Revealing the selective separation of organics from salty solution in novel aqueous-aqueous membrane extraction co-driven by concentration and pressure difference

Abstract

Aqueous-aqueous membrane extraction (AAME) has great potential to revolutionize industrial wastewater treatment, achieving the value-added organic product recovery with low operation cost. Here, we first reported the feasibility, performance and mechanism of selective separation of three typical organics (phenol, ethanol and sodium dodecyl sulfate (SDS)) from salty solution not only in common concentration-difference driven but also in novel concentration-pressure-difference co-driven AAME using porous polyvinylidene fluoride (PVDF), non-porous polydimethylsiloxane (PDMS) and composite PVDF/PDMS membranes. In concentration-difference driven AAME, phenol and ethanol were separated from NaCl solution through three membranes, while SDS permeation only occurred on wetted porous PVDF membrane. Note that, volatile phenol and ethanol transported across the porous PVDF and composite PVDF/PDMS via volatilization-diffusion and solution-diffusion. In concentration-pressure-difference co-driven AAME, highest phenol (10.7) and ethanol fluxes (34.7 g m2 h−1) were obtained through composite PVDF/PDMS membrane (ΔP = 3 kPa) and PVDF membrane (ΔP = 9 kPa), respectively, with complete NaCl rejection. These data showed suitable membrane and high ΔP were beneficial to promote organics transmembrane transport. However, overload ΔP increased the membrane wetting risk on porous membranes. Once membrane was wetted, organics transmembrane mass transfer was simplified to direct pore-flow filtration. These findings provide a crucial step toward understanding the potential of AAME in resource recovery from industrial wastewater.