Extraction of phenolic pollutants from industrial wastewater using a bulk ionic liquid membrane technique

The academia and chemical industry are actively searching for alternative solvents to meet technology requirements since the most widely used solvents are harmful and volatile. For ionic liquids, there are several advantages over conventionally using organic membrane solvents, including high thermal stability, negligible vapour pressure, low volatility, etc. Here in this study, we have analyzed the abilities of ionic liquids as pure solvents as well as their binary mixtures, to recover phenolic compounds from the industrial wastewater. The field of phenol extraction from wastewater using ionic liquids remains less exposed, and we presume that the work of this kind would open up more and more opportunities for the scientific community as well as industrial people. Based on all these assumptions, the present work includes experimental data of a work which explains the possibilities of room temperature ionic liquids (RTILs) as potential bulk liquid membranes (BLM) for extracting phenol and other phenolic compounds from the industrial affluents. Four high hydrophobicity ionic liquids namely: 1-hexyl-3-methylimidazolium hexafluorophosphate [Hmim][PF₆], 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide [Bmim][NTf₂], 1-butyl-3-methylimidazolium hexafluorophosphate [Bmim] [PF₆] and 1-ethyl-3-methyimidazolium bis(trifluoromethanesulfonyl) imide [Emim][NTf₂] were used for investigating the Phenol extraction efficiency and stripping efficiency. To provide a best comprehension of the influence of the phenolic structure as well as the nature of cation on the extraction ability of the ILs, we tried to understand the molecular interactions between the phenolic compounds and the solvents. The influence of hydrophobicity of ionic liquids and different kinds of anions on the extraction of phenol and efficiencies of stripping were investigated. All the experimental investigations performed here indicated that the only cation part of the ionic liquid is not an important aspect directly in this extraction, but the hydrogen bonding and the solute-solvent interactions play a significant role in the phenol removal process from aqueous phase to IL phase. First, the optimal conditions of operating (settling time and stirring) were analyzed for the clarity of the experiments performed. Concentration of NaOH in enhancing the performance of ionic liquids was also inspected here in this study. A binary mixture of ionic liquids (BMILs) membrane was examined for the optimized parameters, and the efficiency of phenol extraction was analyzed with the efficiency obtained for the single ionic liquid (SIL) membranes. The phenol concentration was determined by UV/visible spectrophotometer absorbance measurements. The highest phenol extraction efficiencies of 91% and 98.5%, were achieved by using [Bmim][NTf₂] and [Bmim][NTf₂+PF₆] respectively, and the higher stripping efficiencies came up with 79% and 84% respectively, for [Emim][NTf₂] and [Bmim + Emim][NTf₂]. The results show that the binary mixture ionic liquid (BMIL) membrane is a better choice than single ionic liquid (SIL) membrane solvents. Hence, [Bmim] [(NTf₂+PF₆)] is an excellent selection as it provides high phenol stripping and extraction efficiencies with a minimal solvent loss and better stability in transport process.