Polyzwitterionic hydrogel coating for reverse osmosis membranes by concentration polarization-enhanced in situ “click” reaction that is applicable in modules

Abstract

Abstract The methodology for a polyzwitterionic anti-fouling hydrogel coating for reverse osmosis polyamide (PA) thin-film composite (TFC) membranes by concentration polarization-enhanced in situ thiol-ene “click” reaction has been developed. A copolymer with zwitterionic sulfobetain and reactive methacrylate side groups as well as a bis-thiol crosslinker in water were used as reactive system. By means of rheology, best suited solution composition parameters for efficient cross-linking at ambient temperature toward stable hydrogels were established first. Thereafter, factors that influence hydrogel coating of PA TFC membranes were investigated in dead-end filtrations, such as copolymer concentration, flux and stirring speed. It was found that hydrogel formation will occur within the first few minutes if the critical reactant concentration required for cross-linking is reached at the membrane surface and further filtration/reaction time will increase hydrogel layer thickness. Specific parameters, selected based on results of dead-end filtration experiments yielding thick hydrogel coatings (1–2\xa0μm, in dry state), lead to only very thin hydrogel layers under cross-flow conditions in a spacer-filled channel. However, such thin hydrogel-coated membranes had also very good antifouling properties compared to the unmodified membrane. The extent of coating can be adjusted toward thicker hydrogels by increasing flux also under cross-flow conditions in a spacer-filled channel. Finally, the feasibility of the hydrogel coating of PA TFC membranes in industrial spiral-wound modules and the use of such modules for treatment of cooling water in a steel manufacturing plant were demonstrated. Overall, suited materials and methods as well as partial fundamental understanding of the influence of parameters that can be used for a scalable antifouling hydrogel coating of membranes in spiral-would modules have been established in this work.