Hydroxyl-terminated poly(ethyleneimine) polymer enhanced ultrafiltration for boron removal

Boron removal is an important separation process which requires an excessive operational cost owing to the complex nature of boron in aqueous solutions. Polymer-enhanced ultrafiltration (PEUF) has been widely adopted for boron separation due to the low operational cost and high separation productivity. In this study, novel hydroxyl-terminated poly(ethyleneimine) (HPEI) polymers; namely, HPEI-Diol and HPEI-Gluconamide, were designed and synthesized as the boron chelating polymers. A polyphenylenesulfone (PPSU) UF membrane was fabricated to have a pure water permeance of around 82.8 L.m(-2).h(-1).bar(-1) with a molecular weight cut off (MWCO) of around 128 kDa. The boron rejection coefficient of the pristine PPSU UF membrane was as low as 6.38% which was attributed to the negatively charged surface of the PPSU membrane. Introducing either HPEI or HPEI-Diol polymer into the boron feed solution increased the boron rejection of the UF process to around 45%. Meanwhile, the HPEI-Gluconamide polymer was found to possess the highest boron retention efficiency with a boron rejection of around 94% at pH 4, which may be ascribed to the higher number of grafted hydroxyl groups.