Phase Equilibria of the Systems CO2 + Styrene, CO2 + Safrole, and

Article pubs.acs.org/jced

Phase Equilibria of the Systems CO2 + Styrene, CO2 + Safrole, and CO2 + Styrene + Safrole Ernandes T. Tenório Neto,† Marcos H. Kunita,† Adley F. Rubira,† Bruno M. Leite,‡ Cláudio Dariva,‡ Alexandre F. Santos,‡ Montserrat Fortuny,‡ and Elton Franceschi*,‡ †

Department of Chemistry, Universidade Estadual de Maringá, Av. Colombo 5790, 87020-900, Maringá, PR, Brazil Núcleo de Estudos em Sistemas ColoidaisITP/UNIT, Campus Farolândia, Av. Murilo Dantas, 300, Aracajú, SE, 49032-490, Brazil

‡

ABSTRACT: This work reports phase equilibrium experimental data of binary and ternary systems involving carbon dioxide (CO2), 5-(2-propenyl)-1,3-benzodioxole (safrole), and ethenylbenzene (styrene). The experimental phase equilibrium data were measured using a high-pressure variable-volume view cell based on the static synthetic method in the temperature range of (303 to 343) K, at several CO2-overall compositions and pressures up to 16 MPa. For ternary system measurements, solutions of safrole and styrene with styrene mass fractions of 0.75 and 0.90 on CO2 free basis were prepared. The results showed that, in the experimental range investigated, only vapor− liquid equilibria (VLE) were detected with bubble (BP) and dew (DP) point transitions. The experimental data were satisfactorily represented by the Peng−Robinson equation of state (PR-EoS) with the classical quadratic mixing rules. The EoS interaction parameters were fitted from binary systems and then used to predict the phase behavior of the ternary system with a good agreement.

1. INTRODUCTION

obtaining polymers with specific chemical, biological, and thermal properties.12 Polymerization and copolymerization reactions, with different kinds of monomers, have been conducted at high pressure, mainly in a CO2 environment,13−20 due to its attractive properties, the easy separation of the products during and after the reaction, and also due to the well-defined characteristics of carbon dioxide as solvent medium. Chemical processes that produce a minimum of waste and hazardous substances with a clean, efficient, and safe method, based on green chemistry and green engineering, are receiving increased attention by the industries.21 For the design and operation of high-pressure systems, the phase behavior of the reactional system is a key factor, due to its influence on chemical product formation and process development.21 Many works can be found in the literature about the phase equilibria of different monomers and carbon dioxide systems.22−28 For instance, Suppes and McHugh22 used the synthetic method to obtain bubble, dew, and critical points for the system CO2 + styrene in the temperature range of 308 K to 373 K. Tan et al.23 obtained experimental data of vapor−liquid equilibria for the binary and ternary systems involving ethylbenzene,

The chemical transformation of substances that are naturally present in several biomass feedstocks is an important and useful tool to obtain high added value compounds for chemical, food, and pharmaceutical industries.1 Safrole [5-(2-propenyl)1,3-benzodioxole], a natural alylbenzene widely distributed in nature, is within these chemical substances. This compound is found in large quantities (about 88 % to 95 % of the essential oil composition) in long pepper species such as Piper hispidinervum C. DC., that grow quickly compared to Atlantic rain forest tree native species that gave this oil as Ocotea odorifera (canela sassafras).2,3 Although safrole presents carcinogenic activity to some extent,4−6 it is important as a precursor of a variety of chemicals for pharmaceutical, perfumery, and flavoring industries.2,7−9 The isomerization of safrole to isosafrole, its more thermodynamically stable form, is an important chemical reaction whose product finds out applications in fragrance and pharmaceutical industries.10 Other important chemical modification of safrole is its dimerization, which products present biological activity.11 Safrole can be also potentially applied, due to its reactive groups, as a functional monomer in copolymerization reactions. The resulting copolymer makes possible a series of modifications in their surface due to the free functional groups available in safrole. Surface modifications can be conducted to © XXXX American Chemical Society

Received: February 1, 2013 Accepted: May 2, 2013

A

dx.doi.org/10.1021/je400110c | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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Figure 1. GC-MS chromatogram of safrole used in this work (A) and commercial safrole (B).

The operating conditions were programmed was follows: injector and interface temperature of 553 K, carrier gas (helium) flow rate of 1.0 cm3·min−1, and split ratio 1:10. The temperature program was started at 333 K, raised to 423 K at 1 K·min−1, held at this temperature for 2 min, and raised to 523 at 2 K·min−1. One microliter of sample was injected in each run. Chromatograms of commercial and purified safrole are presented in Figure 1. 2.2. Phase Equilibria Apparatus and Procedure. The apparatus and experimental procedure used in this work for phase equilibrium measurements are similar to that described previously,29−31 and just a brief description is presented here. The experimental apparatus was based on the synthetic method with visualization, as classified by Dohrn and co-workers32 and Fonseca and co-workers.33 The experimental setup consisted of a variable-volume view cell with a maximum internal volume of 25 cm3 and a movable piston, provided with two sapphire windows for observation of phase transitions and for illumination; a syringe pump (Teledyne Isco, 260D) to system pressure and carbon dioxide fed mass control, and a zerovolume absolute pressure transducer (Huba Control, 691) with an uncertainty of ± 0.01 MPa. An ultra thermostatic bath (Julabo, F32) was employed for temperature control. The experimental apparatus also comprised temperature and pressure indicators (NOVUS, N1500) and high pressure valves (HIP, 1511AF1; Swagelok, SS-83KF2). The experimental procedure was started by loading an amount (scaled in Shimazdu AX 200 balance with a precision of ± 0.0001 g) of pure safrole or styrene, or a mixture of them, into the equilibrium cell. After solute load, the cell was connected to the experimental unit and a gently flow of carbon dioxide was passed out through the cell to remove residual air. A precise amount of CO2 was added to the cell by the syringe pump. The system was then kept at continuous stirring with the help of a magnetic stirrer and a Teflon-coated bar inserted into the equilibrium cell. The temperature control was turned on,

styrene, and carbon dioxide at temperatures of 308 K, 318 K, and 328 K by using an analytical method with circulation. Zhang et al.24 investigated the same systems of Tan and coworkers measuring bubble, dew, mixture critical points, and mixture density for several pressures and temperatures. There is a lack of information on the literature regarding the high-pressure phase behavior for the systems involving carbon dioxide + safrole and carbon dioxide + safrole + styrene. The objective of this work is to present new experimental data on the phase behavior for these systems in the temperature range of 303 K to 343 K. The ternary system involving carbon dioxide, styrene, and safrole was also studied with two distinct safrole/styrene mass ratios. All experimental data were modeled with the Peng−Robinson equation of state with classical mixing rules.

2. EXPERIMENTAL SECTION 2.1. Materials. Ethenylbenzene (styrene) was purchased from Sigma-Aldrich (USA) and had a mass fraction purity of 0.99. Carbon dioxide was supplied by White Martins S.A., with a mass fraction purity of 0.999 in the liquid phase. These chemicals were used as received. 5-(2-Propenyl)-1,3-benzodioxole (safrole) was obtained from the long pepper (Piper hispidinervum C. DC.) essential oil distillate. The oil was kindly supplied by an agricultural cooperative of Goiania, Brazil, and was vacuumdistilled (13.33 kPa) in the temperature range of 408 K to 441 K. The purity of safrole was checked by gas chromatography coupled to mass spectrometry (GC-MS), and the chromatograms and spectra obtained were compared with those of a high-purity authentic safrole standard supplied by Merk with a mass fraction purity of 0.995. Thus, the mass fraction purity of vacuum distilled safrole was estimated to be close to the standard one. Chromatographic analyses were performed in a Shimadzu (QP 2010 Plus) gas chromatograph with a mass spectrometer, using a DB-5 capillary column (95 % dimethylpolysiloxane and 5 % diphenyl) (i.d., 0.25 mm; length, 30 m; film thickness, 0.25 μm). B



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adopted in this work. The simulated annealing stochastic algorithm was employed to minimize the maximum likelihood objective function.37,38 The parameters for the system CO2 + styrene were obtained by fitting the experimental data obtained in this work together with those reported in the literature.22−24 Critical properties and constants are presented in Table 1.

and the system was pressurized until one phase is observed within the cell. The system is maintained at this point for about 30 min for stabilization and slowly depressurized at a rate of 6 MPa·h−1 to 30 MPa·h−1 until the observation of a new phase formation. The pressure value is recorded, and the procedure was repeated at least three times for each temperature and global composition. The uncertainty pressure measurement with this apparatus is estimated to be lower than ± 0.05 MPa. Regarding to mass of carbon dioxide loaded into the cell in each experimental run, this is carefully accounted for the volume decay in the syringe pump allowing estimating the uncertainty around ± 0.001 in mole fraction basis. The temperature is controlled with a precision better than ± 0.2 K. 2.3. Modeling. The vapor−liquid equilibrium (VLE) experimental data measured in this work were modeled by the PR-EoS with classical quadratic mixing rules, using two adjustable parameters: kij and lij.34 The binary interaction parameters for the systems CO2 + styrene and CO2 + safrole were estimated through the maximum likelihood method coupled to a bubble- or dewpoint algorithm for VLE calculation according to the Asselineau formulation.35,36 A global temperature fitting procedure was

3. RESULTS AND DISCUSSION Phase equilibrium data obtained in this work for binary and ternary systems were measured in the temperature range from 303 K to 343 K and pressures up to 16 MPa for distinct carbon dioxide mole fractions. The binary interaction parameters for all systems investigated in this work are presented in Table 2. For the system CO2 + styrene, the interaction parameters are estimated by using experimental data of this work and a series of experimental data obtained in literature at different temperatures than that investigated in this work.22−24 For the ternary system modeling, only binary information was taken into account, considering binary interaction parameters for the safrole + styrene system equal to zero. Tables 3 to 6 present the experimental phase equilibrium data for all binary and ternary systems studied. These data are presented as equilibrium pressure with the respective standard deviations uncertainty u(p), transition type (bubble, BP or dew, DP point), temperature, and carbon dioxide mole fractions. Initially, the phase equilibrium data were measured for the binary system CO2 + styrene to check the experimental apparatus and procedure in comparison with literature data.24 These experimental data are shown in Table 3 and depicted in Figure 2 in comparison with the literature experimental data and with the PR-EoS correlation. Figure 2 indicate that the experimental data of this work for CO2 + styrene binary system are in good accordance with the literature ones. Also a satisfactory performance of the equation of state with the experimental phase equilibrium data can be observed. Table 4 presents experimental phase equilibrium data for the binary system CO2 + safrole obtained in this work. Figure 3

Table 1. Critical Properties and Acentric Factor of Carbon Dioxide, Styrene, and Safrole compound

MM/(g·mol−1)

Tc/K

Pc/MPa

ω

44.01 104.10 162.19

304.21 647.15 708.98

7.38 3.99 3.21

0.2236 0.2572 0.3495

CO239 styrene24 safrolea a

Estimated by the Marrero-Gani group contribution method.40

Table 2. Binary Interaction Parameters of the PR-EoS Fitted in This Work system

k12·102

l12·102

N

CO2 (1) + styrene (2) CO2 (1) + safrole (3)

5.5267 6.9546

−5.9331 −3.5749

92 37

Table 3. Experimental VLE Data for Temperature (T), Pressure (p) with Standard Uncertainty u(p), and Mole Fraction x for the Binary System CO2 (1) + Styrene (2)a

a

T/K

x1

p/MPa

u(p)/MPa

T/K

x1

p/MPa

u(p)/MPa

303 303 303 303 303 303 313 313 313 313 313 313 323 323 323 323 323 323

0.614 0.708 0.784 0.877 0.937 0.952 0.614 0.708 0.784 0.877 0.937 0.952 0.614 0.708 0.784 0.877 0.937 0.952

5.47 5.49 5.63 5.94 6.18 6.44 6.48 6.82 6.94 7.31 7.49 7.77 7.58 8.05 8.29 8.79 9.06 9.26b

0.07 0.04 0.07 0.02 0.02 0.01 0.01 0.01 0.03 0.01 0.02 0.02 0.01 0.04 0.02 0.01 0.05 0.01

333 333 333 333 333 333 343 343 343 343 343 343

0.614 0.708 0.784 0.877 0.937 0.952 0.614 0.708 0.784 0.877 0.937 0.952

8.72 9.36 9.82 10.31 10.60b 10.64b 9.90 10.82 11.44 12.13 12.19b 12.17b

0.02 0.03 0.04 0.04 0.03 0.02 0.03 0.01 0.05 0.07 0.02 0.06

u(T) = 0.2 K, u(x) = 0.001. bDew points; all others are bubble points. C



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Figure 3. P−x1−y1 diagram (VLE) for the binary system carbon dioxide (1) + safrole (3). +, BP, T = 303 K; ▲, BP, T = 313 K; ■, BP, T = 323 K; □, DP, T = 323 K; ◆, BP, T = 333 K; ◇, DP, T = 333 K; ●, BP, T = 343 K; ○, DP, T = 343 K. Lines denote calculated values from the PR-EoS.

Figure 2. Comparison between binary P−x1−y1 experimental data (VLE) obtained in this work and literature in different temperatures for the system carbon dioxide (1) + styrene (2). This work: +, BP, T = 303 K; ▲, BP, T = 313 K; ■, BP, T = 323 K; ◆, BP, T = 333 K; ◇ DP, T = 333 K; ● BP, T = 343 K; ○ DP, T = 343 K. Gray +, ref 24 BP T = 303 K; gray ▲, ref 24 BP T = 313 K; gray ■, ref 24 BP T = 323 K; gray ◆, ref 24 BP T = 333 K; gray ◇, ref 24 DP T = 333 K. Lines denote calculated values from the PR-EoS.

force with temperature. Above a certain CO2 mole fraction, at constant temperature, pressure transitions were little influenced by the mixture composition. Dew point transitions were observed for the high CO2 mole fraction in the temperatures of 323 K, 333 K, and 343 K. For all other mixture compositions, only bubble points were observed. To investigate the phase behavior of a comonomer styrene polymerization in high-pressure carbon dioxide medium, phase equilibrium data for two ternary systems composed by carbon dioxide and mixture of monomers in two distinct mass fractions of safrole and styrene were measured. Tables 5 and 6 presents the phase equilibrium data for the CO2 + styrene + safrole

depicts these data in terms of pressure−composition diagrams along with the correlation obtained with the PR-EoS. For this binary system, as for the CO2 + styrene system, only vapor− liquid transitions were observed in all temperatures investigated (303 K to 343 K), and the diagrams can be considered as a type I diagram in the classification of van Konynenburg and Scott.41 As the temperature was increased, at some CO2 mole fraction, the pressure necessary to maintain the system at a homogeneous phase was also increased due to the enhancement in repulsive

Table 4. Experimental VLE Data for Temperature (T), Pressure (p) with Standard Uncertainty u(p), and Mole Fraction x for the Binary System CO2 (1) + Safrole (3)a

a

T/K

x1

p/MPa

u(p)/MPa

T/K

x1

p/MPa

u(p)/MPa

303 303 303 303 303 303 303 303 313 313 313 313 313 313 313 313 323 323 323 323 323 323 323 323

0.492 0.620 0.717 0.808 0.864 0.899 0.936 0.970 0.492 0.620 0.717 0.808 0.864 0.899 0.936 0.970 0.492 0.620 0.717 0.808 0.864 0.899 0.936 0.970

5.06 6.06 6.37 6.56 6.69 6.72 6.61 6.69 5.71 7.27 7.88 8.18 8.43 8.37 8.40 8.26 6.69 8.52 9.51 10.26 10.79 10.93 10.96b 10.38b

0.04 0.01 0.02 0.02 0.02 0.05 0.01 0.15 0.04 0.02 0.01 0.01 0.05 0.02 0.01 0.13 0.03 0.02 0.02 0.05 0.02 0.03 0.03 0.03

333 333 333 333 333 333 333 333 343 343 343 343 343 343 343 343

0.492 0.620 0.717 0.808 0.864 0.899 0.936 0.970 0.492 0.620 0.717 0.808 0.864 0.899 0.936 0.970

7.56 9.87 11.30 12.58 13.31 13.37 13.40b 12.32b 8.49 11.31 13.20 14.93 15.75 15.83 15.81b 14.61b

0.04 0.01 0.07 0.03 0.02 0.02 0.02 0.02 0.03 0.01 0.06 0.01 0.01 0.01 0.04 0.04

u(T) = 0.2 K, u(x) = 0.001. bDew points, all others are bubble points. D



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Table 5. Experimental VLE Data for Temperature (T), Pressure (p) with Standard Uncertainty u(p), and Mole Fraction x for the Ternary System CO2 (1) + Styrene (2) + Safrole (3) with Styrene Mass Fraction of 0.90 in a Styrene/Safrole Mixture on a CO2 Free Basisa

a

T/K

x1

x2

p/MPa

u(p)/MPa

T/K

x1

x2

p/MPa

u(p)/MPa

303 303 303 303 313 313 313 313 323 323 323 323

0.710 0.820 0.908 0.961 0.710 0.820 0.908 0.961 0.710 0.820 0.908 0.961

0.270 0.168 0.086 0.037 0.270 0.168 0.086 0.037 0.270 0.168 0.086 0.037

5.93 5.95 6.13 6.40 7.12 7.25 7.50 7.79 8.39 8.73 9.08 9.23

0.01 0.02 0.06 0.03 0.02 0.01 0.03 0.02 0.02 0.03 0.03 0.02

333 333 333 333 343 343 343 343

0.710 0.820 0.908 0.961 0.710 0.820 0.908 0.961

0.270 0.168 0.086 0.037 0.270 0.168 0.086 0.037

9.81 10.29 10.74 10.78b 11.28 12.02 12.43 12.40b

0.03 0.05 0.02 0.04 0.01 0.04 0.05 0.06

u(T) = 0.2 K, u(x) = 0.001. bDew points, all others are bubble points.

Table 6. Experimental VLE Data for Temperature (T), Pressure (p) with Standard Uncertainty u(p), and Mole Fraction x for the Ternary System CO2 (1) + Styrene (2) + Safrole (3) with Styrene Mass Fraction of 0.75 in a Styrene/Safrole Mixture on a CO2 Free Basisa

a

T/K

x1

x2

p/MPa

u(p)/MPa

T/K

x1

x2

p/MPa

u(p)/MPa

303 303 303 303 313 313 313 313 323 323 323 323

0.719 0.825 0.910 0.958 0.719 0.825 0.910 0.958 0.719 0.825 0.910 0.958

0.231 0.144 0.074 0.035 0.231 0.144 0.074 0.035 0.231 0.144 0.074 0.035

5.77 6.05 6.17 6.36 7.06 7.48 7.59 7.80 8.45 9.06 9.21 9.38

0.02 0.03 0.03 0.04 0.01 0.05 0.01 0.02 0.07 0.01 0.03 0.06

333 333 333 333 343 343 343 343

0.719 0.825 0.910 0.958 0.719 0.825 0.910 0.958

0.231 0.144 0.074 0.035 0.231 0.144 0.074 0.035

9.91 10.78 11.19 11.20b 11.56 12.63 13.11 13.10b

0.01 0.04 0.05 0.08 0.02 0.03 0.12 0.15

u(T) = 0.2 K, u(x) = 0.001. bDew points, all others are bubble points.

Figure 5. P−x1−y1 diagram (VLE) for the ternary system carbon dioxide (1) + styrene (2) + safrole (3). Styrene/safrole mixture with a styrene mass fraction of 0.75 on CO2 free basis (+, BP, T = 303 K; ▲, BP, T = 313 K; ■, BP, T = 323 K; ◆, BP, T = 333 K; ◇, DP, T = 333 K; ●, BP, T = 343 K; ○, DP, T = 343 K. Lines denote calculated values from the PR-EoS.

Figure 4. P−x1−y1 diagram (VLE) for the ternary system carbon dioxide (1) + styrene (2) + safrole (3). Styrene/safrole mixture with a styrene mass fraction of 0.90 on CO2 free basis (+, BP, T = 303 K; ▲, BP, T = 313 K; ■, BP, T = 323 K; ◆, BP, T = 333 K; ◇, DP, T = 333 K; ●, BP, T = 343 K; ○, DP, T = 343 K. Lines denote calculated values from the PR-EoS.

the temperature range of 303 K to 343 K. Only four global compositions were measured in each ternary system with the aim of verify the feasibility and capability of the thermodynamic model to correlate ternary systems with interaction parameters fitted from binary information.

ternary systems for thte styrene + safrole mixture with styrene mass fractions of 0.90 and 0.75 on CO2 free basis, respectively. The experimental data presented in Tables 5 and 6 are depicted in Figures 4 and 5 in terms of pressure−composition diagrams in E



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As can be seen in Figures 4 and 5, the PR-EoS with quadratic mixing rules was capable of satisfactory predict the ternary phase equilibrium data using just binary interaction parameters. As in binary systems, only vapor−liquid equilibria were recorded for the two ternary systems investigated. In all temperatures investigated the pressure transitions of the ternary systems were more close to those of the CO2 + styrene system, mainly due to the greater amount of styrene in the solute mixture. Also, all pressure transitions for a specific isotherm of the ternary systems were at intermediate values compared to the same isotherm of binary systems, in agreement with some previous works in the literature.42,43

4. CONCLUSIONS The phase behavior of binary and ternary systems consisting of styrene, safrole, and pressurized carbon dioxide were investigated in the temperature range from 303 K to 343 K, in a wide range of CO2, resulting in phase transition pressures up to 16 MPa. For all systems vapor−liquid equilibrium were recorded and classified as type I global phase behavior. The PREoS provided a satisfactory representation of the experimental phase equilibrium data obtained adopting a global fitting parameter with respect to temperature. Experimental data obtained here may be useful for conducting chemical modifications of safrole or copolymerization reactions of styrene and safrole in compressed CO2 media.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +55-79-32182157. Fax: +55-79-32182190. E-mail: [email protected]. Funding

The authors thank CAPES, CNPq, and FAPITEC/SE for the financial support and scholarships. Notes

The authors declare no competing financial interest.

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REFERENCES

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Phase Equilibria of the Systems CO2 + Styrene, CO2 + Safrole, and

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