Process for making membranes

Abstract

Process for making membranes M comprising the following steps: a) providing a dope solution D comprising at least one polymer P 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 a membrane M, wherein said at least one solvent S comprises more than 50% by weight of at least one compound according to formula (I) (I), wherein R.sup.1 and R.sup.2 are independently C.sub.1 to C.sub.20 alkyl, R.sup.3 is selected from H or an aliphatic rest, 20 R.sup.4 is selected from H or an aliphatic rest, AO represents at least one alkylene oxide, n is a number from 0 to 100. ##STR00001##

Claims

1. A process for making membranes M, comprising: a) providing a dope solution D comprising at least one polymer P and a solvent S, wherein the at least one polymer P is selected from the group consisting of poly(vinylidene fluoride) (PVDF), polysulfone (PSU), polyphenylenesulfone (PPSU), polyethersulfone (PESU), and mixtures thereof; and b) adding at least one coagulant C to the dope solution D to coagulate the at least one polymer P from the dope solution D to obtain membrane M, wherein the solvent S is N,N-dimethyl-2-hydroxypropanoic amide or N,N-diethyl-2-hydroxypropanoic amide.

2. The process according to claim 1, wherein the at least one coagulant C comprises water or water vapor.

3. The process according to claim 1, wherein the dope solution D further comprises 0.1 to 10% by weight, based on a weight of the of the dope solution, of additives selected from polyvinylpyrrolidone, and polyalkylene oxides.

4. The process according to claim 1, wherein after a) and b) the membrane M is subjected to an oxidative treatment.

5. The process according to claim 1, wherein the membrane M is an ultrafiltration membrane, a microfiltration membrane or a component of a reverse osmosis or forward osmosis membrane.

6. A membrane obtained according to the process according to claim 1.

7. A membrane element comprising membranes obtained in the process according to claim 1.

8. A membrane module comprising membranes obtained in the process according to claim 1.

9. A filtration system comprising the membrane modules according to claim 8.

10. A filtration system comprising the membrane elements according to claim 7.

11. The process according to claim 1, further comprising after a) and b), washing the membrane with water.

Description

EXAMPLES

(1) Abbreviations used in the examples and elsewhere: NMP N-methylpyrrolidone DMAc Dimethylacetamide PWP pure water permeation MWCO molecular weight cutoff DMF dimethylformamide THF tetrahydrofurane PESU polyethersulfone AMD3L N,N-Dimethyl-lactamide 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 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)) 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)) 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 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 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 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 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

(2) 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.

(3) 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 U F-system).

(4) In a subsequent test, a solution of different PEG-Standards was filtered at a pressure of 0.15 bar. By GPC-measurements of the feed and permeate, the molecular weight cut-off of the membranes was determined.

Examples 1 to 5: Preparation of Membranes Using Polyvinylpyrrolidone as Second Dope Polymer

(5) Into a three neck flask equipped with a magnetic stirrer there were added 75 ml of Solvent S1 as given in table 1, Luvitec K30 (K30) and Luvitec K90 (K90) as second dope polymers with the amounts given in table 1 and 19 g of polyethersulfone (Ultrason E 6020P). 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. 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. 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.

(6) TABLE-US-00001 TABLE 1 Compositions and properties of membranes prepared according to examples 1 to 5; MWCO in [Da], PWP in [kg/h m.sup.2bar]. K30 K90 Solvent S1 PWP MWCO 1 0 6 AMD3L 230 6800 2 3 3 AMD3L 360 12100 3 2 4 AMD3L 740 17000 4 1 5 AMD3L 360 13200 5 0 6 NMP 510 42400

Examples 6 to 13: Preparation of Membranes Using Polyalkyleneoxides as Second Dope Polymer

(7) Into a three neck flask equipped with a magnetic stirrer there were added 75 ml of Solvent S1 as given in table 1, POLYOX WSR-N10 (N10), POLYOX WSR-N80 (N80), POLYOX WSR-N750 (N750), Breox 75W55000 (Breox) and/or Pluriol 9000E (P9000) as second dope polymers with the amounts given in table 2 and 19 g of polyethersulfone (Ultrason E 6020P). 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.

(8) After the membrane had detached from the glass plate, the membrane was carefully transferred into a water bath for 12 h. Then, the membrane was transferred into a bath containing 2500 ppm NaOCl at 50 C. for 4.5 h to remove polyalkyleneoxides. 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.

(9) TABLE-US-00002 TABLE 2 Compositions and properties of membranes prepared according to examples 6 to 13; MWCO in [Da], PWP in [kg/h m.sup.2bar]. N10 N80 N750 P9000 Breox Solvent S1 PWP MWCO 6 6 AMD3L 530 9500 7 6 NMP 420 12000 8 6 AMD3L 460 9100 9 6 NMP 380 8900 10 3 3 AMD3L 530 16250 11 3 3 NMP 550 29200 12 3 3 AMD3L 710 9200 13 3 3 NMP 700 14600

(10) Membranes produced with AMD3L according to the invention show improved separation characteristics over membranes known from the art. Membranes produced with AMD3L show improved (smaller) MWCO while maintaining the permeabilities of membranes known from the art.