Modification of porous polyetherimide hollow fiber membrane by dip-coating of Zonyl® BA for membrane distillation of dyeing wastewater

Abstract

Wetting and fouling have significantly affected the application of membrane distillation (MD). In this work, a dip-coating method was used for improving surface hydrophobicity of the polyetherimide (PEI) hollow fiber membrane. An air gap membrane distillation (AGMD) process was applied for treatment of the methylene blue (MB) solution. The porous PEI membrane was fabricated by a dry-wet spinning process and the hydrophobic 2-(Perfluoroalkyl) ethanol (Zonyl® BA) was used as the coating material. From FESEM, the modified PEI-Zonyl membrane showed an open structure with large finger-like cavities. The modified membrane displayed a narrow pore size distribution with mean pore size of 0.028 μm. The outer surface contact angle of the PEI-Zonyl membrane increased from 81.3° to 100.4° due to the formation of an ultra-thin coated layer. The pure water flux of the PEI-Zonyl membrane was slightly reduced compared to the pristine PEI membrane. A permeate flux of 6.5 kg/m2 h and MB rejection of 98% were found for the PEI-Zonyl membrane during 76 h of the AGMD operation. Adsorption of MB on the membrane surface was confirmed based on the Langmuir isotherm evaluation, AFM and FESEM analysis. The modified PEI-Zonyl membrane can be a favorable alternative for AGMD of dyeing wastewaters. HIGHLIGHTS The porous PEI membrane was modified by surface coating of Zonyl® BA.; A narrow pore size distribution with mean pore sizes of 0.028 μm was observed.; The outer surface water contact angle was increased from about 81° to 100°.; A more stable AGMD of the MB solution was found for the modified membrane.; A lower flux decline ratio was observed for the modified PEI-Zonyl membrane.;

Keywords

• air gap membrane distillation
• coating
• dyeing wastewater treatment
• polyetherimide hollow fiber membrane
• zonyl® ba fluorotelomer intermediate