# Cleaning Phenolic Compounds Present in Water Using Salting-Out Effect with DCA-Based Ionic Liquids
## 1 Introduction
In these studies, high extraction efficiencies were obtained, and the influence of both the cation and anion structure of the ILs was studied in the extraction process [11; 25]. [PERSON] et al. [26] studied the efficiency of one aromatic cation (imidazolium) and one non-aromatic cation (pyrrolidininium) [NTf\({}_{2}\)]-based ILs to remove three phenolic compounds from aqueous systems; all the extraction efficiencies were high. It is important to note that the structure of both the cation of the IL and the substance to be extracted influenced the extraction efficiency. Hydrophobic ILs are usually formed by anions with fluorinated ions, which are more expensive and less environmentally friendly than hydrophilic ones. Nevertheless, these kinds of solvents are miscible with water, so it is not possible to carry out a liquid-liquid \begin{table}
\begin{tabular}{c c c} \hline \hline
**Industry** & **Phenol Concentration (mg\(\cdot\)L\({}^{-1}\))** & **Reference** \\ \hline Paper & 79.5 & [2] \\ Textile & 155 & [3] \\ Coal & 551 & [4] \\ Coke & 200 & [5] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The concentration of phenolic compounds found in the wastewater of some industries. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Technique** & **Advantages** & **Disadvantages** \\ \hline Biological degradation & Substitution of chemicals & Growth control, use of co-solvent for low \\  & by microorganisms & phenol concentrations \\ Oxidative process & Simple process & Expensive, hazardous substances, high pressure, \\  & & and temperature \\ Electrochemical & Not an expensive chemical & High consumption of energy, toxic chemicals \\ Adsorption & Economic process, simple equipment & Difficult to regenerate, not suitable for \\  & & low concentrations \\ Liquid–liquid extraction & Easy operation, extraction agents can & Volatile organic solvents, low selectivity \\  & be recycled & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Advantages and disadvantages of techniques used to remove phenolic compounds from water [9; 10; 11; 12]. extraction directly. It is necessary to obtain an aqueous two-phase system (ATPS) using some reactive to produce the separation of both phases, aqueous and organic [27]. There are several published works about the use of liquid-liquid extraction and aqueous two-phase systems (ATPS) to remove phenols from water using hydrophilic ILs as extraction agents. In one of these studies, sugar (glucose) was used to promote the separation of phases using [C\({}_{\text{n}}\)Mim] [BF\({}_{4}\)] as an extraction agent to remove phenol from water. In general, [PERSON] et al. [28] concluded that ATPS formed with these ILs and glucose were good extraction agents, and the obtained results showed that an increase in the sugar concentration increased the extraction efficiency. However, it must be considered that this increase also produces an increase in the viscosity of the mixture. In the other study, [PERSON] et al. [29] used salt (NaH\({}_{2}\)PO\({}_{4}\)) to produce the salting out effect and obtain the ATPS system formed with [BMim] [BF\({}_{4}\)]. They studied the capability of this system to remove 4-chlorophenol, 2,4-dichlorophenol, and 2,6-dichlorophenol from water. In all the studied systems, the obtained results produced a greater than 90% recovery of phenolic compounds. They explained that the presence of salt in the water reduced the capacity of water to establish hydrogen bonds with phenolic compounds. This behavior increased the extraction process, and it was higher when the concentration of salt was increased. Dicyanamide (DCA)-based ILs are hydrophilic and present lower viscosities than those based on NTI\({}_{2}\) (bis(trifluoromethylsulfonyl)imide), and they have adequate extractive properties as well. This low viscosity favors the mixture of the substances and, therefore, the extraction processes [30; 31; 32].