1. Di-sulfonated Poly(Arylene Ether Sulfone) Copolymers as Novel Candidates for Chlorine-Resistant Reverse Osmosis Membranes Di-sulfonated Poly(Arylene Ether Sulfone) Copolymers as Novel Candidates for Chlorine-Resistant Reverse Osmosis Membranes M. Paul, H. B. Park*, B. D. Freeman*, Z. Zhang, G. Fan, A. Roy, J. S. Riffle and J. E. McGrath. Macromolecular Science and Engineering Program, Macromolecules and Interfaces Institute (MII), Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 *Center for Energy and Environmental Resources The University of Texas at Austin $$$- ONR

2. Objective Develop new reverse osmosis membrane materials showing excellent chlorine-tolerance, high water flux, good salt rejection, anti- fouling and arsenic removalproperties relative to the state of the art. Approach Synthesize systematic series of directly copolymerized sulfonated copolymers and vary their structures Study fundamental properties (water permeability, salt permeability and water/salt selectivity) of sulfonated polymers Preparing the most promising new materials as thin membranes. Project Goal 1

3. Problem: a Shortage of Clean Water 41% of the Earth’s population (2.3 billion) live in water-stressed areas; 3.5 billion by 2025. The number of people living without clean, piped water is 1.2 billion (WHO). Water shortages limit economic development and threaten human life. Source: www.abc.net.au/news/newsitems/200609/s1733920.htm 1

4. There are currently more than 15,000 desalinization plants worldwide (1/4 in US) Membranes (reverse osmosis and nano- filtration) provide the most economical desalinization. >98% of U.S. water treatment facilities use chlorine - the most economical disinfectant to deactivate pathogenic microorganisms in drinking water Water Desalinization Report, 42(35), 1, 2006, www.bp.com, Ultrapure Water, 23(3), 14, 2006 www.bp.com Desalination Market Prediction

5. Issues Facing Commercially Available Membranes for Water Desalination Polyamides low chlorine tolerance prevents use in potable water applications and especially food and beverage, medical, biochemical, and pharmaceutical applications where chlorination and other similar oxidative cleaners or sterilants are commonly employed. T. Knoell, Ultrapure Water, 2006, 23, 24-31

6. Search for Chlorine Resistant RO Membranes- Previous Sulfonated Polymer Studies Sulfonated poly(2,6-dimethyl phenylene oxide) (SPPO) Sulfonated polysulfone (SPS) Fouling and chlorine tolerance of sulfonated polysulfone was superior to that of aromatic polyamides. Parise et al., Ultrapure Water, pp. 54-65 (Oct. 1987); Allegrezza et al., Desalination, 64, 285-304 (1987). Howerver, manufacturing reproducibility issues and inability to prepare a product with flux/rejection capabilities equivalent to aromatic polyamides led to limited commercial success.

7. VT Breakthrough- Chlorine Tolerant sulfonated Poly (arylene ether sulfone) RO Membranes  Cost savings via elimination of dechlorination required by current membranes  Extended membrane lifetime reproducible to manufacture & stable against chemical attack. Access to structural variations (e.g., new comonomers, block copolymers, controlled crosslink structures, etc.) to achieve high rejection and high flux.  Sulfonated Poly (arylene ether sulfone) (BPS)  Proposed New Process with VT Membrane VT membrane (BPS) outperforms commercial polyamide membrane (SW30HR) under chlorine exposure

8. Acronym: BPS-xx Bi Phenyl Sulfone: salt (M =Na + ) form (BPS), acid (M = H + ) form (BPSH) xx= molar fraction of disulfonic acid units, e.g., 30, 40, etc. Copolymer Synthesis by Nucleophilic Aromatic Substitution Disulfonated Poly(arylene ether sulfone) (BPS)

9. Effect of Sulfonation Degree (Ion Exchange Capacity) on Water and Salt Transport in Random BPS Copolymers

10. Various Types of Salt Rejection by BPS in Comparison to Commercial Membrane Salt rejection: Na 2 SO 4 > KCl ≥ NaCl > MgSO 4 > MgCl 2 > CaCl 2 Dead-end Feed pressure: 400 psig Feed temperature: 25 o C BPS 35H (IS: Ionic strength) IS (M) = 0.03 0.01 0.01 0.04 0.01 0.03 Commercial SPS composite membranes (Hydranautics) (www.membranes.com) Chemically tolerant NF membranes for aggressive industrial application

11. BPS Type Materials with NaCl Rejection > 97% NameComment mol% sulfonation or IEC Water permeability (L.μm/m 2.h.bar) NaCl rejection (%) PAEB35 Random copolymer (salt form) 35 mol%0.2497.8 PA40 Random copolymer (salt form) 40 mol%0.4397.5 6F25PAEB35 Random copolymer (salt form) 35 mol%0.6498.0 BPS20 Random copolymer (acid form) 20 mol%0.1198.7 Epoxy-crosslinked BPS50 Crosslinked (salt form) 50 mol%1.4197.2 BPS35:Radel Blend (90:10) Blend (salt form) 35 mol%0.7197.2 BPS35:6F35 Blend (95:5) Blend (salt form) 35 mol%0.8698.0 BPSH-15-BPS-15 Block copolymer (salt form) IEC = 1.36 meq/g0.0599.2

12. Lab-Scale FabricationThin-Film Composite Membrane from BPS-40 Lab-Scale Fabrication of Thin-Film Composite Membrane from BPS-40 0.5 % (wt./vol.) Polymer solution in formic acid (1 day) Drying wet support (PSf) at 105 o C (5 min) Brush coating (2~3 times) Air drying at 50 o C for 5 min.

13. Chlorine-Tolerance of Thin-Film Composite (TFC) Membranes Cross-flow, pH = 9.5, Feed = 2000 ppm NaCl, Pressure = 400 psig, Flow rate = 1.2 GPM, Chlorine = 500 ppm 30 h20 h0 h25 h10 h BPS 40H TFC SW30HR (FilmTec) 1 GFD/psi = 24.6 LMH/bar

14. Arsenic Rejection of Sulfonated Copolymer Membranes Sulfonated poly(arylene ether sulfone) (M = H + or Na + ) A: BPS 30H, B: BPS 40H, C: BPS 40N

15. Summary: Trade-off Relationship Between Permeate Flux and NaCl Passage PA (for brackish water) PA (for sea water) PA (for NF) Millipore SPS SPS (this work) SPS composite (BPS40)

16. Conclusions & Future Works Sulfonated poly(arylene ether sulfone) copolymer membranes Stable and reproducible properties High water permeability Moderate salt rejection (between that of NF and RO) with excellent chlorine tolerance Excellent arsenic removal properties Further fundamental studies to define structure/property relations. Prepare and characterize chlorine-resistant composite membrane with higher salt rejection.