Chlorine-resistant sulfochlorinated and sulfonated polysulfone for reverse osmosis membranes by coating method

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Polysulfone (PSf) membranes are widely used but lack sufficient chlorine resistance for many water treatment applications.
• Developing functionalized polysulfones with enhanced properties is crucial for advanced membrane technologies.
• Achieving hydrophilicity and processability in polysulfone derivatives is key for membrane fabrication.

Purpose of the Study:

• To synthesize a chlorine-resistant sulfonated polysulfone (SC-S-PSf) for thin film composite (TFC) membranes.
• To fabricate and characterize TFC membranes with a polysulfone-sulfamide (PSSA) skin layer for reverse osmosis (RO).
• To evaluate the performance and chlorine stability of the novel PSSA membranes compared to traditional polyamide membranes.

Main Methods:

• Sulfochlorination of polysulfone (PSf) followed by partial hydrolysis to create SC-S-PSf.
• Fabrication of TFC membranes by coating SC-S-PSf on a PSf substrate and crosslinking with piperazine (PIP).
• Addition of tetrabutylammonium chloride (TBAC) as a surfactant to improve coating uniformity.
• Performance testing for NaCl rejection and water flux under brackish water conditions.
• Chlorine stability testing using sodium hypochlorite (NaOCl) exposure.

Main Results:

• A flawless PSSA membrane was fabricated using a single coating step with TBAC.
• The PSSA membrane achieved 96.9% NaCl rejection and 17.8 L/m²h water flux.
• The PSSA membrane demonstrated excellent long-term chlorine stability, with only a 1% decrease in salt rejection after 10 days of exposure to 2000 ppm NaOCl.
• In contrast, a polyamide membrane showed an 8% decrease in salt rejection under the same chlorine exposure conditions.

Conclusions:

• The developed SC-S-PSf is a promising material for creating chlorine-resistant RO membranes.
• The PSSA TFC membrane offers superior chlorine stability compared to conventional polyamide membranes.
• The addition of TBAC significantly improved the membrane fabrication process, enabling a single-step coating for flawless membrane formation.