CH658399A5 - METHOD FOR PRODUCING semipermeable membranes. - Google Patents

Description

658 399

PATENT CLAIM Process for the production of semipermeable membranes based on a polyacrylonitrile terpolymer by dissolving the terpolymer in dimethylformamide and adding blowing agent with subsequent shaping, coagulation of the polymer film, annealing and drying of the membrane, characterized in that the polyacrylonitrile terpolymer is a block term polymer , which is derived from acrylonitrile, methyl methacrylate and the sodium salt of vinyl sulfonic acid and has the following ratios of the starting monomers: 82-93% by weight of acrylonitrile, 6-15% by weight of methyl methacrylate and 1-3% by weight. % Sodium salt of vinyl sulfonic acid.

The present invention relates to a method for producing semipermeable membranes based on a polyacrylonitrile terpolymer by dissolving the terpolymer in dimethylformamide and adding blowing agent with subsequent shaping, coagulation of the polymer film, annealing and drying of the membrane. The membranes obtained according to the invention can be used for the concentration of gamma globulin, albumin and milk egg white solutions.

A method for producing polysulfone membranes, in which the membrane is applied to a previously prepared drainage carrier tape, is known. Without this paper tape, the membranes cannot withstand the operating pressures. This complicates their method of manufacture. In addition, a decrease of 0.029 to 0.017 m3 / m2 per hour of membrane permeability is observed during the concentration of the albumin. This reduction is a result of the pore clogging of the membrane, which in turn leads to an extension of the regeneration process of the membrane, which shortens its operating time (see “Pellicon Gassette System” - “Millipore Corp. Bedford; Massachusetts 01730 (catalog)).

A process for the production of cellulose acetate membranes by means of wet molding or by the so-called »production process from solution« is also known; Russian publication. However, the membranes made from this polymer cannot be kept dry. Once dried, they change their asymmetrical structure. The permeability of these membranes also changes in a wide range (from 0.028 to 0.002 m3 / m2 per hour) and they show up to 95% retention (retention) of the protein substances (see Mc Do-nough Protein concentrate from cheese by ultrafiltration; J Daing Sc. 1971, 54 No. 10, pp. 1407-09).

Another process for the production of membranes based on polyacrylonitrile copolymers is known; U.S. Patent No. 4181 694. Isobutene, ethyl vinyl ether, vinylidene chloride, butadiene, methacrylonitrile and the like are used here as monomers. a. used. The membranes produced in this way have a high permeability to distilled water - 1.2 m3 / m2 per hour, but they only retain substances with a molecular mass of over 45,000. With these membranes you can not hold back molecules with a molecular mass of 15,000 to 45,000, which in a large amount z. B. are present in milk products.

Another method of making permeable (semipermeable) membranes based on acrylonitrile-vinyl pyrolidone polymer is known from U.S. U.S. Patent No. 3,950,257. This procedure uses two types

Copolymer solvents such as dimethyl sulfoxide and dimethylformamide are used. When ultrafiltering whey, the membranes based on polymer dimethyl sulfoxide have an initial flow rate of 0.045 m3 / m2 per hour and a selectivity (selectivity) of 95%. The process for making these membranes requires heating the plates onto which the film is poured to 50 ° C. The same procedure has its disadvantages, which are noticeable in the subsequent coagulation stage at 20 ° C. The use of dimethylformamide solvent and lowering the temperature down to 20 ° C helps to reduce the permeability of the membranes while maintaining the same selectivity. In both cases, membranes are produced that cannot be stored in the dry state.

Another method for producing membranes is known from GDR patent No. 134 448, in which a copolymer with the composition: 93% acrylonitrile, 6% methyl ester of acrylic acid and 1% sodium salt of allylic acid is used. The coagulation is carried out in the medium of propyl alcohol or in an alcohol-water mixture. A flow rate that is greater than 0.003 m3 / m2 per hour could not be achieved even by changing some parameters of the work process for the manufacture of these membranes.

The object of the invention is to provide a method for producing semipermeable membranes based on a polyacrylonitrile terpolymer, which have stable and high permeability and selectivity characteristics and have a stable asymmetrical structure and can be stored in a dry state .

The process according to the invention for the production of semipermeable membranes based on a polyacrylonitrile terpolymer by dissolving the terpolymer in dimethylformamide and adding blowing agent with subsequent shaping, coagulation of the polymer film, annealing and drying of the membranes is characterized in that the polyacrylonitrile terpolymer is a terpolymer block which is derived from acrylonitrile, methyl methacrylate and the sodium salt of vinylsulfonic acid and has the following ratios of the starting monomers: 82-93% by weight of acrylonitrile, 6-15% by weight of methyl methacrylate and 1-3% by weight of sodium salt of vinylsulfonic acid.

In a preferred embodiment of the method according to the invention, the polymer produced by the radical polymerization method is dissolved in dimethylformamide by preparing 12% to 18% solutions, preferably a 15% solution. 1% blowing agent (e.g. lithium nitrate) can be added to the prepared solutions. When the polymer is dissolved, it is usually filtered through a Buchner funnel under pressure to separate the mechanical admixtures and the undissolved particles. After a dwell time of approximately 24 hours, the solution is usually completely free of the air that is included. Then, using a frame, this solution can be pulled out on glass plates until the polymer film is made. The film thickness is usually regulated by means of belts through which the plates are folded. The film is preferably stored in a chamber to protect its surface from contamination. In the chamber, the solution is exposed to a certain vapor pressure by varying the residence time of the film from 10 minutes to 60 minutes, thereby regulating the evaporation of the solution from the film surface. The polymer film together with the glass plate is immersed in a coagulation bath. Water or a mixture of water and dimethylformamide are preferred for the coagulation solution

5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

sung used. After a residence time of up to one hour, the polymer film can be detached from the plate and subjected to an intensive rinse with distilled water. All operations can be carried out under standard conditions (temperature 20-25 ° C, humidity 70-80%).

The membrane produced in this way is usually fixed on a metal frame and is preferably made to glow in water at a temperature of 80 ° C. for 10-15 minutes. After that the

3,658,399

Membrane separated from the frame and shaped into the dimensions required for the exploitation.

The structure of the membranes thus produced was checked by scanning electron microscopy. The membrane average illustrated in FIG. 1 (in terms of thickness) precisely characterizes the asymmetry of its structure. The investigation was carried out using the SUPERPROBE-733 apparatus.

The main characteristics of the membranes produced are illustrated in Table 1.

Table 1

No.

determined characteristic values

units

Results

1.

Permeability m3 / m2 per hour from 0.1 to 0.6

towards water

2nd

Electrical

Ohm.m from 3.10-3 to 4.10-3

resistance

3rd

Strength parameters

of the membrane

- Tensile strenght

N / m2

40.IO5 to 60.105

- compressive strength

N / m2

until 30.105

4th

Pore mean size nm

4000 to 6000

5.

Pore volume m3 / kg from 2.10-3 to 3.5 10 "3

6.

Membrane thickness m

from 1.10_4 to 1.5 10-4

7.

Resilience

from 5.5 to 9.5

in the pH range

8th.

Moisture content

%

until 5

a dry one

membrane

9.

Resistance to:

Petrol, toluene, brake oils

and other petroleum products

products

10th

Weather resistance

Good

11.

No resistance to

Sulfur dioxide,

about

Hydrogen sulfide,

Remarks

Depending on the manufacturing method of the membranes

Sulfuric acid, nitric oxide, sulfuric acid and other very aggressive media

The results obtained show that the method according to the invention ensures the production of typical, semi-permeable ultrafiltration membranes that their pore size is from 1000 to 10,000 nm. The membranes produced according to the invention have the following advantages, such as great tensile strength and compressive strength with a relatively low electrical resistance. Thanks to their resistance in a wide pH range, they are well suited for the food industry. Their greatest advantage is that these membranes can be stored in a dry state without changing their characteristic values.

The process according to the invention is explained in more detail with reference to the examples given below, without thereby restricting it.

example 1

A 15% copolymer solution in dimethylformamide of the following composition, 93% acrylonitrile, 6% methyl methacrylate and 1% sodium salt of vinyl sulfonic acid is prepared. 0.5% lithium nitrate is added to the resulting solution as a blowing agent. This solution is then filtered through a Büchner funnel to remove admixtures. After a 24-hour dwell time, the solution is formed into a film on a glass plate using a frame. The film thickness is regulated with the help of tapes with a size of 1.10-4 m. The film produced in this way then remains in a chamber for about 10 minutes under normal temperature conditions and 70% humidity. After the solution has evaporated from the surface of the film, coagulation is carried out in distilled water for 60 minutes and at a temperature of 25 ° C. Water or a mixture of water and dimethylformamide can be used as the coagulation solution. The film is detached from the glass plate and then rinsed abundantly with distilled water. Then the membrane is attached to a metal frame and made to glow in water at a temperature of 80 ° C for about 10 minutes. At a temperature of 40 C the membrane and the frame are dried to a residual moisture of 5%. The dry membrane produced is detached from the frame and shaped to the dimensions required for the exploitation. The membranes produced have the following characteristics: Per

658399

Meability to water compared to -0.2 m3 / m2 per hour, selectivity to protein solutions -99.5%, medium pore size - 4000 nm and tensile strength 45.105 N / m2.

Example 2

The procedure in Example 1 is used to prepare the polymer solution from copolymers with the composition 82% acrylonitrile, 15% methyl methacrylate and 3% sodium salt of vinylsulfonic acid. The membranes are produced according to the described method, the solution mentioned being used in dimethylformamide. It was found that the percentage decrease

The acrylonitrile content in the copolymer increases the brittleness (brittleness) of the dry membranes produced, since the permeability is only slightly reduced and, consequently, it is advisable to work with copolymers that have an increased acrylonitrile content.

The membranes produced according to Example 1 were tested using an ultrafiltration system against gamma globulin and albumin solutions. A comparison between the test results and the polysulphone membranes known to be the most effective in serum protein concentration is shown in Table 2.

Table 2

No. membrane type of operation

System pressure degree of concentration

N / m2

%

Characteristic values of permeability

selectivity

Start end m3 / m2h m3 / m2h%

2nd

Polysulfone membranes

Polyacrylonitrile

Terpolymer

Membranes

Albumin gamma globulin

Albumin gamma globulin

1.5 105 3 105

1.5 105 3 105

30 10

30 10

0.029 0.020

0.035 0.021

0.017 0.012

0.030 0.019

more than 95 more than 95

99.5 99.5

The membranes produced according to Example 1 were immediately between the test results and other membranes.

tested using whey ultrafiltration. A sales

Branches are shown in Table 3.

Table 3

Membranes based on characteristic values

permeability

whey

Beginning m3 / m2h

End of m3 / m2h

Water m3 / m2h

selectivity

%

Membranes type

1. acrylonitrile

Vinyl pyrolidone 0.030 - 0.083

2.Cellulose acetate 0.028 0.002 -

3. terpolymer-acrylonitrile-methyl methacrylate,

Sodium salt of vinyl sulfonic acid 0.015 0.013 0.120

96 95

99.5

wet wet dry

Analysis of the results obtained shows that the polyacrylonitrile membranes obtained according to the invention have better characteristic values for the permeability at the different degrees of concentration of the solutions. The permeability of the membranes from the beginning to the end of the process changes only slightly; the membranes can be regenerated more easily and they have a longer lifespan. In addition, one

55 sufficiently high concentration maintain the high selectivity of these membranes. The asymmetrical structure of the membranes produced according to the invention is stable and guarantees the results mentioned above. The method according to the invention is simplified in that 60 drainage carrier tapes are no longer necessary. According to this process, a sufficiently reliable membrane is produced that can be stored in a dry state.

65

s

1 sheet of drawings