USE OF A SOLUTION OF POLYSULFONE IN N-ACYL-MORPHOLINE FOR THE FABRICATION OF UF MEMBRANES

Abstract

Solution comprising a sulfone polymer, a water-soluble polymer and a N-acyl-morpholine of formula I wherein R.sup.1 is a hydrogen atom or a C1- to C3 alkyl group.

##STR00001##

Claims

1: A solution, comprising: a sulfone polymer, a water-soluble polymer, and a N-acyl-morpholine of formula I: ##STR00006## wherein R.sup.1 is a hydrogen atom or a C1- to C3 alkyl group.

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

3: The solution according to claim 1, wherein the sulfone polymer is an aromatic sulfone polymer consisting to at least 30% by weight of aromatic carbon atoms.

4: The solution according to claim 1, wherein the sulfone polymer is polysulfone of formula II: ##STR00007##

5: The solution according to claim 1, wherein the water-soluble polymer has a solubility in water of at least 30 g polymer in 100 g water at 21 C., 1 bar.

6: The solution according to claim 1, wherein the water-soluble polymer is a vinylpyrrolidone polymer consisting to at least 50% by weight of N-vinylpyrrolidone.

7: The solution according to claim 1, wherein the water-soluble polymer is polyvinylpyrrolidone.

8: The solution according to claim 1, wherein the solution comprises from 1 to 100 parts by weight of the water soluble polymer per 100 parts by weight of the sulfone polymer.

9: The solution according to claim 1, wherein the N-acyl-morpholine is N-formyl-morpholine.

10: The solution according to claim 1, wherein the solution comprises from 5 to 200 parts by weight of a total amount of the sulfone polymer and the water soluble polymer per 100 parts by weight of the N-acyl-morpholine.

11: A process for making a membrane, the process comprising: preparing the membrane with the solution according to claim 1.

12: The process according to claim 11, further comprising: providing the solution contacting the solution with a coagulant, thereby obtaining a membrane, and optionally oxidizing and washing the membrane

13: The process according to claim 12, wherein the coagulant is water.

14: The process according to claim 12, wherein a weight average molecular cut-off of the membrane is 20000 g/mol at maximum.

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

16: A method for treating water, the method comprising: contacting water with the membranes according to claim 15, wherein the method is suitable for water treatment applications, treatment of industrial or municipal waste water, desalination of sea or brackish water, dialysis, plasmolysis, and food processing.

17: The process according to claim 11, wherein the solution comprises the N-acyl-morpholine of formula I: ##STR00008## wherein R.sup.1 is a hydrogen.

Description

EXAMPLES

[0072] Abbreviations and compounds used in the examples:

DMAc Dimethylacetamide

[0073] PWP pure water permeation
MWCO molecular weight cutoff

NFM N-formylmorpholine

[0074] 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 [0075] Luvitec K30 Polyvinylpyrrolidone with a solution viscosity characterised by the K-value of 30, determined according to the method of Fikentscher (Fikentscher, Cellulosechemie 13, 1932 (58))

[0076] 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.

[0077] 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) cutoff 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.

Preparation of Membranes Using NFM as Polymer Solvent

General Procedure

[0078] Into a three neck flask equipped with a magnetic stirrer there were added 75 ml of Solvent 51 as given in table 1, Luvitec K30 (K30) as second dope polymers with the amounts given in table 1 and 19 or 25 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 1) and NFM with (example 1) and without water soluble polymer (comparative 2).

TABLE-US-00001 TABLE 1 Properties of the dope polymer solutions based on different solvents S1. K30 S 6010 Solvent S1 appearance dope solution comparative 1 6 19 DMAc turbid comparative 2 0 25 NFM clear and transparent example 1 6 19 NFM 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]. K30 S 6010 Solvent S1 PWP MWCO comparative 1 6 19 DMAc 180 21500 comparative 2 0 25 NFM 0 example 1 6 19 NFM 390 18100

[0081] Membranes produced with NFM according to the invention show improved separation characteristics over membranes known from the art. Membranes produced with NFM show improved (smaller) MWCO in combination with higher permeability values compared to membranes known from the art. Without water soluble polymer, the obtained membranes have no water permeability.