(565d) Fundamental Approaches to Optimize Sustainable Ultrafiltration Membranes

Polymeric ultrafiltration (UF) membranes are an essential technology for numerous industrial separations, such as pharmaceutical processing and wastewater treatment. The increasing demand for UF membranes is reflected in the global UF market size, which is projected to grow from an estimated $4.1 billion USD in 2021 to $6.8 billion USD in 2030. Commercial UF flat-sheet membranes are commonly fabricated using a polymer/solvent solution in nonsolvent-induced phase separation (NIPS), which utilizes large quantities of toxic, petroleum-based solvents such as N-methyl-2-pyrrolidone (NMP) and N,N-dimethylacetamide (DMAc). To address this issue, researchers have studied a variety of “greener” solvents, which are inherently less toxic, more environmentally friendly, and/or derived from renewable materials. However, directly substituting “greener” solvents is not trivial; the solvent dictates the resulting membrane properties through differing thermodynamic and kinetic effects in the fabrication process. This study investigates the structure-property-performance relationship of polymer/solvent solution parameters on fundamental properties of polysulfone (PSf) membranes prepared using NIPS to develop a “greener” membrane. We hypothesize that optimizing the fabrication parameters of “greener” polymer solutions will produce membranes that meet or exceed the performance of a commercially available UF membrane. To address the hypothesis, flat-sheet membranes were prepared with the NIPS method at various conditions using PSf in 1) a conventional solvent, DMAc, and 2) a “greener” solvent, 2-methylpyrazine (2MP). Glycerol-derived compounds and polyvinylpyrrolidone (PVP) were used as pore forming additives to optimize the resulting membrane structure and separation properties. Cloud point titrations were used to determine the thermodynamic stability of polymer solutions. Membrane formation kinetics were quantified by measuring the nonsolvent bath total organic carbon concentration as a function of time during fabrication. All membranes were characterized to assess morphology, productivity, and molecular weight cutoff (MWCO). We found that pristine 2MP membranes had a dense, closed cellular structure with negligible pure water permeance (PWP); however, the addition of PVP significantly enhanced the membrane PWP and resulted in asymmetric cross-sectional structures. DMAc membranes exhibited high PWP values and decreased solute selectivity. When compared to a commercial 50 kDa UF membrane, the 2MP/PVP membranes had improved PWP values and narrower top surface pore size distributions.