DE2009336A1 - Semi-permeable membrane for desalination of brackish and sea water by means of hyperfiltration and process for their production - Google Patents

Description

DIPL.-ING. KLAUS BEHN ά. UU ΌΟ Ο ©

niPL .-: PHYS. ROBERT MUNZHUBER

PATENT LAWYERS

8 MOLCHEN 22 WIDENMAYERSTRASSE Β TEL. (0811) 222630-296192

A 4570 February 27, I97O

Mü / Se

CONSIGLIO NAZIONALE BELLE RICEHCHE, Piazza delle Scienze 7,

Rome , Italy

Semi-permeable membrane for desalination of brackish and Sea water by means of hyperfiltration and process for their

Manufacturing

- The invention relates to a method of manufacture semi-permeable membranes, which are used for cleaning liquids, especially for desalination of brackish and Sea water through ultrafiltration processes, including under known as inversion osmosis, can be used can. The invention also follows the same process manufactured and in the field of cleaning of Liquids suitable by the hyperfiltration process Membrane to the goal.

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By the term "membrane" is used herein within the limits and ultimate aim of the invention - a Understood material which forms a partition, the thickness of which is slightly, generally much less ·. than its surface area, phenomena appearing which are similar to those of osmosis, that is, in which the flow of a solvent through the membrane is accompanied by a rejection or excretion of at least the greater part of the compounds, especially the Salts that are dissolved in this solvent. In addition, this term is applied here to membranes, which regardless of their geometrical dimensions Have the above-mentioned properties of permeability selectivity, the membranes considered in the present case be flat or have any other design.

The phenomenon of inversion osmosis, given the conditions under which the membranes according to the invention work, more correctly called ultrafiltration, has recently been used for at least partial cleaning or or desalination of brackish and sea water achieve what is obviously of most interest and

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and is of paramount social and industrial importance.

In order to achieve results which have concrete meaning and are actually of practical use, it is obviously important that the membranes used have certain properties with regard to permeability selectivity, mechanical resistance, service life, ability to regenerate and so on. Of particular importance is their ability to allow a considerable flow in relation to the usable membrane surface area within the unit of time, that is to say a considerable amount of penetrating liquid. This amount of penetrating liquid, which is usually simply referred to as "flow", is generally given with a value φ, which corresponds to the daily amount of liquid in liters that penetrates through a membrane with a surface area of 1 square meter, i.e. liters χ m " χ day ~ (1 m "g").

Of course, in addition to the practical need to achieve acceptable flow rates, the property of good filtering ability, in turn, in general It is expressed in percentage ratios

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Upstream Concentration - Downstream Concentration

10Ox

Upstream concentration

The properties of the flow and the filtering are obviously determinants in the evaluation of the quantitative ones or the qualitative productivity of the ultrafiltration system. It is also important that the ultrafiltration process does not require the use of high pressures, be it to achieve an acceptable compromise between the amount of cleaned liquid and the energy absorbed in the cleaning process, or be it to eliminate the difficulties, resulting from the application of excessive pressure. In the field of industrial application of membranes for the For ultrafiltration of brackish and sea water, the operating pressure must never exceed 100 atmospheres.

For the desalination of more or less salty water nowadays almost exclusively ultrafiltration is used Cellulose acetate membranes used. These membranes, which are highly hydrophilic and, to a high degree, the necessary ones However, having properties of permeability selectivity have some serious disadvantages and some

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Restriction of use with it, especially the following:

- poor resistance to hydrolysis and against chemical and biological agents;

- Difficult handling due to their low mechanical IP see resilience;

- Necessity to keep the membranes in when not in use keep moist condition; ,

- Difficulty washing the same with chemical Active ingredients for the purpose of removing crusts that have become have formed during the previous operation.

The object of the invention is therefore the implementation and subsequent application of inversion osmosis, especially g & on the desalination of more or less salty water by means of ultrafiltration, as well as equipped with useful and satisfactory piltering properties Membranes that are not subject to the above and other disadvantages and limitations.

According to the invention, such membranes are by Application of monomeric or polymeric molecules, which

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contain or can accommodate active groups of the polar type on a synthetic plastic material, even water-impermeable or insufficiently water-permeable matrix produced, the application being based on chemical Ways and / or is achieved by irradiation. In this way, under the conditions of inversion osmosis, achieved a permeability at least 10 times greater than that of the said die.

Said matrices are composed of manufactures made through the use of synthetic compounds are obtained, preferably polytetrafluoroethylene (PTFE), polypropylene, homopoly * aids or copolyamides, however, the use of other synthetic materials such as polyethylene, polyvinyl chloride, Polyethylene terephthalate, polydichlorodifluorethylene, polycarbonate, Polyepoxides and others is not excluded.

As indicated above, the monomeric or polymeric molecules to be applied can themselves have polar groups

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contained or active polar as a result of later treatment Record groups.

Monomers containing polar groups which can be used advantageously are those which are summarized in the group are which acrylic acid, methacrylic acid, vinyl sulfonic acid and parastyrenesulfonic acid, as well as the salts thereof Acids, vinyl pyridine and acrylamides. Optionally, the esters and the nitriles of acrylic acid and methacrylic acid, vinyl pyrrolidone, vinyl chloride and Vinylidene chloride, vinylbenzoic acid and their salts and others be used.

As monomers which have no active groups, those which are included in the group are preferably used which contains the styrenes and the divinyibenzenes, using from 2 to 18 carbon containing olefins, polyhydrocarbons having 14 to carbon atoms and the mixtures of these hydrocarbons are not excluded. In this case, the polar ones Punctures by means of known processes of sulphurization, chloromethylphenol, chloridation, oxydrilation, oxy dation and others.

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Palls the applied monomer no active polar Contains groups, is the practically acceptable minimum value of the active groups to be introduced - e.g. aur SuI-fonation - 5 # (mole percent) applied monomeric unit.

It has been found that the essential and critical filtering property is within the usual Flow rate range is surprisingly improved when on the matrix of synthetic material monomers or oligomers mixed with other of the aforementioned monomers which are suitable for bringing about crosslinking, such as divinylbenzene and trivinylbenzene, can be applied and the crosslinking polyhydrocarbures.

In addition, the beneficial results of crosslinking can be achieved through the application of radiation or through the use of chemical reagents that are specific to the crosslinker in question Polymer molecules act.

In the specific field of the use of membranes for inversion osmosis, more precisely for Ultrafiltration of brackish water, are the combined

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Properties of permeability and filtering that together determine the efficiency of ultrafiltration, depending on compliance with a certain Range of the weight ratio between matrix and monomer or compound applied.

Basically, this ratio must be between 20/1 and 1/2. Preferably, when using polyolefin and polyamide matrices, ratios between 3 - k / l and 1 / 1.2 megen are used.

-The flow rate, i.e. the amount of the amount allowed to pass through the ultrafilter, depends on the same Upstream pressure depends on the thickness of the membrane. the

'' - ■ "■

membranes produced according to the invention, which are based on the specific field of ultrafiltration, more precisely the " Desalination of brackish water by ultrafiltration, find use, are made of laminar matrices with a thickness from about 1 to 25 microns.

The process of application to the matrix can either be brought about by known chemical processes or by causing a reaction between matrices and

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Monomers by means of rays that generate radicals, Peroxides or chemical reagent groups are capable of being irradiated with electromagnetic or corpuscular Rays can be made (such as ultraviolet, X-ray, γ "" _ Ol ^ / ^ - rays or ions or the like.), Or with Ions or radical bundles.

The membranes produced according to the invention have thus surprisingly been found for the purification of liquids proven suitable, especially for the desalination of brackish water by means of ultrafiltration, i.e. through processes of Inversion osmosis.

In addition, the membranes made according to the invention have proven themselves among those peculiar to the desalination process Conditions with respect to the action of the chemical active ingredients and hydrolysis proved to be surprisingly stable. Her mechanical resistance has been shown to be quite sufficient in the application of high pressure, in industrial applications Use of this ultrafiltration process is suitable, namely from 100 kg / cm and beyond, creating the desired Flow rate per ultrafiltering membrane surface unit is achieved.

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These membranes also prove to be of particular interest because of their advantageous mode of operation in the operation of desalination plants. They can be completely regenerated in the iat, as they can be covered with chemical reagents. These reagents are used to remove "Λ the formation of crusts caused either by materials in suspension, which in any case are contained in the brackish water treated here, or by products resulting from the corrosion of the materials used in these cleaning systems.

The use of the above-mentioned membranes leads to rejection values greater than 80 #. One such result is of great interest when it comes to cleaning water with a limited amount of salt, which is present in large quantities.

comes, but not directly for food and for agricultural purposes and "can be used for industrial purposes.

Depending on the preferred embodiment of the invention the prepared and cross-linked membranes enable to achieve a rejection up to values from 96 to 98 ^, and these are values that stand for the desalination of sea water suitable.

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In addition to these important advantages, there are and their long life, even with intermittent use reusable after their regeneration by washing with chemical agents.

Some non-limiting examples of practicing the invention using matrices follow of various types and of deposits brought about by different connections and in different ways have been. The membranes made according to the invention have become different in the desalination of brackish water Salinity tested to demonstrate the advantages of the invention in its main field of application.

EXAMPLE 1

A carefully washed polytetrafluoroethylene layer with a thickness of 5 microns was placed in a container with pure monomer! Styrene brought together and irradiation by a gamma ray source with a dose of 0.5 Mrad performed at room temperature. After careful washing with benzene, there was a weight gain of

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/. The membrane treated in this way was then used for 12 hours long in a solution of carbon tetrachloride and sulfur chloride of $ 5 and then with a solution of NaOH hydrolyzes. -

■ - ■

It was found in this way on the styrene treated one Layer measured, a cafcion sulfonate membrane with a weight proportion of group SO of] 50 #. One such membrane was used for the ultrafiltration of sea water tried that contained 3.5 # salt. Under a load

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operating pressure of 100 atm. and with a run of

-1 -2

In 1 hour it showed a flow of 550 3m g "with an execution rate in the order of magnitude from 80 to 85 ^ capable. ·

EXAMPLE 1a

Example 1 was repeated in the same way, only this time using a matrix 15 microns thick became. Under the same conditions, a

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Flow of 52 1m g ι
on the order of $ 90.

-2 -1
Flow rate of 52 1m g and a filtration rate in

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EXAMPLE 2

A layer identical to that used in Example 1 was irradiated in the presence of styrene and, as indicated in Example 1, washed. It was then treated with chloromethyl ether and trimethylamine in order to achieve an anionic membrane instead of a cationic one. The percent application was 45 # by weight after introducing the trimethylammon groups which made up $ 2% by weight of the applied layer.

Under the same operating conditions as in the previous examples, this membrane allowed a flow of 250 1 m
of the order of

-2 -1
Flow rate of 250 .mu.m and a filtering rate in

EXAMPLE 3

A membrane as in Example 1 was irradiated under the conditions given above, but a styrene mixture with J>% divinylbenzene was used as the application until k3% enrichment (increase in weight due to the effect of the application) was achieved

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Treatment was completed by the use of sulfuric acid chlorohydrin, as in Example 1. until the weight of the grafted layer consisted of SCU. the Membrane obtained in this way showed when used for the ultrafiltration of sea water among those in Example 1

2-1

described circumstances the ability 280 Xm g flow to enable with a filtering rate of over 90% up to

This example clearly shows the advantages which result from the preparation and the application of membranes, which result from the treatment of the matrix with monomeric network and subsequent sulphurisation arise. Indeed, albeit by a limited discount, one has of the flow rate (compared to example 1) has a high filtering rate and that means a much higher one Desalination power achieved.

EXAMPLE 4

Membranes were produced using and irradiating matrices as in Example 1, but an aqueous solution with 50 # acrylic

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acid used. These membranes did not require any further chemical treatment. Using these membranes with a content of 25 # of application material resulted in the ultrafiltration of seawater under the conditions described in Example 1, a filtering rate of the order of 95 #> albeit at a flow rate of about 401 m " ² g" ^1st

EXAMPLE 5

Membranes using matrices as in Example 1, as in Example 4 by application prepared, however, vinyl pyridine was used as the monomer. This resulted in a 50 # percentage weight gain the grafting. The membranes treated in this way were then placed in a solution of methyl iodide for 48 hours. To this treatment resulted in a further weight gain of.

These membranes gave when attempting ultrafiltration of sea water under the conditions of

P Λ

Example 1 at a flow rate of 500 pounds per square inch Filtering rate of

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EXAMPLE 6

Further membranes were produced according to the method of Examples 4 and 5, but this time it was used as a

Brinangsmittel used a mixture that consisted of 80 # vinyl acetate and 20 $ ethyl acetate. The procedure was such that a ^v O / O weight percent enrichment resulted.

In the hyperfiltration of sea water under the

known conditions a flow rate of

üd "9 ~ 1
56p. mg and a filtering rate of 84 - 8'5 #.

EXAMPLE 7

In this case, two series of membranes were produced. made, 'including matrices with a layer of polypropylene in a Dicfce of 10 microns were used. These matrices were irradiated as in Example 1, but was Vinyl pyridine chosen as the monomeric application. The membranes of the first series (A) and the series (B) were made exposed to radiation for different lengths of time in order to achieve - after quaternization with methyl iodide - that

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the total weight for (A) by $ 90, or for (B) by $ 150 increased.

The membranes treated in this way were tested in the ultrafiltration of salty water, which was 10 000 ppm. Contained (parts per million) sodium chloride. The experiment was carried out in a laboratory system at a pressure of ¹ JO atm. and a run of 100 liters / h with the following results:

2 1
Membrane (A): flow rate 70 im g; Filtering rate: 92 -95%

2 1
Membrane (B): flow rate 90 im g; Filtration rate: 91 -

EXAMPLE 8

A layer of polyethylene 10 microns thick was treated as in Example 3 to give an add-on of $ 50 by weight and a further increase of 3 ^{1/2 in} weight of the enriched layer as a result of a subsequent treatment with sulfur.

Under the test conditions as in Example 7

described, resulted in the ultrafiltration of salt

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water has a flow rate of 100 μg and a filtering rate of 90 %.

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EXAMPLE Q ■

Matrices were used which consist of a layer of commercially available "nylons 6/6" with a thickness of 10 microns existed. These matrices were made using different ways Enriched vinylpyridine and quaternized as in Example 5, in order in this way a total enrichment between a minimum (C) of # 50 and a maximum (D) of $ 120.

When tested with salty water, as described in Example 7, these membranes showed the following results:

Membrane (C): flow rate 450 lmg; Filtering rate 80 #

—2 1
Membrane (D): flow rate 600 Im gi filtration rate, 72%.

EXAMPLE 10

A layer of polytetrafluoroethylene 3 microns thick was exposed to the action of dilute gas, stimulated by microwaves with an intensity of 100 watts for exactly 5 minutes, and from then on with styrene let react to gain weight in this way

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from ~ $ O% to 4OJ6. Thereupon solfonate was sulfonated to 35 % weight on the enriched layer.

Subjected to a sample under the circumstances as described in Example 7, the following values were measured:

Flow rate: 60 to 120 1 nf ² g ""¹; Filtration rate: 56 ^ to

EXAMPLE 11

Layers of 5 micron thickness made of polytetrafluoroethylene were vacuum with pure monomeric styrene, which Jtf> divinylbenzene containing linked and subjected to the action of accelerated electrons that had an energy of 2 MeV at an intensity of 50 mA. The duration was 1 minute for (E), 2 minutes for (P) and 5 minutes for (G). After purification and sulphurisation (solfonazione) in the manner mentioned in Example 1, the following concentration and sulphurisation yield was measured, expressed in terms of weight compared with the matrix or the enriched layer:

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Membrane (E): enriched styrene 9 * 7 $; SO, - group 7% membrane (F): enriched styrene 23.8 # j SO ^ group 16 # membrane (G): enriched styrene 50.6 $ j SO -, - group J> 0%,

Ultrafiltration tests were carried out at a pressure of 70 atm. and a flow rate of 210 l / h Salt water with 10,000 parts per million (parts per million) sodium chloride. The following values resulted from this experiment:

2 1

Membrane (E): flow rate 70. m g J filtering rate $ 90

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Membrane (F) ': flow rate 205 '< 1 mg ί filtration rate

• »Ρ 1

Membrane (G): flow rate 32ο 1 mg; Filtration Rate EXAMPLE 12

A layer as described in Example 11 was irradiated with ultraviolet rays in a vacuum, in a quartz tube and in the presence of a monomeric styrene (the rays were produced by a mercury lamp) until the concentration was ½ of the weight of the styrene. Then a further $ 20 increase in weight was achieved through sulphurisation. The membrane made in this way

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showed in the experiment under the conditions described in Example 11

-2 -1 very even conditions a flow rate of 220 1 mg

and filtering rates on the order of 8O-8j5 #.

EXAMPLE

Parts of a layer of commercially available "nylon 6" with a thickness of 7 microns were enriched at 25 ° C. in a solution of 6 parts of vinylpyridine, jj parts of H ₂ SO ₂ ^, 4 parts of HCIO ₂ , and 0.5 part of sulfuric acid cerium -Ammonleum exposed in 90 parts of water.
after 3 hours of treatment (H) 52 $ added vinylpyridine, after 6 hours (I) 88 #, each with 85 $ quaternary amino groups.

Portions of the same layer, used as matrices, were subjected to ultrafiltration to compare the same sample subjected.

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These membranes, together with the original nylon 6 rope light, were experimentally used in the ultrafiltration of Brackish water tested, which 10 000 ppm. Contained sodium chloride. The experiment was carried out in a laboratory facility at a Pressure of 60 atm and a flow of 200 l / h carried out with the following results

Nylon 6 layer: flow rate 22 1mg; Filtration rate $ 11

■ 2 1
Membrane (H): flow rate 375 1 mgj filtering rate 66-68 #

Membrane (I): flow rate 350 1 ra " ² g"" ¹ j filtering rate 87-89 ^.

EXAMPLE

Membranes were produced in which matrices and the manner from Example I3 were used, where the only change was that the quaternization was carried out by using 0.2% - alfa- alfa'-dibromo-paraditol sulfate were added. With a percentage of enrichment of $ 90 and 85% ammonium as quaternary amino groups, a through-

—2 —1

Measured flow rate of 280 Img and a filtering rate of $ 95.

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EXAMPLE 14

A layer of nylon 6 as was made in Example 13 * irradiated in air with gamma rays with a dose of Q6 Mrad. After the irradiation, the matrix was enriched, for which vinylpyridine was used as a monomer. Afterward the matrix was immersed in a solution of methyl iodide, as in Example 5. The total increase in weight was $ 105. Under the conditions of ultrafiltration, as in the case of

—2 —1 game 15 applied, a flow rate of 450 lmg was used and achieved a filtering rate on the order of $ 85.

EXAMPLE 15

A matrix formed from a layer of nylon 6 (as in Example I5) was chemically enriched in one Solution containing $ 10 acrylic acid, $ 10 sulfuric acid N / 1 in the presence of 0.1 di-acrylic amide of hexamethylenediamine as a network-forming agent and cerium ammonium sulfate as Trigger. With an enrichment percentage of 92 # Weight, when attempting ultrafiltration are among the

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Conditions as in Example 13 describe a flow through

2 1 ■

of 120 Im "g and a filtering rate of $ 75 been.

EXAMPLE 16

A layer of 24 microns was used as the matrix Thickness used, made of a copolyamide of the following composition duration!

85 $ nylon 6 and 15 $ nylon 11. This matrix was enriched to 60 # with vinyl pyridine using the method described in Example 14. The amino groups were quaternized to 80 $ with a methyl bromide solution. When the ultrafiltration was carried out as in Example 1j, the following 1
rate $ 85.

—2 —1 achieved the following values! Flow rate 60 l in g ; Filtering

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Claims (1)

PATENT CLAIMS 1. A process for the production of semipermeable membranes, characterized in that a matrix which is limitedly permeable to water and consists of a synthetic compound, the molecules in the prepared membrane containing active groups of polar type, is enriched in such a way that the membrane is under pressure and under conditions of inversion osmosis has a water permeability which is at least 10 times greater than the original permeability of the matrix, so that the membrane / ί is able to prevent the passage of at least 70% of the salinity of the water when through at the same pressure the membrane is ultrafiltered through. 2. The method according to claim 1, characterized gekennaeich- net that at least a partial crosslinking of the enriched connection is brought about, j5. Method according to claim 1, characterized in that that the enrichment by irradiating the matrix 109836/0799 - ■ 27- 4. The method according to claim 1, characterized in that The enrichment is promoted by making the matrix a chemical Treatment is subjected. 5. Method according to one of claims 1 to 4, characterized characterized in that molecules are attached to the matrix, which contain no polar groups and that active polar groups as a result of subsequent treatment of the membrane to be added. 6. The method according to claim 5 *, characterized in that that active polar groups are greater than $ 5 (mole percent) of the monomeric unit are added. 7,. · Semi-permeable membrane made after the procedure of claims 1 Jais 6 is made, characterized through-pin matrix made of synthetic material, which is water permeable to a limited extent and on which molecules are attached are at least $ 5 (mole percent) of the monomeric Include unit of active polar groups, the Membrane, used under pressure and under conditions of inversion osmosis, shows a permeability that is at least 10 times larger than that of the original matrix, - 28 - 109836/0799 200P336 and that is capable of at least $ 72 of the salinity of To excrete salt water with an ultrafiltration. 8. Semi-permeable membrane according to claim 7, characterized in that the attached molecules at least are partially network-forming, so that the membrane is capable of at least 85 ^ of the salt content in ultrafiltration to excrete the water. 9. Semi-permeable membrane according to claim 7 or 8, characterized in that it is a matrix with a thickness between 1 and 25 microns, preferably between 3 and 24 Micron. 10. Semi-permeable membrane according to one of claims 7 to 9, characterized in that its weight is between 115 # and 250 ^ of the weight of the untreated matrix. 11. Semi-permeable membrane according to one of claims 7 to 10, characterized in that it contains a matrix which has at least 10 times less water permeability than the membrane, and of a synthetic one - 29 109836/0799 - 29 - ■ '' ■■ ' Compound made of polypropylene, polyethylene, Polytetrafluoroethylene, homopolyamides or copolyamides is composed. 12. Semi-permeable membrane according to claim 11, characterized in that the matrix is enriched with molecules is whose monomers in the group of styrenes and the Divinylbenzenes are included. IJ. Semi-permeable membrane according to claim 11, characterized characterized in that the matrix is enriched with molecules is whose monomers in the group of acrylic acids and Vinylpyridines are included. 14. Application of a 'membrane according to one of the claims 7 to 1J, especially for cleaning liquids for the desalination of salt water by means of ultrafiltration or inversion osmosis. 109836/0799