Ionic liquids (ILs) show a wide range of applications as “green” solvents in the new era and the recovery of water-soluble ILs has become an urgent issue. Herein, for the first time, osmotic distillation is applied to concentrate and recover water-soluble ILs with a series of hydrophobic membranes. Poly(vinylidene fluoride) membrane with vertically oriented pores and stainless steel mesh were hydrophobically modified and then compared with commercial membranes to demonstrate the influence of different pore structures on the osmotic distillation concentration process . With the vapor pressure difference between two sides of the membrane being the driving force, the dilute aqueous solutions of ILs can be concentrated to about 84 wt % after 24 h with a water flux of 7.8 kg m −2 h −1 . It is also able to achieve ultra-high rejections to ILs and MgCl 2 (>99.99%) by this osmotic distillation process. Although there exists a limitation for dewatering the ILs solutions with very high concentrations and thus the final ILs purity cannot reach 100%, this method is promising for practical applications benefiting from its high rejection to ions, easy operability at ambient temperature and remarkable universality in terms of hydrophobic membranes used.
Peizhi Wang,Ji Li,Xiaolei Zhang,Xinglin Lu,Qianliang Liu,Tao Zhang,Wei Cheng,Jun Ma
Selective removal and resource recovery of ammonium nitrogen (NH4+–N) from high-strength ammonium waste streams is of practical importance for biological wastewater treatment and environmental protection. In this study, we demonstrate the simultaneous removal and reclamation of ammonium from synthetic digested sludge centrate via a novel osmosis-distillation hybrid membrane (ODHM) process. Using NaHCO3 as the draw solute, ammonium diffuses from the synthetic centrate to the draw solution by utilizing the bidirectional cation transport nature of the thin film composite (TFC) membrane. Then, NH4+ is converted to gaseous NH3 at 60 °C and recovered by a sweeping gas membrane distillation (SGMD) process. Herein, the bidirectional transport of monovalent cations in the osmotic process, selectivity of TFC membranes for different cations, and recovery of the draw solution following the extraction of ammonia through the SGMD process were systematically investigated. The removal of NH4+–N from the synthetic centrate achieved 21.34% during a 6-h continuous operation of the ODHM system, with ammonium fluxes through the TFC and SGMD membranes at 1.39 and 0.57 mol m–2 h–1, respectively. A secondary interfacial polymerization was proposed to further enhance ammonium transport through the TFC membrane. Results reported here highlight the potential of the ODHM process for the selective removal and reclamation of ammonium from ammonium-rich waste streams.
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