Abstract
In this study, the bottleneck challenge of membrane fouling is addressed via establishing a scalable concentration polarization (CP) enabled and surface-selective hydrogel coating using zwitterionic cross-linkable macromolecules as building blocks. First, a novel methacrylate-based copolymer with sulfobetain and methacrylate side groups was prepared in a simple three-step synthesis. Polymer gelation initiated by a redox initiator system (ammonium persulfate and tetramethylethylenediamine) for radical cross-linking was studied in bulk in order to identify minimum (“critical”) concentrations to obtain a hydrogel. In situ reactive coating of a polyamide nanofiltration membrane was achieved via filtration of a mixture of the reactive compounds, utilizing CP to meet critical gelation conditions solely within the boundary layer. Because the feasibility was studied and demonstrated in dead-end filtration mode, the variable extent of CP was estimated in the frame of the film model, with an iterative calculation using experimental data as input. This allowed to discuss the influence of parameters such as solution composition or filtration rate on the actual polymer concentration and resulting hydrogel formation at the membrane surface. The zwitterionic hydrogel-coated membranes exhibited lower surface charge and higher flux during protein filtration, both compared to pristine membranes. Salt rejection was found to remain unchanged. Results further reveal that the hydrogel coating thickness and consequently the reduction in membrane permeance due to the coating can be tuned by variation of filtration time and polymer feed concentration, illustrating the novel modification method’s promising potential for scale-up to real applications.
Highlights
IntroductionWith the massive population growth, the exponential technological advancements and on-going globalization and industrialization of the planet, the human species encounters a variety of novel challenges
Membrane separation processes were identified as a key technology, which can address the issue of freshwater scarcity
Proteins were dissolved in 0.01 M phosphate-buffered saline (1 g/L) and pH was adjusted to the isoelectric point (IEP) of BSA or Myo with 1 M HCl. 1,3-Propane sultone (PS, Sigma Aldrich) was heated with hot water above its melting point (31 ◦ C) before used in liquid form
Summary
With the massive population growth, the exponential technological advancements and on-going globalization and industrialization of the planet, the human species encounters a variety of novel challenges. The global demand for freshwater is expected to increase and, water is estimated to lack in stressed regions already by the year 2025 [1]. In order to sustain life and biodiversity, improve public health, and guarantee economic prosperity as well as political stability, governments and industry nowadays empower research on modern low-cost separation technologies [2,3]. Membrane separation processes were identified as a key technology, which can address the issue of freshwater scarcity. Pressure-driven membrane separations are, compared to conventional thermal separation technologies such as distillation, less energy consuming and economically and ecologically more attractive alternatives to increase the water supply [5]
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