SOLUTION OF SULFONE POLYMERS IN N-TERT.-BUTYL-2-PYRROLIDONE FOR THE USE OF MEMBRANES

Abstract

A solution contains at least one sulfone polymer and N-tert.-butyl-2-pyrrolidone. The solution can be used in a process of making a membrane, which is useful for water treatment.

Claims

1: A solution, comprising a sulfone polymer selected from the group consisting of a polyethersulfone of formula I, ##STR00004## a polysulfone of formula II, ##STR00005## and polyphenylsulfone of formula III, ##STR00006## wherein an average molecular weight Mw of the sulfone polymers is in the range from 40000 to 95000 g/mol, and N-tert.-butyl-2-pyrrolidone, as the only solvent used.

2: The solution according to claim 1, wherein the sulfone polymer comprises at least 0.02 mol SO2- units per 100 g of the sulfone polymer.

3: The solution according to claim 1, wherein the sulfone polymer is an aromatic sulfone polymer which comprises at least 30 wt.-% of aromatic carbon atoms, based on a total weight amount of the sulfone polymer.

4: The solution according to claim 1, comprising: at least one of the sulfone polymer, at least one water soluble polymer, and the N-tert-butyl-2-pyrrolidone as the only solvent used.

5: The solution according to claim 1, comprising: at least one of the sulfone polymer, an additive, and the N-tert.-butyl-2-pyrrolidone as the only solvent used.

6: The solution according to claim 4, wherein the solution further comprises art additive.

7: The solution according to claim 5, wherein the additive is selected from the group consisting of C2-C4 alkanol, C2-C4 alkanediol, C3-C4 alkanetriol, polyethylene oxide with a molar mass below 200 g/mol, and a mixture thereof.

8: The solution according to claim 1, wherein the solution comprises 1 to 40 wt-% of the sulfone polymer, based on the solution.

9: The solution according to claim 4, wherein the solution comprises 0.1 to 15 wt.-% of the at least one water soluble polymer, based on the solution.

10: The solution according to claim 5, wherein the solution comprises 0.1 to 15 wt.-% of the additive, based on the total weight amount of the solution.

11: A process, comprising: making a membrane with the solution according to claim 4.

12: The process of claim 11, comprising: a) providing the solution, b) contacting the solution with at least one coagulant, and c) optionally, oxidizing and washing the obtained membrane.

13: The process according to claim 12, wherein the at least one coagulant comprises water or vapor.

14: A membrane, obtained by the process according to claim 11.

15: A process, comprising: separating components in a fluid with the membrane according to claim 14, wherein the process is for water treatment applications, treatment of industrial or municipal waste water, desalination of sea or brackish water, dialysis, plasmolysis, or food processing.

16: The solution according to claim 6, wherein the additive is selected from the group consisting of C2-C4 alkanol, C2-C4 alkanediol, C3-C4 alkanetriol, polyethylene oxide with a molar mass below 200 g/mol, and a mixture thereof.

17: The solution according to claim 6, wherein the solution comprises 0.1 to 15 wt.-% of the additive, based on the total weight amount of the solution.

Description

EXAMPLES

[0069] Abbreviations and compounds used in the examples: [0070] PWP pure water permeation [0071] MWCO molecular weight cutoff [0072] NTU nephelometric turbidity unit [0073] TBP N-tert.-butyl-2-pyrrolidone [0074] NMP N-methyl-2-pyrrolidone [0075] NBP N-n-butyl-2-pyrrolidone [0076] DMF N,N-dimethylformamide [0077] 2P 2-pyrrolidone [0078] 12PD 1,2-propandiol [0079] Ultrason E 3010 Polyethersulfone with a viscosity number (ISO 307, 1157, 1628; in 0.01 g/mol phenol/1,2 orthodichlorobenzene 1:1 solution) of 66; a glass transition temperature (DSC, 10 C./min; according to ISO 11357-1/-2) of 225 C.; a molecular weight Mw (GPC in THF, PS standard): 58000 g/mol, Mw/Mn=3.3 [0080] Ultrason P 3020 P Polyphenylenesulfone with a viscosity number (ISO 307, 1157, 1628; in 0.01 g/mol phenol/1,2 orthodichlorobenzene 1:1 solution) of 71; a glass transition temperature (DSC, 10 C./min; according to ISO 11357-1/-2) of 220 C.; a molecular weight Mw (GPC in THF, PS standard): 48000 g/mol, Mw/Mn=2.7 [0081] Ultrason S 6010 Polysulfone with a viscosity number (ISO 307; in 0.01 g/mol phenol/1,2 orthodichlorobenzene 1:1 solution) of 81; a glass transition temperature (DSC, 10 C./min; according to ISO 11357-1/-2) of 187 C.; a molecular weight Mw (GPC in THF, PS standard): 60000 g/mol, Mw/Mn=3.7 [0082] Luvitec K30 Polyvinylpyrrolidone with a MW of greater than 28000 g/mol and a solution viscosity characterised by the K-value of 30, determined according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)) [0083] Luvitec K90 Polyvinylpyrrolidone with a MW of greater than 900000 g/mol and a solution viscosity characterised by the K-value of 90, determined according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)) [0084] Pluriol 400E Polyethylene oxide with an average molecular weight of 400 g/mol cal culated from the OH numbers according to DIN 53240. [0085] Pluriol 9000E Polyethylene oxide with a solution viscosity characterised 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 with 0.01 mol phosphate buffer pH 7.4, TSKgel GMPWXL column, Tosoh Bioscience with poly(ethylene oxide) standard 106-1522000 g/mol): 10800 g/mol. [0086] Breox 75W55000 Polyethyleneoxide-polypropyleneoxide copolymer with a solution vis cosity characterised 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 with 0.01 mol phosphate buffer pH 7.4, TSKgel GMPWXL column, Tosoh Bioscience with poly(ethylene oxide) standard 106-1522000 g/mol): 14300 g/mol

[0087] The polymer solution turbidity was measured with a turbidimeter 2100AN (Hach Lange GmbH, Dusseldorf, Germany) employing a filter of 860 nm and expressed in nephelometric turbidity units (NTU). Low NTU values are preferred.

[0088] The polymer solution viscosity was measured with a Brookfield Viscometer DV-I Prime (Brookfield Engineering Laboratories, Inc. Middleboro, USA) with RV 6 spindle at 60 C. with 20 to 100 rpm.

[0089] The pure water permeance (PWP) of the membranes was tested using a pressure cell with a diameter of 74 mm using ultrapure water (salt-free water, filtered by a Millipore UF-system) at 23 C. and 1 bar water pressure. The pure water permeation (PWP) is calculated as follows (equation 1):

[00001]$\begin{array}{cc}\mathrm{PWP}=\frac{m}{APt}& \left(1\right)\end{array}$ [0090] PWP: pure water permeance [kg/bar h m.sup.2] [0091] m: mass of permeated water [kg] [0092] A: membrane area [m.sup.2] [0093] P: pressure [bar] [0094] t: time of the permeation experiment [h]. [0095] A high PWP allows a high flow rate and is desired.

[0096] In a subsequent test, solutions of polyethylene oxide-standards with increasing molecular weight were used as feed to be filtered by the membrane at a pressure of 0.15 bar. By GPC-measurement of the feed and permeate, the molecular weight of the permeate of each polyethylene oxide-standard used was determined. The weight average molecular weight (MW) cut-off of the membranes (MWCO) is the molecular weight of the first polyethylene oxide standard which is withhold to at least 90% by the membrane. For example, a MWCO of 18400 means that PEG of molecular weight of 18400 g/mol and higher are withhold to at least 90%. It is desired to have a MWCO in the range from 10 to 100 kDa.

[0097] Tensile testing was carried out according DIN Iso 527-3 and the membranes characterized with Emodulus (Emod in MPa) and strain at break (strain in %).

[0098] Preparation of membranes using TBP as polymer solvent

[0099] General Procedure

[0100] Into a three-neck flask equipped with a magnetic stirrer there were added 65 to 80 ml of Solvent S1, 16.3 to 25 g Ultrason polymer with optional water soluble polymers 6 to 8 g Luvitec polyvinylpyrrolidone or polyalkyleneoxide (Pluriol 9000 E, Breox 75W55) and with optional additives (1,2-propandiol, Pluriol 400 E) as given in tables 1-6. The mixture was heated under gentle stirring at 60 C. until a homogeneous clear viscous solution, usually referred to as solution was obtained. The solution was degassed overnight at room temperature.

[0101] 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 (Coatmaster 510, Erichsen GmbH & Co KG, Hemer, Germany) operating at a speed of 5 mm/s. The membrane film was allowed to rest for 30 seconds before immersion in a water-based coagulation 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.

[0102] Optionally afterwards the membrane was transferred into a bath containing 2000 ppm NaOCI at 60 C. and pH9.5 for 2 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 (Posttreatment A).

[0103] Or optionally the membrane was washed with water at 60 C. three times (Posttreatment B). Polymer solutions produced with TBP according to the invention show higher solution viscosity and membranes fabricated thereof showed improved mechanical stability (higher Emodulus) over membranes known from the art.

TABLE-US-00001 TABLE 1 Compositions and properties of Ultrason E 3010 solutions; turbidity@RT [NTU], Visco@60 C. [Pas], example E3010 Solvent S1 Visco NTU example 1 25 g 75 g TBP 4.8 0.40 comp. ex. 1 25 g 75 g NMP 1.0 0.81

TABLE-US-00002 TABLE 2 Compositions and properties of Ultrason E 3010 membranes prepared; MWCO in [kDa], PWP in [kg/h m2 bar], Visco@60 C. [Pas], Emodulus [MPa], Strain@break [%] Posttreatment A (NaOCl). Coagulation water-glycerol (50/50 wt/wt). Solvent Strain example E3010 K30 K90 12PD S1 Visco PWP MWCO Emod @break example 19 g 6 g 0 g 10 g 65 g 4.8 1200 77.9 183 5 20 1 2 TBP example 19 g 3 g 3 g 10 g 65 g 18.2 870 64.6 172 6 26 3 3 TBP example 19 g 2 g 4 g 10 g 65 g 31.2 820 52.5 174 3 22 1 4 TBP example 19 g 1 g 5 g 10 g 65 g 39.0 660 41.3 161 4 16 4 5 TBP example 19 g 0 g 6 g 10 g 65 g 83.3 570 42.0 157 5 20 3 6 TBP comp. 19 g 6 g 0 g 10 g 65 g 1.2 65 15.9 133 11 24 5 ex. 2 NMP comp. 19 g 3 g 3 g 10 g 65 g 5.6 1100 53.3 151 10 35 3 ex. 3 NMP comp. 19 g 2 g 4 g 10 g 65 g 8.0 1300 65.1 150 11 25 7 ex. 4 NMP comp. 19 g 1 g 5 g 10 g 65 g 10.7 1200 41.0 151 4 29 4 ex. 5 NMP comp. 19 g 0 g 6 g 10 g 65 g 13.7 1200 35.7 147 2 48 3 ex. 6 NMP comp. 19 g 6 g 0 g 10 g 65 g 3.4 370 50.0 131 12 10 3 ex. 7 NBP comp. 19 g 3 g 3 g 10 g 65 g 14.2 1700 46.5 131 7 9 2 ex. 8 NBP comp. 19 g 2 g 4 g 10 g 65 g 21.5 1300 62.9 158 8 19 8 ex. 9 NBP comp. 19 g 1 g 5 g 10 g 65 g 30.0 1600 63.5 150 2 29 7 ex. 10 NBP comp. 19 g 0 g 6 g 10 g 65 g 53.0 1500 66.3 137 2 35 3 ex. 11 NBP

[0104] The use of TBP as solvent for the production of the membranes causes formation of more stable membranes even at low viscosity amount e.g. 4.8 Pas with comparable PWP/MWCO values as shown in the comparative examples 2-6 in Table 2, where NMP is used as solvent. The magnitude of Emod and Strain@break by using NMP as solvent are all lower independent of the viscosity amounts. The PWP and MWCO values cannot be amended even if the viscosity is increasing. Compared to NBP as closest state of the art (comparative examples 7 to 11) TBP polymer solutions show higher viscosities and deliver more stable membranes according to tensile testing (Emod and Strain@break). Also, with NBP the PWP and MWCO values cannot be amended.

TABLE-US-00003 TABLE 3 Compositions and properties of Ultrason S 6010 solutions; turbidity@RT [NTU], Visco@60 C. [Pas], Solvent NTU NTU NTU NTU NTU NTU example S6010 S1 Visco (0 d) (14 d) (21 d) (28 d) (35 d) (42) example 7 25 g 75 g TBP 9.8 1.52 1.47 1.44 1.51 1.55 1.55 comp. ex12 25 g 75 g DMF 2.3 2.11 2.76 4.15 6.20 10.4 17.3

[0105] Insoluble crystalline cyclic polysulfone dimers pose in solutions for membrane manufacturing problems either by filter clogging or can cause imperfections on the membrane surface (S. Savarier et. al, Desalination 2002, 144, 15-20). Polymer solutions of S6010 in TBP are clearer and more transparent compared to solutions in DMF over time. The content of cyclic dimers is better dissolved by TBP compared to DMF as shown by solution turbidity. Over time the solution turbidity increases in DMF while in TBP it remains stable.

TABLE-US-00004 TABLE 4 Compositions and properties of Ultrason S 6010 membranes prepared; MWCO in [kDa], PWP in [kg/h m2 bar], Visco@60 C. [Pas], turbidity@60 C. [NTU], Posttreatment B (water wash). Coagulation Water additive S6010 Solvent S1 NTU visco PWP MWCO example 8 g Pluriol 400 E 16.3 g 75.7 g TBP 3.21 1.30 178 9.7 8 comp. 8 g Pluriol 400 E 16.3 g 75.7 g DMF 3.76 0.25 75 10.5 ex. 13 example 8 g Pluriol 9000 E 16.3 g 75.7 g TBP 2.81 1.68 632 15.7 9 comp. 8 g Pluriol 9000 E 16.3 g 75.7 g DMF 37.3* 0.05 ex. 14 example 8 g Breox 75W55 16.3 g 75.7 g TBP 4.85 1.30 1311 85.0 10 comp. 8 g Breox 75W55 16.3 g 75.7 g DMF 1982* ex. 15 *two-phase system: no membranes could be manufactured

TABLE-US-00005 TABLE 5 Compositions and properties of Ultrason P3020P solutions; turbidity@RT [NTU], Visco@60 C. [Pas], example E3010 Solvent S1 Visco NTU example 10 20 g 80 g TBP 2.80 36.3 comp. ex. 16 20 g 80 g DMF 0.55 1070

TABLE-US-00006 TABLE 6 Compositions and properties of Ultrason P3020P membranes prepared; MWCO in [kDa], PWP in [kg/h m2 bar], Visco@60 C. [Pas], Posttreatment A (NaOCl). Coagulation water-glycerol (50/50 wt/wt) example P3020P K30 K90 Solvent S1 Visco PWP MWCO example 11 19 g 3 g 3 g 75 g TBP 39.7 540 30.0 comp. ex. 17 19 g 3 g 3 g 75 g DMF ** ** polymers not soluble: no membranes could be manufactured

[0106] FIG. 1(A) shows a scanning electron micrograph of a membrane of example 4 according to the invention which shows a well-established nano porous filtration layer on the top supported by a sponge-type substructure with increasing pore sizes from top to bottom. No defects or macrovoids are visible in die cross-section. FIG. 1(B) shows a scanning electron micrograph of a membrane of comparative example 4 showing numerous macrovoids which could partially penetrate the filtration layer on the top and cause reduced mechanical stability as seen from the results of the tensile testing.

[0107] Polymer solutions produced with TBP according to the invention and membranes fabricated thereof showed improved mechanical stability (higher Emodulus) over membranes produced from NBP/2P (10/90-90/10 wt/wt) and TBP/2P (10/90-90/10 wt/wt) mixtures as solvents as described in EP-A 3756753. Also, the membrane produced from TBP solution showed a higher permeability value of 870 kg/h m.sup.2bar compared to membranes produced from TBP/2P (10/90 90/10 wt/wt) mixtures with 290-740 kg/h m.sup.2bar. The membrane produced with TBP showed similar separation characteristics taking the MWCO value of 64.4 kDa into account (TBP/2P 10/90-90/10 wt/wt mixtures: 17.8-34.2 kDa). In general, MWCO values of 10-100 kDa account for the ultrafiltration range.

TABLE-US-00007 TABLE 1 Compositions and properties of Ultrason E 3010 membranes prepared with 19 g E3010, 3 g K30, 3 g K90 and 10 g 1,2-propandiol; MWCO in [kDa], PWP in [kg/h m2 bar], Visco@60 C. [Pas], Emodulus [MPa], Strain@break [%] Posttreatment A NaOCl. Coagulation water-glycerol (50/50 wt/wt) Strain example 2P NBP TBP Visco PWP MWCO Emod @break example 3 65 g 18.2 870 64.6 172 6 26 3 comp. ex. 58.5 g 6.5 g 34.1 330 15.8 96 4 28 17 18 comp. ex. 32.5 g 32.5 g 23.2 770 29.6 126 3 28 9 19 comp. ex. 6.5 g 58.5 g 18.3 1366 95.0 143 3 15 26 20 example 12 58.5 g 6.5 g 35.3 290 17.8 83 3 27 8 example 13 32.5 g 32.5 g 26.0 560 23.7 133 1 25 5 example 14 6.5 g 58.5 g 22.4 740 34.2 156 5 24 17