Extractant screening and selection for methyl tert-butyl ether removal from aqueous streams

Recovery of low concentration methyl tert-butyl ether (MTBE) from aqueous solutions is difficult. Activated carbon adsorption or air stripping suffer from low capacity and high energy input. Liquid-liquid extraction is suggested as an alternative separation technique, but requires a suitable extractant. Based on molecular considerations, an extractant screening with COSMO-RS gives a good qualitative trend. Halogenated phenols provide the highest MTBE capacity. This is confirmed by liquid-liquid equilibrium experiments. 3-Iodophenol is selected as the MTBE extractant, because it combines comparatively low toxicity and high distribution coefficient KD. Propylbenzene is selected as the diluent. The KD of MTBE extraction with 3-iodophenol/propylbenzene is 270 at high extractant concentrations and low MTBE concentrations. Water solubility of 3-iodophenol can possibly be minimized by additional branched alkyl chains, preferably in para position at the aromatic ring to avoid steric hindrance during hydrogen bonding. In this study, reactive extraction of MTBE is successfully performed for the first time.