Recovery of 2,4-dichlorophenol from acidic aqueous streams by Membrane Aromatic Recovery System (MARS)

This study describes the successful recovery of 2,4-dichlorophenol (DCP) from wastewater using the Membrane Aromatic Recovery System (MARS). In the MARS process a non-porous membrane separates a wastewater stream and a stripping solution. DCP is extracted from the wastewater and concentrated in its ionic form in the stripping solution, with pH much greater than pK(a) DCP. The MARS extraction stage was operated in batch mode with the stripping solution placed inside, and the wastewater stream outside, the membrane tubes. Advantages of this configuration are avoidance of membrane blockage, reduction of stripping solution volume and operational flexibility. The stability and mass-transfer characteristics of two different membrane materials, poly(dimethylsiloxane) (PDMS) and ethylene-propylene diene terpolymer (EPDM), were tested in DCP solutions with different acidities in order to simulate real industrial waste streams. EPDM exhibits one order of magnitude lower mass-transfer rates than PDMS (1.4 x 10(-7) ms(-1) vs 20 x 10(-7) ms(-1) at 30degreesC and 2.4 x 10(-7) ms(-1) vs 39 x 10(-7) ms(-1) at 60degreesC), however its higher resistance to acid attack provides higher membrane lifetimes. This can be crucial for MARS processes treating real acidic industrial wastewater. A 97% recovery of DCP with a water content of 15 wt% was obtained upon neutralisation of the stripping solution. (C) 2004 Society of Chemical Industry.