Phase Equilibrium Measurements and Thermodynamic Modeling of

Feb 1, 2019 - This work reports phase equilibrium measurements and thermodynamic modeling of the binary systems (CO2 + ethyl levulinate) and (CO2 + ...
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Phase Equilibrium Measurements and Thermodynamic Modeling of the Systems (CO2 + Ethyl Levulinate) and (CO2 + Levulinic Acid) Wanderson R. Giacomin Junior, Claudia A. Capeletto, Fernando A. P. Voll, and Marcos L. Corazza* Department of Chemical Engineering, Federal University of Paraná, 81531-980 Curitiba-PR, Brazil

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S Supporting Information *

ABSTRACT: This work reports phase equilibrium measurements and thermodynamic modeling of the binary systems (CO2 + ethyl levulinate) and (CO2 + levulinic acid). Each composition was carried out in a high-pressure variablevolume view cell at temperatures ranging from 303.15 to 353.15 K and with CO2 mole fraction ranging from 0.4002 to 0.9751 for the system (CO2 + ethyl levulinate) and from 0.4083 to 0.9930 for the system (CO2 + levulinic acid). Under these conditions, only vapor−liquid phase transitions were observed. The experimental data were modeled with the Peng−Robinson cubic equation of state with the Boston− Mathias alpha function (PR-BM) and using the van der Waals quadratic mixing rule. The results showed that the experimental data of the system (CO2 + ethyl levulinate) were adequately represented by the thermodynamic model with a unique set of binary interaction parameters, which were fitted from all isotherms. Whereas the experimental data of the system (CO2 + levulinic acid) were only adequately represented with temperature-dependent binary interaction parameters.

1. INTRODUCTION Energy is necessary for the technological, social, and economic development of any country. However, with the gradual decline of petroleum resources, combined with their increased demand and the environmental deterioration caused by their emissions, their price continues to increase and discussions about biofuels have become far more common. Biofuels are fuels derived from plant biomass, such as bioethanol and biodiesel.1−3 Some of the biofuels that have received great attention are those called “valeric biofuels”, which are derived from lignocellulosic materials, the most abundant and biorenewable biomass on earth. Moreover, studies have suggested that lignocellulosic biomass holds enormous potential for sustainable production,4,5 along with the possibility to be competitive with petroleum-based fuels. Among the valeric biofuels, recent research has shown that γ-valerolactone (GVL) could be considered as a sustainable liquid for global storage and transportation and that ethyl levulinate (EL) could be used in blends with diesel.6,7 While EL can be obtained by the esterification of levulinic acid (LA) with ethanol, one way to obtain GVL is through the conversion of LA in CO2 or EL in supercritical state.8−10 However, there is still a lack of thermodynamic data concerning the phase equilibrium of these compounds and carbon dioxide. The interactions between all components available in the system present a fundamental issue, for designing, modeling, and optimization of these processes, mostly because a supercritical fluid is present. Thereby, knowledge of the correct phase equilibrium data and thermodynamic calculations are a central point of design process. © XXXX American Chemical Society

Thus, the main goal of this work is to report experimental phase equilibrium data (phase saturation data) for binary systems (CO2 + EL) and (CO2 + LA), which have been used, studied, or presented in the production process of GVL, some biofuels, or blends. To the best of our knowledge, phase equilibrium data for these systems are scarce or even new in the literature. The experimental data measured in this work were modeled using the Peng−Robinson equation of state with Boston−Mathis alpha function (PR-BM).

2. EXPERIMENTAL SECTION 2.1. Materials. All chemicals employed in this study, their purity, and supplier are presented in Table 1. All were used without further purification. Table 1. Chemicals Used in This Work, Suppliers, and Mass Fraction Purity

a

chemical

supplier

ethanol carbon dioxide ethyl levulinate levulinic acid

Honeywell White Martins Sigma-Aldrich Sigma-Aldrich

puritya ≥99.8 99.9 ≥98 99

wt wt wt wt

% % % %

As informed by the suppliers.

Special Issue: Latin America Received: November 1, 2018 Accepted: January 18, 2019

A

DOI: 10.1021/acs.jced.8b01023 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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Table 2. Characteristic Parameters of Pure Compoundsa

2.2. Apparatus and Experimental Procedure. The general basis of the experimental apparatus and procedure used in this work have been previously reported by our research group.11−13 Briefly, the experimental data measurements were carried out in a high-pressure variable-volume view cell containing a movable piston, which allows pressure control inside the cell. The apparatus also includes a syringe pump (ISCO, model 260D) for injecting CO2 into the cell and for manipulating pressure into the equilibrium unit, and an electrical heating jacket for the temperature control. Coupled to the cell there are a pressure transducer (Smar, model LD 301, with uncertainty of ±0.03 MPa) and a universal indicator (Novus, model N1500) for pressure data acquisition, and a thermocouple (K-type) to measure and register the temperature inside the cell. The visual observations were achieved through two sapphire windows, one on the side and another frontal to the cell. For each system composition, the procedure was the same as presented by Veiga et al.:12 flushing the cell with CO2 (288.15 K and 6.5 MPa) to remove any residual air; loading the cell with the respective amount of liquid solute (EL or LA) and then with the CO2 (288.15 K and 10 MPa); and setting the pressure to reach the homogeneous phase condition (one phase). At a fixed temperature, the phase transition pressure (the phase saturation condition) was measured by the slow depressurization of the system (using the syringe pump) and read at the incipient new phase formation. The uncertainties related to the mole fraction, temperature, and pressure measurements were estimated using the method of uncertainties (type B) as suggested by Taylor and Kuyatt14 and are reported in tables with the experimental data.

n

n

b=

n

∑ ∑ xixj

(1)

i=1 j=1

1 (bi + bj)(1 − lij) 2

α(Tr ≤ 1) = αSOAVE = [1 + m(1 − Tr )]2 ÄÅ ÉÑ Å 2m Ñ (1 − Tr1 + m /2)ÑÑÑÑ α(Tr > 1) = expÅÅÅÅ ÅÅÇ 1 + m ÑÑÖ

ω

Mw/ (g mol−1)

CO2 levulinic acid ethyl levulinate

304.2 738.0

7.38 4.02

0.223621 0.755750

44.01 116.17

18 19

666.1

29.24

0.607085

144.17

Aspen Plus databank

ref

{CO2(1) + ethanol(2)} were obtained and are reported in the Supporting Information. Figure 1 shows a comparison between these measurements and experimental data available in the literature at 313.15, 323.15, 333.15, and 343.15 K. Considering a type B uncertainty of ±0.20 MPa for our data (Table S1), it can be observed that the present data are in agreement with majority of those reported by other authors.20−26 Tables 3 and 4 present the experimental phase equilibrium data for the binary systems {CO2(1) + EL(2)} and {CO2(1) + LA(2)}, respectively, where temperatures ranged from 303.15 to 353.15 K for both systems. These tables express the experimental data in terms of molar compositions of CO2 (x1) and EL or LA (x2), pressure transition value (p), experimental error for each isotherm in a composition, represented by the standard deviation of replicate pressure measurements (σ), and the type of phase equilibrium transition observed, meaning bubble point (BP) or dew point (DP). Regarding the pressure limitations of the equipment (safe procedures operating up to 30 MPa), experimental phase transition data for the binary {CO2(1) + LA(2)} system was not performed for CO2 mole fractions within 0.75 and 0.95. In this work, thermodynamic modeling using the PR-BM model was performed by fitting a unique set of binary interaction parameters for all isotherms (global fitting). For the binary system {CO2(1) + EL(2)}, the attraction energy parameter (kij) and repulsive energy parameter (lij) fitted were k12 = 3.531 × 10−2 and l12 = −1.0319 × 10−2, respectively, with a root-mean-square deviation (rmsd) of 0.20 MPa considering a quadratic van der Waals mixing rule with temperatureindependent parameters. Likewise, for the binary system {CO2(1) + LA(2)}, the binary interaction parameters fitted were k12 = 2.9609 × 10−2 and l12 = −0.7222 × 10−2, with a root-mean-square deviation of rmsd = 1.06 MPa, calculated as presented in eq 4. As the rmsd values obtained for the former system were high, indicating that the vapor−liquid equilibrium was not properly represented by the temperature-independent parameters (k12 and l12), we proposed a temperaturedependent approach (eqs 5 and 6) for the binary interaction parameters for the system {CO2(1) + LA(2)}, which resulted in a much lower root-mean-square deviation (rmsd = 0.40 MPa). It is worth mentioning that only bubble points (in Tables 3 and 4) were used in the binary interaction parameters estimation.

aiaj (1 − kij)

i=1 j=1

pc / MPa

Tc, critical temperature; pc, critical pressure; ω, acentric factor; Mw, molar mass.

n

∑ ∑ xixj

Tc/K

a

3. THERMODYNAMIC MODELING Thermodynamic modeling of the experimental phase equilibrium data measured in this work followed a previously reported procedure,11−13 using the Peng−Robinson equation of state with Boston−Mathias alpha function (PR-BM)15,16 and the conventional quadratic van der Waals mixing rule (vdW2), eqs 1 and 2. The Boston−Mathias alpha function is given in eq 3. The estimation of the binary interaction parameters (kij and lij) was carried out by minimizing the leastsquares objective function of experimental and calculated pressure values using the Nelder−Mead Simplex method from the Matlab optimization toolbox. The calculation of saturation points followed the procedure present by Michelsen.17 Pure component properties of CO2, levulinic acid and ethyl levulinate are presented in Table 2. a=

compd

(2)

nobs

rmsd =

∑ i=1

(3)

(Picalcd − Piexp)2 nobs

(4)

The temperature-dependent binary interaction parameters for the {CO2(1) + LA(2)} system were used as presented in eqs 5 and 6:

4. RESULTS AND DISCUSSION In order to verify the experimental apparatus and procedure reliability, experimental phase equilibrium data for the system

k12 = (0.04047 − 0.1962 × 10−5)T (K ) B

(5)

DOI: 10.1021/acs.jced.8b01023 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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Figure 1. Pressure−composition diagram for the system {CO2(1) + ethanol(2)} at (A) 313.15 K (◆, this work; ○, Galicia-Luna et al.;20 blue △, Secuianu et al.;21 *, Yeo et al.;22 ×, Knez et al.;23 □, Chang et al.24) and 333.15 K (◆, this work; blue ○, Galicia-Luna et al.;20 △, Suzuki et al.;26 blue *, Yeo et al.;22 ◁, Knez et al.;23 +, Joung et al.25); and (B) 323.15 K (◆, this work; △, Yeo et al.;22 +, Joung et al.25) and 343.15 K (■, this work; △, Yeo et al.;22 ○, Joung et al.25). Bars are the standard uncertainties for the pressure transition measurements (±0.20 MPa).

Table 3. Phase Equilibrium Measurements for the Binary System {CO2(1) + Ethyl Levulinate(2)}a x1 T = 303.15 0.4002 0.5502 0.6987 0.8167 T = 313.15 0.4002 0.5502 0.6987 0.8167 T = 323.15 0.4002 0.5502 0.6987 0.8167 T = 333.15 0.4002 0.5502 0.6987 0.8167 T = 343.15 0.4002 0.5502 0.6987 0.8167 T = 353.15 0.4002 0.5502 0.6987 0.8167

x2

p/MPa

σ/MPa

transition type

x1

x2

p/MPa

σ/MPa

transition type

0.5998 0.4498 0.3013 0.1833

2.60 3.80 5.26 5.98

0.05 0.04 0.02 0.11

VLE(BP) VLE(BP) VLE(BP) VLE(BP)

0.9023 0.9385 0.9597 0.9751

0.0977 0.0615 0.0403 0.0249

6.22 6.65 6.56 6.56

0.03 0.02 0.02 0.05

VLE(BP) VLE(BP) VLE(BP) VLE(BP)

0.5998 0.4498 0.3013 0.1833

3.16 4.58 6.13 7.31

0.10 0.03 0.02 0.05

VLE(BP) VLE(BP) VLE(BP) VLE(BP)

0.9023 0.9385 0.9597 0.9751

0.0977 0.0615 0.0403 0.0249

7.70 8.12 8.02 8.14

0.04 0.04 0.01 0.10

VLE(BP) VLE(BP) VLE(BP) VLE(BP)

0.5998 0.4498 0.3013 0.1833

3.66 5.47 7.43 8.91

0.10 0.03 0.00 0.03

VLE(BP) VLE(BP) VLE(BP) VLE(BP)

0.9023 0.9385 0.9597 0.9751

0.0977 0.0615 0.0403 0.0249

9.34 9.84 9.83 9.67

0.12 0.02 0.04 0.05

VLE(BP) VLE(BP) VLE(BP) VLE(BP)

0.5998 0.4498 0.3013 0.1833

4.22 6.39 8.61 10.40

0.10 0.04 0.01 0.05

VLE(BP) VLE(BP) VLE(BP) VLE(BP)

0.9023 0.9385 0.9597 0.9751

0.0977 0.0615 0.0403 0.0249

11.04 11.53 11.61 11.20

0.05 0.04 0.02 0.05

VLE(BP) VLE(BP) VLE(DP) VLE(DP)

0.5998 0.4498 0.3013 0.1833

4.74 7.32 9.98 11.97

0.10 0.01 0.05 0.01

VLE(BP) VLE(BP) VLE(BP) VLE(BP)

0.9023 0.9385 0.9597 0.9751

0.0977 0.0615 0.0403 0.0249

12.87 13.31 13.13 12.77

0.09 0.06 0.06 0.02

VLE(BP) VLE(BP) VLE(DP) VLE(DP)

0.5998 0.4498 0.3013 0.1833

5.39 8.31 11.18 13.71

0.10 0.03 0.02 0.04

VLE(BP) VLE(BP) VLE(BP) VLE(BP)

0.9023 0.9385 0.9597 0.9751

0.0977 0.0615 0.0403 0.0249

14.84 15.03 14.75 14.17

0.05 0.09 0.07 0.03

VLE(BP) VLE(BP) VLE(DP) VLE(DP)

K

K

K

K

K

K

a Standard uncertainties u are u(T) = 0.5 K, u(p) = 0.20 MPa, u(x) = 0.005. σ/MPa represents the standard deviation of the mean from three measurements. VLE(BP) represent bubble point transitions, and VLE(DP) dew point transitions.

l12 = (0.16433 − 4.9868 × 10−4)T (K )

values using the PR-BM model, where the continuous and dashed lines denote liquid and vapor saturated phase, respectively. In Figures 2A and 3A, the phase equilibrium for both systems is predicted using the thermodynamic modeling setting the binary interaction parameters to zero (kij = 0 and lij = 0), aiming to assess the prediction capability of the equation

(6)

Figures 2 and 3 depict the pressure−composition diagrams for the systems {CO2(1) + EL(2)} and {CO2(1) + LA(2)}, respectively, at temperatures from 303.15 to 353.15 K, for both systems. In these phase equilibrium diagrams, the experimental data of the binary systems are compared to the calculated C

DOI: 10.1021/acs.jced.8b01023 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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Table 4. Phase Equilibrium Measurements for the Binary System {CO2(1) + Levulinic Acid(2)}a x1 T = 303.15 0.4083 0.5165 0.5438 0.5893 0.6169 T = 313.15 0.4083 0.5165 0.5438 0.5893 0.6169 0.6491 T = 323.15 0.4083 0.5165 0.5438 0.5893 0.6169 T = 333.15 0.4083 0.5165 0.5438 0.5893 0.6169 T = 343.15 0.4083 0.5165 0.5438 0.5893 0.6169 T = 353.15 0.4083 0.5165 0.5438

x2

p/MPa

σ/MPa

transition type

x1

x2

p/MPa

σ/MPa

transition type

0.5917 0.4835 0.4562 0.4107 0.3831

5.12 5.92 6.26 6.75 7.80

0.62 0.10 0.00 0.08 0.03

VLE(BP) VLE(BP) VLE(BP) VLE(BP) VLE(BP)

0.6491 0.6806 0.7233 0.9800 0.9930

0.3509 0.3194 0.2767 0.0200 0.0070

9.30 13.25 19.66 17.62 10.15

0.10 0.05 0.11 0.10 0.10

VLE(BP) VLE(BP) VLE(BP) VLE(DP) VLE(DP)

0.5917 0.4835 0.4562 0.4107 0.3831 0.3509

5.93 7.52 8.01 9.16 11.83 13.80

0.05 0.05 0.02 0.05 0.07 0.06

VLE(BP) VLE(BP) VLE(BP) VLE(BP) VLE(BP) VLE(BP)

0.6806 0.7023 0.7233 0.9800 0.9930

0.3194 0.2977 0.2767 0.0200 0.0070

17.27 21.69 24.58 20.08 13.24

0.00 0.05 0.10 0.10 0.02

VLE(BP) VLE(BP) VLE(BP) VLE(DP) VLE(DP)

0.5917 0.4835 0.4562 0.4107 0.3831

6.96 9.51 10.28 12.83 15.69

0.02 0.11 0.05 0.03 0.10

VLE(BP) VLE(BP) VLE(BP) VLE(BP) VLE(BP)

0.6491 0.6806 0.7023 0.9800 0.9930

0.3509 0.3194 0.2977 0.0200 0.0070

17.96 20.84 24.74 22.70 15.66

0.09 0.06 0.10 0.05 0.04

VLE(BP) VLE(BP) VLE(BP) VLE(DP) VLE(DP)

0.5917 0.4835 0.4562 0.4107 0.3831

8.31 12.07 13.18 16.06 19.39

0.05 0.05 0.04 0.05 0.03

VLE(BP) VLE(BP) VLE(BP) VLE(BP) VLE(BP)

0.6491 0.6806 0.9800 0.9930

0.3509 0.3194 0.0200 0.0070

21.65 24.74 25.27 18.15

0.03 0.15 0.19 0.04

VLE(BP) VLE(BP) VLE(DP) VLE(DP)

0.5917 0.4835 0.4562 0.4107 0.3831

9.90 14.61 15.90 19.34 22.62

0.01 0.07 0.16 0.01 0.08

VLE(BP) VLE(BP) VLE(BP) VLE(BP) VLE(BP)

0.6491 0.6806 0.9800 0.9930

0.3509 0.3194 0.0200 0.0070

25.69 27.94 27.41 20.60

0.03 0.01 0.09 0.10

VLE(BP) VLE(BP) VLE(DP) VLE(DP)

0.5917 0.4835 0.4562

11.51 17.13 18.62

0.02 0.07 0.10

VLE(BP) VLE(BP) VLE(BP)

0.5893 0.6491 0.9800

0.4107 0.3509 0.0200

22.33 27.99 29.66

0.04 0.12 0.16

VLE(BP) VLE(BP) VLE(DP)

K

K

K

K

K

K

Standard uncertainties u are u(T) = 0.5 K, u(p) = 0.20 MPa, u(x) = 0.005. σ/MPa represents the standard deviation of the mean from three measurements. VLE(BP) represent bubble point transitions, and VLE(DP) dew point transitions. a

Figure 2. Pressure−composition diagram for the system {CO2(1) + EL(2)} at 303.15 K (○, this work), 313.15 K (+, this work), 323.15 K (◇, this work), 333.15 K (+, this work), 343.15 (□, this work), and 353.15 K (×, this work). Continuous and dashed lines denote liquid and vapor saturated phase, respectively, calculated using the PR-BM (A) with k12 = l12 = 0 and (B) with two temperature-independent parameters.

of stated and mixing rule used. From Figure 2A, it can be observed that for the system {CO2(1) + EL(2)} the

thermodynamic model was capable of predicting it fairly well without using binary interaction parameters. However, a small D

DOI: 10.1021/acs.jced.8b01023 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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Figure 3. Pressure−composition diagram for the system {CO2(1) + LA(2)} at 303.15 K (○, this work), 313.15 K (+, this work), 323.15 K (◇, this work), 333.15 K (*, this work), 343.15 (□, this work), and 353.15 K (×, this work). Continuous and dashed lines denote liquid and vapor saturated phase, respectivelly, calculated using the PR-BM (A) with k12 = l12 = 0 and (B) with two temperature-dependent parameters (1) and (2).

correction in the interaction energy between CO2 and ethyl levulinate (EL) molecules is needed. These results, considering the fitted k12 and l12 for the {CO2(1) + EL(2)} system are presented in Figure 2B. On the other hand, for the second binary system {CO2(1) + LA(2)}, the phase diagram predictions without the binary interaction parameters adjustment (k12 = l12 = 0, Figure 3A) evidenced the incapability of the thermodynamic model used (PR-BM with vdW2) to take into account the molecular interactions between CO2 and levulic acid (LA), leading to a poor prediction of the phase equilibrium at high pressures, mainly at high CO2 molar fractions. Phase equilibrium predictions using the temperaturedependent parameters for the system {CO2(1) + LA(2)} are presented in Figure 3B. For the binary system {CO2(1) + LA(2)}, saturation points were measured at high CO2 concentrations (0.9800 and 0.9930), where dew points were observed. The comparison between the experimental dew point values and predicted values using the thermodynamic model with the temperaturedependent parameters are presented in Figure 4. It can be observed from this figure that the fitted model was capable of predicting the saturated vapor curves (dew points) based on the parameters fitted using just the bubble points for this system. Results presented in Figure 4 show that this thermodynamic model used can be efficiently used to predict solubility values of levulic acid in supercritical CO2 solvent. The shape of the modeling present in Figure 3 may suggest LLV behavior; however, a LLV phase was not observed for this binary system at any temperature and composition, nor at any pressure. Results presented in Figures 2B and 3B show that the PRBM model was capable of predicting the behavior of both binary systems, which is suggested by the low root-meansquare deviation of the global adjustment for the system {CO2(1) + EL(2)} (rmsd = 0.20 MPa), using a unique set of binary interaction parameters and a temperature-dependent set of parameters for the system {CO2(1) + LA(2)} (rmsd = 0.40 MPa). From the results obtained from the thermodynamic modeling, it seems that the binary system {CO2(1) + LA(2)} shows a more evident dependence on temperature, which is shown by the decrease on the root-mean-square deviation when a temperature-dependent parameter is fitted. This means that the Peng−Robinson cubic equation of state with quadratic

Figure 4. Comparison between experimental and calculated values of saturated lines (dew points, dashed lines) for the system {CO2(1) + LA(2)} at high CO2 mole fraction (zoom in from Figure 3B at 303.15 K (○, this work), 313.15 K (+, this work), 323.15 K (◇, this work), 333.15 K (*, this work), 343.15 (□, this work), and 353.15 K (×, this work)).

mixing rule approach is not enough to take into account all molecular interactions between CO2 and levulinic acid (LA), because the cubic equations of state do not take into account important molecular interaction such as hydrogen bonds, and polar and quadrupolar (CO2) interactions. Thus, a more robust thermodynamic model is necessary for predicting correctly the phase behavior of such system. For the binary {CO2(1) + EL(2)}, it seems, by the visual comparison between Figure 2A and B, that PR-BM was capable to predict it fairly well without using binary interaction parameters (k12 and l12 were set to zero). However, for the second binary system {CO2(1) + LA(2)}, the phase diagram predictions without the binary interaction parameters adjustment (k12 = l12 = 0) evidenced the incapability of the thermodynamic model used (PR-BM with vdW2) to predict the phase behavior, which can be observed comparing Figure 3A and B. Additionally, a visual comparison between both systems shown in this work, Figures 2B and 3B, suggests that the carboxylic acid group present in the levulinic acid may have an E

DOI: 10.1021/acs.jced.8b01023 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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Funding

important contribution to the phase behavior of the {CO2(1) + LA(2)} system, where much higher pressures are needed to reach the saturation pressure when compared for the systems {CO2(1) + EL(2)}. This can be observed by the change in the slope of the curve in Figure 3B that begins around a CO2 mole fraction of 0.60 and goes until the critic point of the mixture. In general, the PR-BM model with two temperatureindependent binary interaction parameters resulted in good predictions for the system {CO2(1) + EL(2)}, where CO2− ester molecular interactions are present. However, for the binary {CO2(1) + LA(2)} system, where CO2−carboxylic acid molecular interactions are present, better results for the thermodynamic approach used in this work were achieved with two temperature-dependent parameters. Further studies concerning the thermodynamic modeling of systems involving CO2/esters/carboxylic acids using equations of state based on Statistical Association Fluid Theory (SAFT) are in development in our research group for better understanding the molecular interactions and the thermodynamics of these systems.

The authors thank the CNPq (Grant Numbers 305393/2016-2 and 408836/2017-2) and CAPES (Brazilian Agencies) for financial support and scholarships. Notes

The authors declare no competing financial interest.



5. CONCLUSIONS This work reported phase equilibrium data for CO2 + ethyl levulinate (CO2 + EL) and CO2 + levulinic acid (CO2 + LA) binary systems at temperatures ranging from 303.15 to 353.15 K. Vapor−liquid equilibria were observed for all binary systems investigated over the temperature and composition ranges evaluated. Both systems were modeled with the Peng− Robinson cubic equation of state with the Boston−Mathias alpha function (PR-BM) and using the van der Waals quadratic mixing rule (vdW2). For the range of conditions evaluated, the thermodynamic model was able to effectively represent the binary system (CO2 + EL) using a unique set of binary interaction parameters (kij and lij), both temperatureindependent. On the other hand, for the system (CO2 + LA), a temperature-dependent approach for the binary interaction parameters was necessary in order to adequately represent the phase behavior of the system, especially at high CO2 molar fractions and high pressure conditions. This results from the fact that the PR-BM with vdW2 alone fails to consider significant molecular interactions between CO2 and LA, as hydrogen bonds, for example.



ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.8b01023. VLE data obtained for the binary system carbon dioxide + ethanol (PDF)



REFERENCES

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AUTHOR INFORMATION

Corresponding Author

*Mailing address: Department of Chemical Engineering, Federal University of Paraná, Polytechnique Center, PO BOX 19011, Curitiba 81531-980, State of Paraná, Brazil. Email: [email protected]. Telephone: +55-41-33613587 ORCID

Marcos L. Corazza: 0000-0003-2305-1989 F

DOI: 10.1021/acs.jced.8b01023 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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DOI: 10.1021/acs.jced.8b01023 J. Chem. Eng. Data XXXX, XXX, XXX−XXX