DE2856136A1 - PROCESS FOR THE MANUFACTURING OF SEMIPERMEABLES MEMBRANES BASED ON ACRYLNITRILE POLYMERISATES AND HETEROGENIC MEMBRANES - Google Patents

Description

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Semipermeable membranes are made on an industrial scale Cellulose acetate is prepared, for example, by the methods described in U.S. Patents 3,133,132 and 3,133,137. Membranes made from this material allow water to pass through, but not sodium chloride. Due to the sensitivity to hydrolysis however, the cellulose acetate decomposes rapidly. this also leads to a deterioration in the membrane performance.

The process known from the aforementioned patents for the production of asymmetrical membranes with a skin structure is complex. Therefore this procedure is limited to a few synthetic macromalecular compounds except for cellulose acetate successfully applicable. The reasons for this lie in the difficulty of choosing the solvent used for the casting solution, the additives, the composition and the temperature of the casting solution, the atmosphere into which the solvent evaporates, and the temperature thereof The atmosphere. Therefore, this method can only be used to a limited extent.

Various attempts have already been made to create semipermeable membranes based on acrylonitrile polymer seeds to manufacture the membranes made of cellulose acetate the chemical, mechanical and thermal properties and the water permeability are superior. Such attempts are described, for example, in JP-OS 6257/1972 and 43 878/1974. These attempts go

3Q there, a skin layer and at the same time a carrier layer to form according to the casting process described above. However, the membranes obtained do not allow a stable one Operation, since setting the appropriate casting conditions is very difficult. When using acrylonitrile polymers In addition, the formation of the skin layer is very difficult to achieve after the casting process. To Up to now, no semipermeable membranes, which are not only low molecular weight, could be produced using this process

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Separate substances such as sodium chloride, but also have superior water permeability.

With regard to the good film-forming properties and the resistance to heat, acid and alkali of acrylonitrile polymers have been extensive research on Manufacture of semi-permeable membranes carried out, which hold back low molecular weight substances. This work resulted to the following surprising findings: when sulfonating a porous membrane based on an acrylonitrile polymer the water permeability of the membrane becomes higher. The sulfonated membrane shows a better ability to separate of salts and low molecular weight substances when used as a semipermeable membrane. The properties of the semipermeable membrane obtained are better than those of a semipermeable membrane made of cellulose acetate or other synthetic polymers.

The invention is therefore based on the object of providing semipermeable membranes based on acrylonitrile polymers

create that are characterized by superior water permeability and selective permeability of other substances. Another object of the invention is to provide a method for producing such membranes. 25th

The invention thus relates to what is set out in the claims featured item.

The acrylonitrile polymers used according to the invention, i.e. homopolymers and copolymers, are prepared according to known methods manufactured. The usual monomers are suitable as comonomers of acrylonitrile, such as nonionic monomers, for example acrylamide, diacetone acrylamide, N-vinyl-2-pyrrolidone, Hydroxyethyl methacrylate, methyl acrylate, ethyl acrylate, Butyl acrylate, methyl methacrylate, ethyl methacrylate and vinyl acetate, ionic monomers such as acrylic acid, ethylene

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sulfonic acid, methacrylic acid, methallylsulfonic acid, sulfopropyl methacrylate, Vinylbenzenesulfonic acid and its metal salts, as well as cationic monomers such as tertiary amines, for example 2-vinylpyridine, 4-vinylpyridine and dimethylaminoethyl methacrylate, and quaternary amine salts obtained by alkylating the tertiary amines. The acrylonitrile copolymers can consist of acrylonitrile and one or more monomers.

The acrylonitrile polymers should be at least 4Ό mol percent Acrylonitrile building blocks included. If the acrylonitrile content falls below 40 mol percent, the membranes have one very poor selective permeability. The content of acrylonitrile building blocks is preferably 70 to 95 mol percent. The molecular weight of the acrylonitrile polymer is not particularly critical; it is preferably from 5,000 to 5,000,000.

The porous membranes used in the process according to the invention made of acrylonitrile polymers are not only porous membranes made of acrylonitrile polymers, which according to various customary methods have been obtained, but also modified porous membranes, which by a treatment have been produced with a plasma. The porous membranes can be manufactured by various methods. The customary casting process, in which a solution of the polymer in a solvent to form a The film is cast, the solvent evaporates and the polymer gels, or in which the film is subsequently applied treated with a plasma.

The porous membranes used according to the method can be used in various forms. Preferably have the membranes take the form of fibers, hollow filaments or tubes, or they are in the form of flat planar structures. They can also be used as laminates together with others

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porous supports are used. The membranes become more suitable as a module in practice and after sulfonation Structure used.

In practice, porous membranes made from acrylonitrile polymers are cast as follows: First, the acrylonitrile polymer is dissolved in a solvent up to a concentration of 5 to 30 percent by weight. The solvent used is an aqueous solution containing an inorganic salt or a polar organic solvent such as dimethylacetamide, dimethylformamide or dimethyl sulfoxide. The polymer solution obtained is applied to a suitable carrier, for example a glass plate, with a doctor blade. The layer thickness of the applied solution depends on the desired thickness of the semipermeable membrane. In general, the layer thickness of the applied polymer solution is adjusted so that a semipermeable membrane with a thickness of about 20 to $ 00 / a is obtained. Immediately after the polymer solution has been applied to the support or after the solvent has evaporated, the coated support is immersed in a solvent that is not a solvent for the polymer.

The solvent is preferably allowed to evaporate over a period of up to 60 minutes. The evaporation is preferably carried out at temperatures from ⁰ ° C. to the boiling point of the solvent used. Then the carrier with the polymer film, from which the solvent has possibly been partially evaporated, is immersed in a nonsolvent. Examples of non-solvents which can be used are water or mixtures of water with an organic solvent. The organic solvents used are water-soluble solvents, preferably the same solvents that were used to prepare the polymer solution

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In the production of the porous membranes have the different which working conditions, for example the polymer concentration, the casting temperature, the evaporation time and the Setting temperature, some influence on the functioning of the finished membrane, but the conditions are not of crucial.

The porous membrane obtained is usable if it has a water permeability of 0.01 to 1000 UiH (l / m · h)

2
a pressure of 10 kg / cm and a bubble point of min-

at least 1 kg / cm in the moist state. The bubble point is the value of the air pressure (kg / cm * ~) at which Air is pressed through the pores of the membrane, which has been thoroughly moistened with water. furthermore, according to the invention modified porous membranes can be used, which by plasma treatment of the above-described porous membranes have been obtained. For example, the plasma treatment according to the JP-OS 26 330/77 procedures described are carried out. The plasma is generated, for example, by glow discharge, high frequency discharge or corona discharge generated. For example, a glow discharge plasma is produced by introducing a gas such as Hydrogen, helium, argon, nitrogen, oxygen, carbon monoxide, carbon dioxide, ammonia or water, in an evacuated Vessel, so that the pressure in the vessel has a value of 0.01 to 10 Torr is generated. Then between Electrodes an alternating current or direct current voltage from 0.5 to 50 kV applied. A plasma can also go through creates a corona discharge in the atmosphere or in an inert gas with direct current of 0.1 to 1.3 A at 1 kV will.

The plasma-treated modified porous membrane is so produced that one from the acrylonitrile polymer Brings produced dried porous membrane in the plasma atmosphere described above. Usually amounts to

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the treatment time 0.5 to 120 minutes, preferably 5 up to 120 minutes.

When a plasma-treated porous membrane is used, a semipermeable membrane with superior properties is obtained according to the invention Release properties and better water permeability obtained, due to a synergistic effect of the Plasma treatment and the sulfonation according to the invention.

Various known compounds can be used as sulfonating agents in the process according to the invention. Sulfur trioxide is particularly preferred because of the ease of the sulfonation reaction. When using sulfur trioxide the sulfonation is carried out as follows:

The porous membrane is placed in an atmosphere of sulfur trioxide or a mixture of sulfur trioxide with another gas. Gases inert to sulfur trioxide, such as air, nitrogen or helium, can be used as the gas. The treatment temperature is usually from 0 to 80 ^° C., but it is not restricted. The sulfonation is carried out under a pressure at which the sulfur trioxide is in the gaseous state. The sulfonation is preferably carried out at normal pressure. The membrane can be sulfonated on one or both sides. Preferably, however, only one side of the membrane is brought into contact with sulfur trioxide, since it becomes somewhat brittle when sulfonated on both sides.

The separation properties of the semipermeable membranes produced according to the invention depend on various factors , in particular the concentration of the sulfonant and the suIfonierungszeit. By changing these two factors, the degree of sulfonation can be adjusted to the Control membrane surface. In this way, membranes with any separation properties can be produced. The concentration of the sulfonating agent can range from 0.01

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-ιοί to 100 mol percent and the sulfonation time of 1 second up to 60 minutes. Preferably, however, these two factors are adjusted so that the sulfur content of the sulfonated membrane is 0.01 to 5 percent by weight. If the sulfur content is below 0.01 percent by weight, the Effect of sulfonation too low, while with a sulfur content above 5 percent by weight, the membrane has unsatisfactory mechanical strength and becomes unusable. As a result of the sulfonation, the porous membrane is able to exchange ions. The appropriate ion exchange capacity of the sulfonated Membrane is 0.001 to 1.2 mlq / g.

The inventive method enables the membranes to impart hydrophilic properties in a simple manner and they are due to the crosslinking through the sulfonation reaction to seal, but at the same time maintain the original shape of the porous membranes. The procedure the invention enables the simple production of semipermeable membranes with any separation properties from low molecular weight substances such as sodium chloride to high polymers with a molecular weight of 1,000,000.

The semipermeable membranes of the invention have a thickness of 20 to 500 / u and they consist of a dense surface layer in which no pores can be observed under the electron microscope. This surface layer has a thickness of at most 1 μ. The rest of the membrane consists of a porous layer. The pores have

ben a size of 100 to 1000 Å, which are arranged in the porous layer close to the surface layer. The size of the pores gradually increases from 1 to 100 / u towards the back of the membrane. The thickness of the cross-linked part of the membrane can be controlled as desired, from a value of about 0.1 μ up to the thickness of the membrane.

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The semipermeable membrane produced according to the invention is the cellulose acetate membranes with regard to the chemical, mechanical and thermal properties and the ability to separate substances in reverse osmosis far superior. They can be used in a pH range from 1 to 12 and up to temperatures of about 50 ° C. The membranes are particularly suitable for desalination of seawater, for wastewater treatment and for concentration of fruit juices. Since the membranes are in numerous organisehen Solvents are insoluble, they can also be used to separate non-aqueous liquids.

The examples illustrate the invention. The separation effect is defined by the following equation:

Concentration of the dissolved separating effect 00 = (1- in the solution that has passed through ) _{χ Λ00}

Concentration of the solute in the feed solution

example 1

A copolymer of 89 mole percent acrylonitrile and 11 mole percent Methyl acrylate is produced in a manner known per se. 20 parts of the copolymer are in a mixture of 70 parts of dimethylformamide and 10 parts of formamide solved. The solution obtained is in a thickness of 250 / u.

at 40 ⁰ C poured onto a glass plate. After immediate evaporation, the glass plate is ^{immersed in 16 to 17 0} C cold water. In this case, the polymer solution gels. After 2 hours, the membrane obtained is detached from the glass plate and, in this state, examined for its permeability to water at a pressure of 10 kg / cm ² . The water permeability (water permeability) is 148 LMH (l / m ² .h), and the bubble point is 12 kg / cm ² .

The moist membrane is dried for 24 hours at room temperature. Then the membrane is 20 minutes at Eaumtem-. temperature sulfonated on one side. For this purpose, the

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dry membrane with a gas mixture of 3 volume percent sulfur trioxide and 97 volume percent nitrogen at atmospheric pressure treated. After the sulfonation, a part of the membrane is subjected to elemental analysis to determine the Determine the sulfur content. The sulfur content is 0.60 percent by weight. The ion exchange capacity of the sulfonated Membrane is 0.1 mlq / g. This is evidenced by the introduction of sulfonate groups into the membrane.

The electron microscope! See examination of the membrane reveals Their asymmetrical structure from a dense layer in which there are no pores is like a layer with pores

from 300 A to 20 / α extending to the dense layer.
15th

When the semipermeable membrane is dissolved in dimethylformamide, an insoluble thin film with a thickness of 20 / u remains. It was found that this thin film is crosslinked.
20th

The sulfonated membrane according to the invention is then reversed in a continuously operating device Osmosis used. The effective area of the membrane

2
is 13 cm. The device is a device for laboratory experiments. Their permeability to 0.50 weight percent aqueous sodium chloride solution is investigated.

Test conditions:
Pressure 50 kg / cm

Temperature of the aqueous
Saline solution 25 ° C

Loading speed

the aqueous saline solution 630 ml / min

Test results:

Water permeability 41.3 EMH

Separation effect (separation
of the salt)

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The untreated dry membrane is examined in the same way. In this case the water permeability is 6.2 LMH. The membrane was unable to separate sodium chloride.
5

Example 2

The sulfonated membrane according to Example 1 produced is examined for their thermal stability in the same manner as in Example 1 except that the temperature of the brine at 40 to 50 ⁰ C is set. The following results are obtained:

Temperature of the cook
saline solution Water permeability Separation effect 40 ° C
50 ⁰ C 49.7 LMH
54.0 LMH 94.2%
93.0%

Example 3

A copolymer of 90 mol percent acrylonitrile and 10 mol percent vinyl acetate is produced in a manner known per se. 16 parts of the copolymer are in one Ge. a mixture of 74 parts of dimethylformamide and 10 parts of formamide dissolved. The resulting solution x * ith a thickness of 250yu at 40 ⁰ C cast onto a glass plate. After Iminütigem evaporation, the glass plate is immersed in 16 to 17 ⁰ C cold water. In this case, the polymer solution gels. After 2 hours, the membrane obtained is detached from the glass plate and, in this state, examined for its water permeability at a pressure of 10 kg / cm. The water permeability is 170 LMH and the bubble point is 4 kg / cm.

The moist membrane is then dried at room temperature for 24 hours. The dry membrane is for 5 minutes Room temperature with a gas mixture of 2 mol percent sulfur trioxide and 98 mole percent nitrogen at normal pressure

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treated. After the treatment, the membrane is placed in a continuously operating reverse osmosis device. The effective area of the membrane is 13 cm ^2. The device is a device for laboratory experiments. It is their permeability and separation efficiency tested against various compounds.

Test conditions:

-. ■,.

pressure 2 kg / cm Temperature of the solution 25 ° G Concentration of the Ge solved in the charge £ solution · Loading speed 630 ml / min speed Test results:

Dissolved matter Molecular tfasserper- Separation effect, weight meability,
LMH % Sodium chloride 58 28.3 5.1 Sucrose 342 23.0 28.4 Amaranth 604 24.5 41.5 Polyethylene glycol 2000 18.9 88.7 Polyethylene glycol 20000 12.4 100

In the same way, the untreated dry membrane examined. The water permeability is 7.3 LMH and the membrane was unable to separate the solutes.

example

The dry membrane obtained in Example 1 is placed in an evacuable device in which a pair of electrodes is arranged is treated with a plasma under the following conditions:

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- / 5- gas helium 2 torr $ 4 - pressure O, 0 kV Discharge voltage 3, mA Discharge current 25th Minutes Handily indefinitely 40

Part of the plasma-treated membrane is then placed in a gas mixture of 3 percent by volume sulfur trioxide and 97 percent by volume Nitrogen sulfonated at room temperature "and atmospheric pressure. A portion of the membrane obtained is used for determination of the sulfur content of the elemental analysis. The sulphonated membrane contains 0.57 percent by weight sulfur. The ion exchange capacity of this membrane is

0.16 mlq / g.
15th

Then the plasma-treated membrane and after the Plasma treatment of sulfonated membrane for its water permeability according to the example. 1 examined. The following results are obtained: Plasma-treated membrane: water permeability 14.2 LMH, separation efficiency 97.6%; sulfonated membrane after plasma treatment: water permeability 31.5 EMHj separating effect 98.9%.

It can be seen that both the water permeability and the separation effect by sulfonation of the plasma-treated Membrane is significantly improved.

Example 5 A copolymer of 90 mol percent acrylonitrile and 10 mol percent vinyl acetate is produced in a manner known per se. 21 parts of the copolymer are dissolved in a mixture of 69 parts of dimethylformamide and 10 parts of formamide. The solution obtained is poured onto a glass plate at a thickness of 250 μ at 40 ^{° C.} After evaporation for one minute, the glass plate is immersed in cold water at 16 to 17 ° C. In this case, the polymer solution gels.

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After 2 hours, the membrane obtained is removed from the glass plate detached and in this state on their water permeability

2
examined at a pressure of 10 kg / cm. The water permeability is 104 LMH and the bubble point is 16 kg / cm. The moist membrane is then dried at room temperature for 24 hours. The dry membrane is then plasma-treated according to Example 4 under the following conditions:

Gas helium

Pressure 0.1 torr

Discharge voltage 3 »0 kV

Discharge current 3 ° mA

Treatment duration 4-0 minutes

Then the plasma-treated membrane is a salvation in one

Gas mixture of 5 percent by volume sulfur trioxide and 95 percent by volume Nitrogen sulfonated at room temperature and atmospheric pressure.

The plasma-treated membrane and that after the plasma treatment-20

Treatment sulfonated membranes are examined for ■ the water permeability according to Example 1. The following results are obtained:
Plasma treated membrane:

Water permeability 12.3 LMH

Separation efficiency 98.2%

Awake of the plasma treatment sulfonated membrane:

water permeability 28.6 LMH

Separation efficiency 99.22%.

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Claims (16)

VOSSIUS · VOSSIUS · HILTL · TAUCHinF.R ■ HEUNEMANN PATENTANVJÄUTE. SIEBERTSTRASSE A · 8OOO MÜNCHEN 86 · PHONE: (O89) 47 4O75 CABLE: BENZOLPATENT MUNICH -TELEX 5-29 453 VOPAT D 2856138 oc: M 965 (WH) Case: A 3481-04 SUMITOMO CHEMICAL COMPANY, LIMITED Osaka, Japan "procedure for the production of semipermeable membranes based on acrylonitrile polymers and heterogeneous membranes "priority: December 28, 1977, Japan, No. 159 377/77 January 21, 1978, Japan, No. 5 419/78 Pat ent claims 1. Process for the production of semipermeable membranes based on acrylonitrile polymers, thereby characterized in that one has a porous membrane made of an acrylonitrile polymer with at least 40 mole percent of the basic acrylonitrile building blocks are sulfonated. 2. The method according to claim 1, characterized in that a porous membrane with a bubble point of min- 2
at least 1 kg / cm and a water permeability of 0.01 up to 1000 LMH at a pressure of 10 kg / cm. 30th 3. The method according to claim 1, characterized in that as a porous membrane one on the surface with one Plasma treated porous membrane with a bubble point of at least 1 kg / cm and a V / water permeability 2 from 0.01 to 1000 LMH at a pressure of 10 kg / cm begins. L 909828/0756 οκι «, μ _λ ,,. -J ORIGINAL INSPECTED 4. The method according to claim 3, characterized in that one by glow discharge at a voltage of 0.5 plasma-treated porous membrane generated up to 50 kV under a pressure of 0.01 to 10 Torr. 5 5 · Procedure according to. Claim 1, characterized in that a porous membrane made of a polyacrylonitrile or a copolymer of acrylonitrile with acrylamide, diac et onacrylamid, IT-vinyl-2-pyrrolidone, hydroxyethyl methacrylate, Methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, vinyl acetate, acrylic acid, Ethylene sulfonic acid, methacrylic acid, methallylsulfonic acid, Sulfppropyl methacrylate, vinylbenzenesulfonic acid or their metal salts, 2-vinylpyridine, 4-vinylpyridine, Dimethylamineethyl methacrylate or a quaternary amine salt obtained by alkylation of the tertiary amines. 6. The method according to claim 1, characterized in that a porous membrane made of an acrylonitrile polymer with 70 "to 95 mol percent acrylonitrile basic building blocks begins. 7. The method according to claim 1, characterized in that the sulfonation is carried out with sulfur trioxide. 8. The method according to claim 7? characterized in that one sulfur trioxide as a gas or as a mixture with a inert gas is used. 9 · The method according to claim 8, characterized in that the inert gas used is air, nitrogen or helium. 10. The method according to claim 8, characterized in that sulfur trioxide is used in a concentration of 0.01 used up to 100 percent by volume. 9G9R28 / 07 5 11. The method according to claim 7, characterized in that the sulfonation for 1 second to 60 minutes performs. 12. The method according to claim 1, characterized in that only one surface of the porous membrane is sulfonated . 13. Heterogeneous membrane, consisting of a membrane based on an acrylonitrile polymer with a dense Surface layer with a thickness of 1 micron or less and with pores that are in their size against the back of the membrane gradually increase, and which is crosslinked to a thickness of at least 0.1 / u from the surface. 15th 14. Membrane according to claim I3, characterized in that the acrylonitrile polymer polyacrylonitrile or a copolymer of acrylonitrile and acrylamide, diacetone acrylamide, N-vinyl-2-pyrrolidone, hydroxyethyl methacrylate, Methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, Ethyl methacrylate, vinyl acetate, acrylic acid, ethylene sulfonic acid, methacrylic acid, methallylsulfonic acid, Sulfopropyl methacrylate, vinylbenzenesulfonic acid and their Metal salts, 2-vinylpyridine, 4-vinylpyridine, methylaminoethyl methacrylate or a quaternary amine salt obtained by alkylating the tertiary amines. 15 · Membrane according to claim 13, characterized by a thickness of 20 to 5 μ and pores with a size of 100 to 1000 Å in the layer close to the dense layer, the size of the pores towards the back of the membrane gradually from 1 to 100 / u. increases. 16. Use of the membrane according to claim I3 for separation and concentration of substances by reverse osmosis or ultrafiltration. 9 € 9828/075 6