High pressure phase behavior for the binary mixture of valeronitrile, capronitrile and lauronitrile in supercritical carbon dioxide at temperatures from 313.2 to 393.2 K and pressures from 3.9 to 25.7 MPa☆
Highlights
► Phase equilibria for the (C5H9N), (C6H11N) and (C12H23N) in CO2 were measured. ► Experimental data were correlated with Peng–Robinson equation of state. ► The (carbon dioxide + nitriles) systems exhibit type-I phase behavior.
Introduction
Nitriles are important laboratory and industrial solvents because of their unusual physical properties. For example, nitriles boil much higher than the corresponding hydrocarbon of similar molecular weight; valeronitrile (CH3CH2CH2CH2CN, Mw 83.13) boils at 414.5 K whereas n-hexane (CH3CH2CH2CH2CH2CH3, Mw 86.2) boils at 342.2 K. This increase can be ascribed to the polar nature (uneven distribution of electron density) of nitriles; the CN bond is polarized, and intermolecular alignment of these dipoles increases the intermolecular attraction between the solvent molecules. Its high dielectric constant and dipole moment make nitrile ideal for promoting chemical reactions where ionization is involved, as a solvent for inorganic salts (electrolytes), and a medium for electrochemical studies [1], [2].
The phase behavior for binary mixture of the hydrocarbon with supercritical carbon dioxide (scCO2) plays an important role in the chemical separation process, supercritical fluid extraction, polymerization condition, and industrial application [3], [4]. Recently, phase behavior experiments have been reported on the bubble-point, dew-point and critical-point behavior of mixtures containing scCO2 [5], [6]. scCO2 used in this work is widely used as an environmentally benign solvent which is inexpensive, nonflammable, and nontoxic. Also, scCO2 is a good solvent with low molecular weight in nonpolar molecules because it has a quadrupole moment, no dipole moment, and low dielectric constant. Therefore, phase behavior information for binary mixture containing carbon dioxide is required for practical use. The valeronitrile, capronitrile and lauronitrile monomers are used mainly for a variety of applications such as insecticides manufacture, foaming agent, pharmaceutical, elastomers, and polymerization initiators.
Phase behavior data for the carbon dioxide + acetonitrile and carbon dioxide + acrylonitrile systems were reported by Byun et al. [7], [8]. Byun et al. [7] used a static apparatus and presented the liquid–vapor equilibria curves for carbon dioxide + acetonitrile mixture at 308, 328 and 348 K and pressures up to 12 MPa. Byun et al. [8] reported the phase behavior curves for the carbon dioxide + acrylonitrile system at temperature from 318 to 378 K and pressure up to 14 MPa using a static apparatus.
The goal of this work is to obtain the high-pressure experimental data for (carbon dioxide + capronitrile), (carbon dioxide + valeronitrile) and (carbon dioxide + lauronitrile) mixtures by investigating mixtures of carbon dioxide with three components. Also, the pressure–temperature (p–T) diagrams of the mixture critical curve are presented for the (carbon dioxide + capronitrile), (carbon dioxide + valeronitrile) and (carbon dioxide + lauronitrile) systems in the vicinity of the critical point of pure carbon dioxide. The experimental data for (carbon dioxide + capronitrile), (carbon dioxide + valeronitrile) and (carbon dioxide + lauronitrile) systems obtained in this work are correlated with the Peng–Robinson equation of state (EOS) [9] using a van der Waals one-fluid mixing rule including two adjustable parameters. The properties of critical pressure, critical temperature, and acentric factor of capronitrile, valeronitrile and lauronitrile are reported in the literature and calculated [10], [11], while the vapor pressure is estimated by the Lee–Kesler method [10].
Section snippets
Apparatus and procedure
Described in detail elsewhere are the experimental apparatus and techniques used to measure the phase behavior of monomers in scCO2 [12]. A high-pressure, variable volume view cell (6.4 cm outer diameter × 1.59 cm I.D., a working volume of ∼28 cm3), is used to obtain the bubble-, dew- and critical-point curves, and is capable of operating to pressure of 70.0 MPa. A sapphire window (1.2 cm thick × 1.9 cm diameter) is fitted in the front part of the cell to allow observation of the phases. Typically, scCO2
Experimental results and discussion
Experimental phase equilibria data of binary mixture for the capronitrile, valeronitrile and lauronitrile in supercritical carbon dioxide are measured and the experimental uncertainty was estimated within ±0.3 MPa and ±0.2 K for a given loading of the cell. The mole fractions are accurate to within ±0.002.
Fig. 1(a)–(c) and Table 1, Table 2, Table 3 show the experimental pressure–composition (p–x) isotherms at T = 313.2, 333.2, 353.2, 373.2 and 393.2 K, and pressures from 3.90 to 25.69 MPa for the
Conclusions
High pressure phase equilibria data of (carbon dioxide + valeronitrile), (carbon dioxide + capronitrile) and (carbon dioxide + lauronitrile) systems have been studied using a high-pressure, variable-volume view cell. The (carbon dioxide + valeronitrile), (carbon dioxide + capronitrile) and (carbon dioxide + lauronitrile) mixtures do not exhibit three phases at any five temperatures. We compared the experimental data with the calculated value by Peng–Robinson EOS using two temperature-independent
Acknowledgement
This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (Grant No. 2011-0002766).
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Cited by (0)
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Presented at the 12th European Meeting on Supercritical Fluids, Graz, Austria, May 9–12, 2010.