Abstract
In the single-polyelectrolyte aqueous phase separation (APS) approach, membranes are prepared by precipitating a weak polyelectrolyte from a concentrated aqueous solution using a pH switch. This has proven to be a versatile and more sustainable method compared to conventional approaches as it significantly reduces the use of organic solvents. Poly(styrene-alt-maleic acid) (PSaMA) is a polymer that has been extensively investigated for APS and has been the basis for both open and dense membranes with good performances. These membranes are chemically crosslinked and, in this work, we further investigated ultrafiltration (UF) and nanofiltration (NF) membranes prepared with PSaMA for their stability in various organic solvents and under different pH conditions. It was shown that these membranes had stable performances in both isopropanol (IPA) and toluene, and a slightly reduced performance in N-methyl-2-pyrollidone (NMP). However, PSaMA did not perform well as a selective layer in these solvents, indicating that the real opportunity would be to use the UF-type PSaMA membranes as solvent-stable support membranes. Additionally, the membranes proved to be stable in an acidic-to-neutral pH regime (pH 2–7); and, due to the pH-responsive nature of PSaMA, for the NF membranes, a pH-dependent retention of Mg2+ and SO42− ions was observed and, for the UF membranes, a strong responsive behavior was observed, where the pH can be used to control the membrane permeability. However, long-term exposure to elevated pH conditions (pH 8–10) resulted in severe swelling of the NF membranes, resulting in defect formation, and compaction of the UF membranes. For the UF membranes, this compaction did prove to be reversible for some but not all of the membrane samples measured. These results showed that in aqueous systems, membranes prepared with PSaMA had interesting responsive behaviors but performed best at neutral and acidic pH values. Moreover, the membranes exhibited excellent stability in the organic solvents IPA and toluene
Highlights
Membrane technology is playing an increasingly large role in optimizing and improving industrial processes, making them more efficient, as well as offering new opportunities for advanced separations [1,2,3,4]
We investigated the organic solvent and pH stability of Poly(styrene-alt-maleic acid) (PSaMA) membranes prepared with a single-polyelectrolyte aqueous phase separation (APS) approach
UF and NF membranes were prepared with PSaMA using the single-polyelectrolyte
Summary
Membrane technology is playing an increasingly large role in optimizing and improving industrial processes, making them more efficient, as well as offering new opportunities for advanced separations [1,2,3,4]. The single-polyelectrolyte APS approach uses a weak polyelectrolyte, whose charged state is pH-dependent, which is dissolved at a pH where it is charged and water-soluble and precipitated using a pH switch to a regime where the polyelectrolyte is uncharged and insoluble in water [20,23,24,25] Through parameters such as the pH difference between the polymer solution and the coagulation bath [20], polymer concentration [25], salt identity and concentration [24], and type of acid used [23], the precipitation can be controlled to prepare different types of membranes. We demonstrated that crosslinked membranes prepared with PSaMA using the single-polyelectrolyte APS approach have good solvent stability in various organic solvents. Membranes 2021, 11, 835 and are pH-responsive and stable under neutral and acidic conditions (pH 2–7), but problems are encountered in basic pH regimes (pH 8–10)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
