Membrane Manufacturing With A Cosolvent In The Polymer Dope Solution

Abstract

The invention relates to a process for making a membrane M comprising the following steps: providing a dope solution D comprising a polymer P selected from polyphenylenesulfone or mixtures of polyphenylenesulfone with nonionic polyarylene ethers, a first solvent selected from aprotic polar solvents, and a cosolvent selected from C.sub.2-C.sub.8 alkanediol, C.sub.3-C.sub.8 alkanetriol, polyethylene glycol, or mixtures thereof; and preparing the membrane by bringing the dope solution D into contact with a coagulating agent. The invention further relates to a membrane M obtainable in said process.

Claims

1. A process for making a nonionic membrane M comprising the following steps: providing a dope solution D comprising a polymer P selected from polyphenylenesulfone or mixtures of polyphenylenesulfone with nonionic polyarylene ethers, a first solvent selected from aprotic polar solvents, and a cosolvent selected from C.sub.2-C.sub.8 alkanediol, C.sub.3-C.sub.8 alkanetriol, polyethylene glycol, or mixtures thereof; and preparing the membrane by bringing the dope solution D into contact with a coagulating agent.

2. The process according to claim 1 wherein the weight ratio of the first solvent to the cosolvent is in the range from 30:1 to 1:2, preferably from 10:1 to 1:1, and in particular from 8:1 to 5:1.

3. The process according to claim 1 or 2 wherein the dope solution D comprises 1 to 30 wt %, preferably 2 to 20 wt %, and in particular 5 to 15 wt % of the cosolvent.

4. The process according to any of claims 1 to 3 wherein the dope solution D comprises at least 35 wt %, preferably at least 45 wt %, and in particular at least 55 wt % of the first solvent.

5. The process according to any of claims 1 to 4 wherein the first solvent is selected from high-boiling ethers, esters, ketones, asymmetrically halogenated hydrocarbons, anisole, dimethylformamide, dimethyl sulfoxide, sulfolane, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, or mixtures thereof.

6. The process according to any of claims 1 to 5 wherein the first solvent is selected from N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, or mixtures thereof.

7. The process according to any of claims 1 to 6 wherein the cosolvent is selected from C.sub.2-C.sub.4 alkanediol, C.sub.3-C.sub.4 alkanetriol, polyethylene glycol with a molar mass of 100 to 1000 g/mol, or mixtures thereof.

8. The process according to any of claims 1 to 7 wherein the cosolvent is selected from 1,2-propandiol, 1,3-propandiol, glycerin, polyethylene glycol with a molar mass of 300 to 600 g/mol or mixtures thereof.

9. The process according to any of claims 1 to 8 wherein said polymer P is selected from polyphenylenesulfone and mixtures of polyphenylenesulfone with polyethersulfone or polysulfone.

10. The process according to any of claims 1 to 9 wherein said polymer P is selected from polyphenylenesulfone.

11. The process according to any of claims 1 to 10 wherein the polymer P comprises at least 60 wt %, preferably at least 80 wt %, and in particular at least 95 wt % of the polyphenylenesulfone.

12. The process according to any of claims 1 to 11 wherein said at least one coagulating agent comprises water.

13. The process according to any of claims 1 to 12 further comprising a step of adding to the dope solution D a solution S which comprises a copolymer C in solvent L, wherein said copolymer C comprises blocks of at least one polyarylene ether A and blocks of polyalkylene oxide PAO, wherein the content of polyalkylene oxide PAO in copolymer C is 30 to 90% by weight.

14. A nonionic membrane M obtainable in the process according to any of claims 1 to 13.

15. A use of the nonionic membrane M obtainable in the process according to any of claims 1 to 13 for filtering an aqueous liquid through the membrane.

Description

EXAMPLES

[0127] Ultrason P 3010: polyphenylenesulfone (PPSU) 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. [0128] Luvitec K90: polyvinylpyrrolidone with a polyvinylpyrrolidone with a solution viscosity characterised by the K-value of 90, determined according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58)). [0129] PAO-1: C16/C18-alkylpolyethyleneglycol with hydroxyl number (DIN 53240) of 14 mg/g KOH and a molecular mass (calculated on the basis of hydroxyl number) of 3780 g/mol.

Synthesis of Copolymers C

[0130] The following copolymers were prepared and analyzed according to the copolymers of Examples 1 to 5 in WO 2016/023765. The data are summarized in Table 1.

[0131] Copolymer 1: 287 g of 4,4-Dichlorodiphenylsulfone (DCDPS), 148.5 g of 4,4-Dihydroxydiphenylsulfone (DHDP), 331 g of PAO-1 and 145 g potassium carbonate were suspended in 525 ml NMP in a nitrogen atmosphere. The mixture was heated to 190 C. within one hour. The water that was formed in the reaction was continuously removed by distillation. The solvent level inside the reactor was maintained at a constant level by addition of further NMP. After a reaction time of six hours, the reaction was stopped by addition of 933 ml of NMP with a temperature of 23 C. The potassium chloride formed in the reaction was removed by filtration. The solid content of the so obtained solution was 34% by weight.

[0132] Copolymer 2: 172.3 g of DCDPS, 105.7 g of DHDP, 206.6 g of PAO-1 and 89.1 g potassium carbonate were suspended in 315 ml NMP in a nitrogen atmosphere and further reacted as for Copolymer 1. The solid content of the so obtained solution was 29% by weight.

TABLE-US-00001 TABLE 1 Copolymer 1 2 Viscosity number [ml/g] 12.9 35.5 Polyalkyleneoxide content [% by weight] 39.9 35.5 Tg [ C.] 48 55

Example 1

[0133] i) Providing the Dope Solution

[0134] Into a three neck flask equipped with a magnetic stirrer there were added 65 ml of N-methylpyrrolidone NMP (the first solvent), 6 g Luvitec K90, 10 g 1,2-propandiol (the cosolvent) and 19 g of Ultrason P 3010. 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.

[0135] ii) Preparing the Membrane

[0136] 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.

[0137] The membrane film was allowed to rest for 30 seconds before immersion in a water bath at 25 C. for 10 minutes to coagulate the Ultrason P 3010.

[0138] iii) Workup of the Membrane:

[0139] 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 bisulfate to remove active chlorine. After several washing steps with water the membrane was stored wet until characterization.

[0140] Comparative Example C1

[0141] The membrane was prepared as in Example 1 but without the cosolvent 1,2-propandiol. Instead the amount of NMP was increased from 65 to 75 ml.

Example 2

[0142] The membrane was prepared as in Example 1. In addition, 1.6 g Copolymer 1 was added in step i) to the dope solution.

Comparative Example C2

[0143] The membrane was prepared as in Example 2 but without the cosolvent. Instead the amount of NMP was increased accordingly.

Example 3

[0144] The membrane was prepared as in Example 2. In addition, 1.6 g Copolymer 2 was added in step i) to the dope solution.

Comparative Example C3

[0145] The membrane was prepared as in Example 3 but without the cosolvent. Instead the amount of

[0146] NMP was increased accordingly.

Example 4

Membrane Characterization

[0147] The membranes prepared in Examples 1-3 and the corresponding Comparative Examples C1-C3 were characterized. The results are summarized in Table 2.

[0148] The pure water permeation (PWP in kg/h*m.sup.2*bar) 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 (MWCO in kDa) of the membranes were determined. Tensile testing was carried out according DIN Iso 527-3 and the membranes characterized with Emodulus (Emod in MPa) and elongation at break (Elong.sub.a in %).

TABLE-US-00002 TABLE 2 PWP MWCO Emod Elong.sub.B Example 1 600 35 147 60 Comparative Example C1 500 22 115 32 Example 2 790 36 119 57 Comparative Example C2 610 28 101 31 Example 3 760 42 121 57 Comparative Example C3 660 31 107 36

[0149] The data demonstrated that the advantages of the process, namely that the MWCO increased, and that the PWP also increased. Also mechanical stability and flexibility (elongation at break) improved.