Solubility of ethylene in toluene, norbornene, and toluene + norbornene mixture

doi:10.1016/j.fluid.2013.01.023

Fluid Phase Equilibria

Volume 344, 25 April 2013, Pages 112-116

https://doi.org/10.1016/j.fluid.2013.01.023 Get rights and content

Abstract

The solubility of monomer gases in polymer solutions is important to analyze and optimize polymerization processes. This work investigated the solubilities of ethylene in organic solvents that are related to the production of cyclic olefin copolymers. Solubilities of ethylene in toluene, norbornene and toluene/norbornene mixtures were measured at temperatures of 323, 343, and 363 K and at pressures up to 5.7 MPa. The solubilities of ethylene increased with increasing pressure and they increased with decreasing temperature. The Peng–Robinson equation of state could correlate the experimental solubilities of binary and ternary systems with binary interaction parameters to within about 3%.

Introduction

A great many polymers are contained in products used in our daily life, and many of these have become essential to our present living standards. Among them, a transparent polymer so called cyclic olefin copolymer (COC) has attracted much attention, because it is used in applications requiring glass-like clarity and high moisture barriers in packaging films, lenses, vials, monitors, and medical devices. COC is produced by solution polymerization of cyclic olefin monomers, such as norbornene, with ethylene. In the process, the polymerization rate depends on the concentration of ethylene in the COC solution and its concentration is a function of temperature and pressure.

Wu et al. [1] reported on the solubility of ethylene in toluene at temperatures from 293 K to 343 K and at pressures up to 1.24 MPa. Lee et al. [2] reported on the solubility of ethylene in toluene at temperatures from 323 K to 423 K and at pressures up to 3 MPa. Lee et al. [3] also investigated the solubility of ethylene in toluene, norbornene, and COC mixtures, which contained up to 28 wt% of COC, at temperatures 323 K, 373 K, and 423 K and at pressures up to 2.5 MPa. Solubility data were correlated with the Peng–Robinson equation of sate [4] that used the modified van der Waals one fluid mixing rules [5] and the Zhong–Masuoka mixing rules [6]. However, the solubility of ethylene in norbornene has not been reported to date.

For many of the previous applications, it is necessary to know the ethylene solubility in toluene + norbornene + COC quaternary systems. The approach taken in this work is to first measure the solubility of ethylene in mixture without the COC and then to measure the solubility of ethylene in mixtures containing the COC. A synthetic method was applied for the solubility measurements in toluene, norbornene, and their mixtures, because the method can be applied to bubble point pressure measurements of polymer solutions. In this work, the solubility of ethylene in norbornene as a monomer of the cyclic olefin, toluene as a solvent, and norbornene/toluene mixtures were investigated at temperatures of 323 K, 343 K, and 363 K and at pressures up to 6 MPa.

Section snippets

Chemicals

Ethylene (purity >99.9%) was purchased from Japan fine products. Toluene (purity >99.9%, Sigma–Aldrich) and norbornene (purity >99%, Sigma–Aldrich) were used without further purification. The suppliers and purity of the chemicals and other related description were given in Table 1.

Apparatus and procedure

The solubilities were determined from bubble point pressure measurements with an apparatus based on a synthetic method. Details of the apparatus and procedure are described elsewhere [7]. Estimated standard

Correlation model

In this work, the Peng–Robinson equation of state (PR EOS) [4] was used to correlate bubble point pressures: $P = \frac{R T}{V - b} - \frac{a α}{V (V + b) + b (V - b)} .$

The original mixing rules [5] were used as follows: $a = \sum_{i} \sum_{j} x_{i} x_{j} a_{i j},$ $b = \sum_{i} x_{i} b_{i},$ $a_{i j} = (1 - k_{i j}) \sqrt{a_{i} a_{j}} .$ In Eq. (4) k_ij is an empirically determined binary interaction parameter.

Critical properties and acentric factors used in this work are listed Table 1. Critical values of norbornene were estimated with the group contribution method by Marrero and Gani [8] and acentric factor

Ethylene + toluene system

Experimental results of bubble point pressure of ethylene + toluene system at 323 K are shown in Fig. 1 and Table 2. Literature data reported by Lee et al. [2] and Wu et al. [1] are also plotted. Bubble point pressures obtained in this work were slightly higher than those of the literature data, however extrapolation of our data to zero ethylene mole fraction, which corresponds to vapor pressure, gave lower value than that of the literature data and is closer to the vapor pressure of pure toluene

Conclusions

In this work, solubility of ethylene in toluene, norbornene, and toluene/norbornene mixtures were reported at temperatures 323 K, 343 K, and 363 K at pressures up to 5.7 MPa. The bubble point pressures for both binary systems (ethylene-toluene, ethylene-norbornene) were almost the same at given temperature. However the solubility of ethylene in norbornene is slightly higher than that in toluene. In the ternary system, ethylene solubility did not seem to vary much with the toluene/norbornene ratio

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Solubility of ethylene in toluene, norbornene, and toluene + norbornene mixture

Abstract

Introduction

Section snippets

Chemicals

Apparatus and procedure

Correlation model

Ethylene + toluene system

Conclusions

Fluid Phase Equilib.

Fluid Phase Equilib.

Fluid Phase Equilib.

Fluid Phase Equilib.

Fluid Phase Equilib.