NL8201617A - PROCESS FOR THE MANUFACTURE OF A SEMI PERMEABEL MEMBRANE. - Google Patents

Description

N / 30 .919-Kp / Pf / vdM * '«- 1 -

Method for the production of a sera permeable membrane.

The invention relates to a method of manufacturing a semipermeable membrane that can be used to concentrate solutions of gamma globulin, albumin and milk proteins.

A method is known for the preparation of polysulfone membranes, wherein the membrane is applied to a pre-prepared blotting paper carrier. Without this carrier, the membrane could not withstand the working pressures. This leads to a complication of the method of manufacturing these membranes. In addition, during the albumin concentration process, a reduction of 0.029 to 0.017 m / m · h in the membrane permeability occurs.

This reduction is due to the clogging of the membrane pores. Thus, on the one hand, the method of obtaining the membrane is extended and, on the other hand, its life is shortened (see: "Pellicon Gassette System" * in the catalog of Millipore Corporation, Bedford, United States of America).

A further process is also known for the production of cellulose acetate membranes by liquid formation (ie the so-called "solution method"). However, membranes obtained in this way could not be stored in the dry state. Once dried, their asymmetrical structure is also lost. the permeability of these membranes varies over a wide range (from 0.028 to 0.002 m / m. h) at 95% retention capacity with respect to egg proteins (FE McDonough: "Protein concentrate from cheese whey by ultrafiltration" in J. Dairy Sci, 1971, 54, biz. 1407-1409).

A method is known for the manufacture of membranes based on polyacrylonitrile copolymers. Isobutylene, ethyl vinyl ether, vinylidene chloride, butadiene, methacrylonitrile, etc. are used as monomers. The membranes thus obtained show a high permeability to distilled water (i.e., 1.2 m / m h), but they retain only 35 substances with a molecular weight above 54,000. These membranes cannot be used to trap molecules whose weight is in the range of 15,000-45,000, which molecules are typical of milk proteins (U.S. Patent 4,181,694).

Furthermore, a method is known for the manufacture of a semipermeable membrane based on acrylonitrile vinyl pyrrolidone. Two types of copolymer solvents are used, such as dimethyl sulfoxide and dimethyl formamide.

Polymer dimethyl sulfoxide based membranes, when used in the ultrafiltration of whey, had an initial flow rate of 0.045 m / m h and a selectivity of 95%. The method of manufacturing these membranes requires heating the plates onto which the film is poured to a temperature of 50 ° C. This procedure causes some inconveniences at the subsequent stage of coagulation at 20 ° C and contributes to. the reduction in permeability at one and the same selectivity. Both cases lead to membranes that could not be stored in the dry state (U.S. Patent No. 3,950,257).

Finally, a further method is known for the manufacture of membranes, using the following copolymer composition: 93% acrylonitrile, 6% methyl ester of acrylic acid and 1% sodium salt of allylic acid. The coagulation process is carried out in a propyl alcohol medium or in an alcohol-water mixture. Variations in some parameters of the process for the manufacture of these membranes have not resulted in a flow rate greater than 0.003 m / m / h (DDR Patent 134,448).

The object of the present invention is to provide a process for the manufacture of a triple polyacrylonitrile copolymer based semi-permeable membrane, wherein the membrane has both stable and high permeability and selectivity ratios, a stable structure and storage when dry.

This object is achieved according to the invention by a process for the production of a semipermeable membrane based on a triple copolymer with the following 8201617-3 - the composition: 82-93% acrylonitrile; 6-15% methyl methacrylate and 1-3% sodium salt of vinyl sulfonic acid.

The polymer obtained by free-radical polymerization is dissolved in a suitable solvent (such as 5-dimethylformamide). and 12-18% solutions are prepared (preferably a 15% solution). A foaming agent, e.g. lithium nitrate, is added in amounts of up to 1% to the solutions so prepared. The polymer solution is filtered under pressure through a Buchner filter to remove both the mechanical impurities and undissolved particles. After storage for a period of approx. 24 h, the solution is completely free of air. The polymer film is then obtained by spreading the solution on glass plates with an edge. The thickness of the film is controlled by strips serving as edges for the plates. The film is kept in a room in order to keep the surface clean. A certain vapor pressure of the solvent is used in this. chamber and the storage time is varied from 10 to 60 minutes, thereby controlling the solvent evaporation process which takes place on the surface of the film.

The polymer film. is immersed in the coagulation bath together with the glass plate. Water or a mixture of water and dimethylformamide is used as a coagulation solution. After storage for a period of 1 h, the polymer film is separated from the plate and subjected to rinsing with an excess of distilled water. All procedures are performed under standard conditions (i.e. 20-25 ° C and 70-80% relative humidity).

The membrane thus obtained is (usually) fixed in a metal frame and tempered in water for a period of 10-15 min at a temperature of 80 ° C. The membrane (while still on the frame) is then dried at temperatures below 80 ° C. Finally, the membrane is detached from the frame and formed into the desired size.

The structure of the membranes thus obtained was examined by scanning electron microscopy. The cross-section of the membranes, as shown in 8201617-4 - Figure 1 of the drawing, shows the asymmetry of the membrane structure. (The study was performed using a SUPERPROBE 733 device).

Important parameters of the membranes are listed in Table A.

TABLE A

number of parameters units units results comments 1 2 3 4 5 - 2 '' 10 1. permeability m / mh 0.1-0.6 depending on the condition of the membrane preparation 2 .. electrical resistance 3.10 ~ 15 Ohm. m. , n-3 4.10 3-strength parameters: 5 - tensile strength N / m ^ 10.10 - 60.10b 2 5 - pressure resistance N / m up to 30.10 20 4 · *. average pore size nm 40-60 3 —3 —3 5 .. mass density m / kg 2.10 -3.5.10 -4 -4 6 .. membrane thickness m 1.10 -1.5.10 7. stability in the pH range from 5.5-9.5 8. moisture content of the dry membrane% up to 5 9 resistant to benzene, toluene, emetic fluids 30 and other petroleum products 10. weather resistance good 11. not resistant to: sulfur dioxide, water- very dust sulphide, nitrogen oxides of oxide, nitric acid, sulfuric acid, etc. media

The results thus obtained demonstrate that particular semi-permeable ultrafiltration membranes with a 8201617 * ΐ - 5 pore size in the range of 10-100 nm can be produced by the present process.

The membranes have advantages such as a high tensile strength, as well as pressure resistance with a relatively low electrical resistance. Their stability in a wide pH range makes them well suited for use in the food industry.

The main advantage of the present membranes lies in their ability to store them in a dry state without any change in their parameters. The following examples are illustrative of the invention only and are not limiting.

EXAMPLE I

A 15% dimethylformamide solution of a copolymer of the following composition was prepared: 93% acrylonitrile, 6% methyl methacrylate and 1% sodium salt of vinyl sulfonic acid. As a foaming agent, 0.5% lithium nitrate was added to the solution. The solution was then filtered through a Buchner filter to remove the inclusions therein and after storage for a period of 24 hours, the solution was spread within a frame on a glass plate and formed into a film. The thickness of the film was controlled by strips and was of the order of 1.10 m. The film was stored for a period of approx. 10 min in a room under a normal atmosphere of 70% relative humidity. The solvent was then evaporated and coagulation in distilled water was carried out at a temperature of 25 ° C for 60 min. Water or a mixture of water and dimethylformamide served as coagulation solutions. Then the film was separated from the plate and subjected to a rinsing operation with an excess of distilled water. Then the membrane was attached to a metal frame and was tempered in water at a temperature of 80 ° C for a period of about 10 min. The membrane (together with the frame) was then dried at a temperature of 40 ° C to a relative humidity of 5%. Finally, the dry membrane thus obtained was separated from the frame and formed into the desired size. The membranes thus manufactured have the following parameters: a water permeability of 0.2 m / m h; a selectivity to protein solutions of 99.5%; an average pore size of 2 nm of 40 nm and a tensile strength of 45.10 N / m.

EXAMPLE II

As in Example 1, a polymer solution was prepared using copolymers of the following composition: 82% acrylonitrile, 15% methyl methacrylate, and 3% sodium salt of vinyl sulfonic acid. According to the method described above, membranes were prepared using this solution in dimethylformamide. It was found that a decrease in the percentage of acrylonitrile in the copolymer leads to an increase in the brittleness of the dry membranes, as well as a slight decrease in the membrane permeability. It is therefore preferable to use copolymers with a high percentage of acrylonitrile.

The membranes prepared according to Example I were tested on an ultrafiltration device for gamma globulin and albumin solutions. A comparison between the test results and the polysulfone membranes known in the art as the most effective membranes for concentrating serum proteins is shown in Table B.

TABLE B

degree of PARAMETERS

membrane system - concentration permeability selectivity 25 type regime pressure tration beginning end 2 3 2 3 2 nrN / m% m / mhm / mh% 1. polysulfone albumin 1.5.10 ^ 30 0.029 0.017 above 95 gamma glo- 3,105 1Q 0f020 0.012 above 95 buline 2 1 1 '30 polyacrylic albumin 1.5.10 30 0.035 0.030 99.5 2. nitrile gamma gamma 3.10S 10 0.021 0.019 99.5 buline

The membranes prepared according to Example I were tested for the ultrafiltration of whey. A comparison between the test results and the parameters of other 8201617 Λ - 7 membranes is shown in Table C.

TABLE · C

_PARAMETERS_ permeability 5, whey water membrane on the basis of membrane selectivity m ^ / m ^ h m ^ / m ^ h. mVm ^ h% type 1. acrylonitrile-vinyl pyrrile 030 083 083 96 wet 10 don 2. cellulose. .028 0.002 - 95 wet acetate 3.three-copolymer vol- Q ^ 0l5 0.013 0/120 99.5 dry15 according to the invention

A closer look at the results shows that the currently proposed polyacrylonitrile membranes exhibit better permeability ratios during different stages of solution concentration. The variation of membrane permeability that occurs during the period from the beginning to the end of the process is negligible. In addition, the membranes are easier to recover and have an extended life. In addition, the present membranes still maintain a high selectivity at a sufficiently high concentration rate. The asymmetric structure of the membranes according to the invention is stable and guarantees the above-mentioned results. The need for carriers has been eliminated, so that the method of manufacturing the present membranes is simplified.

The method provides a sufficiently reliable membrane that can be stored in the dry state.

8201617

Claims (1)

- 8 - C ONCLUSION A process for the manufacture of a polyacrylonitrile copolymer based semi-permeable membrane, wherein the copolymer is dissolved in a solvent such as dimethylformamide and a foaming agent is added, followed by forming, tempering and drying the membrane, with the characterized in that the polyacrylonitrile copolymer is a block copolymer of acrylonitrile, methyl methacrylate and vinyl sulfonic acid sodium salt, wherein the ratio of the initial components is 82-93% acrylonitrile, 6-15% methyl methacrylate and 1-3% sodium salt of vinyl sulfonic acid. 15 i 8201617