Elsevier

Fluid Phase Equilibria

Volume 446, 25 August 2017, Pages 28-35
Fluid Phase Equilibria

Extraction of phenolic compounds from aqueous solution using choline bis(trifluoromethylsulfonyl)imide

https://doi.org/10.1016/j.fluid.2017.04.022Get rights and content

Highlights

  • Equilibrium data of ternary mixtures are measured experimentally.

  • Influence of parameters on the extraction rate of phenolic compounds are investigated.

  • Guaiacol and syringol are easily extractable from water.

  • A process design for the extraction of phenolic compounds is proposed.

Abstract

The efficiency of choline bis(trifluoromethylsulfonyl)imide [choline][NTf2] was evaluated as extractant media for the extraction of phenolic compounds from aqueous solution. Solid-liquid and liquid-liquid equilibria of the ternary mixtures {water + phenolic compounds (phenol, guaiacol, syringol or pyrocatechol) + ionic liquid} were first measured at 295.15 K at atmospheric pressure. The selectivity and the solute distribution ratio values calculated from experimental data indicate that [choline][NTf2] is suitable for the extraction of phenolic compounds. Thermodynamic data of ternary mixtures were used to regress the parameters of the NRTL and UNIQUAC thermodynamic models. The influence of experimental conditions on the extraction of phenolic compounds from aqueous solutions using [choline][NTf2] were evaluated. Process design shows that phenol, guaiacol and syringol are easily extractable with few amount of solvent, number of theoretical steps and energy.

Introduction

Plants produce a large variety of natural compounds, among them, phenolic compounds. Known for their antioxidant or antimicrobial properties, phenolic compound are often used as raw material or intermediate for the production of resins [1], food additives [2], food flavor, pharmaceutical or perfumery products [3], [4], [5]. To date, most of the phenolic compounds are produced from petroleum. Yet, due to the increasing of greenhouse effect and the reducing stocks of fossil fuels, researches lean towards new sources of fuel and chemicals, such as lignin [6]. These last decades, thermochemical conversion processes of biomass have demonstrated their potentials to produce gasoline-compatible liquid fuels [7]. The liquefaction of lignin produces mixtures rich in phenolic compounds but their extraction required several and complexes steps [8]. For example, the separation of phenolic compounds from primary oils of Eucalyptus wood tar can be obtained after 5-stage alkaline extraction and 4-stage ethyl acetate extraction [9]. Separation processes require a good knowledge of phase diagrams of mixtures and of the interactions between the solutes and the extractant media. Liquid-liquid equilibria of systems containing water, phenolic compounds and a solvent allow evaluating the performance of the extraction processes through the calculation of selectivity and solute distribution ratio values. Many organic solvents such as esters [10], [11], ether [12], carbonates [13], [14], ketones [15], [16], [17], [18], [19], [20], [21], alcohols [16], [22], aromatic [23], [24] and aliphatic hydrocarbons [25] have been tested but mostly in systems containing phenol and water, even if researches are more concerned about other monophenols such as guaiacol [26] or pyrocatechol [27]. Ghanadzadeh Gilani et al. [28] and Alvarez Gonzalez et al. [29] have studied the extracting capability of several solvents and shown that organic esters are the most effective solvent for the extraction of phenol from water. Recently, new solvents such as ionic liquids or deep eutectic solvents have shown an important interesting in various processes extraction due to their unique physico-chemical properties. These solvents could replace ethyl acetate or esters for the extraction of phenol from aqueous solution. The use of such solvents may lead to a simplification of the process. Indeed, their low volatility implies an easy way to recover the phenolic compounds. Moreover, such processes could improve the yield and purity of the products. Because ionic liquid (IL) are easily recovered and reusable, their use could also reduce the cost of the process. Pili et al. [30] demonstrated the performance of ILs to remove phenol from aqueous solution using supported ionic liquid membrane. However, studies on the extraction of phenolic compounds using of ionic liquid are still lacking [26]. It is now well established that bis(trifluoromethylsulfonyl)imide based ILs are hydrophobic. Therefore, this family can be used as an extractive media in aqueous liquid-liquid extraction. Indeed, Nockemanns et al. studied the binary system {choline bis(trifluoromethylsulfonyl)imide + water}. They showed that these compounds are partially miscible and presents an upper critical solution temperature at 72 °C [31]. The choice of choline as cation was dictated for its low toxicity compared to imidazolium or pyridinium IL [32]. This family of ILs is more environmentally friendly than some traditional industrial solvents.

The aim of this study was to evaluate the feasibility of the use of choline bis(trifluoromethylsulfonyl)imide for the extraction of phenolic compounds from aqueous solution. For the first time, full phase diagrams of ternary systems containing {water + phenol or guaiacol or syringol or pyrocatechol + choline bis(trifluoromethylsulfonide)imide} required for the process design were first determined. Thermodynamic data were then used to fit interaction parameters of NRTL [33] and UNIQUAC [34] models and then to facilitate the process simulation. The last part of the paper is devoted to the process sizing of a column for the extraction of phenolic compounds using choline bis(trifluoromethylsulfonyl)imide.

Section snippets

Chemicals and materials

The names, abbreviation, CAS numbers, molar masses, structures, producers and purity of the substances are listed in Table 1. Phenol (CAS 108-95-2), guaiacol (CAS 90-05-1), syringol (CAS 91-10-1), pyrocatechol (CAS 120-80-9), 1-propanol (CAS 71-23-8) and 2-pentanone (CAS 107-87-9) were supplied by Sigma Aldrich. All materials were used as received without any further purification. The ionic liquid choline bis(trifluoromethylsulfonide)imide [choline][NTf2] was supplied by Io-li-tec with a purity

Thermodynamic correlation

The liquid-liquid equilibrium data of the investigated ternary systems {phenolic compounds + water + IL} were correlated using the NonRandom Two-Liquid equation (NTRL) [33] and the UNIversal QUAsi-Chemical (UNIQUAC) theory [34]. For NRTL model, the value of the non-randomnes parameter α was set to 0.3 according to the literature [35]. For UNIQUAC model, the relative volume and surface area of the pure component I, ri and qi, were calculated using the same method as in Ref. [36].

Two parameters

Ternary mixtures {phenolic compounds + water + IL}

The liquid-liquid equilibrium (LLE) and solid-liquid equilibrium (SLE) compositions for the ternary systems {[choline][NTf2] (1) + phenol (2) + water (3)}, {[choline][NTf2] (1) + guaiacol (2) + water (3)}, {[choline][NTf2] (1) + syringol (2) + water (3)}, {[choline][NTf2] (1) + pyrocatechol (2) + water (3)} at 298.15 K under atmospheric pressure are listed in Table 2, Table 3 and the corresponding triangular phase diagrams are presented in Fig. 1. The consistency of the LLE experimental

Conclusion

Ternary diagrams of mixture containing {water, phenolic compound (phenol, guaiacol, syringol or pyrocatechol), [choline][NTf2]} were studied at 298.15 K at atmospheric pressure. [choline][NTf2] is a suitable solvent for the extraction of phenolic compounds from aqueous solution. Such process required less equipment (one extraction column and one flash) and less energy compared to other organic based ones. After distillation, the vapor stream can allow the recovery of phenolic compounds in few

Acknowledgment

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

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