosage levels. In recent decades, the processes of dosage form preparation based on scCO2 have been given much attention.18−20 The solubility data of VEA in scCO2 could help aid scCO2 formulation processes of VEA involving processes such as RESS, GAS, etc. In addition, cosolvents are often used in the scCO2 process.21−25 Therefore, the solubility of VEA in scCO2 with a cosolvent is also important. The solubility of VEA in scCO2 has previously been reported. Belhadj-Ahmed et al.26 measured the solubility of VEA in scCO2 at 313 K and the pressures ranging of 10−20 MPa by the static cloud-point method. Han et al.27determined the solubility of VEA in scCO2 at the temperatures of 308.15− 328.15 K and the pressures of 8−15 MPa. It has been mentioned that the processes of dosage form preparation (e.g., rapid expansion of supercritical solution (RESS)28) require the cosolvent (e.g., ethanol) to enhance the dissolving capacity of scCO2. The systematic VEA solubility in scCO2 with ethanol as cosolvent is Received: August 24, 2018 Accepted: October 17, 2018

A

DOI: 10.1021/acs.jced.8b00745 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Teja (MST) modified by Sauseau (MST-S),33 Reddy,34 and Pérez35 are applied to correlate the experimental data and predict the solubility at the experimental range of this study.

Table 1. Cloud-Point Pressures of VEA (0.2500 g) in scCO2 with Ethanol (2.0 mol %) at the Temperatures of 313.15−328.15 Ka P/MPa 1 2 3 average AD (%)b

T/K = 313.15

T/K = 318.15

9.74 9.73 9.73 9.73 0.33

11.00 11.03 11.03 11.02 1.33

2. EXPERIMENTS 2.1. Materials. Carbon dioxide gas (CO2) (CAS No. 12438-9, 99.9 wt %) was purchased from Nanjing Shangyuan Gas Company. Vitamin E acetate (VEA) (CAS No. 52225-20-4, 96 wt %) was purchased from Shanghai Macklin Biochemical Company. It was further purified by vacuum distillation before measurements (>99 wt %). Ethanol (CAS No. 64-17-5, 99.7 wt %) was purchased from Sinopharm Chemical Reagent Co., Ltd. 2.2. Apparatus and Procedures. The solubility data of VEA in scCO2 with ethanol as cosolvent were determined through a high-pressure setup and a variable-volume view cell to determine the cloud-point pressure by observing the cloudpoint with a common static method. The detailed introduction of the schematics and experimental equipment can be found in our previous manuscript.27 In this study, the procedure for the determination was similar to that in our previous manuscript.27 Briefly, a certain quality of VEA and ethanol was added into the clean view cell. Then, the cell was sealed and placed in the water bath at the constant temperature. After that, carbon dioxide was introduced into the cell using a high-pressure pump and stopped when the pressure of the cell reached the experimental target pressure to ensure complete dissolution of the VEA

T/K = 323.15 T/K = 328.15 12.20 12.24 12.22 12.22 1.33

13.35 13.37 13.36 13.36 0.67

a Standard uncertainties u are u(T) = 0.1 K and u(P) = 0.10 MPa. Each experimental data point was the average value of at least three 100 replicate measurements. bAD(%) = n ∑ |P − P ̅ |, where n means the number of measurement data points.

the fundamental data for the process design. However, the limited data reported in the literature could not meet this requirement. In this paper, the static cloud-point method is employed to measure the solubility of VEA in scCO2 with ethanol (0.5, 1.0, and 2.0 mol %) as cosolvent at temperatures of 313.15, 318.15, 323.15, and 328.15 K, and pressures of 8−15 MPa, which has been employed to determine the solubility of compounds in scCO2 with good precision by some literature.11,29 The effects of temperature, pressure and concentrations of ethanol on the solubility are discussed in detail. Furthermore, six semiempirical models including Chrastil modified by González (Chrastil-G),30 Kumar and Johnston (K-J),31 Bartle,32 Mendez-Santiago and

Table 2. Solubility of VEA in scCO2 with Different Concentrations of Ethanol at Various Temperatures and Pressuresa y’ = 0.005 ± 0.0001 P/MPa

ρ /kg/m

S/kg/m

9.40 9.60 9.85 10.07 10.25 10.47

566.35 591.97 616.53 633.72 645.73 658.44

1.66 2.22 2.86 3.47 3.94 4.57

10.52 10.75 11.06 11.30 11.56 11.82

562.79 583.85 607.37 622.60 637.03 649.75

11.56 11.84 12.18 12.46 12.78 13.07 12.60 12.90 13.28 13.58 13.89 14.16

y’ = 0.01 ± 0.0006 10 y

P/MPa

ρ /kg/m

2.71 3.48 4.30 5.07 5.65 6.42

± ± ± ± ± ±

0.08 0.07 0.07 0.07 0.07 0.07

9.15 9.36 9.52 9.73 10.03 10.18

521.62 560.31 582.52 605.55 630.85 641.27

1.63 2.20 2.81 3.44 3.87 4.49

2.69 3.48 4.29 5.12 5.63 6.40

± ± ± ± ± ±

0.05 0.06 0.06 0.06 0.06 0.06

10.23 10.51 10.73 10.99 11.33 11.49

530.09 561.79 582.18 602.44 624.37 633.34

553.64 574.20 595.63 610.94 626.48 639.03

1.61 2.16 2.77 3.41 3.81 4.41

2.70 3.49 4.30 5.17 5.63 6.39

± ± ± ± ± ±

0.04 0.05 0.05 0.05 0.05 0.05

11.25 11.58 11.85 12.16 12.51 12.71

527.18 555.21 574.87 594.47 613.54 623.26

547.45 565.67 586.12 600.51 613.95 624.71

1.59 2.13 2.72 3.38 3.75 4.34

2.70 3.48 4.30 5.22 5.65 6.43

± ± ± ± ± ±

0.04 0.04 0.05 0.05 0.05 0.05

12.25 12.66 12.92 13.29 13.64 13.85

523.51 551.25 566.82 586.63 603.21 612.30

b

3

3

4

b

3

S/kg/m

3

T/K = 313.15 1.71 2.29 2.90 3.36 3.98 4.55 T/K = 318.15 1.68 2.25 2.85 3.32 3.93 4.49 T/K = 323.15 1.65 2.23 2.82 3.28 3.88 4.41 T/K = 328.15 1.63 2.19 2.77 3.24 3.81 4.34

y’ = 0.02 ± 0.001 4

10 y

P/MPa

ρ /kg/m3

S/kg/m3

b

104y

3.02 3.77 4.59 5.11 5.81 6.53

± ± ± ± ± ±

0.13 0.11 0.11 0.09 0.08 0.04

8.89 9.06 9.15 9.30 9.53 9.73

455.17 500.76 521.72 550.53 583.79 605.5

1.70 2.32 2.78 3.32 3.95 4.56

3.39 4.21 4.86 5.50 6.17 6.87

± ± ± ± ± ±

0.21 0.20 0.20 0.18 0.14 0.13

2.92 3.70 4.52 5.07 5.80 6.53

± ± ± ± ± ±

0.08 0.08 0.08 0.07 0.07 0.07

9.94 10.19 10.35 10.51 10.78 11.03

489.07 524.96 544.57 561.78 586.41 605.30

1.69 2.31 2.76 3.27 3.89 4.48

3.15 4.01 4.62 5.30 6.04 6.76

± ± ± ± ± ±

0.11 0.11 0.11 0.11 0.10 0.09

2.89 3.70 4.52 5.08 5.82 6.52

± ± ± ± ± ±

0.06 0.06 0.06 0.06 0.06 0.06

10.93 11.22 11.44 11.64 11.93 12.20

495.25 524.46 543.90 559.83 580.20 596.81

1.68 2.30 2.71 3.21 3.84 4.43

3.10 3.99 4.55 5.23 6.03 6.77

± ± ± ± ± ±

0.07 0.08 0.08 0.08 0.08 0.08

2.87 3.66 4.50 5.08 5.82 6.53

± ± ± ± ± ±

0.05 0.05 0.05 0.05 0.05 0.05

11.89 12.24 12.51 12.73 13.08 13.35

495.64 522.70 541.57 555.58 575.70 589.60

1.68 2.30 2.66 3.16 3.77 4.35

3.10 4.01 4.48 5.19 5.98 6.74

± ± ± ± ± ±

0.06 0.06 0.06 0.07 0.07 0.07

a ρ is the density of pure CO2. S (kg/m3) is the solubility of VEA, y is the solubility of VEA (mole fraction), y′ is the mole fraction of ethanol in the mixture. Standard uncertainties u are u(T) = 0.1 K and u(P) = 0.10 MPa. Standard uncertainties in the cosolvent concentrations and mole-fraction solubilities are reported following the ± signs. bValues provided by NIST.40

B



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Figure 1. Cloud-point pressures of VEA in scCO2 at different weights of VEA with cosolvent ethanol at the concentrations of (a) 0.5 mol %, (b) 1.0 mol %, (c) 2.0 mol % ethanol.

Figure 2. Solubility of VEA in scCO2 at different temperatures and pressures with cosolvent ethanol at the concentrations of (a) 0.5 mol %, (b) 1.0 mol %, (c) 2.0 mol % ethanol.

with an increment of 5 K. The experimental data shown in Table 1 reveal that the average deviation (AD) of VEA cloudpoint pressures is less than 1.33%, which demonstrates the repeatability of the experimental results. The experimental solubility data of VEA in scCO2 with different concentrations of ethanol along with the density of CO2 loaded in the cell at different temperatures and pressures are listed in Table 2. The experimental cloud points are determined as a function of temperature (T) and pressure (P), and each data point is the average value of at least three measurements. Figure 1 shows the cloud-point pressure−temperature (P−T) isopleths of different weights of VEA in scCO2 with different concentrations of ethanol. It shows that the cloudpoint pressure of VEA increases with the enhancing temperature at the constant ethanol concentration, indicating the system has typical low critical solution temperature (LCST) behavior.36 This phenomenon is similar to that of many compounds in scCO2.27,37−39 It could also be found that the addition of ethanol can effectively decrease the cloud-point pressure of VEA in scCO227 which would further be decreased with the increasing ethanol concentration in scCO2. Figure 2 shows the solubility of VEA in scCO2 with ethanol (0.5 mol % (a), 1.0 mol % (b), and 2.0 mol % (c)) as a function of pressure at different temperatures. The results indicate that the solubility of VEA increases with the enhancing pressure while it decreases with the higher temperature. The density of scCO2 is a key factor to the solubility of the compounds. Stronger solute−solvent interactions are established with the higher density of scCO2 at lower temperatures and higher pressures. The phenomenon leads to a stronger solvation power of scCO2, resulting in the higher solubility of the compound.

loaded into the high pressure view cell. The solution in the cell was stirred by a magnetic stirrer during the whole experiment. After the pressure and temperature remained constant for at least half an hour, the pressure of the cell was decreased very slowly and carefully controlled by gradually increasing the volume of the cell via a screw rotating upward until the cloud point was observed. The pressure drop rate was about 0.1 MPa·min−1. The cloud point demonstrated that the solute in the system started to dissolve out, and the pressure at this point was called the cloud-point pressure. Each cloud point pressure value was repeated at least three times and the average one was obtained. The solubility of VEA can be calculated by means of the amount of VEA, ethanol, and scCO2 in the cell at the cloud point pressure (eq 1). The determination was carried out during the temperature from 313.15 to 328.15 K with an increment of 5 K in this study. nVEA y= nVEA + nEtOH + nCO2 (1) where y is the solubility of VEA in mole fraction; nVEA is the number of moles of VEA charged in the view cell; nEtOH is the number of moles of ethanol charged in the view cell; nCO2 is the number of moles of carbon dioxide charged in the view cell.

3. RESULTS AND DISCUSSION 3.1. Solubility Determination. The reliability of the system used in this study has been verified elsewhere.27 Before the determination, VEA (0.2500 g) and ethanol (2.0 mol %) are selected to conduct the solubility procedure of the repeatability test. The cloud-point pressures of VEA are measured three times at the temperatures ranging from 313.15 to 328.15 K C


m +n T

m + n + z ln y′ T

P = (k + my’)y2 + (n + zy’)y + (C1 + C2)

n + zρ + C1y′ i P y ln y = (k + m − 1) lnjjj zzz + + m ln(y′) + C2ρ + C3 T k P* {

T ln(yP) = kρ+mT + n + zy′

ij Py yz m lnjjjj zzzz = k(ρ − ρref ) + +n T k Pref {

ln y = kρ +

ln S = k ln ρ +

equation

k 6.565 5.340 4.274 0.0100 0.0075 0.0061 0.0113 0.0087 0.0070 3.6194 2.7777 2.2351 −1.759 3190.7 4.075 −21.95 −17.86 −11.96

y’ 0.005 0.01 0.02 0.005 0.01 0.02 0.005 0.01 0.02 0.005 0.01 0.02 0.005 0.01 0.02 0.005 0.01 0.02

n −17116 797.43 639.09 1.8054 −0.4764 −4.0775 20.87 16.57 11.44 −6532.2 −4629.1 −2492.8 999.97 1322.29 1013.99 179.16 152.37 101.85

m −875.89 −623.18 4.26 −2030.2 −768.3 740.8 −4345.1 −2981.8 −1313.4 17.49 13.26 8.10 4.256 −3192.6 −4.794 0.8862 0.8118 31.82

correlation parameters

−58.09 2503.9 −2611 0.7502 −14.57 −7.138 1.3122 1.574 9.386

−3223 179.89 −302.9

z

5.68 50.3 93.6 321 289 201

C1

0.01 0.06 0.03 0.26 1.93 13.4

C2

−9.01 14697 16.50

C3 5.35 3.62 6.11 2.44 3.79 6.06 2.43 4.01 6.53 2.74 4.33 6.86 2.83 2.93 5.84 3.05 2.80 2.70

AARD (%)

0.9669 0.9822 0.9476 0.9896 0.9715 0.9216 0.9926 0.9771 0.9347 0.9917 0.9770 0.9398 0.9870 0.9812 0.9249 0.9870 0.9876 0.9872

R2

a In this work, values of solubility y are substituted by y × 104 for convenient operation, where y (mole solute/mol CO2) is the solubility of VEA in scCO2, y′ is the mole fraction of ethanol in the mixture, S (kg/m3) represents the solubility of VEA in scCO2, P (MPa) and T(K) are the system pressure and temperature, Pref is the standard pressure of 0.1 MPa, and ρref is a reference density with a value of 700 kg/m3, and k, m, n, z, C1, C2 and C3 are adjustable parameters that can be obtained by fitting the least-squares method to experimental data.

Pérez

Reddy

MST-S

Bartle

K−J

Chrastil-G

model

a

Table 3. Correlation Parameters for the Solubility of VEA in scCO2 with Cosolvent and AARD of Different Models

Journal of Chemical & Engineering Data Article

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Figure 3. Comparison of the Chrastil-G correlation and the experimental data with cosolvent ethanol at concentrations of (a) 0.5 mol %, (b) 1.0 mol %, (c) 2.0 mol %.

Figure 4. Comparison of the K−J correlation and the experimental data with cosolvent ethanol at concentrations of (a) 0.5 mol %, (b) 1.0 mol %, (c) 2.0 mol %.

Figure 5. Comparison of the Bartle correlation and the experimental data with cosolvent ethanol at concentrations of (a) 0.5 mol %, (b) 1.0 mol %, (c) 2.0 mol %.

3.2. Correlation of Solubility. The solubility determination of drugs in scCO2 is difficult and time-consuming. Therefore, some correlation models are used to correlate the solubility data and predict them during the experimental range. In this study, six typical semiempirical correlation models (e.g., Chrastil modified by González (Chrastil-G),30 Kumar and Johnston (K-J),31 Bartle,32 Mendez-Santiago and Teja (MST) modified by Sauseau (MST-S),33 Reddy34 and Pérez35) are employed to correlate the solubility of VEA in scCO2 with ethanol as cosolvent. The descriptions and the correlation parameters of these models are listed in Table 3. Figures 3−8 show the results of the correlation. The R-square (0 < R2< 1) represents the fitness index. Its values shown in Table 3 are close to 1, indicating the regression lines correlated by the models match the experimental data well in this study.

Ethanol is miscible with scCO2 and usually has good dissolving capacity for many compounds. Therefore, ethanol often acts as the cosolvent commonly used in scCO2 systems to increase their dissolving capacity. As expected, our experimental results demonstrate that the addition of ethanol can effectively improve the solubility of VEA in scCO2, and the solubility of VEA increases with the enhancing concentration of ethanol in the system. For example, under the temperature of 318.15 K and the similar pressure, the solubility of VEA in scCO2 at the ethanol concentrations of 0.0 mol %, 0.5 mol %, 1.0 mol %, and 2.0 mol % is 3.84 × 10−4 (11.13 MPa),27 4.31 × 10−4 (11.06 MPa), 5.13 × 10−4 (10.99 MPa), and 6.90 × 10−4 (11.03 MPa), respectively. The results prove that ethanol is an effective cosolvent to increase the solubility of VEA in scCO2. E



Article

Figure 6. Comparison of the MST-S correlation and the experimental data with cosolvent ethanol at concentrations of (a) 0.5 mol %, (b) 1.0 mol %, (c) 2.0 mol %.

Figure 7. Comparison of the Reddy correlation and the experimental data with cosolvent ethanol at concentrations of (a) 0.5 mol %, (b) 1.0 mol %, (c) 2.0 mol %.

Figure 8. Comparison of the Pérez correlation and the experimental data with cosolvent ethanol at concentrations of (a) 0.5 mol %, (b) 1.0 mol %, (c) 2.0 mol %.

2.85% for Chrastil-G, K-J, Bartle, MST-S, Reddy, and Pérez, respectively. The results indicate that the prediction accuracy of all the models is good, and the accuracy of the Pérez model seems slightly better than the other models. It seems that the prediction accuracy of the solubility at 328.15 K would slightly decrease. It could also be found that the prediction accuracy decreases slightly with the increase of ethanol concentration for all the models except Chrastil-G and Pérez model. The reason might be that the hydrogen bonding has a less strong electrostatic interaction between VEA and ethanol established in ethanol-modified scCO2.

The accuracy of these models is evaluated by the average absolute relative deviations (AARD) calculated by eq 2. A lower AARD value represents better correlation results. AARD(%) =

1 N

∑

|ycal − yexp | |yexp |

100 (2)

where N is the total number of experimental data, ycal and yexp present the calculated results and the experimental ones, respectively. In this study, the calculated AARD values of all the models are below 6.86%, showing the calculated data has good accuracy compared with the experimental ones (Figures 3−8 and Table 3). The average AARD value of the model for three ethanol concentrations is 5.03%, 4.10%, 4.32%, 4.64%, 3.86%, and

4. CONCLUSIONS The solubility of VEA in scCO2 with ethanol (0.5, 1.0, and 2.0 mol %) as cosolvent is determined at temperatures of F



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313.15, 318.15, 323.15, and 328.15 K and pressures of 8−15 MPa. The results show that the solubility of VEA in scCO2 can be remarkably enhanced by adding ethanol as cosolvent. Under the temperature of 318.15 K and the similar pressure, the solubility of VEA in scCO2 at the ethanol concentrations of 0.0 mol %, 0.5 mol %, 1.0 mol %, and 2.0 mol % is 3.84 × 10−4 (11.13 MPa),27 4.31 × 10−4 (11.06 MPa), 5.13 × 10−4 (10.99 MPa), and 6.90 × 10−4 (11.03 MPa), respectively. Furthermore, six semiempirical models including Christil-G, K-J, Bartle, MST-S, Reddy, and Pérez are employed to correlate the experimental data. The AARD values of these models range from 2.43 to 6.86%, indicating that these models could well predict the VEA solubility data in scCO2 + ethanol system of this study. The experimental data provided in this study can be used to design the processes based on scCO2, such as the rapid expansion process of supercritical solution (RESS).

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Zhen Jiao: 0000-0001-5383-5077 Funding

This study was supported by the Natural Science Foundation of Jiangsu Province (BK20130602), Applied Basic Research Program of Suzhou (SYG201836), Collaborative Innovation Center of Suzhou Nano Science and Technology, the Priority Academic Program Development of Jiangsu Higher Education Institutions and the Fundamental Research Funds for the Central Universities. Notes

The authors declare no competing financial interest.

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REFERENCES

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