PROCESS FOR MAKING MEMBRANES

Abstract

A membrane contains a polymer composition is described. The polymer composition contains a) at least one polymer of PA, PVA, Cellulose CA, CTA, CA-triacetate blend, cellulose ester, cellulose nitrate, regenerated cellulose, aromatic, aromatic/aliphatic or aliphatic polyamide, aromatic, aromatic/aliphatic or aliphatic polyimide, PBI, PBIL, PAN, PAN-PVC copolymer, PAN-methallyl sulfonate copolymer, PEI, PEEK, sulfonated SPEEK, PPO, poly-carbonate, polyester, PTFE, PVDF, PP, a polyelectrolyte complex, PMMA, PDMS, aromatic, aromatic/aliphatic or aliphatic polyimide urethane, aromatic, aromatic/aliphatic or aliphatic polyamidimide, crosslinked polyimide or poly-arylene ether, PSU, PPSU and PESU, and b) at least one dope polymer DP1, which is a polyalkylene oxide with a molecular mass Mw of more than 100,000 g/mol and/or a K-value of 60 or 20 more.

Claims

1. A membrane M, comprising a polymer composition comprising a) at least one polymer P selected from the group consisting of polyamide (PA), polyvinylalcohol (PVA), Cellulose Acetate (CA), Cellulose Triacetate (CTA), CA-triacetate blend, Cellu-lose ester, Cellulose Nitrate, regenerated Cellulose, aromatic, aromatic/aliphatic or aliphatic Polyamide, aromatic, aromatic/aliphatic or aliphatic Polyimide, Polybenzimidazole (PBI), Polybenzimidazolone (PBIL), Polyacrylonitrile (PAN), PAN-poly(vinyl chloride) copolymer (PAN-PVC), PAN-methallyl sulfonate copol-ymer, polyetherimide (PEI), Polyetheretherketone (PEEK), sulfonated polyetheretherketone (SPEEK), Poly(dimethylphenylene oxide) (PPO), Polycarbonate, Polyester, Polytetrafluroethylene (PTFE), Poly(vinylidene fluoride) (PVDF), Pol-ypropylene (PP), Polyelectrolyte complex, Poly(methyl methacrylate) PMMA, Polydimethylsiloxane (PDMS), aromatic, aromatic/aliphatic or aliphatic polyimide urethane, aromatic, aromatic/aliphatic or aliphatic polyamidimide, crosslinked polyimide or polyarylene ether, polysulfone (PSU), polyphenylenesulfone (PPSU) and polyethersulfone (PESU), and b) at least one dope polymer DP1, which is a poly-alkylene oxide with a molecular mass M.sub.W of more than 100,000 g/mol and/or a K-value of 60 or more.

2. The membrane according to claim 1, wherein said polymer P is at least one selected from the group consisting of Poly(vinylidene fluoride) (PVDF), polyarylene ether, polysulfone (PSU), polyphenylenesulfone (PPSU) and polyethersulfone (PESU).

3. The membrane according to claim 1, wherein said dope polymer DP1 is present in an amount of 0.1 to 20% by weight relative to a total weight of the membrane M.

4. The membrane according to claim 1, wherein said polymer composition further comprises at least one second dope polymer DP2 selected from the group consisting of polyalkylene oxide with a molecular mass M.sub.W below 100,000 g/mol and/or a K-value of less than 60, and polyvinylpyrrolidone.

5. The membrane according to claim 4, wherein said second dope polymer DP2 is present in an amount of 0.1 to 19.9% by weight relative to a total weight of the membrane M with the proviso that a combined amount of said dope polymer DP1 and said second dope polymer DP2 is from 0.2% by weight to 20% by weight.

6. The membrane according to claim 1, wherein said membrane M is an ultrafiltration membrane, a microfiltration membrane or a carrier of a reverse osmosis membrane or forward osmosis membrane.

7. A process for making a membrane M, the process comprising: a) providing a dope solution D comprising at least one polymer P, at least one dope polymer DP1 and optionally at least one second dope polymer DP2 and at least one solvent S, b) adding at least one coagulant C to said dope solution D to coagulate said at least one polymer P from said dope solution D to obtain the membrane M, c) optionally performing an oxidative treatment of the membrane obtained in a) and b), and d) optionally washing the membrane with water.

8. (canceled)

9. A membrane element, comprising the membrane according to claim 1.

10. A membrane module, comprising the membranes the membrane according to claim 1.

11. A filtration system, comprising the membrane element according to claim 9.

12. A filtration system, comprising the membrane module according to claim 10.

Description

EXAMPLES

[0239] Abbreviations used in the examples and elsewhere: [0240] NMP N-methylpyrrolidone [0241] DMAc Dimethylacetamide [0242] PWP pure water permeation [0243] MWCO molecular weight cutoff [0244] DMF dimethylformamide [0245] THF tetrahydrofurane [0246] PESU polyethersulfone [0247] Ultrason? E 6020P polyethersulfone with a viscosity number (ISO 307, 1157, 1628; in 0.01 g/mol phenol/1,2 orthodichlorobenzene 1:1 solution) of 82; a glass transition temperature (DSC, 10? C./min; according to ISO 11357-1/-2) of 225? C.; a molecular weight Mw (GPC in DMAc, PMMA standard): 75000 g/mol [0248] Ultrason? E 7020P polyethersulfone with a viscosity number (ISO 307, 1157, 1628; in 0.01 g/mol phenol/1,2 orthodichlorobenzene 1:1 solution) of 105; a glass transition temperature (DSC, 10? C./min; according to ISO 11357-1/-2) of 225? C.; a molecular weight Mw (GPC in DMAc, PMMA standard): 92000 g/mol [0249] Luvitec? K90 Polyvinylpyrrolidone with a solution viscosity characterized by the K-value of 90, determined according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)) [0250] Luvitec? K30 Polyvinylpyrrolidone with a solution viscosity characterized by the K-value of 30, determined according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)) [0251] POLYOX? WSR-N10 Polyethyleneoxide with a solution viscosity characterized by the K-value of 68, determined according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)) and a molecular weight Mw (GPC in water, polyethyleneoxide standard): 102000 g/mol [0252] POLYOX? WSR-N80 Polyethyleneoxide with a solution viscosity characterized by the K-value of 84, determined according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)) and a molecular weight Mw (GPC in water, polyethyleneoxide standard): 187000 g/mol [0253] POLYOX? WSR-N750 Polyethyleneoxide with a solution viscosity characterized by the K-value of 109, determined according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)) and a molecular weight Mw (GPC in water, polyethyleneoxide standard): 456000 g/mol [0254] Pluriol? 9000E Polyethyleneoxide with a solution viscosity characterized by the K-value of 33, determined according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)) and a molecular weight Mw (GPC in water, polyethyleneoxide standard): 10800 g/mol [0255] Breox? 75W55000 Polyethyleneoxide-polypropyleneoxide copolymer with a solution viscosity characterized by the K-value of 42, determined according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)) and a molecular weight Mw (GPC in water, polyethyleneoxide standard): 14300 g/mol

[0256] The molecular weight distribution and the average molecular weight of the polyalkyleneoxide polymers obtained were determined by GPC measurements. GPC-measurements were done using water as solvent. After filtration (pore size 0.2 ?m), 100 ?l of this solution was injected in the GPC system. For the separation two hydroxylated polymethacrylate columns (TSKgel GMPWXL, 30 cm) were used. The system was operated with a flow rate of 0.8 ml/min at 35? C. As detection system an RI-detector was used (DRI Agilent 1100). The calibration was carried out with polyethyleneoxide-standards (company Polymer Labs, Agilent easy vial) with molecular weights in the range from 106 to 1.522.000 g/mol.

[0257] The molecular weight distribution and the average molecular weight of the polyvinylpyrrolidone polymer obtained were determined by GPC measurements. GPC-measurements were done using acetonitrile/water (20/80 vol/vol) as solvent. After filtration (pore size 0.2 ?m), 100 ?l of this solution was injected in the GPC system. For the separation two Suprema-Gel (HEMA) columns (Suprema linear S and XL, 30 cm) were used. The system was operated with a flow rate of 0.8 ml/min at 35? C. As detection system an RI-detector was used (DRI Agilent 1100). The calibration was carried out with polyvinylpyrrolidone-Standards (company Polymer American Standards) with molecular weights in the range from 4.300 to 1.065.000 g/mol.

[0258] The pure water permeation (PWP) of the membranes was tested using a pressure cell with a diameter of 60 mm using ultrapure water (salt-free water, filtered by a Millipore UF-system). In a subsequent test, a solution of different PEG-Standards was filtered at a pressure of 0.15 bar. By GPC-measurement of the feed and permeate, the molecular weight cut-off of the membranes were determined.

Examples 1 to 8: Preparation of Membranes

[0259] Into a three neck flask equipped with a magnetic stirrer there were added 75 ml of N-methylpyrrolidone, 6 parts of dope polymer DP1 as named in table 1 and 19 g of polymer P. The mixture was heated under gentle stirring at 60? C. until a homogeneous clear viscous solution was obtained. The solution was degassed overnight at room temperature. After that the membrane solution was reheated at 60? C. for 2 hours and casted onto a glass plate with a casting knife (300 microns) at 60? C. using an Erichsen Coating machine operating at a speed of 5 mm/min. The membrane film was allowed to rest for 30 seconds before immersion in a water bath at 25? C. for 10 minutes.

[0260] After the membrane had detached from the glass plate, the membrane was carefully transferred into a water bath for 12 h. Afterwards the membrane was transferred into a bath containing 2500 ppm NaOCl at 50? C. for 4.5 h to remove PVP. The membrane was then washed with water at 60? C. and one time with a 0.5 wt.-% solution of sodium bisulfite to remove active chlorine. After several washing steps with water the membrane was stored wet until characterization regarding pure water permeability (PWP) and minimum pore size (MWCO) started.

[0261] The amount of polyethyleneoxide remaining in the processed membranes (PEO content) is estimated by the means of .sup.1H-NMR spectroscopy (400 MHz). The dried membrane samples are dissolved in CDCl3 and trifluoroacetic acid (TFA) and analyzed by the means of signal intensity for PEO at 3.7 ppm (CH.sub.2CH.sub.2O, 4H) and the Ultrason E repetition unit at 7.3 ppm and 7.9 ppm (aromatic, 8H). With the molecular weights of the repetition units (M.sub.Ultrason=232.26 g/mol, M.sub.PEO=44.05 g/mol), the corresponding shares are assessed and the PEO content is calculated according to:

PEO content[%]=[m.sub.PEO/(m.sub.PEO+m.sub.Ultrason)]*100

TABLE-US-00001 TABLE 1 Compositions and properties of membranes prepared according to examples 1 to 8; MWCO in [Da], PWP in [kg/h m.sup.2bar]. Polymer P DP1 PEO content [%] PWP MWCO 1 E7020 K90 0 490 45100 2 E7020 N10 9.7 585 11200 3 E7020 N80 10.6 570 9580 4 E7020 N750 11.3 443 9350 5 E6020 K90 0 510 42400 6 E6020 N10 15.6 400 12800 7 E6020 N80 16.6 330 6600 8 E6020 N750 12.4 500 11000

Examples 9 to 22: Preparation of Membranes

[0262] Into a three neck flask equipped with a magnetic stirrer there were added 75 ml of N-methylpyrrolidone, 6 parts of dope polymer DP1 and second dope polymer DP2 as named in table 2 and 19 g of polyethersulfone Ultrason? E6020P. The mixture was heated under gentle stirring at 60? C. until a homogeneous clear viscous solution was obtained. The solution was degassed overnight at room temperature. After that the membrane solution was reheated at 60? C. for 2 hours and casted onto a glass plate with a casting knife (300 microns) at 60? C. using an Erichsen Coating machine operating at a speed of 5 mm/min. The membrane film was allowed to rest for 30 seconds before immersion in a water bath at 25? C. for 10 minutes.

[0263] After the membrane had detached from the glass plate, the membrane was carefully transferred into a water bath for 12 h. Afterwards the membrane was transferred into a bath containing 2500 ppm NaOCl at 50? C. for 4.5 h to remove the second dope (PT NaOCl). The membrane was then washed with water at 60? C. and one time with a 0.5 wt.-% solution of sodium bisulfite to remove active chlorine. As alternative, the membranes so obtained were washed six times with water, referred to as H2O. After several washing steps with water the membrane was stored wet until characterization regarding pure water permeability (PWP) and minimum pore size (MWCO) and PEO content started.

TABLE-US-00002 TABLE 2 Compositions and properties of membranes prepared according to examples 9 to 22; MWCO in [Da], PWP in [kg/h m.sup.2bar]. DP1 DP2 PEO (name, amount (name, amount content [parts]) [parts]) PT [%] PWP MWCO 9 K90, 6 H2O 0 82 7180 10 K90, 6 NaOCl 0 510 42400 11 N750, 1 E9000, 5 H2O 13.3 63 15300 12 N750, 1 E9000, 5 NaOCl 12.7 90 11300 13 N750, 2 E9000, 4 H2O 14.6 185 18500 14 N750, 2 E9000, 4 NaOCl 11.9 290 13800 15 N750, 3 E9000, 3 H2O 14.9 285 16950 16 N750, 3 E9000, 3 NaOCl 11.4 525 13000 17 N750, 4 E9000, 2 H2O 16.1 133 18000 18 N750, 4 E9000, 2 NaOCl 12.3 450 13100 19 N750, 6 H2O 15.7 51 12300 20 N750, 6 NaOCl 12.4 500 11000 21 N750, 3 Breox, 3 H2O 13.5 130 19600 22 N750, 3 Breox, 3 NaOCl 12.1 800 15500

[0264] From tables 1 and 2 it can be seen that the inventive membranes have comparable pure water permeability values but clearly lower MWCO below 20 kDa compared to examples 5 and 10. For post treatment with water (PT H2O) the inventive membranes have significantly higher PWP's compared to example 9 but maintain MWCO values below 20 kDa.

Examples 23 to 26: Evaluation of the Fouling Behavior of Membranes

[0265] For the assessment of fouling tendency the pure water permeation (PWP.sub.0) of the membranes obtained according to examples 5, 6, 7 and 16 was tested using a pressure cell with a diameter of 60 mm using ultrapure water (salt-free water, filtered by a Millipore UF-system). Then, a solution of different PEG-Standards was filtered at a pressure of 0.15 bar. Finally, the pure water permeation (PWP.sub.PEO) of the membrane was tested again and the Fouling index (FI) calculated according to:

FI=[PWP.sub.0/PWP.sub.PEO]

TABLE-US-00003 TABLE 3 Fouling index and properties of selected Ultrason? E6020P membranes prepared according to previous examples; MWCO in [Da], PWP in [kg/h m.sup.2bar]. DP1 DP2 Membrane (name, (name, used (Ex. amount amount No.) [parts]) [parts]) PT FI PWP MWCO 23 5 K90, 6 NaOCl 12.0 510 42400 24 6 N10, 6 NaOCl 4.2 400 12800 25 7 N80, 6 NaOCl 5.7 330 6600 26 16 N750, 3 E9000, 3 NaOCl 6.0 525 13000

[0266] No fouling is observed for a fouling index of FI=1. Table 3 shows for the reference membrane (example 23) a significant higher FI than for the inventive membranes (FI=4.2 to 6) from examples 24 to 26.