Extraction of Phenol from Aqueous Solutions Using Bulk ionic Liquid Membranes

Abstract

Room temperature ionic liquids show potential as an alternative to conventional organic membrane solvents mainly due to their properties of low vapour pressure, low volatility and they are often stable. In the present work, the technical feasibilities of room temperature ionic liquids as bulk liquid membranes for phenol removal were investigated experimentally. In this research several hydrophobic ionic liquids were synthesized at laboratory. These ionic liquids include (1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide[Bmim][NTf2], 1-Hexyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide[Hmim][NTf2], 1-octyl-3-methylimidazolium bis (trifluoromethylsulfonyl)imide[Omim][NTf2],1‐butyl‐1‐methylimidazoliumhexafluorophosphate[Bmim][PF6], 1‐hexyl‐1‐methylimidazoliumhexafluorophosphate[Hmim][PF6], 1-butyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl) imide[Bmpyr][NTf2], and 1-octyl-3-methyl imidazolium tetra fluoroborate[Omim][BF4]. The distribution coefficients for phenol in these ionic liquids were measured at different pH values and found to be much larger than those in conventional solvents. Through the values of the distribution coefficients and the experiments that were conducted on bulk liquid membrane applying various types of prepared ionic liquids, 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide was selected as the best ionic liquid which gave the highest extraction and stripping efficiencies. The effect of several parameters, namely, feed phase pH(2-12), feed concentration(100-1000 ppm), NaOH concentration(0-0.5M), temperature (20-50oC), feed to membrane volume ratio (200-400ml/80ml ionic liquid) and stirring speeds(75-125 rpm) on the performance of the choosen ionic liquid membrane were also studied. The preliminary study showed that high phenol extraction and stripping efficiencies of 97% and 95% respectively were achieved by ionic liquid membrane with a minimum membrane loss which offers a better choice to organic membrane solvents.