Separation and recovery of phenols from an aqueous solution by a green membrane system

Abstract Oil-refinery alkali residue wastewater (ORARW) contains large amounts of phenol and its derivatives, which are highly toxic and valuable but difficult to biodegrade. In this study, using vegetable oil as the liquid membrane phase, a green polypropylene-hollow-fiber supported liquid membrane (SLM) system was constructed to simultaneously separate and recover phenol, m-cresol and o-cresol from aqueous solutions. After screening several types of vegetable oil, linseed oil was selected as the liquid membrane phase. Based on a single SLM module and using a NaOH solution as the stripping reagent with feed phase and stripping phase hydraulic retention times (HRTs) of 7.8 and 6.9 min, respectively, the phenol separation and recovery rates were 92.9% and 88.8%, respectively. The separation rates for m-cresol and o-cresol were both greater than 96%, their recovery rates were approximately 92%, and the membrane separation flux of every phenolic compound exceeded 0.40 g/m2·h. When two SLM modules were operated in series at room temperature for 3 h, the separation efficiency for phenols increased by approximately 9% compared with that obtained with a single SLM module. After applying two SLM modules in series to treat ORARW with an initial concentration of phenols of 4800–5200 mg/L, the simultaneous separation and recovery rates of phenols were near 95% and 92%, respectively. This work concluded that vegetable oil can be used as a nontoxic and renewable green liquid membrane phase and that two SLM modules in series efficiently separated and recovered phenols from aqueous solutions.