DE2441311C2 - Process for the manufacture of membranes for reverse osmosis - Google Patents

Description

30th

The invention relates to a method for producing membranes for reverse osmosis Solidifying or precipitating a polymer-containing casting solution and optionally applying the solidified Membrane on a carrier material.

It is known in water purification and fresh water extraction from sea and brackish water, as well as in the concentration of liquid mixtures according to the principle of reverse osmosis a starting solution continuously under pressure in an osmotic cell in contact with a semipermeable membrane bring and continuously withdraw the enriched starting solution from the cell as a concentrate further processed or discarded, while the purified liquid is on the low-pressure side of the membrane z. B. is obtained as service water.

So far, cellulose esters, polyamides, polyimides and others have been used to manufacture the membranes Water permeable materials are used, which do not allow the dissolved salts to pass through. From solutions These polymers are cast into the membranes and then precipitated. It is possible to go through Compliance with certain conditions during the precipitation e.g. according to US-PS 3122 132 and 3133137 or KoIIoId-Z. et al., Polymers 246 (1971) 669, relatively high permeability asymmetric membranes.

All of these membranes have the disadvantage that they are In extreme pH ranges between 1 and 14 are not stable and especially of organic solvents and in particular are attacked by phenol and therefore not when cleaning industrial wastewater can be used.

The invention has set itself the task of this To eliminate disadvantages and in particular a phenol component. to manufacture acid and alkali-resistant membranes, especially for cleaning industrial wastewater can be used.

The invention relates to a process for the production of membranes for the reverse Osmosis by solidifying or precipitating a polymer-containing casting solution and optionally applying the solidified membrane on a carrier material, which is characterized in that it is used as a casting solution one based on polyvinyl alcohol or its derivatives, cellulose esters, polyamides or polyimides used and after the onset or termination of solidification or precipitation, the membrane formed at least on one side with a barium salt or hydroxide or an aluminum or chromium (III) salt containing solution treated.

Is advantageously carried out the treatment BZI temperatures of from 20 through to 80 ° C.

Appropriately, the procedure is that one Casting solution used, the esters or ketals of the poly-

rniTiaihutiuiD, iiioucauiiuctc um my ms jtü iicicfi on- contains groups. It is particularly advantageous if a boric acid-esterified polyvinyl alcohol or a solution containing a polyvinyl alcohol with a molecular weight of 20,000 to 100,000 is used as the casting solution. Good results have also been obtained using a casting solution containing polyvinyl butyral.

Appropriately, the procedure is that one of the membranes during or after their production on a Applying carrier material of the same or a different type.

The invention is based on the fact that, following the precipitation, the membranes through Treatment with solutions of the compounds mentioned both against alkaline and acidic solutions also resistant to aqueous solutions containing phenol in a concentration of about 1% by weight can be made and at the same time become impermeable to phenol.

The crosslinking is expediently done with aqueous solutions of the compounds mentioned. the However, solutions can also contain organic solvents such as water-soluble ketones, alcohols, polyethers, etc. contain. Normally the after-treatment of the Membranes made at room temperature. However, it is often beneficial to have follow-up treatment to undertake elevated temperatures. This gives certain films better mechanical properties and better retention behavior compared to phenol.

! if you let the metal salt solution from one side If the film is affected, films that are initially homogeneous become asymmetrically structured Membranes preserve what according to Sourirajan (Reverse Osmosis, Academic Press, New York, 1970) can be detected by reversing the flow.

The invention is also based on the selection of certain polymers for the casting solution, namely Cellulose esters, in particular cellulose acetates, also polyvinyl alcohols, polyamides and polyimides. Farther For the purposes of the invention, derivatives of polyvinyl alcohols, especially the partial esters, are suitable des polyvinyl alcohols, which are about 8 to 100% free alcoholic Groups included. Acids whose esters with polyvinyl alcohol form the basis for membranes for dephenolation are acetic acid, boric acid, propionic acid, formic acid. In particular the partial Boric acid esters of polyvinyl alcohols result in membranes which, by treatment with Barlum salts,

can be made soluble and phenol resistant. Treatment with chromium salts also leads to Membranes with very good properties.

Furthermore, for the purposes of the invention, ketals of polyvinyl alcohols, especially ketals of Polyvinyl alcohols that contain more than 5% free alcoholic groups are used, such as. B. Ketals obtained with formaldehyde, acetaldehyde and butyraldehyde.

These polymers are soluble in various solvents depending on the content of free OH groups. is the number of free alcoholic groups is very high, e.g. B. 80% and more, the polymers are in water, Methyl sulfoxide and mixtures which, in addition to water or dimethyl sulfoxide, dimethylformamide, methanol, Contains ethanol, propanol, glycol, glycerine, polyalcohols and polyethers, soluble. The ones from such solutions cast films can be made with the help of tetrahydrofuran, dioxane, furfural and ketones such as acetone, Methyl ethyl ketone, acetylacetone, etc. are precipitated. In these water-miscible solvents are the polymers rich in free alcoholic groups are insoluble. By observing certain felling conditions asymmetrical membranes can be produced, whereby it is necessary in the intermediate area, Compile solvent mixes separately for each individual case.

Membranes can be used for reverse osmosis processes by combining a very beneficial membrane thin film of a polymer according to this invention with a porous base which serves as a support for the film is used to be produced. These porous substrates or supports can be made of suppurative polymers Material of the same type as the film after this one Invention or from completely different materials such. B. cellulose fleece or glass fleece.

According to the invention, the polymer materials can be in the form of shaped bodies, such as films, membranes, porous Layer carriers, hollow fibers or hoses are present and are characterized by high chemical resistance the end. In particular, they are insensitive to fluctuations in the pH range from 1 to 14 and are thermally stable within a wide temperature range. They have good mechanical strength, are tough and flexible both when dry and when wet and can be used within a wide temperature range can be used.

Furthermore, in contrast to the known membranes, the membranes show with increasing salt or Metal ion concentration in the outlet water increases the stability of the membranes.

The polymer materials according to the invention are preferably used for the dephenolation of waters, for the desalination of salt water and for the extraction of drinking water from brackish water or sea water single-stage or multi-stage process used. In addition, they can be advantageous in all separation processes which work on the principle of reverse osmosis can be used. Examples of such Processes are the treatment and purification of industrial water, concentration and extraction various chemical compounds such as chlorides, sulfates, borates, carbonates, nitrates, fertilizers, Glutamates, fir and heavy metal salts, the concentration of foods such as citrus juices, Tomato juice, canned fruit and fruit juices in general, sugar solutions, milk, coffee and tea extracts. the separation of liquid mixtures, the separation and concentration of biological and pharmaceutical substances such as hormones, proteins, vitamins, Antibiotics, vaccines, amino acids etc. as well as for all other separation and concentration processes, where the principle of reverse osmosis is applicable.

example 1

A. Preparation of the polymer

30 g of polyvinyl alcohol with a molecular weight of 100,000 (degree of saponification 86 to 89%) were vigorously Stir "dissolved in 3.3 liters of water. Then 6 ml of an aqueous solution of 20% by weight of sodium hydroxide added. A solution of 5.25 g of boric acid in 95 ml of ethanol was then slowly added dropwise at the boiling point to. After boiling for about 1 hour, the mixture was cooled to 20 ° C. The product was precipitated with acetone and washed.

B. Preparation of the casting solution

21 g of the polymer obtained were left for one day in a mixture of 60% DMSO, 30% ethanol and Pre-swell 10% water. The polymer was then dissolved in 285 g of solvent with slow heating solved.

C. Making the membrane

The casting solution turned into a film of approx 1 mm thick. After a waiting time of 5 minutes, the Membrane like. Thereafter, the membrane was treated with a saturated solution of barium hydroxide in water Treated at 20 ° C. The membrane was then detached from the plate and appropriate areas for examination cut out on their properties.

D. Properties of the membrane

At a pressure of 50 bar on the inflow side and a pressure of 1 bar on the product side the flow and the phenol retention measured in a test apparatus. The feed consisted of a solution of 0.2 wt% phenol in water. Experiments on solutions with pH 12 and 5 were carried out. The following results were found:

pH of the solution phenol retention

Product flow

83%

55%

Example 2

0.100m / d
0.100 m / d

Made from a polyvinyl alcohol with a molecular weight of 45,000 and a degree of saponification from 97 to 99.5% (Polyvlol from Wacker) a solution of 16% by weight in water was prepared. The solution became a Stored at 50 ° C for a week before turning into a film about 1 mm thick on a V2A plate was pulled out. After pulling the film, it was left to stand in the air for 5 minutes and then precipitated the membrane by immersion in an acetone bath

pH value of the solution Phenol retention Product flow 12th 86% 0.1 m / d 5 61% 0.1 m / d Example 3

20 ° C. After the completion of the precipitation, the membrane was coated with a saturated solution of potassium chrome alum Treated at 40 ° C for a few hours. The membrane was then rinsed with water at 20 ° C remove excess chrome. Appropriate areas were selected to investigate their properties separated from the membrane and clamped in a test apparatus

At a pressure of 50 bar on the inflow side and a pressure of 1 bar on the product side Water flow through the membrane and phenol retention measured. The feed consisted of a solution of 0.2% by weight phenol la water. Tests were carried out on solutions with a pH of 12 and 5. The following results were obtained:

20th

A polyvinyl butyral with a degree of polymerization of 60 and a content of 12 to 16% of alcoholic groups and a content of 1% of acetate groups, the remainder butyrai with a concentration of 25% by weight in a mixture of dimethylformamide and ethanol with stirring and heating dissolved. The solution was drawn out on a V2A steel plate at room temperature to form a film about 1 mm thick. After a waiting time of 5 minutes, the membrane was precipitated by immersion in ice water. After the end of the precipitation, the membrane was ^{treated with a saturated solution of potassium chrome alum at 40 °} C. for a few hours. The membrane was then rinsed with water at 20 ° C. in order to remove excess chromium. In order to investigate their properties in the reverse osmosis process, pieces of the appropriate size were removed from the membrane and packed into egg. Test apparatus clamped.

At a pressure of 50 bar on the inflow side and a pressure of 1 bar on the product side Water flow through the membrane and phenol retention measured. The feed consisted of a solution of 0.2% by weight phenol in water and had a pH value of 12. The following results were obtained:

pH of the solution phenol retention product flow

33%

Example 4

3.29 m / d

55

Polyvinyl acetate with a molecular weight of 110,000 (Mowilith 30 from the company Farbwerke Hoechst) were with a Concentration of 20% by weight dissolved in a mixture of methanol and acetone. The clear, viscous solution was drawn out on a plate made of V2A steel to form a film about 1 mm thick. After a wait The membrane was precipitated by immersion in ice water for 5 minutes. After the precipitation is complete was the MeiPbran with a saturated solution of Treated potassium bromalauri at 40 ° C for a few hours. The membrane was then rinsed with water at 20 ° C. in order to remove excess chromium. To the Studying their properties in the reverse osmosis process, pieces became more appropriate Size separated from the membrane and clamped in a test apparatus.

At a pressure of 50 bar on the inflow side and a pressure of 1 bar on the product side Water flow through the membrane and phenol retention measured. The feed consisted of a solution of 0.2% by weight phenol in water and had a pH value of 5. The product flow under these conditions was 0.75 m / d; the phenol retention 32%.

Example 5

A polyvinyl alcohol with a molecular weight of 80,000, which was 86 to 89% saponified (residual acetate groups) esterified with boric acid according to the procedure explained in Example 1. Up to to a small remainder of about 1 to 2 * the free ones esterified alcoholic groups. The product became a 7.5% by weight solution in one Mixture of 60% DMSO, 30% ethanol and 10% Water produced. The solution became one at a slightly elevated temperature on a plate made of V2A steel Film about 1 mm thick pulled out. After a waiting time of 5 minutes, the membrane was broken Immersion in methyl ethyl ketone at 20 ° C precipitated. After the completion of the precipitation, the membrane was with a saturated solution of potassium chrome alum in water Treated at 40 ° C for a few hours. The membrane was then rinsed with water at 20 ° C. to remove excess Remove chrome. To study their properties in the process of the reverse Osmosis, pieces of appropriate size were separated from the membrane and placed in a test apparatus clamped.

At a pressure of 50 bar on the inflow side and a pressure of 1 bar on the Prcriuktselte were the water flow through the membrane and the phenol retention were measured. The tributary consisted of one Solution of 0.2% by weight phenol in water. The pH values were 12 and 5. In an experiment were 0.02% by weight of sodium chloride was added to a phenol solution of pH 5. The following results were received.

PH value
the solution

Salinity

Phenol retention product nut

0 82%

0 46%

0.02 wt% 69%

Example 6

0.15 m / d
0.2 m / d
0.18 m / d

A polyvinyl alcohol with a molecular weight of 45,000 and a degree of silvering of 97 to 99.5% was im Example 1 described working catfish esterified accordingly with boric acid. About 75% of the free esterified alcoholic groups. The product was in a mixture of 60% DMSO, 30% ethanol and 10% V / ater dissolved, leaving a clear, viscous solution with a concentration of 10 wt .-% resulted. The obtained solution was at a slightly elevated temperature a plate made of V2A steel to form a film about 1 mm thick. After a waiting period of The membrane was precipitated by immersion in acetone at 20 ° C. for 5 minutes. After the precipitation is complete was the membrane with a saturated solution of

Potassium chrome alum treated in water at 40 ° C some tent. Then the membrane was covered with water Rinsed 20 ° C to remove excess chromium. To study their properties in the process the reverse osmosis pieces of appropriate size were separated from the membrane and into a Test apparatus clamped.

At a pressure of 50 bar on the inflow side and a pressure of 1 bar on the product side the water flow through the membrane and the phenol retention measured. The feed consisted of a solution of 0.2% by weight phenol in water. The pH levels the solution was 12 and 5. In one experiment, a phenol solution of pH 5 was 0.02 Weight * table salt added. The following results were obtained:

pH Weri the solution

Salinity Phenol retention product flow

91% 0.07 m / d

46% 0.12 m / d

0.02% by weight 60% 0.12 m / d

Example 7

20th

Polyvinyl alcohol of molecular weight 100,000 with a degree of saponification of 86 to 89% was the im Example 1 described procedure esterified accordingly with boric acid. About 25% of the free esterified alcoholic groups. The product was in a mixture of 60% DMSO, 30% ethanol and 10% Dissolved water, so that a clear, viscous solution with a concentration of 5 wt .-% was formed. The received At a slightly elevated temperature, the solution turned into a film of about

VI U "i,. ti / _{> n} ~ _A l »..« - "«

! now thick undressed. After a
The membrane was precipitated by immersion in acetone at 20 ° C. for 5 minutes. After the end of the precipitation, the membrane was treated with a saturated solution of potassium alum [K Al (SO ₄ ) ₂ ] in water at 40 ° C. for some time. The membrane was then ^{rinsed with water at 20 c} C to remove excess aluminum

nium to remove. To study their properties in the reverse osmosis process, pieces of appropriate size were separated from the membrane and clamped in a test apparatus.

At a pressure of 50 bar on the inflow side and a pressure of 1 bar on the product side the water flow and the phenol retention were measured. The feed consisted of a solution of 0.2 Wt% phenol in water. Solutions with pH values 12 and 5 were used. The following results were received:

pH of the solution

Phenol retention

Product flow

75%
43%

Example 8

0.12 m / d
0.15 m / d.

Cellulose acetate of molecular weight 24,000 with a degree of acetalization of 39.8% is in a mixture dissolved from 60 wt .-% acetone and 40 wt .-% formamide with a concentration of 25 wt .-%. the The solution obtained was drawn out on a plate made of V2A steel to form a film about 1 mm thick. To After a waiting time of about 1 minute, the membrane was precipitated by immersion in ice water. After completion the membrane was saturated with a precipitate Solution of potassium chrome alum [K Cr (SO ^ l bei 40 ° C for about 4 hours. The membrane was then used to remove excess chromium Rinsed with water at 20 ° C. To study their properties in the process of the reverse Osmosis, pieces of appropriate size were separated from the membrane and placed in a test apparatus clamped.

Let a pressure of 50 bar on the influx slope and the water flow and the phenol retention were measured at a pressure of 1 bar on the product side. Of the Inflow consisted of a solution of 0.2 wt .-% phenol in water of pH 5. At one With a product flow of 0.5 m / d, the phenol retention was 58%.

Claims (5)

Patent claims: 1. Process for the manufacture of membranes for reverse osmosis by solidification or Precipitation of a polymer-containing casting solution and, if necessary, application of the solidified membrane a carrier material, characterized in that the casting solution is based on Polyvinyl alcohol or its derivatives, cellulose esters, polyamides or polyimides are used and after the onset or termination of the solidification or precipitation, the membrane formed at least open one side with a barium salt or hydroxide or an aluminum salt or chromium (IH) sa! z containing solution treated. 2. The method according to claim 1, characterized in that a casting solution is used which Contains esters or ketals of polyvinyl alcohol. 3. Movers, according to claim 2, characterized gekenr.-draws, that a boric acid esterified polyvinyl alcohol is used as the casting solution. 4. The method according to claim 1, characterized in that there is a polyvinyl butyral containing Casting solution used. 5. Use of membranes according to claim 1 to 4 for removing phenol from wastewater.