DE2263774A1 - ANISOTROPIC POLYMERIC MEMBRANES AND METHODS FOR THEIR MANUFACTURING DETERMINED FOR REVERSE OSMOSIS - Google Patents

Description

PATENT LAWYERS

DR.-ING. BY KREtSLER DR.-IN <?. SCHÜNV / ALD DR.-ING. TH. MEYER OR. FUES DIPL.-CHEM. ALEK VON KREISLER DIPL-CHEM. CAROLA KELLER DR.-ING. KLOPSCH DIPL-ING. SELTING

COLOGNE 1, DEICHMANNHAUS

Cologne, December 27, 1972 Ke / Ax

MONTECATINI EDISON SPA ,? ? R? 7 7 A

31. Forο Buonaparte, Milan (Italy).

Reverse osmosis certain anisotropic polymeric membranes and processes for their manufacture

The invention relates to anisotropic polymeric membranes with very good mechanical properties intended for reverse osmosis and electrical properties and a method for their production.

Membranes with selective permeability have long been known. Likewise, the principle of the reverse has long been Osmosis is known, according to which it occurs when pumping a solution of one or more substances contained in a joint Solvents are dissolved against a permselective membrane, i.e. a membrane that contains the solvent, but not allows the dissolved substance to pass under a pressure above the osmotic pressure of the solution, becomes possible, to separate the components of the solution.

For many years the principle of reverse osmosis has been applied on a large scale to the desalination of brackish water and sea water applied. For this purpose it is necessary to use membranes that allow the water to pass through, but the reject salts dissolved therein. In general, membranes made of cellulose acetate are used for this purpose strong flow of water (solvent) and a

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Allow little passage of the salt (solute).

The cellulose acetate membranes of the "anisotropic" type (also referred to as "deposited membranes") consist of one dense and homogeneous surface layer with a thickness of 0.1 "to 0.2 u and a porous base that supports the thin Layer wears. The high permeability of cellulose acetate membranes for water is due to the thin surface layer, which is responsible for the desalination capacity of the membrane. The term "anisotropic" means that the homogeneous thin layer is only present on one of the two sides of the membrane.

Cellulose acetate anisotropic membranes are most commonly used for reverse osmosis processes, however they have certain disadvantages that considerably limit their possible uses. The main disadvantages of these membranes are due to the following causes:

1) Saponification (deacetylation) of the acetyl groups and consequently a change in the chemical structure the membrane and increasing its permeability to salts.

2) Compression of the porous structure of the membrane due to the pressure generated during the reverse osmosis process is exerted, and consequently a reduction in the amount of water that can pass through the membrane.

3) Bacteriological degradation of the cellulose acetate and consequently a breakdown of the chemical and physical structure of the membrane.

For all of these reasons, the reverse osmosis membranes described above have been developed numerous and in-depth studies, especially in recent years. These investigations and Research is detailed in numerous reports from the "Office of Saline Water" of the US Department of the Interior described.

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Of the numerous materials examined, proved to be the polyamides as particularly interesting and promising. However, it has been found that the linear aliphatic Polyamides have too little water permeability compared to cellulose acetate. From the report Kr.150 the "Office of Saline Water" shows that polyamides, whose amide hydrogen is substituted, have good water permeability, but insufficient mechanical properties Have strength for processing into membranes. On the other hand, polyamides that do not have any substituents on the Contain amide hydrogen atoms, high mechanical strength, but such a low permeability to water, "That they are useless in practice. It is also known that those for the production of membranes polymeric materials to be used have a certain structural rigidity and strength in the polymer chain must have so that membranes can be made with good resistance to compression.

Besides the polyamides, other polymeric materials have also been used for the manufacture of membranes for the reverse Osmosis tested. In all of these investigations and researches, at least to date, there have been no practical results achieved.

In the Italian patents 868 524 and 868 525 of the applicant are dense and homogeneous membranes for the reverse osmosis based on polyamides derived from piperazine is described. These membranes have a greater water permeability than the same membranes based on cellulose acetate. Furthermore, these membranes show good mechanical properties based on a certain structural rigidity and strength based on the presence of the piperazine ring is due. The polypiperazinamides described in these patents can, but not to, gel-type membranes anisotropic membranes are processed. These membranes

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however, do not have satisfactory properties overall.

The invention relates to the reverse osmosis be certain anisotropic (deposited) membranes of the gel type, the are based on polypiperazine amides and do not have the disadvantages mentioned above. The invention also includes a method of making these membranes.

The objects set by the invention are achieved with the aid of anisotropic reverse osmosis membranes based on polypiperazine amides according to the invention a structure of the formula

have in the

1) η is an integer so high that the molecular weight is suitable for the formation of membranes,

2) P for a divalent organic residue of the structure

-CO - N ^^ -CO-

VJ / (II)

* x

j stands, in which -N V - the piperazine ring, χ a whole Number between 1 and 8 and R is a substituent group, e.g. an alkyl radical, in particular a methyl radical or ethyl radical, the substituent groups R if they are present in the piperazine ring in a larger number ala 1, in any steric position to the Can stand ring, so that the formula (II) includes the pure stereoisomers (cis-trans) and their mixtures, and particularly advantageous results are obtained when R is lower alkyl, e.g. Is methyl or ethyl and χ is 1 or 2, and

3) K is a divalent organic residue of the structure

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- 5 - ". I" (XXX)

where Y is 0 or S.

A preferred group of polypiperazine amides of the formula defined above to be used according to the invention £ ~ Ρ - kJ7 form poly-2-methylpiperazinthiofurazanamide, Poly-trans- ^ jS-dimethylpiperazine thiofurazanamide, poly-2-methylpiperazine furazanamide and poly-trans-2,5-dimethylpiperazine furazanamide.

These polyamides can be prepared according to the procedures outlined in

German patent specification (patent application

P 21 36 931.) by the applicant will. They can be used alone or in suitable mixtures with one another or with other polyamides or materials of another type are used.

The presence of the divalent organic radical of structure (III) confers on the membranes according to the invention excellent resistance to compaction and generally good chemical resistance to both oxidizing agents as well as other chemicals that may be present in the water to be treated are, as well as high thermal stability. The membranes according to the invention have an anisotropic structure, which by a dense and homogeneous layer, which to a large extent enables the repulsion of salts, and by an as Supporting effective substructure, which enables the achievement of a very good flow of water.

The membranes of the type described above can according to the invention produced by a process which is characterized in that

1) prepares a solution of the polypiperazinamides in a suitable organic solvent,

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2) applying the solution to a flat glass plate,

3) the solvent partially evaporates and thereby forms the membrane,

4) the membrane is agglomerated to form the gel structure by immersing the membrane in water and

5) preferably subjecting the membrane to a final, but not absolutely necessary, heat treatment.

I. stage

The concentration of the polyamide in the solution can be within a wide range and is generally from 5 to 60 percent by weight of the solution. To prepare the solution, polar, water-soluble organic solvents are used for the polyamide that belong to class m of solvents that form hydrogen bonds (m = hydrogen bond groups) and have a solubility parameter oT of more than 8 (cal / cm) 'according to the classification of H. .Burrell in "Polymer Handbook" IV, 341 (J.Brandrup, ENImmergut Editor-Interscience New York) and in which the polymer used is soluble to at least 5% of its weight. Examples of such solvents include: dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone and tetramethyl sulfone. Preferred solvents are N-methylpyrrolidone and dimethylacetamide.

A salt soluble in water and in the organic solvent is preferably present as the third component of the solution. The following salts, for example, are suitable: IiCl, LiNO ₅ , LiBr, CaCl ₂ , ZnCl ₂ , MgCl ₂ and MgClO ₄ .

In addition to the salt component, water can sometimes be present as the fourth component of the solution. In general, can the salt is also present in the solution in large quantities.

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The solution can be prepared in various ways, for example using a mechanical mixer, followed by it is preferably filtered through a porous membrane or a filtration membrane or through other filter systems will. Generally the solution is at room temperature manufactured. In certain cases, at least initially, the polyamide is dissolved by heating in a closed Vessel accelerates.

2nd stage

The solution obtained in the first stage is applied to a flat glass plate with a pilm knife. The application is generally carried out at room temperature. The thickness of the film formed varies widely and is generally between 0.02 and 2 mm. In this way it is possible to keep the membranes in their final form to get flat shape. In addition to glass, any other suitable material, e.g. sheet metal, Polyethylene terephthalate sheets, porous supports and other similar materials in flat form, tubular form or can be used in other forms.

3rd stage

The solution poured onto the flat glass plate is heated to partially evaporate the solvent. The duration and the temperature of partial evaporation of the solvent can be in a wide range on the type of solvent used, on the composition the solution and the thickness of the membrane to be produced.

In general, the solvent at a temperature between 70 ° and 200 ⁰ C, preferably evaporates between 80 ° and 180 C partly. The evaporation time is generally 1 minute to 5 hours, preferably 3 to 30 minutes. By suitably varying the duration and the temperature of the evaporation, it is possible to produce membranes which, in their final form, have the desired shape

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Have properties related to the flow and repellency of the salt.

4th stage

After partial evaporation of the solvent, the membrane is coagulated to form a gel structure by immersion in water. The temperature of the coagulation bath is generally between 0 and 30 ° C., preferably between 0 and 5 ^° C. In certain cases it is advantageous to use an aqueous salt solution as the coagulation bath. In general, NaCl, MgSO, CaCl ₂ and other similar substances can be dissolved in the coagulation water as salts. The concentration of the salts can be within a wide range, but is preferably from 0 to 20% by weight. Organic substances such as methanol, ethanol, isopropyl alcohol and their mixtures with water and other similar liquids can be used as the coagulating bath.

The coagulation time can be within a wide range. In general, the membranes are 60 minutes at a Maintained temperature of 0 ° to 5 ° C in the coagulation bath and then stored in water at room temperature.

5th stage

The coagulated membranes are generally ready to use and do not require any further treatment. In certain cases, however, it may be appropriate to subject the membranes to a further treatment with hot water for a time between 1 minute and 5 hours. The temperature of the water can be between 60 ° and 100 ⁰ C.

The method according to the invention is mainly directed to the production of flat membranes, but the membranes based on polypiperazine amides of the type described above, also in tubular form and in the form of hollow fibers by the methods known for this purpose.

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_ 9 -

According to the method according to the invention, "anisotropic ¹ 'membranes are produced which are characterized by a dense and homogeneous surface, which is able to repel the salts during the reverse osmosis process, and by a supporting or base layer that allows very good water passage, distinguish.

The "anisotropic" structure of these membranes can be due to two tests using the reverse osmosis membranes are detected. When harvesting Test, the membrane is clamped in a cell for reverse osmosis so that its dense, homogeneous surface facing the saline solution to be treated. The membrane has a very strong water penetration and points the salt largely off.

In the second test, a membrane of the same type is clamped in a reverse osmosis cell so that its porous surface faces the salt solution to be treated. That way, the membrane has another one strong water penetration, but practically does not repel any Sal2. The membranes according to the invention thus have a high flow of water and repel the salt to a great extent. The permeability to water can be like can be defined as follows:

Water flow «passed water (1)

(l / m * day) membrane surface (m ^) time (days)

It can also be defined as membrane constant A as follows:

Membrane constant A = water flow / actual pressure used (l / ^ day atm.) (1 / m ^ day) (atm.)

Here, the pressure actually applied is to be understood as the difference ΔP - A'TT, where ΔΡ is the difference between the hydraulic pressures prevailing on the two sides of the membrane and AIf is the difference

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between the osmotic pressure of the supplied solution and the osmotic pressure of the solution that has passed through the membrane.

The membranes according to the invention generally have one

Membrane constant of at least 4.2 l / m day atm. (At 80 atm. with a supply of 10000 ppm NaCl this corresponds to one

Flow of about 300 l / m day), preferably of more than

8.3 l / m day atm. (this corresponds to 80 atm. with an influx

drove 10000 ppm NaCl a flow of about 600 l / m day),

The osmotic pressure (in atm.) For an NaCl solution can be calculated approximately with the help of the equation TT = 8.2.C ₁ , in which C- corresponds to the salt concentration of the solution in wt .- # .

The salt repellency of the membranes according to the invention is never less than 20 # in the case of sodium chloride, but generally more than 90 #, and in certain cases is even close to $ 100. For magnesium sulphate it is never less than 60%, generally more than £ 98 and in certain cases even close

As is well known, the higher its membrane constant and its impermeability to salt, the more effective a membrane is. The membranes according to the invention make it possible, starting from brackish water or seawater, to obtain desalinated water (with a salt content of less than 500 ppm) with water flow in a single pass, which makes this application extremely advantageous. For example, it is possible to desalinate sea water with a flow of more than 300 l / m day and brackish water with a flow of more than 600 1 / md day.

It can also be more useful for certain preparations, Use membranes with very high flow rates, but with moderate salt repellency. For example, membranes can

with a constant A between 50 and 90 l / m day atm. have a salt rejection for NaCl between 90 and 50 #.

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The membranes according to the invention have a gel structure with a water content of 40 "to $ 80. They are particularly suitable for the desalination of water, but are also advantageous for all known separation and concentration processes that work on the principle of reverse osmosis, e.g. for water purification, the extraction of dissolved organic substances, the treatment of food solutions, e.g. milk, coffee, tea, citrus juices, whey, tomato juice and sugar solutions, for the separation of azeotropic mixtures, the separation and concentration of biological and pharmaceutical products such as hormones , Proteins, vitamins, antibiotics, vaccines, amino acids and the like.

example 1

A. Production of a membrane from poly (fcrans-2,5-dimethylpiperazanthiofurazanamide) with the repeating unit of the formula

CO -

- CO -

C (IV)

In 90 g of a solution of 3.5 g of LiCl and 86.5 g of N-methylpyrrolidone (Carlo Erba RP), 10 g of the polymer (with the recurring units IV), which had an intrinsic viscosity of 2.78 dl / g, were determined at 3O ⁰ C in a solution of 0.5 g of the polymer dissolved in 99.5 g of 98 # sulfuric acid (Carlo Erba RS)). The solution was kept in a heating cabinet at 80 ^° C. for 30 minutes and then treated in a Werner-Pfleiderer mixer for 1 hour. It was then filtered through a porous diaphragm under nitrogen pressure and finally left to degas for about 8 hours. The degassed solution was then applied to a glass plate to a thickness of 2 mm at room temperature, a film having a thickness of 0.3 ram being formed. The glass plate was then placed on an elec-

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triachen hot plate heated to 120 ⁰ C for 10 minutes. The evaporated solvent was removed from the surface of the film with a gentle stream of nitrogen *. The glass plate was then cooled to room temperature within 90 seconds and immersed in a vessel containing water and ice. After an immersion time of about 10 minutes, the membrane could easily be removed from the glass plate. It was kept in water and ice for an additional 30 minutes and then kept in water at room temperature.

This membrane showed a positive and a negative side. The positive side is the side that is during the production of the membrane of the glass plate is turned away. The negative side is to be understood during the Making the membrane is in contact with the glass plate.

B. Using the membrane for reverse osmosis

The membrane prepared in the manner described above was placed in a standard reverse osmosis cell, through which an aqueous solution containing 10,000 ppm of sodium chloride was passed. The membrane was inserted into the cell in such a way that the side facing away from the glass plate during manufacture of the membrane (positive side) facing the solution to be desalinated. The saline solution was then pressurized to 80 atm. brought. The water which had passed through the membrane contained 40 ppm NaCl. The flow rate of the water was 1200 l / m day. The membrane had a constant A of 16.6 l / m day atm.

Example 2

A. Production of a membrane based on poly (trans -2,5-dimethylpiperazine-thiofurazanamide)

10 g of polymer which contained the repeating units (IV) and had an intrinsic viscosity of 40 were at room temperature in 90 g of a solution of 85.5 g of N-methylpyrrolidone and 4.5 g of LiCl suspended. The suspension was

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heated with stirring to 16O ⁰ C, the polymer is dissolved quickly. The transparent and clear solution at 95 ⁰ C was filtered through a PiIter, which had a pore size of 5 m. The filtered solution was degassed and applied to a glass plate in a thickness of 2 mm at room temperature, leaving a film with a thickness of 0.45. mm was formed. The glass plate was then kept ^{at 120 °} C. in an electric heater for 10 minutes. It was then cooled to room temperature within 90 seconds and immersed in a vessel containing water and ice. After about 10 minutes, the membrane could be easily peeled off the glass plate. It was kept in water and ice for an additional 50 minutes and then kept in water at room temperature.

B. Using the membrane for reverse osmosis (positive

The membrane prepared in the manner described above was placed in a standard cell for the reverse Osmosis was used, through which a solution containing 1000O ppm NaCl was passed. She was so in the cell inserted that side that the glass plate during the Production of the membrane was turned away (positive side), the solution to be desalinated was facing. The saline solution was to a pressure of 80 atm. brought. The water which had passed through the membrane contained 355 ppm NaCl. Of the The water flow rate was 1235 l / m day. The membrane constant was 17 * 0 l / m day atmosphere.

C. Using the membrane for reverse osmosis (negative side)

The membrane was inserted into the cell with the negative side facing the solution to be desalted. Under The following results were obtained under the conditions mentioned in Example 2B:

Water flow 1450 l / dm ²
Salinity (NaCl) 900 ppm

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These results, especially the same water flow with a very different salt repellency compared to Example 2B make the anisotropic structure of the deposited Membranes according to the invention are particularly clear.

Example 3

In the manner described in Example 2A, a solution was prepared which contained 13.5 g of poly (trans-2,5-dimethylpiperazine biofurazanamide) (IV) with an intrinsic viscosity of 2.8, 82.15 g of N-methylpyrrolidone and 4, Contained 35 g LiCl. The solution was filtered and degassed in the manner described in Example 2A and applied to a glass plate in a thickness of 2 mm at room temperature, a film having a thickness of 0.45 mm being formed. The glass plate was then ^{heated to 100 °} C. for 15 minutes, cooled to room temperature within 90 seconds and immersed in a bath of water and ice.

After 10 minutes, the membrane could easily be peeled off the glass plate. It was kept in water and ice for an additional 50 minutes and then stored in water at room temperature. The membrane was tested in a standard reverse osmosis cell in the manner described in Example 1B. The water that has passed through the membrane

ο contained 120 ppm NaCl. The water flow rate was 580 l / m

ρ per day and the membrane constant 8.0 l / m day Atm.

Example 4

A membrane prepared according to Example 3 was placed in a standard reverse osmosis cell in the manner described in Example 1B. The cell was exposed to an aqueous solution containing 35,000 parts per million of NaCl (synthetic sea water) under a pressure of 110 atm. fed. The water which had passed through the membrane contained 455 ppm NaCl. The water flow rate was 545 l / m per day.

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Example 5

10 g of poly (trans-2,5-dimethylpiperazinthiofurazanamide) (IV) with an intrinsic viscosity of 2.7 were suspended in a solution consisting of 85.5 g of N-methylpyrrolidone and 4.5 g of LiCl. The suspension was ^{heated to 80 °} C. with stirring, the polymer rapidly dissolving. The solution was passed through a filter having a pore size of 20 w at room temperature. The filtered solution was degassed and applied in a thickness of 2 mm to a glass plate at room temperature, a film with a thickness of 0.3 now being formed. The glass plate was kept at 120 ° C. in an electric heater for 5 minutes. It was cooled to room temperature within 90 seconds and immersed in a bath of water and ice. After about 10 minutes, the membrane could be stripped from the glass plate. It was kept in water and ice for an additional 50 minutes and then kept in water at room temperature.

The experiment described in Example 1B was carried out with the membrane using an aqueous solution containing 50000 ppm NaCl under a pressure of 50 atm. carried out. The following results were obtained: water flow rate 4500 l / m day; Salt repellency about 50 %; Membrane constant 88 l / m day atm.

Example 6

10 g of poly (trans-2,5-dimethylpiperazinthiofurazanamide) (IV) with an intrinsic viscosity of 3.78 were suspended at room temperature in 90 g of a solution of 85.5 g of N-methylpyrrolidone and 4.5 g of LiNO. The suspension was ^{heated to 160 °} C. with stirring, the polymer rapidly dissolving. The transparent and clear solution was passed ^{through a filter at 85 °} C. which had a pore size of.

The filtered solution was degassed and applied to a glass plate in a thickness of 2 mm, with a film a thickness of 0.45 mm. The glass plate

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was then boi for 10 minutes in an electric heater Maintained 120 C, cooled to room temperature within 90 seconds and immersed in a bath of water and ice. After 10 minutes, the membrane could be easily peeled off the glass plate. She was in water for another 50 minutes and ice and then stored in water at room temperature.

In the experiment described in Example 1B, the following results were obtained with the membrane: water flow rate 800 l / m ² day

Salt repellency =

10,000 - 800 10,000

χ 100 =

(NaCl).

Example 7

15 g of poly (trans-2,5-dimethylpiperazine furazanamide), the the recurring unit

CH,

CO-Ii trans Ti - CO -

(V)

and had an intrinsic viscosity of 2.1 (determined in the manner described in Example 1) were dissolved in 85 g of a solution consisting of 3.4 g of LiCl and 81.6 g of dimethylacetamide. The solution was kept for 30 minutes in an oven at 8O ⁰ C, then treated for one hour in a Werner-Pfleiderer mixer, and then filtered under nitrogen pressure through a porous diaphragm, and finally degassed for about 24 hours. The degassed solution was applied to a glass plate in a thickness of 2 mm at room temperature, whereby a film with a thickness of 0.6 mm was formed. The glass plate was kept in an electric heater at 123 ° C for 12 minutes. The evaporated solvent was removed with a gentle stream of nitrogen.

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The glass plate was then opened within about 90 seconds Cooled to room temperature and put in water and ice existing bath submerged. After about 10 minutes in the bath, the membrane could easily be stripped from the glass plate, It was kept in water and ice for an additional 50 minutes and then stored in water at room temperature.

Like the membrane described in Example 1A, this membrane had a positive and a negative side. she was placed in a standard reverse osmosis cell in the manner described in Example 1B. Of the An aqueous solution containing 35,000 ppm NaCl (synthetic seawater) was fed to the cell. The saline solution was under a pressure of 110 atm. brought.

The water which had passed through the membrane contained 420 ppm NaCl. The water flow rate was 58O l / m day. The membrane constant A was 7.1 l / m day atm.

Example 8

10 g of the polyamide (V) described in Example 7, which, however, had an intrinsic viscosity of 3.27, were suspended in 90 g of a solution which consisted of 85.5 g of dimethylacetamide and 4.5 g of LiCl. The suspension was heated to 80 ° C. with stirring, the polymer rapidly dissolving. The transparent and clear solution was filtered through a filter having a pore size of 20 µ. The filtered solution was degassed and applied in a layer thickness of 2 mm to a glass plate, a film with a thickness of 0.45 mm being formed. The glass plate was then kept ^{at 100 °} C. in an electric heater for 15 minutes. It was cooled to room temperature within 90 seconds and immersed in a bath made of water and ice.

In the manner described in Example 7, a membrane was made obtained in a standard reverse osmosis cell. The cell became an aqueous one

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Solution containing 5000 ppm NaCl under a pressure of 80 atm. fed. The following results were obtained: water flow 1200 l / m ² day

Salt repellency = _{x 100 = 91} % (NaCl)

Membrane constant 16.1 l / m day atm.

Example 9

In 90 g of a solution consisting of 3.5 g LiCl and 86.5 g dimethyl acetamide, 10 g of poly-2-methylpipera zinthiofurazanamid were dissolved, which is the repeating unit

-N N-CO- C

\ / Il

I 'N N

(VI)

contained and an intrinsic viscosity of 2.2 was ( "determined in the manner described in Example 1). The solution was treated in the manner described in Example 1, and at room temperature in a layer thickness of 2 mm on a glass plate coated to form a film of a thickness was formed of 0.6 mm. The glass plate was held in a heater 10 minutes at 120 ⁰ C. The evaporated solvent was removed with a gentle stream of nitrogen. The glass plate was then cooled within 90 seconds to room temperature, ^un $ _ei JT ⁿ _r . like the in maintained and ice existing bath, and then stored in water at Raucztemperatur: £ _r V ⁿ dipped ^of water and ice existing Bad Die / this was easily from the glass plate strip It was a further 50 minutes in the water.. The membrane described in Example 1A, this membrane also had a positive and a negative side.

The membrane was placed in a standard reverse osmosis cell. The cell was given an aqueous solution containing 10,000 parts per million of sodium chloride

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under a pressure of 80 atm. fed. The water which had passed through the membrane contained 280 ppm NaCl. The water flow rate was 990 l / m day. The membrane constant A was 15.7 l / m ² day atm.

Example 10

A membrane produced according to Example 2A was for a long time (up to 80 hours) in a standard cell for the reverse osmosis tested and with a membrane made of cellulose acetate (Commercial product of Eastman Kodak) compared. Both membranes rested in the cell on a porous steel base with a porosity of 0.5 Ji.

The cell was exposed to an aqueous solution containing 10,000 ppm NaCl under a pressure of 80 atm. fed. In Pig. A and Pig. B. The water flow and the salt rejection ("NaCl) are plotted as a function of time. Curve 1 represents the results obtained with the membrane according to the invention and curve 2 the results obtained with the cellulose acetate membrane. The curves show that the change of these two characteristics is very similar during the test period (80 hours) and in particular the water flow decreases as the test period progresses and the salt rejection (NaCl) increases sharply at the beginning and is constant thereafter Part and in the last part of the experiment is practically the same, the water flow in the membrane according to the invention is always greater (by about 30 %).

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Claims (1)

2 26 37 7 / * - 20 claims 1.) For reverse osmosis certain anisotropic polymeric membranes based on polypiperazine amides, gekenn is characterized by a structure of the general formula in which η means such a high integer that the molecular weight of the polymer is suitable for membrane formation,
P is a divalent organic radical of the general formula - CO - N N-CO- is in the ^R x N N - denotes the piperazine ring, χ is an integer between 1 and 8 and groups substituting R, such as alkyl radicals, represent, and K is a divalent organic radical of the general formula -C C - N N is in which Y is S or is 0th 2.) membranes according to claim 1, characterized in that R dnß lower alkyl radicals, in particular methyl or alkyl radicals, and χ mean either 1 or 2. 8/1 U b J.) membranes according to claim 1 and 2, characterized in that that they are made from poly-2-methylpiperazinthiofurazanamid, polytrans-2,5-dimethylpiperazinthiofurazanamid, Poly-2-methylpiperazine furazanamide and / or poly-trans-2,5-dimethylpiperazine furazanamide exist. 4.) Process for the production of membranes according to claim 1 to J5> characterized in that the polypiperazinamides in a water-soluble, polar, aprotic dissolves organic solvent, applies the solution to a flat glass plate, partially evaporates the solvent, the gel-like membrane formed in this way is coagulated by immersion in water and, if necessary, a heat treatment subject. 5.) Process according to claim 4, characterized in that one in the solution of the polypiperazinamides there is also a salt which is soluble in water and the organic solvent . used. 3 O 9 8 2 8/1 U 5