Measurement and correlation of critical properties for binary mixtures and ternary mixtures containing gasoline additives
Introduction
Supercritical fluid technology is widely used in industrial separations and chemical reaction processes, and the critical properties of the relevant pure substances and mixtures are an essential part of the technology. In addition, critical properties are important for the theoretical development of thermodynamic equations of state. But the critical properties of mixtures are scarce in the open literatures, especially for the mixtures with more than two components. Prediction is a useful way to determine the critical properties of mixtures, but the lack of experimental critical properties for mixtures with more than two components hinders the development of prediction methods. Therefore, it is urgent to report more critical properties of mixtures and develop prediction methods for estimating the critical properties of mixtures with more than two components. Some scholars have tried to predict the critical properties of ternary mixtures. For instance, Tao Liu et al. [1] predicted the critical properties of ternary mixtures by the interaction parameters obtained from binary mixtures with the hard-sphere three-parameter equation [2], [3], the Powell method [4], and the Hicks–Young method [5]. Soo [6] found that the Cibulka’s equation [7] was suitable for correlating ternary critical properties. The above methods are either complicated or correlated with the experimental data. It is necessary to find simple and accurate methods to predict the critical points of mixtures with more than two components.
In the gasoline industry, the critical properties of the additive mixtures are very scarce. Among the gasoline additives, short chain alcohols (methanol, ethanol and 1-propanol) and methyl tert-butyl ether (MTBE) are widely used for their excellent properties, such as high octane number, degradability, and low exhaust emission. In this work, we measured the critical temperatures and critical pressures of three binary mixtures (methanol + 1-propanol, heptane + ethanol, heptane + 1-propanol) and three ternary mixtures (methanol + 1-propanol + heptane, methanol + 1-propanol + MTBE, ethanol + heptane + MTBE) containing gasoline additives. Some critical properties of heptane + ethanol [6], [8] and heptane + 1-propanol [9] have been reported, but the experimental data covering the full concentration range is lack. The critical properties of the other four systems are reported for the first time. The Peng–Robinson equation of state [10] combined with the Wong–Sandler mixing rule [11], [12] (PR–WS), was used to predict the critical temperatures and critical pressures of ternary mixtures. The experimental data was also correlated with empirical equations, the Redlich–Kister equation [13] for binary mixtures, the Cibulka’s equation [7] for ternary mixtures.
Section snippets
Materials
Chemicals used in this work are listed in table 1. Their purities were all above 0.990 (mass fraction) and checked by gas chromatograph. All of the chemicals were purchased from Tianjin Guangfu Technology Development Co., Ltd. and used without further purification.
Apparatus
A high-pressure view cell was designed in our previous work [14] to determine the critical properties of mixtures. This apparatus is made of titanium material with two sapphire glass windows for visual observation. Its maximum
Experimental results
The apparatus’ reliability and the experiment procedure were checked by measuring the critical properties of pure cyclohexane, heptane, MTBE, methanol, ethanol, 1-propanol, and a binary mixture (hexane + ethanol) in the previous work [14]. The critical properties of three binary mixtures (methanol + 1-propanol, heptane + ethanol, heptane + 1-propanol) and three ternary mixtures (methanol + 1-propanol + heptane, methanol + 1-propanol + MTBE, and ethanol + heptane + MTBE) were measured over the whole range of the
Conclusions
The critical temperatures and the critical pressures of three binary mixtures (methanol + 1-propanol, heptane + ethanol, heptane + 1-propanol) and three ternary mixtures (methanol + 1-propanol + heptane, methanol + 1-propanol + MTBE, ethanol + heptane + MTBE) were measured with visual observation method by a high-pressure cell. The phase diagrams of all the binary mixtures belong to type I. Heptane + ethanol system and heptane + 1-propanol system show visible non-ideal behavior, because of the great differences
Acknowledgments
This research was supported by the Programme of Introducing Talents of Discipline to Universities (No. B060006), National Natural Science Foundation of China (No. U1162104).
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