Phase behavior measurement on the binary mixture for isopropyl acrylate and isopropyl methacrylate in supercritical CO2

Fluid Phase Equilibria 249 (2006) 55–60

Phase behavior measurement on the binary mixture for isopropyl acrylate and isopropyl methacrylate in supercritical CO2 Hun-Soo Byun a,∗ , Ki-Pung Yoo b a

Department of Chemical System Engineering, Chonnam National University, Yeosu, Jeonnam 550–749, South Korea b Department of Biochemical Engineering, Sogang University, Seoul 121–742, South Korea Received 22 March 2006; received in revised form 30 July 2006; accepted 25 August 2006 Available online 30 August 2006

Abstract Vapor–liquid phase equilibrium data are obtained for mixtures of CO2 + isopropyl acrylate and CO2 + isopropyl methacrylate systems at 313.2, 333.2, 353.2, 373.2, and 393.2 K and pressures up to 14.20 MPa. The solubility of CO2 for the CO2 + isopropyl acrylate and CO2 + isopropyl methacrylate systems decreases as the temperature increases at constant pressure. The CO2 + isopropyl acrylate and CO2 + isopropyl methacrylate systems exhibits type-I phase behavior, characterized by a continuous critical line from pure CO2 to the second component with a maximum in pressure. The experimental results for the CO2 + isopropyl acrylate and CO2 + isopropyl methacrylate systems were correlated with Peng–Robinson equation of state using a van der Waals one-fluid mixing rule. The correlation results have shown a good agreement with the Peng–Robinson equation using two adjustable interaction parameters for the systems. © 2006 Elsevier B.V. All rights reserved. Keywords: Supercritical carbon dioxide; Isopropyl acrylate–CO2 ; Isopropyl methacrylate–CO2 ; Peng–Robinson EOS; High pressure phase behavior; Solubility

1. Introduction Supercritical carbon dioxide (scCO2 ) is used as a chemical reaction solvent for separation process, polymerization condition and related field industry [1], because it is non-toxic, nonflammable, and inexpensive. Specially, scCO2 has a quadrupole moment, no dipole moment and low dielectric constant. scCO2 is a good solvent of low molecular weight in non-polar molecules. However, phase behavior information for mixtures containing scCO2 is required for practical uses such as an industrial application, supercritical fluid extraction and process design [2]. Recently, phase behavior data for the CO2 + alkyl (meth)acrylate system were reported by Lora and McHugh, [3] McHugh et al. [4], and Byun [5,6]. The miscibility for supercritical CO2 + monomer system is important condition needed for polymer synthesis and polymerization process. Lora and McHugh [3] presented the phase behavior for CO2 + methyl methacrylate solution and for CO2 + butyl acrylate [4] system

∗

Corresponding author. Tel.: +82 61 659 3296; fax: +82 61 653 3659. E-mail address: [email protected] (H.-S. Byun).

0378-3812/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2006.08.019

at 35 and 75 ◦ C using a static apparatus. Byun [5] used a static apparatus and presented the liquid–vapor equilibria curves for CO2 + cyclohexyl acrylate and CO2 + cyclohexyl methacrylate mixtures at 313.2, 333.2, 353.2, 373.2, and 393.2 K and pressures up to 20.6 MPa. Byun [6] reported the solubility curve for the CO2 + propyl acrylate and CO2 + propyl methacrylate system at 313.2–393.2 K and pressure up to 16.6 MPa. However, acrylate and methacrylate are very important monomers that widely used in the plastic manufacture technology. The monomers and polymers are used for a variety of applications such as prostheses, contact lenses and coating [7]. The purpose of this work is to obtain the high-pressure experimental data for CO2 + isopropyl acrylate and CO2 + isopropyl methacrylate mixtures by investigating mixtures of CO2 with two components. Also, the pressure–temperature (P–T) diagrams of the mixture critical curve are presented for the CO2 + isopropyl acrylate and CO2 + isopropyl methacrylate systems in the vicinity of the critical point of pure CO2 . The measured bubble-, critical- and dew-point data of binary systems are modeled using the Peng–Robinson equation of state [8], providing valuable information for rational design and operation of the supercritical region.

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2. Experimental 2.1. Apparatus and procedure Phase behavior data are obtained with a high-pressure, variable-volume cell described in detail elsewhere [9,10]. The main component is a high pressure, variable-volume cell, which is constructed of a high-nickel-content austenitic steel with working volume of ∼28 cm3 and is capable of operating up to pressure of 100 MPa. A sapphire window (1.9 cm thick) is fitted in the front part of the cell to allow observation of the phases. Typically, a quantity of liquid isopropyl acrylate or isopropyl methacrylate was loaded into the cell to within an accuracy of ±0.002 g by using a syringe after the empty cell was purged several times with CO2 to remove air and organic substance. CO2 was then added to the cell to within an accuracy of ±0.004 g by using a high-pressure bomb. The piston was moved using water pressurized by a highpressure generator (HIP, Model 37-5.75-60) The pressure of the mixture was measured with a Heise gauge (Dresser Ind., model CM-53920, 0–34.0 MPa) accurate to ±0.03 MPa. The temperature of the cell was typically maintained to within ±0.2 K. The mixture inside the cell can be viewed on a video monitor using a camera coupled to a borescope (Olympus Corp., model F100-038-000-50) placed against the outside of the sapphire window. At a fixed temperature, the solution in the cell was compressed to the desired pressure by moving a piston located within the cell and to one-phase in the cell. The solution was maintained in the one-phase region at the desired temperature for at least 40 min for the cell to reach phase equilibrium. The pressure was then slowly decreased until the bubble-, dewand critical-point appeared. A bubble point pressure is obtained when small vapor bubbles appear first in the cell and a dew point is obtained if a fine mist appears in the cell. Critical points are obtained by adjusting the temperature and pressure of the mixture until critical opalescence was observed along with equal liquid and vapor volume upon the formation of the second phases.

Fig. 1. Comparison of the experimental data (symbols) for the CO2 + isopropyl acrylate system with calculated data (solid lines) obtained with the Peng–Robinson equation of state with kij = −0.0093 and ηij = −0.0503.

value at least two independent data points that have an estimated accumulated error of less than ±1.0%. Fig. 1 and Table 1 show the experimental pressure– composition (P–x) isotherms at 313.2, 333.2, 353.2, 373.2 and 393.2 K, and the range of pressures of 2.69–13.68 MPa for the CO2 + isopropyl acrylate system. As shown in Fig. 1, three phases was not observed at any of five temperatures studied. In Fig. 1, the mixture critical pressures were 9.52 MPa (at 333.2 K), 11.41 MPa (at 353.2 K), 12.69 MPa (at 373.2 K) and 13.68 MPa (at 393.2 K). The P–x isotherms appears to be consistent with those expected for a type-I system [11]. Fig. 2 and Table 2 show the experimental phase behavior of P–x isotherms at 313.2–393.2 K and pressure up to 14.2 MPa for the CO2 + isopropyl methacrylate. As shown in Fig. 2, the mixture critical pressures were 8.03 MPa (at 313.2 K), 10.22 MPa (at 333.2 K), 11.85 MPa (at 353.2 K), 13.10 MPa (at 373.2 K) and 14.20 MPa (at 393.2 K). Also, the pressure of each mixture-critical point continually increases as the temperature increases. The CO2 + isopropyl methacrylate system does not exhibit three phases at any of five temperatures investigated.

2.2. Materials CO2 was obtained from Daesung Industrial Co. (99.8% minimum purity) and was used as received. The isopropyl acrylate (>95% purity; CAS 689-12-3) and isopropyl methacrylate (>95% purity; CAS 4655-34-9) used in this work were obtained from Scientific Polymer Products Inc. Both components were used without further purification in the experiments. 3. Experimental results and discussion Bubble, critical, and dew point curves for both the CO2 + isopropyl acrylate and CO2 + isopropyl methacrylate systems are measured and reproduced at least twice to within ±0.03 MPa and 0.2 K for a given loading of the cell. The mole fractions are accurate to within ±0.002. The CO2 + isopropyl acrylate and CO2 + isopropyl methacrylate mixtures for the solubility isotherms at 313.2–393.2 K are arranged according to the

Fig. 2. Comparison of the experimental data (symbols) for the CO2 + isopropyl methacrylate system with calculated data (solid lines) obtained with the Peng–Robinson equation of state with kij = 0.0136 and ηij = −0.0446.

H.-S. Byun, K.-P. Yoo / Fluid Phase Equilibria 249 (2006) 55–60 Table 1 Experimental data for the CO2 + isopropyl acrylate system measured in this study Mole fraction of the isopropyl acrylate

P (MPa)

Transition

T = 313.2 K 0.040 0.080 0.103 0.136 0.145 0.167 0.193 0.225 0.242 0.280 0.300 0.312 0.386 0.436 0.457 0.520 0.625 0.683

7.38 6.93 6.70 6.44 6.36 6.20 6.11 5.92 5.83 5.41 5.13 5.09 4.53 4.39 4.07 3.59 3.05 2.69

BP BP BP BP BP BP BP BP BP BP BP BP BP BP BP BP BP BP

T = 333.2 K 0.040 0.080 0.103 0.136 0.145 0.167 0.193 0.225 0.242 0.280 0.300 0.312 0.386 0.436 0.457 0.520 0.625 0.683

9.52 9.47 9.06 8.87 8.70 8.53 8.32 8.03 7.93 7.42 6.70 6.77 6.04 5.55 5.35 4.65 3.83 3.23

CP BP BP BP BP BP BP BP BP BP BP BP BP BP BP BP BP BP

T = 353.2 K 0.040 0.080 0.103 0.136 0.145 0.167 0.193 0.225 0.242 0.280 0.300 0.312 0.386 0.436 0.457 0.520 0.625 0.683

10.38 11.41 11.33 11.28 11.16 10.93 10.79 10.30 9.82 9.32 8.81 8.63 7.52 6.82 6.55 5.78 4.59 3.76

DP CP BP BP BP BP BP BP BP BP BP BP BP BP BP BP BP BP

T = 373.2 K 0.080 0.103 0.136

12.29 12.07 12.55

DP DP DP

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Table 1 (Continued) Mole fraction of the isopropyl acrylate

P (MPa)

Transition

0.145 0.167 0.193 0.225 0.242 0.280 0.300 0.312 0.386 0.436 0.457 0.520 0.625 0.683

12.69 12.66 12.59 11.86 11.48 11.04 10.58 10.26 8.97 8.02 7.76 6.68 5.18 4.31

CP BP BP BP BP BP BP BP BP BP BP BP BP BP

T = 393.2 K 0.080 0.103 0.136 0.145 0.167 0.193 0.225 0.242 0.280 0.300 0.312 0.386 0.436 0.457 0.520 0.625 0.683

12.28 13.05 13.63 13.64 13.68 13.62 13.28 12.96 12.35 11.91 11.57 10.11 9.16 8.90 7.62 5.84 4.81

DP DP DP DP CP BP BP BP BP BP BP BP BP BP BP BP BP

The experimental data obtained in this work were correlated with Peng–Robinson equation of state using van der Waals one fluid mixing rules including two binary interaction parameters. This equation of state is briefly described here. The Peng–Robinson equation [8] of state is used with the mixing rules given by: P=

RT a(T ) − V − b V (V + b) + b(V − b)

a(T ) = a(Tc )α(Tr , ω) a(Tc ) = 0.45724

R2 Tc2 Pc

  √ 2  α = 1 + m (1 − Tr ) m = 0.37464 + 1.5422ω − 0.26992ω2   RTc b = 0.07780 Pc  amix = xi xj aij i

(1) (2) (3) (4) (5) (6) (7)

j

aij = (aii ajj )1/2 (1 − kij )

(8)

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Table 2 Experimental data for the CO2 + isopropyl methacrylate system measured in this study Mole fraction of the isopropyl methacrylate

P (MPa)

Transition

T = 313.2 K 0.016 0.047 0.055 0.097 0.144 0.185 0.228 0.294 0.330 0.390 0.445 0.497 0.606 0.735

8.03 7.73 7.62 6.93 6.43 6.23 6.03 5.72 5.45 4.82 4.42 3.86 3.14 2.48

CP BP BP BP BP BP BP BP BP BP BP BP BP BP

T = 333.2 K 0.016 0.047 0.055 0.097 0.144 0.185 0.228 0.294 0.330 0.390 0.445 0.497 0.606 0.735

9.14 10.22 10.17 9.52 9.35 8.79 8.28 7.59 7.14 6.31 5.93 5.14 4.14 3.00

DP CP BP BP BP BP BP BP BP BP BP BP BP BP

T = 353.2 K 0.047 0.055 0.097 0.144 0.185 0.228 0.294 0.330 0.390 0.445 0.497 0.606 0.735

11.68 11.85 11.72 11.45 11.03 10.31 9.38 8.86 7.93 7.21 6.37 5.03 3.52

DP CP BP BP BP BP BP BP BP BP BP BP BP

T = 373.2 K 0.047 0.055 0.097 0.144 0.185 0.228 0.294 0.330 0.390 0.445 0.497 0.606 0.735

11.93 12.59 13.10 13.21 12.79 12.38 11.14 10.31 9.38 8.31 7.41 5.82 3.83

DP DP CP BP BP BP BP BP BP BP BP BP BP

T = 393.2 K 0.047 0.055

11.48 12.28

DP DP

Table 2 (Continued) Mole fraction of the isopropyl methacrylate

P (MPa)

Transition

0.097 0.144 0.185 0.228 0.294 0.330 0.390 0.445 0.497 0.606 0.735

13.86 14.20 14.14 13.59 12.41 11.76 10.59 9.38 8.40 6.54 4.14

DP CP BP BP BP BP BP BP BP BP BP

bmix =

 i

xi xj bij

(9)

j



bij = 0.5 (bii + bjj ) (1 − ηij )

(10)

These two binary interaction parameters, kij and ηij , were determined by regression experimental data with Peng–Robinson equation of state. The expression for the fugacity coefficient using these mixing rules is given by Peng and Robinson [8] and is not reproduced here. Objection function (OBF) and root mean squared relative deviation (RMSD) percent of this calculation were defined by: OBF =

 N   Pexp − Pcal i

RMSD (%) =

2

(11)

Pexp 

OBF × 100 ND

(12)

ND in Eq. (12) means the number of data point. We used Marquardt [14] to optimize the objection function. Table 3 lists the pure component critical temperatures, critical pressures, and the acentric factors for CO2 , isopropyl acrylate, isopropyl methacrylate that are used with the Peng–Robinson equation of state in this work [12,13]. The properties of isopropyl acrylate and isopropyl methacrylate were calculated by the Joback group-contribution method [13]. Also, the vapor pressures were calculated by the Lee-Kesler method [13]. Fig. 3 shows a comparison of experimental result of CO2 + isopropyl methacrylate with calculated value obtained using Peng–Robinson equation at a temperature of 353.2 K. The binary interaction parameters of Peng–Robinson equation of state are fitted by the experimental data at 353.2 K. The values of the optimized parameters (bubble-point data = 11, RMSD = 1.09%) of the Peng–Robinson equation of state for the CO2 + isopropyl acrylate system are kij = 0.0136 and ηij = −0.0446. Table 3 Pure component parameters for the Peng–Robinson equation of state [12,13] Compounds

Mw

Tc (K)

Pc (MPa)

ω

CO2 Isopropyl acrylate Isopropyl methacrylate

44.01 114.15 128.17

304.3 560.54 572.99

7.39 3.31 2.97

0.225 0.4037 0.4492

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Fig. 3. Comparison of the best fit of Peng–Robinson equation of state to the CO2 + isopropyl methacrylate system at 353.2 K.

We compared experimental results with calculated P–x isotherms at temperatures of 313.2, 333.2, 373.2 and 393.2 K for the CO2 + isopropyl methacrylate system using the optimized values of kij and ηij determined at 353.2 K. As shown in Fig. 2, a good fit of data are obtained with Peng–Robinson equation using an adjustable mixture parameters for the CO2 + isopropyl methacrylate system. The RMSD at five temperatures (313.2, 333.2, 353.2, 373.2 and 393.2) K for CO2 + isopropyl methacrylate system was 3.18% of the 57 bubble points. Fig. 4 shows the mixture-critical curve for the CO2 + isopropyl methacrylate system predicted by the Peng–Robinson equation of state, and also it presents the experimentally determined pressure–temperature (P–T) trace of the mixture critical curve in the vicinity of the critical point of CO2 [12,13]. The mixture critical curves calculated by the two mixture parameters are type-I. In Fig. 4, the solid lines for the vapor pressure for pure isopropyl methacrylate was obtained by Lee-Kesler method [13]. The dashed lines represent calculation obtained using the Peng–Robinson equation of state, with kij = 0.0136 and

59

Fig. 5. Pressure–temperature diagram for the CO2 + isopropyl acrylate system. The solid line and solid circles represent the vapor–liquid lines and the critical points for pure CO2 and isopropyl acrylate. The open square are mixture critical points determined from isotherms measured in this study. The dashed lines represent calculation obtained using the Peng–Robinson equation of state with kij = −0.0093 and ηij = −0.0503.

ηij = −0.0446. The agreement between calculated and experimental mixture-critical curves is reasonably good using two optimized parameters with Peng–Robinson equation of state. Fig. 1 shows a comparison of experimental with calculated P–x isotherms at temperature of 313.2, 333.2, 353.2, 373.2 and 393.2 K for the CO2 + isopropyl acrylate system. These isotherms are calculated using the optimized values (bubblepoint data = 16, RMSD = 1.34%) of kij equal to −0.0093 and ηij equal to −0.0503 determined at 353.2 K in the same way as above. The RMSD at five temperatures for CO2 + isopropyl acrylate system was 3.30% of the 79 bubble points. Fig. 5 shows the mixture-critical curve for the CO2 + isopropyl acrylate system predicted by the Peng–Robinson equation of state. The calculated mixture-critical curve is type-I, in good agreement with experimental observations at five temperatures. In Fig. 5, the solid lines represent the vapor pressure for pure CO2 [12,13] and isopropyl acrylate [13]. The solid circles represent the critical point for pure CO2 and isopropyl acrylate. The upper part of the dashed line is single phase, while the lower part is vapor–liquid (two phases). The open squares are for the mixture-critical points determined from isotherms measured in this experiment. The dashed lines represent the calculated value obtained using the Peng–Robinson equation of state. 4. Conclusions

Fig. 4. Pressure–temperature diagram for the CO2 + isopropyl methacrylate system. The solid line and solid circles represent the vapor–liquid lines and the critical points for pure CO2 and isopropyl methacrylate. The open square are mixture critical points determined from isotherms measured in this study. The dashed lines represent calculation obtained using the Peng–Robinson equation of state with kij = 0.0136 and ηij = −0.0446.

High pressure phase behavior data of CO2 + isopropyl acrylate and CO2 + isopropyl methacrylate systems are obtained at 313.2–393.2 K and pressure range of 2.48–14.20 MPa for binary mixtures. The CO2 + isopropyl acrylate and CO2 + isopropyl methacrylate systems exhibit type-I phase behavior, which is characterized by an uninterrupted critical-mixture curve. For CO2 + isopropyl acrylate and CO2 + isopropyl methacrylate systems, we did not observe three-phase behavior. The solubility of isopropyl acrylate and isopropyl methacrylate for the CO2 + isopropyl acrylate and CO2 + isopropyl methacry-

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late systems increases as the temperature increases at constant pressure. The Peng–Robinson equation of state models the pressure–composition isotherms for CO2 + isopropyl acrylate and CO2 + isopropyl methacrylate systems using the independent-temperature mixture parameters. We obtained good correlation results. RMSD (%) for the CO2 + isopropyl acrylate system was 3.30% and for the CO2 + isopropyl methacrylate system was 3.18%. List of symbols a attraction parameter b van der Waals covolume k binary interaction parameter m characteristic constant in Eq. (4) P pressure R gas constant T temperature V volume x mole fraction Greek letters α scaling factor defined by Eq. (2) η secondary binary interaction parameter ω acentric factor Subscripts c critical property cal calculated exp experimental mix mixture r reduced property Acknowledgements The author gratefully acknowledge the financial support from the Korea Ministry of Commerce, Industry & Energy and the Korea Energy Management Corporation.

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