Fundamental investigation on controlling factors of reverse solute flux of branched thermo-responsive oligomer in forward osmosis process

Abstract

Forward osmosis (FO) has attracted research attention as the energy-effective water separation process. For a FO process, it is important to prevent leakage of a solute of the DS. As a low-leakage solute, a branched thermo-responsive oligomer, pentaerythritol-oligo(ethylene oxide)m-b-(butylene oxide)n oligomers (PEBs), had been reported. In this study, the relationship between the chemical structure and the permeability of the PEBs through a FO membrane had been investigated in detail. For the detailed investigation, the mole fraction of each component having different absolute molecular weights in the PEBs was determined by the MALDI/TOF-MS, then the permeabilities of the components through the FO membrane were independently quantified. As the result, for the PEBs with low absolute molecular weight, the permeability of the PEBs was strongly affected by the molecular weight of the PEBs. On the other hand, for the PEBs with high absolute molecular weight, it was confirmed that the permeability of the PEBs was affected by the hydrophobicity of the PEBs. Conclusively, it was indicated that not only the molecular weight but also the affinity between the PEBs and the FO membrane is important for the reverse solute flux.