High Pressure Phase Equilibrium Data for the Ternary System

Article pubs.acs.org/jced

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

High Pressure Phase Equilibrium Data for the Ternary System Containing Carbon Dioxide, Dichloromethane, and ε‑Caprolactone Diego Alex Mayer,† Evertan Antonio Rebelatto,† Papa Matar Ndiaye,‡ Marcelo Lanza,† Deb́ ora de Oliveira,† Selene M. A. Guelli U. de Souza,† and Jose ́ Vladimir Oliveira*,† †

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Department of Chemical and Food Engineering, Federal University of Santa Catarina, P.O. Box 476, Florianópolis, Santa Catarina 88040-900, Brazil ‡ Programa de Engenharia Química/COPPE, Universidade Federal do Rio de Janeiro, Cidade Universitária, Rio de Janeiro, RJ CEP: 21949-972, Brazil S Supporting Information *

ABSTRACT: This work reports experimental phase equilibrium data for the ternary system involving ε-caprolactone, carbon dioxide, and dichloromethane. Such data provide fundamental information to conduct polymerization reactions in supercritical carbon dioxide medium. The experiments were performed using a variable-volume view cell over the temperature range from 323.15 to 353.15 K and different mass ratios of dichloromethane to ε-caprolactone (0.5:1, 1:1, and 2:1). Phase transitions of vapor−liquid at the bubble point (VLE-PB), liquid−liquid (LLE), and vapor−liquid−liquid (VLLE) types were observed. The experimental results were modeled using the Peng−Robinson EoS with the van der Waals mixing rule, resulting in a good representation of experimental phase equilibrium data.

1. INTRODUCTION Recently, considerable attention has been given to the production of biocompatible, biodegradable, and nontoxic aliphatic polyesters. These compounds play an important role in biomedical, pharmaceutical, and food applications.1−3 One polyester that has received growing interest is poly(εcaprolactone) because besides being compatible it can also be degraded and eliminated from the human body as low molar mass byproducts, with no residual side effects.3−5 Poly(ε-caprolactone) is a semicrystalline polymer with a melting temperature between 329.15 and 338.15 K.6 There are in the literature described two techniques for producing poly(ε-caprolactone): polycondensation of a hydroxycarboxylic acid of 6-hydroxyhexanoic, and the ring-opening polymerization (ROP) of ε-caprolactone.6 Synthesis of poly(εcaprolactone) by ROP can be performed by enzymatic, organic, and metal catalysts. However, biomedical and food applications require highly pure polymers. Thus, in order to produce a polymer free of toxic residues, the ring-opening polymerization via enzyme-catalyzed reaction, also known as enzymatic ring-opening polymerization (e-ROP), stands out in relation to the other techniques.3,7 Literature reveals several studies on ε-caprolactone polymerization in organic solvents, such as toluene, benzene, and cyclohexane.8−10 Nevertheless, these solvents are toxic and hence supercritical carbon dioxide (scCO2) appears as a good candidate for replacing such solvents due to its well-known © XXXX American Chemical Society

characteristics (low-cost solvent, nontoxic, and nonflammable) and favorable transport properties that can accelerate the mass transfer in enzymatic reactions.3,11 Though scCO2 may be a good solvent for ε-caprolactone, it is not a proper solvent for poly(ε-caprolactone), leading to the sedimentation of its organic solutions upon mixing.5,12 An alternative to overcome such drawback is to use a cosolvent together with scCO2, for example, dichloromethane. Dichloromethane is a colorless and volatile liquid at ambient conditions, being widely used as a solvent because it is considered one of the least harmful organochloride compounds.13 The literature presents some experimental data for the binary system (carbon dioxide + dichloromethane) at different temperatures.14−20 Gonzales et al.15 invetigated the highpressure vapor−liquid equilibrium for binary systems carbon dioxide + dichloromethane at 311.41 and 326.95 K, and Corazza et al.16 investigated the behavior of phase equilibrium between the carbon dioxide and dichloromethane in the temperature range from 313.15 at 343 K. Regarding the binary system (carbon dioxide + εcaprolactone), there are in the literature some experimental Special Issue: Latin America Received: November 1, 2018 Accepted: March 11, 2019

A

DOI: 10.1021/acs.jced.8b01017 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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Table 1. Chemical Name, Molecular Formula, CASRN, Supplier, Purification Method and Minimum Mass Fraction Purity of the Materials Used (Purity Provided by Suppliers) chemical name ε-caprolactone carbon dioxide dichloromethane a

molecular formula C6H10O2 CO2 CH2Cl2

CASRN 502-44-3 124-38-9 75-09-2

supplier Sigma-Aldrich White Martins S.A. Sigma-Aldrich

purification method dried none none

b

minimum mass fraction purity 0.970 0.999 0.998

6-Hexanolactone. bThe ε-caprolactone was dried at 333.15 K in a vacuum oven (0.01 MPa) for 72 h.

a

Figure 1. High-pressure phase equilibria apparatus: (C1) solvent reservoir (CO2); (RB1) recirculation bath; (SP) syringe pump; (EC) equilibrium cell; (MS) magnetic stirrer; (LS) light source; (SW) sapphire windows; (TI) temperature indicator; (TC) thermocouple; (PI) pressure indicator; (PT) pressure transducer; (PS) power supply; (V1, V3, V4, V5 and V6) ball valve; (V2) check valve; (V7 and V8) micrometric valve.

data of phase equilibrium at different temperatures.5,21,22 Bergeot et al.21 presented high pressure P−x data for the system ε-caprolactone/carbon dioxide, while Xu et al.22 investigated the (vapor + liquid) equilibrium of different lactones in supercritical carbon dioxide. Bender et al.5 reported a study on the high-pressure phase equilibria of supercritical carbon dioxide and different lactones, among them, the εcaprolactone. It is worth noting that there are no experimental data of phase equilibrium for the ternary system (carbon dioxide + εcaprolactone + dichloromethane) at different temperatures. This type of experimental data is important in the kinetics of polymerization. Veneral et al.23 investigated the kinetics of enzymatic ring-opening polymerization of ε-caprolactone by Novozym 435 using scCO2 as solvent and dichloromethane as cosolvent in a packed-bed reactor (PBR) system. In that work, the authors observed that the use of dichloromethane as cosolvent resulted in an impressive improvement in the solubility and mass transfer of the studied system, which prevented accumulation or precipitation of a polymer on the enzymatic porous beads surface. In this context, the knowledge of phase behavior involving εcaprolactone, scCO2, and dichloromethane is very important to better understand the several aspects in the polymerization reaction, mainly the mass transfer between chemical species involved in the polymerizations reactions. The main objective of this work was to investigate experimentally the use of dichloromethane as cosolvent to the system (carbon dioxide + ε-caprolactone) at different dichloromethane-to-monomer mass ratios (0.5:1; 1:1, and 2:1). In addition, the Peng− Robinson EoS24 with the van der Waals mixing rule was employed to represent the experimental phase equilibrium data.

2. EXPERIMENTAL SECTION 2.1. Materials. The solvent carbon dioxide was bought from White Martins S.A. (Brazil), dichloromethane was used as a cosolvent and bought from Sigma-Aldrich (U.S.A.) and εcaprolactone (6-hexanolactone, CAS number 502-44-3) was bought from Sigma-Aldrich (U.S.A.). The ε-caprolactone was dried in a vacuum oven at 333.15 K and 0.01 MPa for 72 h, resulting in a water content of 0.184% with standard uncertainty of 0.03%, measured by the Karl Fischer Coulometric Titrator for moisture determination (HI-904HANNA instruments). Table 1 provides the chemical names, molecular formula, CASRN (CAS Registry Number), supplier, purification method, and minimum mass fraction purity of all components used in this work. The minimum mass fraction purity of all components was reported by the supplier. 2.2. Phase Equilibrium Apparatus and Procedure. To obtain the experimental data of phase equilibrium at high pressures the synthetic static method was used. In this method, the composition of the equilibrium phases is determined indirectly, without the need for removal of the respective samples. Initially, precise quantities of the pure substances (εcaprolactone, dichloromethane, and CO2) were introduced into the equilibrium cell, such that the overall composition of the mixture, at the beginning of the experiment, was known. The pressure and temperature conditions were adjusted, promoting the formation of a homogeneous solution. Figure 1 shows a schematic diagram of the experimental apparatus used in this work. This is described in detail in a variety of previous studies.25−27 This apparatus can be safely operated up to 27.50 MPa with a pressure expanded uncertainty of 0.1 MPa, provided by the indicator systems. For the phase equilibrium experiments, precise amounts of ε-caprolactone and dichloromethane were weighed on a precision balance scale (Shimadzu, model AY220 with 0.0001 g accuracy) and placed quickly inside the equilibrium B



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cell, which was quickly closed and connected to the pressure source. A known volume of CO2 was added to the equilibrium cell using the syringe pump which was maintained at 10.0 MPa and 280.15 K. The system was continuously stirred with the help of a Teflon-coated magnetic stir bar and the internal pressure of the cell was gradually increased until reaching a single-phase system. Finally the heating system was started using the circulation bath (RB2). After stabilization of the temperature, measurements of the phase equilibria (bubble point) were initiated by reducing the pump pressure, by programming, until the appearance of a second phase that was detected through the visualization through the sapphire window. Each measurement was repeated at least three times For the system (carbon dioxide + ε-caprolactone + dichloromethane) the vapor−liquid equilibrium at the bubble point (VLE-BP), liquid−liquid equilibrium (LLE), and vapor− liquid−liquid equilibrium (VLLE) by changing the system pressure at constant temperature were investigated. According to Santos et al.6 the VLE-BP transition is characterized by the formation of a bubble at the top of the cell during system depressurization. When the liquid−liquid equilibrium (LLE) appeared, the transition point was identified by the appearance of a new phase, which stretched across the top of the cell, followed by the complete system clouding. The depressurization was followed by the appearance of a third vapor phase at the top of the cell characterizing the vapor−liquid−liquid equilibrium (VLLE). To facilitate the understanding of the effect of dichloromethane on system investigated, the ternary system {(carbon dioxide (1) + ε-caprolactone (2) + dichloromethane (3)} was treated as a pseudobinary system {carbon dioxide (1) + εcaprolactone (2)} in dichloromethane free-basis, at three different mass ratios of dichloromethane to ε-caprolactone. The experimental phase equilibrium data were obtained in the temperature range from 323.15 to 353.15 K and pressures up to 25.8 MPa; the investigated mass ratio of dichloromethane to ε-caprolactone was kept constant at 0.5:1, 1:1, and 2:1, corresponding to the following molar ratio: 0.67:1, 1.35:1, and 2.69:1, respectively. The overall mass fraction (w1′) of the system {carbon dioxide (1) + ε-caprolactone (2) + dichloromethane (3)}, in dichloromethane free-basis, was varied from 0.3671 to 0.6867; 0.3681 to 0.8010, and 0.6895 to 0.9376 for the mass ratio of dichloromethane to ε-caprolactone of 0.5:1, 1:1, 2:1, respectively. 2.3. Thermodynamic Modeling. In this work, the Peng− Robinson (PR) EoS28 was employed to represent the experimental phase equilibrium data. For PVT data correlations, the PR EoS represents a significant improvement when compared to the Soave−Redlich−Kwong (SRK) state equation.24,29 While the SRK equation predicts that the critical compressibility factor Zc is 0.333 and, consequently, poor liquid density predictions are obtained; the value of Zc predicted by the PR EoS is 0.307.29 P=

RT a − v−b [v(v + b) + b(v − b)]

a=

(3)

f (ω , Tr) = (0.3764 + 1.5422ω − 0.2699ω 2)(1 − Tr0.5) (4)

For components with large acentric factor values (ω > 0.49), the following function is used: f (ω , Tr) = (0.379642 + 1.48503ω − 0.164423ω 2 − 0.016666ω3)(1 − Tr0.5)

(5)

Application of the PR EoS to fluid mixtures requires a mixing rule in order to describe the mixture from the pure-component properties of the system, as n

a=

n

∑ ∑ xixjaij (6)

i=1 j=1 n

b=

∑ xibi

(7)

i=1

with, aij = [(aiaj)0.5 ](1 − kij)

(8)

where kij is the binary interaction parameter, usually estimated from fitting experimental data to the EoS. The pure component properties for carbon dioxide, ε-caprolactone, and dichloromethane are presented in Table 2. Table 2. Characteristic Parameters of Pure Compounds Used in this Worka Tc (K)

compound ε-caprolactone carbon dioxide dichloromethane

b

549.16 304.21c 510c

Pc (MPa) b

3.68 7.38c 6.08c

MM (g mol−1)

ω b

2.0567 0.2236c 0.1990c

114.15d 44.01d 84.93d

a Tc , critical temperature; Pc , critical pressure; ω, acentric factor; MM , molar mass. bReference 5. cReference 28. dReference 35.

A point of fundamental importance in the parameter estimation step is the definition of the objective function. In this work, for the estimation of the binary interaction parameters (k12 , k13 and k 23) the following objective function was defined: nobs

OF =

∑ (Pical − Piexp)2

(9)

i=1

Piexp

where OF denotes the objective function, represents the arithmetic mean of three experimental measurements of phase transition pressures, Pical represents the calculated pressure by the mathematical model, and nobs denotes the number of observations. In this work, the OF was minimized and the results of the generated residues were presented by absolute deviation (AD) (eq 10) and root-mean-square deviation values (rmsd ) (eq 11):

(1)

where RT b = 0.0778 c Pc

0.45724R2Tc2 [1 + f (ω , Tr)]2 Pc

nobs

AD = (2)

∑ i=1

C

(Pical − Piexp) nobs

(10) DOI: 10.1021/acs.jced.8b01017 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data nobs

rmsd =

∑ i=1

(Pical − Piexp)2 nobs

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Table 3. Phase Equilibrium Results for the Ternary System {Carbon Dioxide (1) + ε-Caprolactone (2) + Dichloromethane (3)}, in Dichloromethane-Free Basis, at Dichloromethane to ε-Caprolactone Mass Ratio of 0.5:1a

(11)

The estimation of the binary interaction parameters was performed by minimizing eq 9 using the particle swarm optimization (PSO), a stochastic method, while the optimization procedure was refined using the simplex method. The PSO has been used in last years for parameter estimation in the phase equilibria process, where the traditional newton methods face convergence problems.30,31 The main characteristic of the stochastic PSO method is the independence of initial estimates, Stochastic methods are characterized by performing a large number of evaluations of the objective function throughout the search region, in order to increase the probability of finding the global optimum of the objective function. In addition, the randomness of the search procedure is high, to prevent local minima. Furthermore, these techniques do not need a very precise initial estimate of the solution and do not use the derivatives to reach the optimal point, thus, overcoming the difficulties associated with the uses of jacobian methods. The deterministic simplex methods have as their main characteristic the use of derivatives function and are highly dependent on the initial guess. In this way, these methods can converge to local minimums. The main advantages are the rapid convergence at values close to the solution.

T/K

P/MPa

w1′ = 0.3671 (w2′ = 323.15 6.83 333.15 8.02 343.15 9.42 353.15 10.87 w1′ = 0.4221 (w2′ = 323.15 7.76 333.15 9.24 343.15 10.97 353.15 12.83 w′1 = 0.5006 (w′2 = 323.15 8.53 333.15 10.64 343.15 13.19 353.15 15.40 w1′ = 0.5360 (w2′ = 323.15 9.00 333.15 11.09 343.15 13.82 353.15 16.42 w1′ = 0.5715 (w2′ = 323.15 9.66 333.15 12.52 343.15 15.02 353.15 17.60

3. RESULTS AND DISCUSSION Tables 3 to 5 show the experimental phase transition data measured for the ternary system {carbon dioxide(1) + εcaprolactone(2) + dichloromethane(3)} in dichloromethane free-basis, at three different dichloromethane to ε-caprolactone mass ratios, 0.5:1, 1:1, 2:1, respectively. These tables show the equilibrium results in terms of pressure and the phase transition type of phase equilibrium: VLE-BP, LLE, and VLLE. The values of the absolute global compositions for the ternary system are shown in the Supporting Information. Figures 2 to 4 present the experimental and calculated phase equilibrium value in P−w diagram forms to different εcaprolactone and for the temperatures of 323.15, 333.15, 343.15, and 353.15 K. The upper limit of experimental pressure measurements was defined as 27.5 MPa, the pressure that the apparatus can be safely operated. For the systems with mass ratio of 0.5:1, 1:1, and 2:1 of dichloromethane to ε-caprolactone, for all isotherms of the 323.15, 333.15, 343.15, and 353.15 K, as shown in Tables 3 to 5 and Figures 2 to 4, it was observed that phase transitions of VLE-BP type occurred until the mass fraction of carbon dioxide was 0.5715, 0.6638, and 0.7783, respectively. The VLE-BP was characterized by the formation of a bubble at the top of the cell during the depressurization of the system. For mass fractions of carbon dioxide greater than or equal to 0.6638, 0.6872, and 0.8011 the occurrence of phase transitions of LLE and VLLE types was observed. The LLE was identified from the appearance of a new phase which stretched across the top of the cell and the appearance of clouding of the complete system, and the VLLE was characterized by the appearance of a third vapor phase at the top of the cell during the depressurization of the system. It can also be noted that a decrease in the dichloromethane mass ratio required higher pressures to solubilize all components, in other words, to reach a one-phase region. In addition, it has been observed that the

transition type 0.6329) VLE-BP VLE-BP VLE-BP VLE-BP 0.5779) VLE-BP VLE-BP VLE-BP VLE-BP 0.4994) VLE-BP VLE-BP VLE-BP VLE-BP 0.4640) VLE-BP VLE-BP VLE-BP VLE-BP 0.4285) VLE-BP VLE-BP VLE-BP VLE-BP

T/K

P/MPa

transition type

w1′ = 0.6070 (w2′ = 0.3930) 323.15 10.53 LLE 323.15 10.40 VLLE 333.15 13.77 LLE 333.15 13.30 VLLE 343.15 16.93 LLE 343.15 16.50 VLLE 353.15 19.85 LLE 353.15 19.60 VLLE w1′ = 0.6454 (w2′ = 0.3546) 323.15 12.75 LLE 323.15 10.45 VLLE 333.15 16.62 LLE 333.15 13.40 VLLE 343.15 19.77 LLE 343.15 16.50 VLLE 353.15 22.83 LLE 353.15 19.70 VLLE w′1 = 0.6867 (w′2 = 0.3133) 323.15 16.35 LLE 323.15 10.50 VLLE 333.15 19.78 LLE 333.15 13.50 VLLE 343.15 23.89 LLE 343.15 16.60 VLLE 353.15 19.70 VLLE

a

VLE-BP denotes vapor−liquid-equilibrium, type bubble point; LLE denotes liquid−liquid-equilibrium; VLLE denotes vapor−liquid− liquid equilibrium, T, system temperature, P, system pressure w1′, denotes the mass fraction of carbon dioxide on a dichloromethane free-basis and w2′ denotes mass fraction of ε-caprolactone on a dichloromethane free-basis.Variable expanded uncertainties with 95% of confidence level U(T) = 0.50 K; U(P) = 0.50 MPa; U(w1′) and U(w′2 ) = 0.0010; U(dichloromethane to monomer mass ratio) = 0.0019.

higher is the mass ratio of dichloromethane to ε-caprolactone, the greater VLE-BP predominated to higher mass fractions of carbon dioxide. With the increase of carbon dioxide mass fraction, a greater increase in system pressure was required for the solubilization of the system to occur (mainly in the liquid−liquid region), which made it difficult to measure data (liquid−liquid equilibrium) for the mass fractions higher than 0.6867, 0.8100, and 0.8260 for the respective dichloromethane to εcaprolactone mass ratio of 0.5:1, 1:1, and 2:1. This type of behavior was also observed in the work of Santos et al.,32 who reported data for the system {carbon dioxide (1) + methyl methacrylate (2) + poly(dimethylsiloxane) (3)}. In both systems, the increase in the mass fraction of carbon dioxide perturbed the interactions between solute and cosolvent, due to the strong interactions that carbon dioxide has with dichloromethane in this work, and with methyl methacrylate in the other case. Thus, carbon dioxide acts in this case as an antisolvent, due to the partition of the cosolvent (dichloromethane) to the lightest phase CO2-richest component, leading to higher pressure values to solubilize the system, that is, to reach the one-phase region. D



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Table 4. Phase Equilibrium Results for the Ternary System {Carbon Dioxide (1) + ε-Caprolactone (2) + Dichloromethane (3)}, in Dichloromethane-Free Basis, at Dichloromethane to ε-Caprolactone Mass Ratio of 1:1a T/K

P/MPa

w1′ = 0.3681 (w2′ = 323.15 5.54 333.15 6.35 343.15 7.24 353.15 8.17 w1′ = 0.5022 (w2′ = 323.15 7.02 333.15 8.09 343.15 9.50 353.15 10.93 w′1 = 0.6066 (w′2 = 323.15 7.96 333.15 9.54 343.15 11.60 353.15 13.96 w1′ = 0.6453 (w2′ = 323.15 8.36 333.15 10.06 343.15 12.49 353.15 15.26 w1′ = 0.6638 (w2′ = 323.15 8.70 333.15 10.30 343.15 13.00 353.15 16.16

transition type 0.6319) VLE-BP VLE-BP VLE-BP VLE-BP 0.4978) VLE-BP VLE-BP VLE-BP VLE-BP 0.3934) VLE-BP VLE-BP VLE-BP VLE-BP 0.3547) VLE-BP VLE-BP VLE-BP VLE-BP 0.3362) VLE-BP VLE-BP VLE-BP VLE-BP

T/K

P/MPa

w1′ = 0.6872 (w2′ = 323.15 9.65 323.15 8.40 333.15 12.68 333.15 10.63 343.15 16.11 343.15 13.07 353.15 19.47 353.15 15.10 w1′ = 0.7312 (w2′ = 323.15 11.76 323.15 8.66 333.15 14.87 333.15 10.83 343.15 18.50 343.15 13.07 353.15 21.53 353.15 16.30 w′1 = 0.7728 (w′2 = 323.15 19.07 323.15 8.90 333.15 22.02 333.15 11.00 343.15 25.47 343.15 13.20 w′1 = 0.8010 (w′2 = 323.15 25.75 323.15 8.81

Table 5. Phase Equilibrium Results for the Ternary System {Carbon Dioxide (1) + ε-Caprolactone (2) + Dichloromethane (3)}, in Dichloromethane-Free Basis, at Dichloromethane to ε-Caprolactone Mass Ratio of 2:1a T/K

transition type

P/MPa

transition type

w1′ = 0.5012 (w2′ = 0.4988) 323.15 5.05 VLE-BP 333.15 5.77 VLE-BP 343.15 6.57 VLE-BP 353.15 7.50 VLE-BP w1′ = 0.6342 (w2′ = 0.3658) 323.15 6.28 VLE-BP 333.15 7.49 VLE-BP 343.15 8.78 VLE-BP 353.15 10.20 VLE-BP w1’= 0.6857 (w′2 = 0.3143) 323.15 6.97 VLE-BP 333.15 8.18 VLE-BP 343.15 9.64 VLE-BP 353.15 11.20 VLE-BP w1′ = 0.7296 (w2′ = 0.2704) 323.15 7.54 VLE-BP 333.15 8.95 VLE-BP 343.15 10.48 VLE-BP 353.15 12.15 VLE-BP w1′ = 0.7528 (w2′ = 0.2472) 323.15 7.76 VLE-BP 333.15 9.11 VLE-BP 343.15 10.75 VLE-BP 353.15 12.53 VLE-BP w′1 = 0.7783 (w′2 = 0.2211) 323.15 7.98 VLE-BP 333.15 9.57 VLE-BP 343.15 11.38 VLE-BP 353.15 13.16 VLE-BP

0.3128) LLE VLLE LLE VLLE LLE VLLE LLE VLLE 0.2688) LLE VLLE LLE VLLE LLE VLLE LLE VLLE 0.2272) LLE VLLE LLE VLLE LLE VLLE 0.1990) LLE VLLE

a

VLE-BP denotes vapor−liquid-equilibrium, type bubble point; LLE denotes liquid−liquid-equilibrium; VLLE denotes vapor−liquid− liquid equilibrium, T, system temperature, P, system pressure w′1, denotes the mass fraction of carbon dioxide on a dichloromethane free-basis and w′2 denotes mass fraction of ε-caprolactone on a dichloromethane free-basis.Variable expanded uncertainties with 95% of confidence level U(T) = 0.50 K; U(P) = 0.50 MPa; U(w′1) and U(w2′ ) = 0.0010; U(dichloromethane to monomer mass ratio) = 0.0070.

T/K

P/MPa

transition type

w1′ = 0.8011 (w2′ = 0.1989) 323.15 10.99 LLE 323.15 8.00 VLLE 333.15 14.19 LLE 333.15 10.20 VLLE 343.15 17.18 LLE 343.15 12.00 VLLE 353.15 20.59 LLE 353.15 13.20 VLLE w1′ = 0.8260 (w2′ = 0.1740) 323.15 15.55 LLE 323.15 8.20 VLLE 333.15 18.83 LLE 333.15 10.30 VLLE 343.15 21.58 LLE 343.15 12.10 VLLE 353.15 24.53 LLE 353.15 13.50 VLLE w1’= 0.8799 (w′2 = 0.1201) 323.15 8.30 VLLE 333.15 10.30 VLLE 343.15 12.20 VLLE 353.15 13.40 VLLE w1′ = 0.9376 (w2′ = 0.0624) 323.15 8.20 VLLE 333.15 10.40 VLLE 343.15 12.10 VLLE 353.15 13.60 VLLE

a

VLE-BP denotes vapor−liquid-equilibrium, type bubble point; LLE denotes liquid−liquid-equilibrium; VLLE denotes vapor−liquid− liquid equilibrium, T, system temperature, P, system pressure w1′, denotes the mass fraction of carbon dioxide on a dichloromethane free-basis and w2′ denotes mass fraction of ε-caprolactone on a dichloromethane free-basis.Variable expanded uncertainties with 95% of confidence level U(T) = 0.50 K; U(P) = 0.50 MPa; U(w1′) and U(w′2 ) = 0.0010; U(dichloromethane to monomer mass ratio) = 0.0126.

Figures 5 to 7 illustrate the experimental and calculated phase equilibrium value in P−T diagram forms at different mass ratios of dichloromethane to ε-caprolactone of 0.5:1, 1:1, and 2:1, respectively. In these figures, it is possible to observe that higher pressures are needed to solubilize all components in only one-phase with the increase of temperature. This is a behavior characteristic of a lower critical solution temperature (LCST), where below this temperature the components of a system are soluble in any proportion and above occurs the formation of two phases, vapor−liquid or liquid−liquid. This behavior is characteristic of the system involving lactones, solvents as chloroform and dichloromethane, and antisolvent as carbon dioxide.11,33 According to the classification of van Konynenburg and Scott,34 the phase behavior of the ternary systems studied in this work may be classified as type V, that was also found in the binary systems containing ε-caprolactone and carbon dioxide. The PR EoS model with the van der Waals quadratic mixing rule was employed to predict the phase equilibrium behavior for the ternary system {carbon dioxide (1) + ε-caprolactone

(2) + dichloromethane (3)}. The binary interaction parameters (k12 , k13 and k 23) were adjusted using the experimental phase equilibrium data obtained in this work. Several strategies were tested. First experimental data were fitted using all binary parameters independent to temperature. In a second step the temperature dependence was included in all parameters. Results show that k13 and k 23 are not sensitive to temperature and thus, their values were kept constant and the temperature dependence of k12 was investigated. For this purpose, at each given temperature, the objective function was minimized to find the corresponding k12 and then the obtained parameters were fitted as a function of temperature to give the eq 12: k12 = 0.001·T[K ] − 0.2865

(12)

The binary interaction parameters (k12 , k13 and k 23) together with the absolute deviation (AD) and mean square value (rmsd ) are presented in Table 6, where it can be observed that E



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Figure 2. Pressure−overall composition diagram for the system {carbon dioxide (1) + ε-caprolactone (2) + dichloromethane (3)}, on a dichloromethane free-basis, at a dichloromethane to ε-caprolactone mass ratio of 0.5:1. Experimental data: 323:15 K: ◨ (BP), ■ (LL), and □ (LLV). 333:15 K: ◑ (BP), ● (LL), and ○ (LLV). 343:15 K: ◮ (BP), ▲ (LL), and △ (LLV). 353:15 K: ⧩ (BP), ▼ (LL), and ▽ (LLV). Continuous lines denote calculated values applying the PREoS model with global temperature fitted parameters.

Figure 4. Pressure-overall composition diagram for the system {carbon dioxide (1) + ε-caprolactone (2) + dichloromethane (3)}, on a dichloromethane free-basis, at a dichloromethane to ε-caprolactone mass ratio of 2:1. Experimental data: 323:15 K: ◨ (BP), ■ (LL), and □ (LLV). 333:15 K: ◑ (BP), ● (LL), and ○ (LLV). 343:15 K: ◮ (BP), ▲ (LL), and △ (LLV). 353:15 K: ⧩ (BP), ▼ (LL), and ▽ (LLV). Continuous lines denote calculated values applying the PREoS model with global temperature fitted parameters.

Figure 3. Pressure-overall composition diagram for the system {carbon dioxide (1) + ε-caprolactone (2) + dichloromethane (3)}, on a dichloromethane free-basis, at a dichloromethane to ε-caprolactone mass ratio of 1:1. Experimental data: 323:15 K: ◨ (BP), ■ (LL), and □ (LLV). 333:15 K: ◑ (BP), ● (LL), and ○ (LLV). 343:15 K: ◮ (BP), ▲ (LL), and △ (LLV). 353:15 K: ⧩ (BP), ▼ (LL), and ▽ (LLV). Continuous lines denote calculated values applying the PREoS model with global temperature fitted parameters.

Figure 5. Pressure−temperature diagram for the system {carbon dioxide (1) + ε-caprolactone (2) + dichloromethane (3)}, on a dichloromethane free-basis, at a dichloromethane to ε-caprolactone mass ratio of 0.5:1. Experimental data: ◨ (BP) [w1 = 0.2788; w2 = 0.4807; w3 = 0.2405]; ◑ (BP) [w1 = 0.4003; w2 = 0.3993; w3 = 0.2004]; ▶ (LL) [w1 = 0.5482; w2 = 0.3012; w3 = 0.1506]; ◀ (LL) [w1 = 0.5943; w2 = 0.2711; w3 = 0.1347]. Continuous lines denote calculated values applying the PR-EoS model with global temperature fitted parameters.

the thermodynamic model was able to correlate properly phase equilibrium transition, with AD and rmsd smaller than or equal to 0.0101 MPa by isotherms. The good performance of PR EoS model with the van der Waals mixing rule becomes more evident when Figures 2 to 7 are analyzed. Here the model was able to represent different types of phase equilibrium, vapor−liquid and liquid−liquid equilibrium, for different mass ratio of dichloromethane to εcaprolactone of 0.5:1, 1:1, and 2:1, with a set of parameters

(k12 , k13 and k 23), for all isotherms of the 323.15, 333.15, 343.15, and 353.15 K. Figure 8 shows the experimental values obtained in this work at temperatures of 333.15 K for the ternary system {carbon dioxide (1) + ε-caprolactone (2) + dichloromethane (3)}, on a dichloromethane free-basis, for the mass ratios of dichloromethane to ε-caprolactone 0.5:1, 1:1, and 2:1. These values are compared with experimental results reported by Bender et al.5 for the binary system of (carbon dioxide (1) + ε-caprolactone F



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Table 6. Binary Interaction Parameters of PR-EoS Fitted in This Work for the Ternary System {Carbon Dioxide (1) + εCaprolactone (2) + Dichloromethane (3)}

a

T/K

k12a

k13

k 23

AD/MPa

rmsd

323.15 333.15 343.15 353.15

0.0343 0.0417 0.0510 0.0642

0.0220 0.0220 0.0220 0.0220

−0.0360 −0.0360 −0.0360 −0.0360

0.08 0.08 0.07 0.07

0.10 0. 10 0.10 0.10

k12 calculated as k12 = 0.001 × T[K] − 0.2865.

Figure 6. Pressure−temperature diagram for the system {carbon dioxide (1) + ε-caprolactone (2) + dichloromethane (3)}, on a dichloromethane free-basis, at a dichloromethane to ε-caprolactone mass ratio of 1:1. Experimental data: ◨ (BP) [w1 = 0.2255; w2 = 0.3870; w3 = 0.3875]; ◑ (BP) [w1 = 0.4347; w2 = 0.2819; w3 = 0.2834]; ▶ (LL) [w1 = 0.5249; w2 = 0.2389; w3 = 0.2362]; ◀ (LL) [w1 = 0.5764; w2 = 0.2119; w3 = 0.2117]. Continuous lines denote calculated values applying the PR-EoS model with global temperature fitted parameters.

Figure 8. Comparison between experimental values obtained in this work for the ternary system {carbon dioxide (1) + ε-caprolactone (2) + dichloromethane (3)}, on a dichloromethane free-basis with three different dichloromethane to ε-caprolactone mass ratios: 0.5:1 ◨ (BP), ■ (LL), and □ (LLV)]; 1:1 ◑ (BP), ● (LL), and ○ (LLV)]; and 2:1 ◮ (BP), ▲ (LL), and △ (LLV)] with the literature5 for the binary system {carbon dioxide (1) + ε-caprolactone (2)} ◇(BP), crossed diamond (DP)] at the temperature of 333.15 K.

a nonpolar solvent. As the monomer used in this work is also polar, a decrease in dichloromethane content caused a corresponding decrease in the system polarity, reducing the solvating power of the whole solvent medium (CO2 + dichloromethane) in the mixture, hence requiring higher pressures to reach a homogeneous, one phase, system. Figure 7. Pressure−temperature diagram for the system {carbon dioxide (1) + ε-caprolactone (2) + dichloromethane (3)}, on a dichloromethane free-basis, at a dichloromethane to ε-caprolactone mass ratio of 2:1. Experimental data: ◨ (BP) [w1 = 0.2485; w2 = 0.2473; w3 = 0.5042]; ◑ (BP) [w1 = 0.3664; w2 = 0.2113; w3 = 0.4223]; ▶ (LL) [w1 = 0.5395; w2 = 0.1536; w3 = 0.3069]; ◀ (LL) [w1 = 0.5719; w2 = 0.1420; w3 = 0.2861]. Continuous lines denote calculated values applying the PR-EoS model with global temperature fitted parameters.

4. CONCLUSIONS Phase behavior of the ternary system {carbon dioxide (1) + εcaprolactone (2) + dichloromethane (3)} at different dichloromethane to ε-caprolactone mass ratios (0.5:1, 1:1, and 2:1) was experimentally investigated in this work over the temperature range of 323.15 to 353.15 K in a wide overall composition range of carbon dioxide, resulting in phase transition pressures up to 25.8 MPa. Experimental observations show that for all cases investigated an increase in dichloromethane to ε-caprolactone mass ratio resulted in a decrease in pressure necessary to reach a single phase. Besides vapor− liquid equilibrium with bubble point transitions presented for all systems, liquid−liquid, and vapor−liquid−liquid equilibrium transitions were observed for the system studied in this work. The PR-EoS provided good performance of the experimental phase equilibrium results obtained when the global fitting was employed for data fitting. Experimental results obtained here are of value for conducting polymer-

(2)) at a temperature of 333.15 K. It can be clearly seen from this figure that an increase in dichloromethane concentration results in reduction of the phase transition pressures, when compared to the binary system. This fact elucidates the effect of dichloromethane on the system phase behavior, showing that it can be advantageously used as a cosolvent to solubilize the system investigated. The presence of dichloromethane can be highlighted in terms of its polar characteristic, different from carbon dioxide, G



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ization reactions with ε-caprolactone in carbon dioxide as solvent and dichloromethane as cosolvent.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.8b01017. Tables with absolute composition values of the experimental data (PDF)

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +55 48 37212508. Fax: +55 48 37219687. E-mail: jose. [email protected]. ORCID

Débora de Oliveira: 0000-0001-7544-5045 José Vladimir Oliveira: 0000-0002-6196-3498 Funding

This study was financed in part by the Coordenaçaõ de ́ Aperfeiçoamento de Pessoal de Nivel Superior (CAPES), Brazil, Finance Code 001. Notes

The authors declare no competing financial interest.

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High Pressure Phase Equilibrium Data for the Ternary System

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