Improving the chemical stability of filtration membranes

Abstract

Polyethers (A), whose main chain essentially consists of repeating units of the formulae (1) and (2) in alternating order, are useful as an additive to a porous polymer membrane, or as the main polymer constituent of a porous polymer membrane, for stabilizing said membrane against detrimental effects of oxidizing agents and/or for improving the stability of a filtration module comprising said membrane against detrimental effects of oxidizing agents. ##STR00001##

Claims

1. A filtration process, comprising subjecting a membrane polymer material to a chemically enhanced backwash comprising an aqueous solution comprising an oxidizing agent, wherein the oxidizing agent is hypochlorite, wherein the chemically enhanced backwash is a plurality of chemically enhanced backwashes with a period between chemically enhanced backwashes being between 3 and 24 hours, and wherein the hypochlorite is present in the chemically enhanced backwashes at a concentration of 1000 ppm or higher; wherein the membrane polymer material comprises a polyether (A), whose main chain comprises 95 to 100% by weight of repeating units of the formulae (1) and (2) ##STR00009## in alternating order, wherein the polyether (A) has a molecular weight Mw in a range of 10 to 500 kDa, wherein the membrane polymer material is an asymmetric polymer membrane obtained from a polymer solution in a coating process or in a phase inversion process, and the polyether (A) has been added to the polymer solution, wherein the asymmetric polymer membrane has a dense layer and a supporting layer, wherein a thickness of the supporting layer is from 30 to 2000 m, and a thickness of the dense layer is not more than 0.5 m, wherein the polyether (A) is present in the membrane polymer material in a total amount of not less than 85% by weight, and wherein the filtration process is a water filtration process.

2. The filtration process according to claim 1, wherein the polyether (A) containing repeating units of the formulae (1) and (2) has a formula (3) ##STR00010## wherein n ranges from 30 to 1000.

3. The filtration process according to claim 1, wherein the membrane polymer material comprises the polyether (A) and a further polyether (B) comprising 95 to 100% by weight of repeating units of the formula (2), in an amount of 85 to 100% of the total weight of membrane polymers.

4. The filtration process according to claim 1, wherein the membrane polymer material is a water filtration membrane.

5. The filtration process of claim 1, wherein the membrane polymer material is in a form of a filtration module or plant.

6. The filtration process of claim 1, wherein the oxidizing agent is NaOCl.

7. The filtration process of claim 1, wherein the supporting layer has a pore size of from 1 to 100 m.

8. The filtration process of claim 1, wherein the dense layer has a pore size of from 0.01 to 1.0 m.

9. The filtration process of claim 1, wherein the chemically enhanced backwash is performed with a washing time of from 10 to 60 minutes.

Description

EXAMPLE 1: GENERAL PROCEDURE FOR PREPARATION OF PESU FLAT SHEET MEMBRANES (REFERENCE MEMBRANE A)

(1) In a three neck flask equipped with a magnetic stirrer, a mixture of 80 ml of N-methylpyrolidone, 5 g of polyvinylpyrolidone (Luvitec K90) and 15 g of PESU (Ultrason E 3010P) are heated under gentle stirring at 60 C. until a homogeneous clear viscous solution is obtained. The solution is degassed overnight at room temperature. After that, the membrane solution is reheated at 60 C. for 2 hours and casted on a glass plate with a casting knife (300 microns) at 40 C. temperature. The membrane film is allowed to rest for 30 seconds before immersion in a water bath at 25 C. for 10 minutes.

(2) After rinsing and removal of the superfluous PVP, a flat sheet continuous film with micro structural characteristics of UF membranes having dimension of at least 1015 cm size is obtained. The membrane presents a top thin skin layer (1-3 microns) and a porous layer underneath (thickness: 230-250 microns).

EXAMPLE 2: GENERAL PROCEDURE FOR PREPARATION OF PPSU FLAT SHEET MEMBRANES (INVENTION, MEMBRANE D)

(3) In a three neck flask equipped with a magnetic stirrer, a mixture of 80 ml of N-methylpyrolidone, 5 g of polyvinylpyrolidone (Luvitec K90) and 15 g of PPSU (Radel R5000) is heated under gentle stirring at 60 C. until a homogeneous clear viscous solution is obtained. The solution is degassed overnight at room temperature. After that, the membrane solution is reheated at 60 C. for 2 hours and casted on a glass plate with a casting knife (300 microns) at 40 C. temperature. The membrane film is allowed to rest for 30 seconds before immersion in a water bath at 25 C. for 10 minutes.

(4) After rinsing and removal of the superfluous PVP, a flat sheet continuous film with micro structural characteristics of UF membranes having dimension of at least 1015 cm size is obtained. The membrane presents a top thin skin layer (30-100 nm) and a porous layer underneath (thickness: 230-250 microns).

EXAMPLE 3: GENERAL PROCEDURE FOR PREPARATION OF PESU/PPSU BLEND FLAT SHEET MEMBRANES AT 90:10 RATIO (INVENTION, MEMBRANE B)

(5) In a three neck flask equipped with a magnetic stirrer, a mixture of 80 ml of N-methylpyrolidone, 5 g of polyvinylpyrolidone (Luvitec K90) and 13.5 g of PESU (Ultrason E 3010P) and 1.5 g of PPSU (Radel R5000) is heated under gentle stirring at 60 C. until a homogeneous clear viscous solution is obtained. The solution is degassed overnight at room temperature. After that the membrane solution is reheated at 60 C. for 2 hours and casted on a glass plate with a casting knife (300 microns) at 40 C. temperature. The membrane film is allowed to rest for 30 seconds before immersion in a water bath at 25 C. for 10 minutes.

(6) After rinsing and removal of the superfluous PVP a flat sheet continuous film with micro structural characteristics of UF membranes having dimension of at least 1015 cm size is obtained. The membrane presents a top thin skin layer (30-100 nm) and a porous layer underneath (thickness: 230-250 microns).

EXAMPLE 4: GENERAL PROCEDURE FOR PREPARATION OF PESU/PPSU BLEND FLAT SHEET MEMBRANES AT 80:20 RATIO (INVENTION, MEMBRANE C)

(7) In a three neck flask equipped with a magnetic stirrer, a mixture of 80 ml of N-methylpyrolidone, 5 g of polyvinylpyrolidone (Luvitec K90) and 12 g of PESU (Ultrason E 3010P) and 3 g of PPSU (Radel R5000) is heated under gentle stirring at 60 C. until a homogeneous clear viscous solution is obtained. The solution is degassed overnight at room temperature. After that, the membrane solution is reheated at 60 C. for 2 hours and casted on a glass plate with a casting knife (300 microns) at 40 C. temperature. The membrane film is allowed to rest for 30 seconds before immersion in a water bath at 25 C. for 10 minutes.

(8) After rinsing and removal of the superfluous PVP a flat sheet continuous film with micro structural characteristics of UF membranes having dimension of at least 1015 cm size is obtained. The membrane presents a top thin skin layer (30-100 nm) and a porous layer underneath (thickness: 230-250 microns).

EXAMPLE 5: GENERAL PROCEDURE FOR PREPARATION OF PESU CYLINDRICAL SINGLE CHANNEL MICROFILTRATION MEMBRANES (REFERENCE, MEMBRANE E)

(9) A polymer solution of 20% PESU (Ultrason E 3010P), 7% polyvinylpyrrolidone (Luvitec K90), 10% of glycerol and 63% N-methylpyrrolidone is extruded through an extrusion nozzle having a diameter of 1.0 mm and a needle of 0.5 mm. A solution of 25% NMP in 75% water is injected through the needles, as a result of which channels are formed in the polymer solution. The diameter of the channels is 0.8 mm, the outer diameter is 1.3 mm. The extrusion speed is 15 m/min, the coagulation bath has a temperature of 80 C. and the length of the path through water vapour is 30 cm. After rinsing and removal of the superfluous PVP a membrane is obtained having a permeability higher than 400 l/(m h bar) (in relation to the channels).

EXAMPLE 6: GENERAL PROCEDURE FOR PREPARATION OF PPSU CYLINDRICAL SINGLE CHANNEL MICROFILTRATION MEMBRANES (INVENTION, MEMBRANE F)

(10) A polymer solution of 23% PPSU (Radel R5000), 8% polyvinylpyrrolidone (Luvitec K90) and 69% N-methylpyrrolidone is extruded through an extrusion nozzle having a diameter of 1.0 mm and a needle of 0.5 mm. A solution of 25% NMP in 75% water is injected through the needles as a result of which channels are formed in the polymer solution. The diameter of the channels is 0.8 mm, the outer diameter is 1.3 mm. The extrusion speed is 15 m/min, the coagulation bath has a temperature of 80 C. and the length of the path through water vapor is 30 cm. After rinsing and removal of the superfluous PVP a membrane is obtained having a permeability higher than 200 l/(m h bar) (in relation to the channels).

EXAMPLE 7: GENERAL PROCEDURE FOR PREPARATION OF PESU CYLINDRICAL MULTIPLE CHANNEL ULTRAFILTRATION MEMBRANES (REFERENCE, MEMBRANE G)

(11) A polymer solution of 20% PESU (Ultrason E 3010P), 9% polyvinylpyrrolidone (Luvitec K90), 10% of glycerol and 61% N-methylpyrrolidone is extruded through an extrusion nozzle having a diameter of 4.0 mm and 7 needles of 0.8 mm. A solution of 40% NMP in 60% water is injected through the needles as a result of which channels are formed in the polymer solution. The diameter of the channels is 0.9 mm, the total diameter is 4.0 mm. The extrusion speed is 7 m/min, the coagulation bath has a temperature of 80 C. and the length of the path through water vapor is 20 cm. After rinsing and removal of the superfluous PVP a membrane is obtained having a permeability higher than 400 l/(m h bar) (in relation to the channels).

EXAMPLE 8: GENERAL PROCEDURE FOR PREPARATION OF PPSU CYLINDRICAL MULTIPLE CHANNEL ULTRAFILTRATION MEMBRANES (INVENTION, MEMBRANE H)

(12) A polymer solution of 23% PPSU (Radel R5000), 11% polyvinylpyrrolidone (Luvitec K90) and 66% N-methylpyrrolidone is extruded through an extrusion nozzle having a diameter of 4.0 mm and 7 needles of 0.9 mm. A solution of 40% NMP in 60% water is injected through the needles as a result of which channels are formed in the polymer solution. The diameter of the channels is 0.9 mm, the total diameter is 4.0 mm. The extrusion speed is 7 m/min, the coagulation bath has a temperature of 80 C. and the length of the path through water vapor is 20 cm. After rinsing and removal of the superfluous PVP a membrane is obtained having a permeability higher than 200 l/(m h bar) (in relation to the channels).

EXAMPLE 9: MECHANICAL PROPERTIES AND GPC EVALUATION OF FLAT SHEET MEMBRANES AFTER EXPOSURE TO CONCENTRATE NAOCL SOLUTION AT PH=6

(13) Flat sheet membranes of examples 1 to 4 are tested for NaOCl chemical stability. Flat sheets, 1012 cm long, preliminary washed in 500 mL of water for 30, are placed wet in 500 mL closed flask with 1000 ppm (total free chlorine) NaOCl solution at room temperature. HCl 0.1 N is used to adjust pH=6 and pH=8.

(14) NaOCl solution is replaced every 24 h and the test is run for 3 days. After this time, membranes are removed from NaOCl solution and washed several times with 0.5% NaHSO.sub.3(aq) and water. Then, membranes are conditioned at 50% humidity at r.t for 48 h before evaluating their mechanical properties and molecular weight variation. Dumbbell-shaped probes 7.5 cm long and 1.3/0.5 cm wide are cut out and used to evaluate membrane mechanical properties.

(15) Reduction of mechanical properties and molecular weight (Mw and Mn) due to NaOCl exposure is related to membrane polymer degradation. Results are reported in Table 1 & Table 2.

(16) TABLE-US-00001 TABLE 1 Reduction of mechanical properties for flat sheet membranes exposed for 4 days at NaOCl (1000 ppm, pH = 6) due to chemical degradation. Data as average of 5 sample measurements. Test method: ISO527-1; Probe Type: Typ 5A. Force probe: 100N; Speed: 50 mm/min. Elongation@break (%) Flat sheet PESU/PPSU After Membrane ratio Start 4 days A 100/0 20.0 1.4 5.5 1.1 (73%) (Reference) B 90/10 21.6 2.4 6.9 1.2 (68%) C 80/20 18.5 1.8 7.1 1.1 (62%) D 0/100 18.5 1.7 10.4 1.6 (44%)

(17) TABLE-US-00002 TABLE 2 Reduction of molecular weight for flat sheet membranes exposed for 4 days in 1000 ppm NaOCl (total free chlorine) at pH = 6 due to chemical degradation. Gel permeation chromatography (GPC) done in Dimethylacetamide + 0.5% LiBr. Calibration: polymethylmethacrylate Mw (Da) Mn (Da) Flat Sheet PESU/PPSU After After Membrane ratio Start 4 days Start 4 days A 100/0 54730 43630 21280 12460 (Reference) (20%) (41%) B 90/10 53760 47430 18170 15050 (12%) (17%) C 80/20 54670 48560 20510 17250 (11%) (16%) D 0/100 57910 52230 20420 17100 (10%) (16%)

(18) Table 1 and Table 2 clearly indicate that for flat sheet membranes resistance to high chlorine concentration exposure at pH=6 (acid condition) is extended for membranes produced with polyphenylsulfone, alone or in blend with polyethersulfone. This higher tolerance for chlorine is translated in a lower reduction of elongation properties as well as membrane molecular weight if compared with 100% polyethersulfone (PESU) reference membrane.

EXAMPLE 10: MECHANICAL PROPERTIES AND MOLECULAR WEIGHT EVALUATION OF FLAT SHEET MEMBRANES AFTER EXPOSURE TO CONCENTRATE NAOCL SOLUTION AT PH=8 (TEST PERFORMED AS IN EXAMPLE 9, BUT AT PH=8; HCL 0.1 N IS USED TO ADJUST PH VALUE

(19) Reduction of mechanical properties and molecular weight (Mw and Mn) due to NaOCl exposure is related to membrane polymer degradation. Results are reported in Table 3 & Table 4.

(20) TABLE-US-00003 TABLE 3 Reduction of mechanical properties for flat sheet membranes exposed for 4 days at NaOCl (1000 ppm, pH = 8) due to chemical degradation. Data as average of 5 sample measurements. Test method: ISO527-1; Probe Type: Typ 5A. Force probe: 100N; Speed: 50 mm/min. Elongation@break (%) Flat sheet PESU/PPSU After Membrane Ratio Start 4 days A 100/0 19.9 1.4 5.1 1.2 (74%) (Reference) B 90/10 19.6 2.4 7.8 1.8 (60%) C 80/20 18.5 1.8 7.3 1.3 (61%) D 0/100 18.5 1.7 10.2 1.8 (45%)

(21) TABLE-US-00004 TABLE 4 Reduction of molecular weight for flat sheet membranes exposed for 4 days in 1000 ppm NaOCl (total free chlorine) at pH = 8 due to chemical degradation. Gel permeation chromatography (GPC) done in Dimethylacetamide + 0.5% LiBr. Calibration: polymethylmethacrylate Mw (Da) Mn (Da) Flat Sheet PESU/PPSU After After Membrane ratio Start 4 days Start 4 days A 100/0 54730 47360 21280 14860 (Reference) (13.5%) (30%) B 90/10 53760 50290 18170 15850 (6.5%) (13%) C 80/20 54670 50580 20510 18350 (8%) (13%) D 0/100 57910 54200 20420 18850 (6%) (10%)

(22) Table 3 and Table 4 clearly indicate that, for flat sheet membranes, resistance to high chlorine concentration exposure at pH=8 (basic condition) is extended for membranes produced with polyphenylsulfone, alone or in blend with polyethersulfone. This higher tolerance for chlorine is translated in a lower reduction of mechanical properties as well as membrane molecular weight if compared with 100% polyethersulfone (PESU) reference membrane.

(23) Of course the remarkable improvement of mechanical property after chlorine degradation achieved with membrane based on polyphenylsulfone both at pH=6 and pH=8 is reflected into initial slightly lower flexibility especially for membrane with an increased amount of polyphenylsulfone polymer (membranes C, D).

EXAMPLE 11: EVALUATION OF WATER FLUX, FLUX RECOVERY AND PVP RETENTION IN PESU/PPSU FLAT SHEET MEMBRANES

(24) Water flux and cleanability (flux recovery) of flat sheet membranes of examples 1 to 4 are performed. Blank PESU membrane is considered as reference, and PVP 1% (Kollidon K30 from BASF) is used to evaluate retention and flux recovery.

(25) Two membranes for each composition are tested and the results are the average of the two measurements.

(26) The experiment consists of five main steps: initial water flux, retention of PVP, water rinse, chemical cleaning and final water flux. This sequence is repeated for 2 times for each membrane.

(27) In a typical run, a membrane strip of appropriate dimensions is cut out from the corresponding flat sheet and is mounted in the cross flow cell (PP backing is used for support). Membrane is pre-compacted until a constant water flux is obtained, then the pressure is reduced and the initial water flux is measured for about 1 hour (Table 5). PVP retention is obtained using a 1% solution of PVP at P=0.5 bar under cross flow condition at room temperature for about 1 hour.

(28) Water flux is measured before and after PVP filtration at P=1.0 bar. It is also measured after 15 minutes of chemical cleaning (NaOH 0.2%) buffering the membrane cell. The overall cycle is repeated 2 times and the remaining flux for the different membranes is estimated.

(29) TABLE-US-00005 TABLE 5 Water flux, flux recovery and PVP retention for flat sheet membranes based on different composition of PESU/PPSU. Membranes produced at 300 micrometer thickness. Flat PESU/ Initial Final Flux PVP sheet PPSU water flux water flux recov- Reten- membrane ratio (Kg/m2*h*bar) (Kg/m2*h*bar) ery (%) tion (%) A 100/0 430 300 70% 88% (Ref.) B 90/10 535 335 63% 92% C 80/20 525 345 66% 92% D 0/100 390 270 69% 91%

EXAMPLE 12: MECHANICAL PROPERTIES AND MOLECULAR WEIGHT EVALUATION OF CYLINDRICAL SINGLE CHANNEL MICROFILTRATION MEMBRANES AFTER EXPOSURE TO CONCENTRATE NAOCL SOLUTION AT PH=8

(30) Cylindrical membranes of examples 5 and 6 are tested for NaOCl chemical stability. Membranes, 4 cm long and with a diameter of 2.25 mm, preliminary washed in 500 mL of water for 30, are placed wet in 500 mL closed flask with 2000 ppm (total free chlorine) NaOCl solution at room temperature. HCl 0.1 N is used to adjust pH=8.

(31) NaOCl solution is replaced every 24 h and the test is run for 7 days. After this time, membranes are removed from NaOCl solution and washed several times with 0.5% NaHSO3(aq) and water. Then, membranes are conditioned at 50% humidity at r.t for 48 h before evaluating their mechanical properties and molecular weight (by GPC) variation.

(32) Reduction of mechanical properties and molecular weight (Mw and Mn) due to NaOCl exposure is related to membrane polymer degradation. Results are reported in Table 6 & Table 7.

(33) TABLE-US-00006 TABLE 6 Reduction of mechanical properties for cylindrical single channel membranes exposed for 7 days at NaOCl (2000 ppm, pH = 8) due to chemical degradation. Data as average of 6 sample measurements. Test method: ISO527-1; Probe Type: Typ 5A. Force probe: 100N; Speed: 50 mm/min. Elongation@break (%) Cylindrical single PESU/PPSU After channel Membrane ratio Start 7 days E 100/0 40.2 4.4 9.7 1.5 (76%) (Reference) F 0/100 44.6 3.6 29.5 1.2 (34%)

(34) TABLE-US-00007 TABLE 7 Reduction of molecular weight for cylindrical single channel membranes exposed for 7 days in 2000 ppm NaOCl (total free chlorine) at pH = 8 due to chemical degradation. Gel permeation chromatography (GPC) done in Dimethylacetamide + 0.5% LiBr. Calibration: polymethylmethacrylate Mw (Da) Mn (Da) Cylindrical single PESU/PPSU After After channel Membrane ratio Start 7 days Start 7 days E 100/0 55.900 40.400 16.300 11.200 (Reference) (28%) (31%) F 0/100 54.400 43.400 18.700 13.800 (20%) (26%)

EXAMPLE 13: MECHANICAL PROPERTIES AND MOLECULAR WEIGHT EVALUATION OF CYLINDRICAL MULTIPLE CHANNEL ULTRAFILTRATION MEMBRANES AFTER EXPOSURE TO CONCENTRATE NAOCL SOLUTION AT PH=8

(35) Cylindrical membranes of examples 7 and 8 are tested for NaOCl chemical stability. Membranes, 4 cm long and with a diameter of 3.75 mm, preliminary washed in 500 mL of water for 30, are placed wet in 500 mL closed flask with 2000 ppm (total free chlorine) NaOCl solution at room temperature. HCl 0.1 N is used to adjust pH=8.

(36) NaOCl solution is replaced every 24 h and the test is run for 7 days. After this time, membranes are removed from NaOCl solution and washed several times with 0.5% NaHSO3(aq) and water. Then, membranes are conditioned at 50% humidity at r.t for 48 h before evaluating their mechanical properties and molecular weight (by GPC) variation.

(37) Reduction of mechanical properties and molecular weight (Mw and Mn) due to NaOCl exposure is related to membrane polymer degradation. Results are reported in Table 8 & Table 9.

(38) TABLE-US-00008 TABLE 8 Reduction of mechanical properties for cylindrical multiple channel membranes exposed for 7 days at NaOCl (2000 ppm, pH = 8) due to chemical degradation. Data as average of 6 sample measurements. Test method: ISO527-1; Probe Type: Typ 5A. Force probe: 100N; Speed: 50 mm/min. Elongation@break (%) Cylindrical multiple PESU/PPSU After channel Membrane ratio Start 7 days G 100/0 37.0 3.9 6.6 1.3 (82%) (Reference) H 0/100 42.6 4.9 13.4 1.5 (69%)

(39) TABLE-US-00009 TABLE 9 Reduction of molecular weight for cylindrical multiple channel membranes exposed for 7 days in 2000 ppm NaOCl (total free chlorine) at pH = 8 due to chemical degradation. Gel permeation chromatography (GPC) done in Dimethylacetamide + 0.5% LiBr. Calibration: polymethylmethacrylate Mw (Da) Mn (Da) Cylindrical multiple PESU/PPSU After After channel Membrane ratio Start 7 days Start 7 days G 100/0 55.800 43.700 16.500 11.300 (Reference) (22%) (32%) H 0/100 54.100 45.600 18.500 15.000 (16%) (19%)

(40) Tables 6 to 9 clearly indicate that for cylindrical single or multiple channel membranes resistance to high chlorine concentration exposure at pH=8 (basic condition) is extended for membranes produced with polyphenylsulfone. This higher tolerance for chlorine is translated into a lower reduction of mechanical properties as well as membrane molecular weight if compared with 100% polyethersulfone (PESU) reference membrane.

EXAMPLE 14: ORGANIC CHLORINE AND MOLECULAR WEIGHT EVALUATION OF CYLINDRICAL MULTIPLE CHANNEL MEMBRANES AFTER EXPOSURE TO CONCENTRATE NAOCL SOLUTION AT PH=8 AND T=45 C.

(41) Cylindrical membranes of examples 7 and 8 are analysed based on the amount of organic chlorine linked to membrane polymer and reduction of molecular weight due to extensive NaOCl exposure. Membranes, 12 cm long and with a diameter of 3.75 mm, preliminary washed in 500 mL of water for 30, are placed wet in 500 mL closed flask with 2000 ppm (total free chlorine) NaOCl solution at T=45 C. HCl 0.1 N is used to adjust pH=8.

(42) NaOCl solution is replaced every 24 h and the test is run for 6 days. After this time, membranes are removed from NaOCl solution and washed several times with 0.5% NaHSO3(aq), water and then EtOH. Membranes are then dried in oven under reduce pressure at 40 C. overnight. Organic chlorine is evaluated by element analysis (ICP-MS) as difference between Total and Ionic chlorine.

(43) TABLE-US-00010 TABLE 10 Reduction of molecular weight (Mw and Mn) for multiple channel membrane based on PESU exposed to 2000 ppm NaOCl (total free chlorine) at pH = 8 and T = 45 C. Organic chlorine bounded to membrane due to NaOCl exposure. Gel permeation chromatography (GPC) done in Dimethylacetamide + 0.5% LiBr. Calibration: polymethylmethacrylate PESU cylindrical multiple channel membrane Chlorine Organic exposure Mw Mn Chlorine (ppm/h) (Da) (Da) (g/100 g) 0 55.420 15.160 0.40 4.475 51.840 12.720 1.02 44.375 48.730 10.880 1.93 71.625 44.400 9.640 2.23 116.125 39.780 8.844 2.97 141.625 34.900 7.937 3.2 251.125 34.520 7.398 3.77

(44) TABLE-US-00011 TABLE 11 Reduction of molecular weight (Mw and Mn) for multiple channel membrane based on PPSU exposed to 2000 ppm NaOCl (total free chlorine) at pH = 8 and T = 45 C. Organic chlorine bounded to membrane due to NaOCl exposure. Gel permeation chromatography (GPC) done in Dimethylacetamide + 0.5% LiBr. Calibration: polymethylmetacrylate. PPSU cylindrical multiple channel membrane Chlorine Organic exposure Mw Mn Chlorine (ppm/h) (Da) (Da) (g/100 g) 0 52.000 18.400 0.31 7000 50.100 18.300 0.42 35.000 47.600 17.000 0.53 72.000 45.300 15.100 0.83 100.000 44.100 14.400 0.93 150.000 42.500 13.400 1.01 260.000 40.900 12.900 1.07

(45) Table 10 to 11 clearly show that for multiple channel membranes reduction of molecular weight, Mw and Mn, is lower for membrane based on polyphenylsulfone (PPSU) than for the one based on polyethersulfone (PESU). The lower reduction of molecular weight caused by the aggressive hypochlorite radical activity is also reflected in a lower chlorination of the polymer membrane based on polyphenylsulfone.