Phase behavior and densities of propylene + toluene and ethylene + toluene systems to 580 K and 70 MPa

doi:10.1016/j.fluid.2017.06.022

Fluid Phase Equilibria

Volume 449, 15 October 2017, Pages 138-147

https://doi.org/10.1016/j.fluid.2017.06.022 Get rights and content

Abstract

In this study, we report phase behavior data for propylene + toluene and ethylene + toluene mixtures at temperatures to 580 K and pressures to 8.5 MPa. We also report high-pressure, mixture density data for the two mixtures at temperatures to 555 K and pressures to 70 MPa. Both the phase behavior and density data are simultaneously determined using a windowed variable-volume, high-pressure view cell coupled with a linear variable differential transformer. The phase behavior and mixture density data are modeled with the Soave–Redlich–Kwong (SRK), Peng–Robinson (PR), Modified Sanchez–Lacombe (MSL), and Perturbed–Chain Statistical Associating Fluid Theory (PC-SAFT) equations of state (EoS). The PC-SAFT and MSL EoS provide very good fits of the phase behavior for both the propylene + toluene and ethylene + toluene systems with each binary interaction parameter, k_ij, set to zero. The PC-SAFT equation also provides the best fit of the high-pressure, mixture density data for the ethylene + toluene system. However, the SRK EoS provides the best fit of the high-pressure, mixture density data for the propylene + toluene system. Although both equations slightly over predict the solution density for the two studied systems, the fit of the densities are insensitive to small variations in k_ij.

Graphical abstract

Introduction

Propylene and ethylene are important monomer gases in the polymer industry. The design, optimization, and control of chemical and petrochemical processes depend directly on the phase behavior and fluid property data of these gases in the presence of typical hydrocarbon reaction solvents [1]. Although several authors have reported phase equilibrium data for propylene + toluene and ethylene + toluene binary mixtures, most of these data are limited to temperatures below 423 K and pressures below 5.7 MPa [2], [3], [4]. In the present study, vapor-liquid equilibrium (VLE) data for the propylene + toluene and ethylene + toluene systems are measured to temperatures of 580 K and to pressures of 8.5 MPa. Thus, the present study complements previously reported studies on the phase behavior of propylene + toluene and ethylene + toluene mixtures [2], [3], [4].

Mixture density data are also important fluid property information needed for efficient process design [5]. In the present study, we report high-temperature, high-pressure density data for propylene + toluene and ethylene + toluene mixtures. Tyvina et al. [6] report liquid-phase densities for propylene + toluene mixtures along the saturation line at temperatures from ∼318 to 460 K. The present study extends the density database for propylene + toluene mixtures to 555 K and pressures to 70 MPa. To the best of our knowledge, there are no density data available in the literature for ethylene + toluene mixtures.

The phase behavior and mixture densities of propylene + toluene and ethylene + toluene mixtures are modeled with contemporary equations of state (EoS) over the entire investigated experimental temperature, pressure, and composition ranges. The employed EoS include the Perturbed–Chain Statistical Associating Fluid Theory (PC-SAFT) [7], Modified Sanchez–Lacombe (MSL) [8], [9], Soave–Redlich–Kwong (SRK) [10], and Peng–Robinson (PR) [11]. In addition to the EoS model calculations, mixture density data are also correlated with the modified Tait equation that can be used to calculate mixture density at any given state point within the range of experimental conditions reported in this study.

Section snippets

Materials

Table 1 lists the mole fraction purities of the chemicals used in this study. Ethylene, propylene, and toluene are purchased from Sigma-Aldrich Corporation and used as received.

Methods

The detailed description of view cell used for VLE and density experiments is presented in a previous publication by our group [12]. Briefly, the system pressure, generated by delivering water into an internal bellows, is measured with a Heise^® pressure gauge (Heise Corporation, Model CM57303, 0–68.9 MPa, standard

Phase equilibrium

Table 2, Table 3 list bubble point (BP) and critical point (CP) data measured in this study for propylene + toluene and ethylene + toluene mixtures. VLE data for propylene + toluene mixtures are measured at propylene mole fractions of 0.1159, 0.5300, and 0.7612, from temperatures 295–555 K. VLE data for ethylene + toluene mixtures are measured at ethylene mole fractions of 0.1194 and 0.3067 from temperatures 295–579 K. Fig. 1 shows the p-T isopleths for the propylene + toluene and

Modeling

The Tait equation is useful for interpolating mixture density data however, it is not a robust tool for predicting the thermodynamic properties of mixtures over wide ranges of temperature, pressure, and composition. Therefore, in this study, the PC-SAFT [7], MSL [8], [9], SRK [10], and PR [11] equations are used to predict VLE and mixture densities for the propylene + toluene and ethylene + toluene systems. Only brief descriptions of the MSL and PC-SAFT equations are given here; details for the

Conclusions

VLE data for propylene + toluene and ethylene + toluene mixtures are reported at temperatures to 580 K and pressures to 8.5 MPa together with mixture density data also at high temperatures and pressures to 70 MPa. These data complement previously reported VLE data for propylene + toluene and ethylene + toluene mixtures. Very little difference is observed in the performance of the PC-SAFT, MSL, SRK, and PR equations when predicting VLE and mixture densities for these two toluene mixtures. Small

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Phase behavior and densities of propylene + toluene and ethylene + toluene systems to 580 K and 70 MPa

Abstract

Graphical abstract

Introduction

Section snippets

Materials

Methods

Phase equilibrium

Modeling

Conclusions

Eur. Polym. J.

Chem. Eng. Sci.

Fluid Phase Equilib.

Fluid Phase Equilib.

Vapor−liquid equilibrium data for the ethylene + hexane system

J. Chem. Eng. Data

Propylene solubility in toluene and isododecane

Can. J. Chem. Eng.

Solubility of ethylene and propylene in organic solvents

Khim. Prom-st

Densities of the binary systems n-hexane + n-decane and n-hexane + n-hexadecane up to 60 MPa and 463 K

J. Chem. Eng. Data

Volume relations in the toluene-propene system along liquid-gas equilibrium boundary curves

Russ. J. Phy. Chem.

Perturbed-Chain SAFT: an equation of state based on a perturbation theory for chain molecules

Ind. Eng. Chem. Res.