SOLUTION OF POLYSULFONE IN N-ACYL-PYRROLIDINE AND USE THEREOF FOR UF MEMBRANES

Abstract

Solution comprising a sulfone polymer and a N-acyl-pyrrolidine of formula I wherein R.sup.1 to R.sup.9 independently from each other are a hydrogen atom or a methyl group. The solution is applied in membrane formation with polyvinylpyrrolidone as optional component.

##STR00001##

Claims

1. A solution comprising: a sulfone polymer; and a N-acyl-pyrrolidine of formula (I): ##STR00006## wherein R.sup.1 to R.sup.9 are each independently selected from the group consisting of a hydrogen atom and a methyl group.

2. The solution according to claim 1, wherein the sulfone polymer comprises at least 0.02 mol SO.sub.2.sup. units per 100 g of sulfone polymer.

3. The solution according to claim 1, wherein the sulfone polymer is an aromatic sulfone polymer, comprising at least 30% by weight of aromatic carbon atoms, based on a total weight of the sulfone polymer.

4. The solution according to claim 1, wherein the N-acyl-pyrrolidine of formula (I) is N-formyl-pyrrolidine or N-acetyl-pyrrolidine.

5. The solution according to claim 1, wherein the solution comprises 5 to 200 parts by weight of the sulfone polymer per 100 parts by weight of the N-acyl-pyrrolidine of formula (I).

6. A process for making the solution of claim 1, the process comprising dissolving or synthesizing the sulfone polymer in the N-acyl-pyrrolidine of formula (I).

7. A process for making a membrane, the process comprising: a) mixing the solution according to claim 1 with a water-soluble polymer to obtain a second solution; b) contacting the second solution with a coagulant to obtain a membrane; and c) optionally oxidizing and washing the obtained membrane.

8. The process according to claim 7, wherein the water-soluble polymer in a) is polyvinylpyrrolidone.

9. The process according to claim 7, wherein the coagulant in b) is water.

10. A membrane obtained by the process according to claim 7.

11. A separation article for water treatment applications, treatment of industrial or municipal waste water, desalination of sea or brackish water, dialysis, plasmolysis, or food processing, the article comprising the membrane according to claim 10.

Description

EXAMPLES

[0067] Abbreviations and compounds used in the examples:

[0068] DMAc Dimethylacetamide

[0069] PWP pure water permeation

[0070] MWCO molecular weight cutoff

[0071] NFP N-formylpyrrolidine [0072] Ultrason? S 6010 Polysulfone with a viscosity number (ISO 307, 1157, 1628; 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 [0073] Luvitec? K90 Polyvinylpyrrolidone with a solution viscosity characterised by the K-value of 90, determined according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58))

[0074] 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). A high PWP allows a high flow rate and is desired.

[0075] In a subsequent test, solutions of PEG-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 PEG-Standard used was determined. The weight average molecular weight (MW) cut-off of the membranes (MWCO) is the molecular weight of the first PEG 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 and higher are withhold to at least 90%. It is desired to have a lowest MWCO as possible.

[0076] Preparation of Membranes Using NFP as Polymer Solvent

[0077] General Procedure

[0078] Into a three neck flask equipped with a magnetic stirrer there were added 75 ml of Solvent S1 as given in table 1, Luvitec K90 (K90) as second dope polymers with the amounts given in table 1 and 19 g of polysulfone (Ultrason? S 6010). The mixture was heated under gentle stirring at 60? C. until a homogeneous clear viscous solution, usually referred to as dope solution was obtained. The solution was degassed overnight at room temperature.

[0079] In table 1 results are listed for DMAc (comparative) and NFP (example).

TABLE-US-00001 TABLE 1 Properties of the dope polymer solutions based on different solvents S1. K90 Solvent S1 appearance dope solution Comparative 6 DMAc turbid Example 6 NFP clear and transparent

[0080] 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. Table 2 summarizes the membrane properties.

TABLE-US-00002 TABLE 2 Compositions and properties of membranes prepared; MWCO in [Da], PWP in [kg/h m.sup.2bar]. K90 Solvent S1 PWP MWCO Comparative 6 DMAc 530 30700 Example 6 NFP 730 18400

[0081] Membranes produced with NFP according to the invention show improved separation characteristics over membranes known from the art. Membranes produced with NFP show improved (smaller) MWCO in combination with higher permeability values compared to membranes known from the art.