(Liquid + liquid) extraction of phenols from aqueous solutions with cineole
Introduction
Phenols (phenolic compounds) such as phenol, cresols, nitrophenol, benzenediol, etc., are permanent organic pollutants and form a class of high-priority pollutants because of their toxic nature, harmful effects [1], and possible accumulation in the environment [2]. Phenols are major pollutants in wastewater produced by many industrial processes, including petroleum refining, coking, coal gasification, and wood processing. Phenolic wastewater was a typical organic chemical industrial wastewater which was poor degradable and toxic. Petrochemical wastewater is one of the most serious sources in all pollution sources of phenolic compounds. The concentrations of different phenolic wastewaters can vary greatly from a higher to a lower concentration. Generally, the concentration of phenols in different wastewaters is in the range of (10–104) mg·L−1 [3]; phenols are present in waste water of various industries, such as refineries (6–500 mg·L−1), coking operations (28–3900 mg·L−1), coal processing (9–6800 mg·L−1), and manufacture of petrochemicals (2.8–1220 mg·L−1) [4].
Removal of phenols from wastewater has been of great environmental interest over recent years [5], [6]. Various methods have recently been applied for phenolic compounds removal like biological-based processes, membrane extraction, distillation, adsorption, ozonation, electrochemical methods, fenton, pervaporation, and liquid–liquid extraction [7]. As one of the important mass transfer processes in chemical engineering, (liquid + liquid) extraction is an alternative method to distillation [8], because of the lower energy cost of the process. Phenolic compounds from aqueous solution using (liquid + liquid) extraction method are industrially and economically important [9]. Studies of (liquid + liquid) equilibria of systems consisting of water, phenolic compounds and organic solvent are very important in various industries [10].
From an industrial point of view, knowledge of the phase equilibria is essential in the modern methods for the processes design and control. (Liquid + liquid) distribution is the basis of simulation and optimization of (liquid + liquid) extraction. A survey of the recent literature on solvent extraction of phenols is presented. Greminge et al. [11] studied solvent extraction of phenols (phenol, benzenediol, pyrogallol, etc.) from water with methyl isobutyl ketone (MIBK) and diisopropyl ether (DIPE). Li et al. [4] researched extraction of phenol from wastewater by N-octanoylpyrrolidine (OPOD). Chen et al. [12] studied phenol distribution behaviour in aqueous biphasic systems with ([Cnmim]BF4, n = 3 to 8) ionic liquids. Fan and Wang et al. [13] researched solvent extraction of selected endocrine-disrupting phenols using ionic liquids [Cnmim][PF6] (n = 4, 6, 8) and [Cnmim][BF4] (n = 6, 8). Tar removal from biosyngas with paraxylene and methyl hexadecanoate in the biomass gasification process was reported by Bassil and Mokbel et al. [14]. Gilani et al. [15] determined the LLE tie-lines for systems (water + phenol + 1-octanol or cyclohexanone or 2-ethyl-1-hexanol or isobutyl acetate) at 298.2 K. Lei and Chen et al. [16] studied LLE for the ternary system (2-methoxy-2-methylpropane + phenol + water). Chasib [17] reported extraction of phenolic pollutants (phenol and pchlorophenol) with five solvents [ethylene glycol, diethylene glycol, poly (ethylene glycol) (2 0 0), dimethylsulfoxide and tetramethylene sulfolone (sulfolane)]. Moreover, complex extraction of phenol and cresol from model coal tar with polyols, ethanol amines, and ionic liquids thereof by Meng and Li et al. [18]; LLE (methyl butyl ketone + phenol + water) and (methyl butyl ketone + hydroquinone + water) by Chen et al. [19]; ternary system (methyl isobutyl ketone + 1,2-benzenediol + water) [20] and (methyl isobutyl ketone + m-benzenediol + water) by yang et al. [21], have been reported in the literatures. Furthermore, LLEs for ternarys (water + cresols + methyl butyl ketone) [22], (methyl isopropyl ketone + phenol + water) [23], and (mesityl oxide + phenol + water) [24] are available in the literature.
On the other hand, cineole (primary constituent of Eucalyptus oils), as an environmental-friendly chemical compound, can potentially replace ozone depleting industrial solvents which are currently phased out due to the Montreal Protocol [25]. Due to nontoxic behavior and the possibility of obtaining it from renewable sources, cineole might be considered as an alternative to petroleum solvents [26]. So far, the (liquid + liquid) equilibria of systems consisting of cineole are available in the literatures [27], [28]; but no LLE values for (water + phenols + cineole) have been reported.
In this work, we focus on two phenolic pollutants: phenol and p-cresol as the test subjects. We studied the extraction property of cineole as an extractant in phenols-water mixtures. To provide fundamental data for the extraction process of phenols removal from wastewater, we determined measured LLE tie-line data for (water + phenol or p-cresol + 1,8-cineole) system at T = (283.15, 298.15, and 313.15) K under atmospheric pressure. Specifically, since this study is aimed at removal of diluted phenols from industrial wastewater, according to the above mentioned concentrations of phenolic wastewaters, the concentrations of feed phenols-water solution were prepared to a wide range of mass percentage from (4 to 0.015)% for phenol mixture, and (2 to 0.0312)% for p-cresol mixture by the dilution method.
The reliability of the experimental LLE tie-line values was verified by the Hand and Bachman equations. From the tie-line results, extraction properties (distribution ratio, selective coefficient, and extraction rate) were determined for the ternary system. Moreover, the experimental LLE values were correlated using the UNIQUAC and the NRTL activity coefficient models in order to obtain the binary interaction parameters.
Section snippets
Materials
The materials 1,8-cineole (synonyms: eucalyptol, 1,3,3-trimethyl-2-oxabicyclo[2.2.2]octane), phenol, and p-cresol were supplied by Aladdin Company and were used without further purification. Double-distilled water prepared in our laboratory was used throughout the experiment. Prior to the measurements, chemical purities were confirmed by gas chromatography. The purities in mass fraction of the chemical reagents used in this work are listed in Table 1. The densities and refractive indices for
Experimental results
Experimental mutual solubility x (mole fraction) as well as w (mass fraction for comparison with available literature) for the binary (water + phenol), (water + p-cresol), and (water + cineole) systems at T = (283.15, 298.15, and 313.15) K and P = 0.1 MPa are listed in Table 3. The experimental ternary LLE tie-line values x (mole fraction) for the (water + phenol + cineole), (water + p-crosol + cineole) systems are presented in Table 4, Table 5, respectively. For the convenience of the calculation of the
Conclusion
The determination of composition of the (liquid + liquid) equilibria for the (water + phenol + cineole) and (water + p-cresol + cineole) systems was carried out with a tie-line method at T = (283.15, 298.15, and 313.15) K.
The experimental results showed that cineole as extraction solvent exhibited high extraction ability for phenols from water solution. Lower temperature was helpful to the increase of the extraction ratio for phenols.
The NRTL and UNIQUAC models were used to correlate the experimental LLE
Acknowledgements
The authors thank the financial support from Natural Science Foundation of Guangdong Province of China (No. 2014A030313508) and the National Natural Science Foundation of China (No. 21276052).
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