Separation of Phenolic Compounds from Coal Tar via LiquidâLiquid

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Separation of Phenolic Compounds from Coal Tar via Liquid-Liquid Extraction Using Amide Compounds Tiantian Jiao, Xulei Zhuang, Hongyan He, Chunshan Li, Hongnan Chen, and Suojiang Zhang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie504892g • Publication Date (Web): 10 Feb 2015 Downloaded from http://pubs.acs.org on February 18, 2015

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Industrial & Engineering Chemistry Research

Separation of Phenolic Compounds from Coal Tar via Liquid-Liquid Extraction Using Amide Compounds Tiantian Jiao, Xulei Zhuang, Hongyan He, Chunshan Li*, Hongnan Chen, Suojiang Zhang*\

Beijing Key Laboratory of Ionic Liquids Clean Process, State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, PR China

Abstract Phenolic compounds are widely used in chemical industrial applications. The traditional method of extracting phenolic compounds, which uses strong alkaline and acid, is harmful to the environment. In this research, amide and its homologues were developed as new extraction agents. And they could form deep eutectic solvent (DES) with phenols, and this DES was immiscible with oil. Formation mechanism of the DES was investigated using a Fourier transform infrared spectrometer (FT-IR). Hydrogen bond (H-bond) between acylamino and phenolic hydroxyl groups was observed. Different experimental conditions, such as different substituents of amide compounds, reaction temperature, reaction time, and mole ratio of extraction agent to phenols were studied. The influence rules of different experimental conditions were obtained, so did the optimized conditions. The extraction agent was recycled through back extraction, and exhibited good recycling properity and high extraction efficiency. Based on above experimental results, a separation process was proposed. Keywords: Coal tar; phenol; DES; amide; nicotinamide; liquid-liquid extraction *

Corresponding author:

Chunshan Li. TEL/FAX: +86-10-82544800; E-mail: [email protected] Suojiang Zhang. TEL/FAX: +86-10-82627080; E-mail: [email protected]

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1.

Introduction Phenol and cresols, which are important basic industrial chemicals, are widely

used in producing phenolic resins, pesticides, medicines, synthetic fibers, and etc. 1. They are obtained mainly from coal tar and coal liquefied oil, especially low-temperature coal tar, in which the phenols content reaches approximately 20% to 30% 2. Hence, an efficient method for the full utilization of phenols should be developed. The traditional method of separating phenols uses strongly alkaline aqueous solutions, such as NaOH, to react with phenols and form a precipitate (i.e., phenolate), and mineral acid, such as H2SO4, to acidify the phenolate 3. A large quantity of phenol-containing waste water is produced during separation, and the process equipment easily corrodes because of the large amount of strong alkalis and acids 4. An environmental friendly method that does not employ acid or base during separation is necessary to prevent the above problem. Liquid-liquid extraction is an increasingly promising method in extracting phenols because this type of extraction exhibits large capacity and easy accessibility. However, the selectivity and recyclability of extraction agents limit the application of this method, exploration of new extraction agent becomes extremely essential. Different organic solvents and ionic liquids (ILs) were screened to determine the best extraction agent 5. Although ILs have been successfully applied in various separation processes, but they exhibit limited selectivity, poor biodegradability, and high cost of synthesis. Thus development of these extraction agents did not push through 6.


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Recently, deep eutectic solvents (DES), which are a new kind of solvent, were developed, DES are easily formed by simply mixing two compounds together. In general, DES are used in liquid form. In addition, the melting points of DES are lower than those of their individual compounds 7. To a particular extent, the physicochemical properties of DES are extremely similar to those of ILs. Abbott et al. 8 initially mixed amide compounds with quaternary ammonium and produced low-melting point eutectics. This kind of eutectics was defined as DES. A series of DES composed of quaternary ammonium and other H-bond donors were designed and synthesized 9. These DES are widely used in electrochemistry, synthesis, nonmaterial, and biochemistry because of their unusual properties 10. DES in liquid form exhibits great potential as extraction medium. Abbott et al.

11

applied DES in separating glycerol

from biodiesel, Hayyan et al. 12,13 showed that DES with quaternary ammonium salt successfully separated glycerol from palm-oil based biodiesel. Mukhtar et al. synthesized phosphonium-based DES 14, which were used in separating toluene from toluene/heptane mixtures; liquid-liquid equilibrium data of phosphonium-based DES were measured at different temperatures 15, 16. Zaira et al. 17 used DES to separate alcohols from easters, and tedious separation chromatographic steps might be overcome. Sarwono et al. 18 used a DES of tetrabutylammonium salt and sulfolane to separate aromatics from aliphatics, and studied the equilibrium data of the ternary system. Pang et al. found that choline chloride reacted with phenols to form DES 19, this process was an efficient method to separate phenols. Guo et al. studied homologous compounds, and their extraction efficiencies were compared 20. DES are



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expected to attract considerable attention because of the emergence of novel green solvents, moreover, the great potential of DES in separating compounds will be studied. In the experiment process, DES which were immiscible with oil formed when amide compounds added to phenols. Therefore, amide compounds can be used in the separation of phenols from coal tar. In this study, Fourier transform infrared spectrometer (FT-IR) was used to study the generation mechanism of DES by analyzing the chemical bond of DES. A series of DES containing amide compounds and phenols was designed and synthesized. And the effect of the structure of the amide compounds on phenols removal efficiencies was investigated. In addition, the effects of different experimental conditions such as reaction temperature, reaction time and mole ratio of extraction agent to phenols were studied, and the experimental conditions were optimized. Finally, a separation process was proposed.


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2. Experiment 2.1 Reagents Table 1. The reagents used in the experimental process All the reagents used in the experimental process were listed in Table 1., also with their CAS registry numbers, manufacturer, and quality standard. In all cases, the percentage purities mentioned above refer to mass fractions as reported by the suppliers. All of the chemical agents were used without further purification, and water was distilled before it was used. 2.2 Reactions 2.2.1 Preparation of model oil Phenol, o-cresol, p-cresol, and m-cresol were chosen as the typical phenolic compounds because of the complexity of low-temperature coal tar. A mass ratio of 2:1:1:1 in terms of the bulk density of low-temperature coal tar was used, and hexane was chosen as the solvent. In this study, 80.10 g of phenol, 40.26 g of o-cresol, 40.28 g of p-cresol, and 40.03 g of m-cresol were placed in a 500 mL beaker. Hexane was used to completely dissolve the phenols with continuous shaking. The resulting solution was placed in a volumetric flask and diluted to 1000 mL with hexane at 303.15 K. The concentrations of the model oil were 80.10 g/L for phenol, 40.26 for g/L p-cresol, 40.28 g/L for o-cresol, and 40.03 g/L for m-cresol. 2.2.2 Experimental procedure A specific amount of model oil and extraction agent with a fixed mole ratio were mixed in a graduated cylinder and placed in a thermostatic water bath. The



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temperature of the water bath was controlled within ± 0.1 K, and the revolutions were 400 rpm. A known mass of the extraction agent was measured with a precision of ± 0.001 g. The graduated cylinder was set aside after the reaction finished until two layers clearly formed. The two layers were separated using a separating funnel, and the volumes of the two layers were carefully measured. The phenols extraction efficiency was calculated using the phenols concentrations of the upper layer, which was detected using a gas chromatograph (GC). Then, diethyl ether (DE) was used as back-extraction agent to recycle amide compounds. A certain amount of DE was added in the lower layer, a white solid was immediately precipitated when DE was added. The mixture was filtered via suction filtration using a Hirsch funnel and washed with a specific amount of DE. The solid was collected and dried in vacuum desiccators at 335.0 K to remove DE and the phenols. The liquid in the Buchner flask was distilled to remove the DE and to obtain the phenols. The weight of the recycled NA was measured until the mass became constant. 2.3 Analysis methods The concentrations of phenol, o-cresol, p-cresol, m-cresol, and hexane were determined using a GC equipped with a flame ionization detector (FID). A 50-m Shinwa ULBON WCOT column with an inner diameter of 0.20 mm was used in this study. The chromatographic conditions employed included a constant temperature of 130 °C for the oven and 250 °C for the injector and detector. The recycled extraction agent was qualitatively analyzed using an FT-IR (Nicolet 380, Thermo Fisher


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Scientific, and America). The reaction mechanism of extraction was investigated by analyzing the difference in the chemical bonds of the DES. All of the spectrums were obtained at room temperature. 3. Reaction mechanism of extraction It is meaningful to explore the generation mechanism of DES. And a mechanism was proposed to explain the formation of the DES via the reaction of amide compounds and phenols. The reaction of Nicotinamide (NA) and m-cresol was used to explain the mechanism of extraction as an example. NA (solid)⇌NA (molecule)

(1)

NA (molecule) + m-cresol (liquid) ⇌ DES

(2)

This process included two steps: first, the solid extraction agent NA dissolved in the m-cresol solution (200.0 g/L), and H-bond generated between m-cresol and NA. DES+solution⇌ Liquid − Liquid

(3)

Adding more NA produced more DES. Initially, the formed DES was completely dissolved in the model oil, however, two apparent layers eventually formed because of the solubility difference between DES and phenols in hexane. The lower layer formed when DES became saturated in the oil, and it was composed mainly of DES. The chemical bond between m-cresol and NA were analyzed via FT-IR. Figure 1 shows the FT-IR spectrums of m-cresol, NA, and DES. These spectrums were obtained to investigate the force of interaction present in the samples. The ν-OH stretching vibration of phenols was significantly affected by H-bond. Figure 1. shows that the ν-OH stretching vibration of m-cresol was observed at 3331 cm-1, this peak



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shifted to 3258 cm-1 in the spectrum of the DES. The ν-NH stretching vibration could be observed between wavenumbers 3100 cm-1 and 3500 cm-1. The ν-NH stretching vibration of NA was observed between 3367.25 cm-1 and 3160.67 cm-1, and this vibration shifted to wavenumbers that ranged between 3488 cm-1 and 3368 cm-1 in the spectrum of the DES 21, 22. Usually, a ν-CO stretching vibration was present in the wavenumbers range from 1630 cm-1 to 1680 cm-1. This vibration shifted from 1681.77 cm-1 of NA to 1658 cm-1 of DES. These changes in the absorption bonds are mainly due to the changes between different vibrational states of bonds in molecules. A portion of the electron cloud in the oxygen atom transfers to H bond, thus, the FT-IR spectrum of phenols in DES exhibited a change in vibrational states. All of these informations are extremely important in exploring the mechanism of the reaction. The results suggest the presence of H-bond between m-cresol and NA when the DES was formed. Figure 1. FT-IR spectra of m-cresol, IMZ, and formed DES The differences of the substitute have certain affection on the reaction process 23, 24

. And the vibration shift of ν-OH could be a criterion of the hydrogen-bond

interactions. Then a series of the FT-IR spectra of amide compounds were investigated, the amide compounds used in this process were DMF, AA, procainamide (PA), BA, and NA. The spectra of the DES formed by these amide compounds and m-cresol were shown in Figure 2. The ν-OH stretching vibration of m-cresol was observed at 3331 cm-1, this peak shifted to 3260 cm-1 in the DES spectrum of DMF, and 3259 cm-1 of AA, 3261 cm-1 of PA, 3262 cm-1 of BA, and 3258 cm-1 of NA. As


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the increasing of the alkyl substituents length, the vibration shift of ν-OH decreased to some extent. The increasing vibration shift of ν-OH represented the stronger H-bond interactions ability. So it could be seen from the FT-IR spectra that longer alkyl substituents means smaller vibration shift and weaker H-bond interactions ability.

Figure 2. The FT-IR spectra of m-cresol and the DES of DMF, AA, PA, BA, and NA

The vibration shift of ν-OH of different amide compounds showed the strong degree of the hydrogen bond. And the strong degree of the hydrogen bond decided the stability of the DES formed by phenols and amide compounds. That is to say, the extraction efficiency of phenols from model wash oil increased as the increasing of the vibration shift of ν-OH. 4. Results and discussion In this study, the single phenol removal efficiency and the total phenols removal efficiency were used as a measurable indicator to evaluate the ability of the extraction agents in separating the phenols from oil. The phenol removal efficiency was calculated using the phenol concentration of the upper layer that was detected via GC. The specific formula used is shown in Eq. (4): Phenol removal efficiency(%) =

! " # !# × 100 !

(4)

Where, Co and Ca represent the phenol concentration in the original model oil, and in the upper layer after reaction, respectively. Vo, and Va represent the volume of the original model oil and the upper layer after reaction, respectively.



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4.1 Effect of amide compound substituents on the reaction The amide groups had a critical function during the extraction of phenols. Therefore, the effects of the substituents present on the amide compounds were thoroughly investigated. Different substituents, including alkyl (i.e., methyl, ethyl, and butyl), and aromatic groups (i.e. benzyl, and pyridyl) were investigated, and the amide compounds were Nicotinamide (NA), Acetamide (AA), Butyrylamide (BA), Benzamide (BNA), and Dimethylformamide (DMF), respectively. A 1:1 mole ratio of the amide compounds to phenols was used in the study. Around 4.78 g of NA, which represented the amide compounds, and 20 mL of the model oil were placed in a graduated cylinder. The reaction temperature and time were 303.15 K and 30 min respectively. All of the experiments were performed using the stated conditions. A DES phase, which was formed at the bottom layer, was immediately observed after adding the amide compound in the model oil. Figure 3. shows that all of the calculated phenols removal efficiencies were more than 90% and the different substituents in the amide compounds exhibited different effects on the phenol removal efficiencies. The effects of the alkyl groups, from greatest to least, on the phenols removal efficiencies follow the order: butyl > ethyl > methyl. The phenols removal efficiencies were 95.2%, 96.6%, and 96.2% of phenol; 94.0%, 95.9%, and 95.2% of o-cresol; 95.2%, 96.4%, and 96.1% of p-cresol; 95.0%, 96.4%, and 96.1% of m-cresol, 95.94%, 97.40%, and 96.97% of total phenols for BA, AA, and DMF, respectively. These results are attributed to the steric hindrance caused by long alkyl groups; consequently, weak H-bond interactions were observed. Increasing the length of alkyl


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substituents increased the molecular volume of the amide compounds; thus, affected the distance of the charge centers between the phenols and amide compounds, so did their interactions. The phenols removal efficiency of the amide compound containing benzyl decreased by a specific degree compared with those containing alkyl substituents. This finding is attributed to the larger volume of the benzyl group than that of the alkyl substituents. When the amide compound was changed to NA (i.e., N was replaced with C in the benzene ring), N had a lone electron pair, which provided more electric charge that increased the electronegativity of the acylamino group. This condition was beneficial in generating H-bond, thus, the phenols removal efficiency of NA was greater than that of BNA. The experiment results were in consistent with the FT-IR results of different substitutes.

Figure 3. The phenols removal efficiencies of amide compounds from model oil (initial concentration: phenol (80.00 g/L), o-cresol (40.26 g/L), p-cresol (40.28 g/L), m-cresol (40.03 g/L); reaction temperature: 303.15 K; mole ratio of phenol to extraction agent: 1:1; reaction time: 30 min) Amide compounds provide an efficient way of separating phenols from oil. Amide compounds exhibit removal efficiencies more than 90%. However, the mechanisms on how different experimental conditions affect the reaction process remain unclear. Therefore, parameters, such as mole ratio, reaction temperature, and reaction time, were studied. 4.2 Effect of various parameters on phenols removal efficiencies 4.2.1 Effect of mole ratio Mole ratios greatly affect the separation process, therefore, the effect of the



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parameter was thoroughly investigated. When NA was added in the model oil at the mole ratio of 0.05, NA was completely dissolved, and no DES layer was observed. A lower layer appeared when the mole ratio reached 0.1. This result means that a minimum mole ratio was necessary during the formation of DES. Therefore, the mole ratios of NA to phenols employed were 0.1, 0.3, 0.5, 0.7, and 1.0. Figure 4 shows that increasing the mole ratio increased the phenols removal efficiencies. The phenols removal efficiencies increased rapidly from 50% to more than 95% when the mole ratio increased from 0.1 to 0.5, and the efficiencies increased gradually when the mole ratio exceeded 0.5. The optimal phenols removal efficiencies were 97.12%, 92.50%, 96.61%, 96.70%, and 96.24% for phenol, o-cresol, p-cresol, m-cresol, and total phenols respectively, when the mole ratio was 0.5. The optimum mole ratio of 0.5 was used in succeeding experiments to ensure the economic efficiency of the separation process.

Figure 4. Phenols removal efficiencies from model oil at different mole ratio (initial concentration: phenol (80.00 g/L), o-cresol (40.26 g/L), p-cresol (40.28 g/L), m-cresol (40.03 g/L); reaction temperature: 303.15 K; reaction time: 30 min) 4.2.2 Reaction temperature The reaction temperature was varied (i.e., 303.15 K, 313.15 K, 323.15 K, and 333.15 K) to investigate the effect of temperature on the separation process. The employed reaction time and mole ratio of NA to phenols were 30 min and 0.5:1, respectively. Figure 5. shows that increasing the reaction temperature decreased the phenols removal efficiencies from 96.7%, 92.7%, 95.8%, 95.7%, 95.53% at 303.15 K


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to 93.0%, 90.3%, 92.1%, 91.8%, 92.05% at 333.15 K for phenol, o-cresol, p-cresol, m-cresol, and total phenols respectively. The maximum phenols removal efficiencies were obtained at 303.15 K, which was at room temperature. This result is attributed to the increased solubility of phenols with the increasing reaction temperature. Moreover, this reaction was exothermic, therefore, increasing the temperature did not result in a positive effect during extraction process, and room temperature is the suitable temperature. A temperature of 303.15 K was chosen as the optimum temperature.

Figure 5. The phenols removal efficiencies of different reaction temperature from model oil (initial concentration: phenol (80.00 g/L), o-cresol (40.26 g/L), p-cresol (40.28 g/L), m-cresol (40.03 g/L); mole ratio of phenol to extraction agent: 1:0.5; reaction time:30 min) 4.2.3 Reaction time The reaction time was also varied (i.e., 5, 10, 30, and 60 min) to study the effect of reaction time on the separation process. A mole ratio of 0.5:1 and a reaction temperature of 303.15 K were employed in this part of the experiment. An obvious mass transfer of oil from the bottom layer to the top layer was immediately observed when NA was combined with the model oil. Figure 6. shows that the phenols removal efficiencies increased sharply from 5 to 10 min and a gradually increase was observed from 10 to 60 min. The reaction time should be short in the premise of completing reaction. Therefore, 30 min was chosen as the suitable reaction time, and the phenols removal efficiencies were 96.13% for phenol, 93.30% for o-cresol, 95.71% for p-cresol, 95.82% for m-cresol, and 95.42% for total phenols respectively.



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Figure 6. The phenols removal efficiencies at different reaction time from model oil (initial concentration: phenol (80.00 g/L), o-cresol (40.26 g/L), p-cresol (40.28 g/L), m-cresol (40.03 g/L); mole ratio of phenol to extraction agent: 1:0.5; reaction temperature: 303.15 K) 4.4 Recycling of extraction agent The phenols and extraction agent must be separated to obtain the product (i.e. phenols) and recycle the extraction agent. Diethyl ether (DE) was used as an efficient solvent to recover the extraction agent. DE was chosen because amide compounds and phenols exhibit significant solubility difference in DE. A white solid appeared at the bottom of the test tube when the DE was added in the DES. This white solid was identified as extraction agent, and the liquid remaining was mainly composed of DE and phenols. Take NA as an example, the recycle of amide compounds was studied. The whole reaction parameters were as follow: 2.391 g of NA; 20 mL of the model oil; mole ratio of NA to phenols 0.5:1; 30 min of reaction time; 303.15 K of reaction temperature; 30 mL of DE. The recycle efficiency could be calculated through the recycled mass divided by the original mass. The structure of NA and the recycled NA were characterized using FT-IR, and their spectra are shown in Figure 9. The characteristic absorption peaks of the recycled NA were identical to those of standard NA. This result confirmed that the recycled solid was NA. The same experiments were repeated six times at the same reaction conditions to determine the extraction efficiency and the multiple recycle efficiency of NA. Figures 7 and 8. show that NA can be reused more than six times because the recycled NA still exhibited high phenols removal efficiencies, which were more than 90%,


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even after repeated usage. The recovery efficiencies of NA were more than 85% after six regeneration cycles. The recovery efficiencies gradually decreased. This result is attributed to the loss of NA during the reaction and recycling processes. However, this process was an efficient way to recycle the NA.

Figure 7. Phenols removal efficiencies versus regeneration cycle

Figure 8. Recycle efficiencies of NA versus regeneration cycle

Figure 9. FT-IR spectrums of recycled NA and standard NA 4.5 Separation process

Figure 10. Flow sheet for the removal of phenols from synthetic coal tar oil. B1. Extraction column, B2.Filter, B3. Flash separator, B4. Heater, B5. Purifier, B6. Extraction agent tank. Figure 10. shows the designed separation process based on the obtained experimental results. The separation equipment mainly included an extraction column, filter, flash separator, purifier, and tank. First, the extraction agent (stream 1) and the synthetic coal tar oil (stream 2) were placed in the extraction column, in which the reaction of DES occurred when the phenols were converted by more than 90%. Stream 3, which flowed from the top of the extraction column, was the obtained oil after removing the phenols. The DES (stream 4), which was at the bottom of the extraction column, was moved to B2 by the back-extraction agent DE (streams 8 and



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12), and then the white solid immediately appeared. This white solid was separated using a filter. The liquid phase (stream 6), which was composed mainly of DE and phenols, was fed to the flash separator to obtain the phenols and to recycle the back-extraction agent. Approximately 85% of the extraction agent (stream 11) was recycled during the process. The lower layer (stream 7) was further purified to obtain the phenols (stream 10). The whole separation process was performed at ambient temperature and pressure. The proposed process provides an important reference for the green separation of phenols. 5. Conclusion Amide compounds and phenols could react to form DES that were insoluble with oil, thus, the DES could be used as a successful extraction medium. The FT-IR spectrum of DES showed that there were H-bonds presented between phenols and the acylamino group and the volume of the substitutes had a certain effect on the v-OH shift. The effects of different parameters such as the structure, mole ratio, reaction temperature, and reaction time, were investigated in this study. Increasing the length of the linear substituents and the presence of aromatic subsituents caused week H-bond interaction because of greater steric hindrance. The optimum mole ratio of NA to the phenols was 0.5:1 and this mole ratio exhibited maximum phenols removal efficiencies of more than 92%. A reaction time of 30 min was adequate because the reaction rate was fast, and room temperature was appropriate because temperature did not affect the reaction. The extraction agent was recycled using anti-solvent DE. The phenols removal efficiencies remained more than 90% during the six recycle


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processes. Meanwhile, the recycle efficiencies of the extraction agent exceeded 85%. The proposed separation process can be potentially used in industrial applications. In contrast with traditional methods, this method is environmental-friendly because large quantities of waste water can be avoidable.

Acknowledgment The authors gratefully acknowledge financial support from the "Strategic Priority Research Program" of the Chinese Academy of Sciences (Grant No. XDA0702100) and National Natural Science Foundation of China (U1162106 and 51104140).



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Notations List of symbols Co Vo Ca Va

Original oil concentration (g·mol-1) Original oil volume(mL) Oil concentration after reaction(g.mol-1) Oil volume after reaction (mL)

Abbreviations NA AA BA BNA DMF PA FT-IR GC DES

Nicotinamide Acetamide Butyrylamide Benzamide Dimethylformamide Propionamide Fourier transform infrared spectrometer Gas chromatograph Deep eutectic solvent

Subscripts

o a

original data data after reaction


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References [1] Xue, X.K.; Chen, Q.W. Coal tar processing technology; Chemical Industry: Beijing, 2007 [2] Sun, M.; Feng, G.; Wang, R.C. Separation and GC-MS Analysis of Shanbei low temperature coal tar. Petrochemical Technology. 2011, 40, 667. [3] Richard, H.S.; Charles, G.S. Removal of phenols from phenol-containing stream. US Patent 4256568 1981. [4] Shui, H.F.; Zhang, D.X.; Zhang, C.Q. Separation and refined of coal tar; Chemical Industry: Beijing, 2007. [5] Tian, M.; Feng, J. Selective enrichment of phenols from coal liquefaction oil by solid phase extraction method. Energ. Source. Part A, 2009, 31, 1646. [6] Tang, B.K.; Row, K.H. Recent developments in deep eutectic solvents in chemical sciences. Monatsh. Chem. 2013, 144, 427. [7] Dai, Y.T.; Spronsen, J.V.; et. al. Ionic Liquids and Deep Eutectic Solvents in Natural Products Research: Mixtures of Solids as Extraction Solvents. J. Nat. Prod. 2013, 76, 2162. [8] Abbott, A.P.; Boothby, D.; Capper, G.; et. al. Deep Eutectic Solvents Formed between Choline Chloride and Carboxylic Acids: Versatile Alternatives to Ionic Liquids. J. Am. Chem. Soc. 2004, 126, 9142. [9] Abbott, A.P.; Capper, G.; Davies, D.L.; et. al. Ionic Liquids Based upon Metal Halide/Substituted Quaternary Ammonium Salt Mixtures. Inorg. Chem. 2004, 43, 3447.



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[10] Dai, Y.T.; Spronsen, J.V.; et. al. Natural deep eutectic solvents as new potential media for green technology. Anal. Chim. Acta. 2013, 766, 61. [11] Abbott, A.P.; Cullis, P.M.; Gibson, M.J.; et. al. Extraction of glycerol from biodiesel into a eutectic based ionic liquid. Green. Chem. 2007, 9, 868. [12] Hayyan, A.; Hashim, M.A.; Mjalli, F.S.; Hayyan, M.; AINashef, I.M. A novel

phosphonium-based deep eutectic catalyst for biodiesel production from industrial low grade crude palm oil. Chem. Eng. Sci. 2012, 92, 81. [13] Hayyan, A.; Hashim, M.A.; Hayyan, M.; Mjalli, F.S.; AlNashef, I.M. A novel ammonium based eutectic solvent for the treatment of free fatty acid and synthesis of biodiesel fuel. Ind. Crop. Prod. 2013, 46, 392. [14] Mukhtar, A.K.; Farouq, S.M.; Mohd, A.H.; Inas M.A. Phosphonium-Based Ionic Liquids Analogues and Their Physical Properties. J. Chem. Eng. Data. 2010, 55, 4632. [15] Mukhtar, A.K.; Farouq, S.M.; Mohd, A.H.; Mohamed, K.H.; Fatemeh, S.G.B.; Inas, M.A. Phase equilibria of toluene/heptane with deep eutectic solvents based on ethyltriphenylphosphonium iodide for the potential use in the separation of aromatics from naphtha. J. Chemthermodyn. 2013, 65, 138. [16] Mukhtar, A.K.; Farouq, S.M.; Mohd, A.H.; Mohamed, K.H.; Fatemeh, S.G.B.; Inas, M.A. Phase equilibria of toluene/heptane with tetrabutylphosphonium bromide baseddeep eutectic solvents for the potential use in the separation of aromatics from naphtha and separation. Fluid. Phase. Equilibr. 2012, 333, 47. [17] Zaira, M.; Walter, L.; Pablo, D.M. Practical separation of alcohol–ester mixtures using Deep-Eutectic-Solvents. Tetrahedron. lett. 2012, 53, 6968.


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[18] Sarwono, M.; Hanee, F.H.; Inas, M.A.; Mohd, A.H.; Anis, H.F.; Mohamed, K.H. Separation of BTEX aromatics from n -octane using a (tetrabutylammonium bromide + sulfolane) deep eutectic solvent-experiments and COSMO-RS prediction. RSC. Adv. 2014, 4, 17597. [19] Pang, K.; Hou, Y.C.; Wu, W.Z.; et al. Efficient separation of phenols from oils via forming deep eutectic solvents. Green. Chem. 2012, 14, 2398. [20] Guo, W.J.; Hou, Y.C.; Wu, W.Z.; et al. Separation of phenols from model oils with quaternary ammonium salts via forming deep eutectic solvents. Green. Chem. 2013, 15, 226. [21] Atac, A.; Karabacak, M.; Kose, E.; et.al. Spectroscopic (NMR, UV, FT-IR and FT-Raman) analysis and theoretical investigation of nicotinamide N-oxide with density functional theory. Spectrochim. Acta. Part A. 2010, 75, 1552. [22] Ramalingam, S.; Periandy, S.; Govindarajan, M.; et.al. FT-IR and FT-Raman vibrational spectra and molecular structure investigation of nicotinamide: A combined experimental and theoretical study. Spectrochim. Acta. Part A. 2010, 75, 1552. [23] Jiang, H.; Fang, Y.; Fu, Y.; Guo, Q.X. Studies on the extraction of phenol in wastewater. J. Hazard. Mater. 2003, 101, 179. [24] Jiang, H.; Fang, Y.; Fu, Y.; Guo, Q.X. Separation and recycle of phenol from wastewater by liquid-liquid extraction. Separ. Sci. Technol. 2003, 38, 2579.



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Table and Figure Captions Table 1. The reagents used in the experimental process Figure 1. FT-IR spectra of m-cresol, IMZ, and formed DES Figure 2. The FT-IR spectra of m-cresol and the DES of DMF, AA, PA, BA, and NA Figure 3. The phenols removal efficiencies of amide compounds from model oil (initial concentration: phenol (80.00 g/L), o-cresol (40.26 g/L), p-cresol (40.28 g/L), m-cresol (40.03 g/L); reaction temperature: 303.15 K; mole ratio of phenol to extraction agent: 1:1; reaction time: 30 min) Figure 4. Phenols removal efficiencies from model oil at different mole ratio (initial concentration: phenol (80.00 g/L), o-cresol (40.26 g/L), p-cresol (40.28 g/L), m-cresol (40.03 g/L); reaction temperature: 303.15 K; reaction time: 30 min) Figure 5. The phenols removal efficiencies of different reaction temperature from model oil (initial concentration: phenol (80.00 g/L), o-cresol (40.26 g/L), p-cresol (40.28 g/L), m-cresol (40.03 g/L); mole ratio of phenol to extraction agent: 1:0.5; reaction time:30 min) Figure 6. The phenols removal efficiencies at different reaction time from model oil (initial concentration: phenol (80.00 g/L), o-cresol (40.26 g/L), p-cresol (40.28 g/L), m-cresol (40.03 g/L); mole ratio of phenol to extraction agent: 1:0.5; reaction temperature: 303.15 K) Figure 7. Phenols removal efficiencies versus regeneration cycle Figure 8. Recycle efficiencies of NA versus regeneration cycle Figure 9. FT-IR spectrums of recycled NA and standard NA Figure 10. Flow sheet for the removal of phenols from synthetic coal tar oil. B1. Extraction column, B2.Filter, B3. Flash separator, B4. Heater, B5. Purifier, B6. Extraction agent tank.


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Table 1. Compound

CAS NO

Purity

Phenol

108-95-2

>99.0% w

P-cresol

106-44-5

>99.0% w

M-cresol

108-39-4

>99.0% w

O-cresol

95-48-7

>99.0% w

Hexane

110-54-3

>95.0% w

Nicotinamide (NA)

98-92-0

Acetamide (AA)

60-35-5

>98.0% w

J&K Scientific Co., Ltd

Butyrylamide (BA)

541-35-5

>98.0% w


Benzamide (BNA)

55-21-0

>98.0% w


68-12-2

>98.0% w


79-05-0

>98.0% w


Dimethylformamide (DMF) Procainamide(PA)

A. R. grade

Manufacturer Sinopharm Chemical Reagent Co., Ltd Sinopharm Chemical Reagent Co., Ltd Sinopharm Chemical Reagent Co., Ltd Sinopharm Chemical Reagent Co., Ltd Sinopharm Chemical Reagent Co., Ltd J&K Scientific Co., Ltd



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Figure 1.


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Figure 2.



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Figure 3.


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Figure 4.



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Figure 5.


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Figure 6.



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Figure 7.


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Figure 8.



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Figure 9.


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Figure 10.

Research Highlights 1. Amide compounds could form DES with phenols from coal tar. 2. Hydrogen bond was observed using Fourier transform infrared spectrometer. 3. Influence rules were obtained, and the extraction agents had good recyclability.


Separation of Phenolic Compounds from Coal Tar via LiquidâLiquid

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