Surface modified porous polyetherimide hollow fiber membrane for sweeping gas membrane distillation of dyeing wastewater

Abstract

Highly porous polyetherimide (PEI) hollow fiber membranes were prepared through a spinning process. The membranes were modified by a dip-coating method using polydimethylsiloxane (PDMS) to increase surface hydrophobicity. The membranes were used in a sweeping gas membrane distillation (SGMD) process for separation of methylene blue (MB) solutions. From FESEM examination, an open structure with large finger-like cavities was observed in the membrane structure. The PEI-PDMS membrane presented a high surface porosity with N2 permeance of 15300 GPU and mean pore size of 72 nm. Formation of an ultra-thin PDMS coated layer resulted in an improved surface hydrophobicity with water contact angle of around 104º. Moreover, the coated layer resulted in the increment of critical water entry pressure from 250 to 400 kPa. The PEI and PEI-PDMS membranes indicated pure water flux of 26.2 and 22.5 kg/m2 h, respectively, through the SGMD process at feed temperature of 60 °C. During 5 days of the SGMD process, the PEI and PEI-PDMS showed an approximate permeation flux reduction of 42% and 19%, respectively. The PEI-PDMS membrane showed a good antifouling property with flux recovery ratio of about 89.4%. Adsorption of MB on the outer surface of the membranes was confirmed by studying the variation of fouling factor vs. MB concentration in the feed solution. The improved PEI-PDMS membrane demonstrated a high permeation flux and antifouling properties which are promising parameters for a prolonged membrane distillation operation.