Membrane aromatic recovery system (MARS) — a new membrane process for the recovery of phenols from wastewaters

Abstract

This paper describes a new process for recovery of aromatic acids and bases, the membrane aromatic recovery system (MARS). The process comprises a stripping vessel, where phenols are extracted through nonporous membranes and concentrated into a NaOH solution as phenolate, and a two-phase separator in which the solution collected from the stripping vessel is separated into a phenolic phase and an aqueous phase by adjusting pH to acidic conditions with the addition of HCl. Silicone rubber tubing was used as a membrane in this study. The temperature in the stripping vessel and NaOH concentration in the solution fed into the stripping vessel are two important operating parameters. In this study the temperature was 50°C and NaOH concentration 12.5 wt.%. At steady-state, the total phenol concentration in the stripping solution can be orders of magnitude higher than in the wastewater, ensuring a high phenol recovery efficiency. The work found phenol recovery efficiencies of over 94%, with a recovered organic-rich phase comprising 86.5 wt.% phenol, and the balance water. The overall mass transfer coefficients (OMTCs) for other phenols were investigated to demonstrate the wide potential applications of MARS technology. Insights into OMTCs and permeabilities of phenols include the effect of Reynolds number in the tube side on OMTC, and the effect of temperature on the permeabilities of phenolic compounds in the membrane. The membrane resistance dominates the OMTCs of phenols in this study. The van’t Hoff–Arrhenius relationship for the temperature dependence of the permeability of the penetrant through the polymer gave excellent agreement with our experimental data.