Liquid–liquid equilibria for the extraction of phenols from alkane using ethylene glycol
Introduction
Coal tar, as a byproduct of coal coking, is an important feedstock for the coal chemical industry due to its numerous and valuable components. In the chemical industry, distillation is widely applied to separate light components of coal tar. After distillation, several fractions of high temperature tar are roughly obtained: BTX, carbolic oil, naphthalene oil, wash oil, anthracene oil and coal-tar pitch [1]. However, the distillation process demands high energy at a high cost. Therefore, it is necessary to find a lower consumption process like the extraction technology to obtain phenols in low-temperature tar. Phenol and phenol derivatives mainly obtained from coal tar are widely used in the production of polycarbonates and phenolic resins [1].
An optimized planning and realization of extraction plants in the chemical industry will require comprehensively qualitative and quantitative phase equilibrium data [2]. Due to the complicated components of tar, it would be an insurmountable task to completely obtain the liquid–liquid equilibrium data of every individual compound and solvent. Therefore, a simplification method is used in this work, as referred to that in Catherine A. Peter's report [3]. 1-Heptane and phenols are used as the main representative components in low temperature tar. Considering the polarities of these components are different, the polar solvent may be used as the extractant to separate coal tar. Ethylene glycol, as a typical polar solvent, has been used for phenol extract and arenes separation from nonaromatic compounds [4], [5].
At present, the liquid–liquid equilibria data of a coal tar system is rarely reported in literature, especially for the system containing phenol. According to Zhang's report [6], phenol, o-cresol, m-cresol, and p-cresol are the main phenols in low temperature coal tar. So, the LLE data for the ternary mixture of 1-Heptane + phenols + ethylene glycol were measured at 323.15 and 343.15 K under atmospheric pressure. Tie-lines are determined for the ternary systems according to the LLE data. The distribution coefficient and separation factor were calculated according to the LLE data and used as the standard to evaluate the separation efficiency. The experimental data are also correlated with Non-Random Two Liquids (NRTL) [7] and Universal Quasi-Chemical (UNIQUAC) [8] activity coefficient models.
Section snippets
Materials
The chemicals used were 1-Heptane, phenol, o-cresol, m-cresol, p-cresol and ethylene glycol, which were purchased from Sinopharm Chemical Reagent. The details about the chemicals are presented in Table 1. The purities of these components were tested by gas chromatography and no appreciable peaks of impurities were found, which indicated no purification methods were needed for the LLE measurements.
Apparatus and procedure
LLE data for the studied ternary system were obtained at 323.15 and 343.15 K under atmospheric
Thermodynamics modeling
The NRTL and UNIQUAC models were applied to correlate the experimental mole fractions by using the Aspen Plus 7.2 software.
There are three adjustable parameters gij, gji, and αij in the NRTL model. The recommended αij values for mixtures of different types are commonly between 0.1 and 0.47.
There are two contributions to the excess Gibbs energy and the activity coefficient in UNIQUAC model [8]. They are a combinatorial term related to differences in size and shape between the components and a
Experimental data
The LLE data for the ternary systems (1-Heptane + phenols + ethylene glycol) at temperatures of 323.15 and 343.15 K are shown in Table 3, Table 4 with all concentrations expressed in mass fraction. 1-Heptane, phenols and ethylene glycol are identified as component 1, 2 and 3 respectively. The phase diagrams for the ternary mixtures are presented in Fig. 2, Fig. 3, Fig. 4, Fig. 5. The tie-lines and feed compositions are also plotted in Fig. 2, Fig. 3, Fig. 4, Fig. 5. As displayed in these
Conclusions
The liquid–liquid equilibria for 1-Heptane + phenols + ethylene glycol ternary system were investigated at 323.15 and 343.15 K under atmospheric pressure. It was found that phenols have a higher solubility in ethylene glycol than in 1-Heptane. The separation factors are much larger than one, implying the feasibility of ethylene glycol to extract the phenols from low-temperature coal tar. NRTL and UNIQUAC models are applied to correlate experimental data. The corresponding optimized interaction
Acknowledgments
This study is supported by Qingdao postdoctoral fund (NO. T1504117) and the Project of Natural Science Research of Higher Education Institutions of Jiangsu Province (NO. 15KJD530001). Harold G. Sherrard is greatly acknowledged for his attribution to the manuscript's language modification.
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