Real-scale chlorination at pH4 of BW30 TFC membranes and their physicochemical characterization

• Published in: Journal of membrane science Vol. 551; pp. 123 - 135
• Main Authors: Verbeke, Rhea, Gómez, Verónica, Koschine, Tönjes, Eyley, Samuel, Szymczyk, Anthony, Dickmann, Marcel, Stimpel-Lindner, Tanja, Egger, Werner, Thielemans, Wim, Vankelecom, Ivo F.J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.04.2018; Elsevier
• Subjects: Active chlorination; Analytical chemistry; Chemical Sciences; PALS; Pilot-scale; Polyamide; Tightening effect; Active chlorination; Polyamide; Tightening effect; Pilot-scale; PALS; tightening effect; polyamide; pilot-scale; active chlorination
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/j.memsci.2018.01.019

Chlorination remains a big hurdle in membrane technology as the most commonly used membranes for water purification consist of a polyamide top-layer, which is not fully resistant towards chlorine-induced oxidation. In this work, DOW FILMTEC™ BW30 membrane elements were systematically chlorinated with NaOCl at pilot-scale under acidic conditions (pH4) at 10bar for 2.5h. Variations in membrane performance and their physicochemical properties were determined by ATR-FTIR, XPS, WD-XRF, SEM, AFM and zeta-potential measurements. With increasing bleaching concentration, both membrane roughness and chlorine incorporation via N- and ring-chlorination increased, while surface charge remained quasi unaltered. Both water flux and salt passage decreased proportionally over the whole concentration range. Accordingly, positron annihilation lifetime spectroscopy (PALS) revealed a decrease in the size of the top-layer free-volume elements as chlorine concentration increased, confirming, for the first time in a quantitative manner, the so-called tightening effect. The obtained results also show that thin-film composite (TFC) membranes are altered differently when chlorinated under pressure than via simple immersion, as conventionally performed in literature. •DOW FILMTEC™ BW30 8″ modules were chlorinated (0, 1, 2, 50ppm) at pH4 under industrial conditions.•With increasing chlorine concentration, the salt passage and water flux dropped proportionally.•The so-called tightening effect of PA could be quantitatively proven for the first time via PALS.•The application of pressure during the chlorination process is an important parameter in the ageing process.