DE2441311A1 - Membrane for purifying indl. effluents - by casting membrane from polymer soln. and treating with metal ion soln. - Google Patents

Abstract

Membranes for reverse osmosis are produced by (a) preparing a casting soln. contg. PVA or one of its derivatives, a cellulose ester, polyamide, or polyimide, (b) solidifying or precipitating the casting soln. to form a membrane, and (c) treating the formed membrane on >1 side with a soln. contg. a metal ion from main-gps. (II) and/or (III), and/or sub-gps. (VI) and/or (VIII), during or after step (b). Also claimed is the use of the membranes in the treatment of water, esp. the removal of phenol from effluents. The prods. remain tough and flexible in both wet and dry states; have good mechanical strength; can be used over a wide temp. range; are resistant to pH variations; and have good resistance to chemicals, e.g. phenols. DETAILS The casting soln. pref. contains a PVA having a mol. wt. of 20,000-100,000, PVA esterified with boric acid, or polyvinylbutyral, the PVA derivatives pref. contg. >5% free OH groups. In step (c), pref. only one side of the membranes is treated with the soln., pref. at 20-80 degrees C, contg. a barium, aluminium or chromium (III) salt, or barium hydroxide.

Description

Process for the manufacture of membranes for reverse osmosis The invention relates to a method of making membranes for the reverse Osmosis and its use for water purification.

It is known to be used in water purification and fresh water extraction Sea and brackish water, as well as the concentration of liquid mixtures according to the Principle of reverse osmosis in a starting solution continuously under pressure to bring an osmotic cell into contact with a semipermeable membrane and continuously withdrawing the enriched starting solution from the cell, the processed further as a concentrate or discarded, while on the low-pressure side the cleaned liquid is obtained from the membrane, e.g. as service water.

Cellulose esters, polyamides, Polyimide and other water-permeable materials are used that support the dissolved salts do not pass through permit. From solutions to this The membranes are cast in polymers and then precipitated. It is possible by observing certain conditions during the precipitation, e.g. according to US Pat. No. 3,122 132 and 3 133 137 or Colloid-Z. et al., Polymers 246 (1971) 669 asymmetric membranes produce with relatively high permeability.

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

The invention has set itself the task of eliminating these disadvantages and in particular to produce a phenol-resistant, acid- and alkali-resistant membrane, which can be used in particular for cleaning industrial waste water.

To solve this problem, a method for the production of membranes is provided for reverse osmosis by solidifying or precipitating a polymer-containing casting solution and, if necessary, application of the solidified membrane to a carrier material is proposed, that is characterized in that the casting solution is 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 metal ion of II. and / or III. Main group and / or the VI. and / or VIII. Containing subgroup of the periodic table Solution treated. Treatment of only one side is preferred because then Form membranes with asymmetrical behavior.

The treatment is preferably carried out with a barium salt or. -hydroxide- or an aluminum salt or chromium (III) salt solution by, in particular the treatment is carried out at temperatures of 20 to 800c.

It is expedient to proceed in such a way that a casting solution is used, the esters or ketals of polyvinyl alcohol, especially with more than 5% free Contains OH groups. It is particularly advantageous if one is used as a casting solution with boric acid esterified polyvinyl alcohol or a polyvinyl alcohol with a Solution containing molecular weight from 20,000 to 100,000 is used. Good results are also obtained when using a casting solution containing polyvinyl butyral.

The procedure is preferably such that the membranes at or after their production applies to a carrier material of the same or a different type.

The invention is based on the fact that following the precipitation the membranes by treatment with solutions of polyvalent metal ions both against alkaline and acidic solutions as well as against aqueous solutions, which contain phenol in a concentration of about 1% by weight, made resistant and at the same time become impermeable to phenol.

Particularly suitable for the crosslinking of membranes made from the above Materials and thus for achieving phenol resistance and phenol retention capacity are i.a.

the ions of aluminum, the metals of the sixth subgroup and of the metals of the eighth subgroup. The networking is expediently done with the aqueous solutions of their salts. However, the solutions can also be organic solvents such as water-soluble ketones, alcohols, polyethers, etc.

Usually the post-treatment of the membranes is done with metal ions made at room temperature. However, it is often beneficial to have follow-up treatment to be carried out at elevated temperatures. This makes certain films better mechanical properties and better retention of phenol.

If you let the metal salt solution from one side onto the precipitated When the film acts, films that are initially homogeneous become asymmetrically structured Membranes get what after Sourirajan (Reverse Osmosis, Academic Press, New York, 1970) can be detected by flux reversal.

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. Also suitable for the purposes of the invention are the Polyvinyl alcohol esters, especially the partial polyvinyl alcohol esters, which contain about 8 to 100% free alcoholic groups. Acids, their esters with Polyvinyl alcohol can 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 alcohol result Membranes made water-insoluble and phenol-resistant by treatment with bariuitis salts can be made.

Also treatment with salts of the metals of the sixth and eighth Subgroup of the Periodic System of the Elements, especially with chromium salts, leads to membranes with very good properties.

Furthermore, for the purposes of the invention, ketals of polyvinyl alcohol, especially ketals of polyvinyl alcohol, which have more than 5% free alcoholic groups contain, find use, such as ketals, those with formaldehyde, acetaldehyde and butyraldehyde can be obtained.

These polymers are different depending on the content of free OH groups Solvents soluble. If the number of free alcoholic groups is very high, e.g. 80% and more, the polymers are in water, dimethyl sulfoxide and mixtures, which in addition to water or dimethyl sulfoxide, dimethylformamide, methanol, ethanol, propanol, Glycol, glycerine, polyalcohols and polyethers contain, 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.

be felled. In these are water-miscible solvents the polymers rich in free alcoholic groups are insoluble. By adherence Under certain precipitation conditions, asymmetric membranes can be produced, with it is necessary in the intermediate area, solvent mixtures for each individual Case to be put together specially.

According to a preferred embodiment, membranes can be used for processes reverse osmosis is advantageous by combining a very thin film a polymer according to this invention with a porous support, which is used as a support used for the film. These porous substrates or supports can of a polymeric material of the same type as the film of this invention or consist of completely different materials such as cellulose fleece or glass fleece.

The polymer materials can according to the invention in the form of moldings, such as films, membranes, porous substrates, hollow fibers or tubes and are characterized by high chemical resistance. In particular, they are insensitive to fluctuations in the pH range from 1 to 14 and are within thermally stable over a wide temperature range. You have good mechanical Strength, are tough and flexible both when dry and when wet and can be used within a wide temperature range.

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

The polymer materials according to the invention are preferably used for Dephenolation of waters, for the desalination of salt water and for the extraction of drinking water from brackish water or sea water according to single-stage or multi-step processes are used.

In addition, they can be used advantageously in all separation processes that work on the principle of reverse osmosis. Examples of such Procedures are ur processing.

Purification of industrial water, the concentration and Cet ir.r.u ..- der various chemical compounds such as chlorides, sulfates, borates, carbonates, Nitrates, fertilizers, glutamates, Wannine ur.

Heavy metal salts, the concentration of foods like 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: -: ormone, Proteins, vitamins, antibiotics, vaccines, amino acids, etc. as well as for everyone else Separation and concentration processes using the principle of reverse osmosis is applicable.

Example 1 A. Preparation of the polymer 30 g of polyvinyl alcohol des Molecular weight 100,000 (degree of saponification 86-89%) were with vigorous stirring in 3.3 liters of water dissolved. Then 6 ml of an aqueous solution of 20% by weight of sodium hydroxide added. At the boiling point, a solution of 5.25 g of boric acid in 95 ml of ethanol lar.

sam to. After boiling for about 1 hour, the mixture was cooled to 20 ° C. Product was precipitated with acetone and washed.

B. Preparation of the casting solution 21 z of the recovered polymer was allowed pre-swell a Tae in a mixture of 60% DMSO, 30% ethanol and 10% water.

Subsequently, while slowly heating the polymer in 285 z Solvent dissolved.

C. Preparation of the membrane The casting solution was at an elevated temperature drawn out on a plate made of V2A steel to form a film about 1 mm thick.

After a waiting time of 5 minutes, it was immersed in acetone like the membrane. After that, the membrane became a saturated solution of barium hydroxide Treated in water at 20 ° C. The membrane was then detached from the car and corresponding areas cut out for examination of 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 were the flight and the phenol retention measured in a test apparatus. The inflow consisted of a solution of 0.2 wt % Phenol in water. Experiments were carried out on solutions with pH values of 12 and 5 dur .-- - - The following results were found: pH value of the phenol retention solution Product flow 12 83 8 0.100 d 5 55% 0.103 rid BeisDiel 2 From a polyvinyl alcohol with a molecular weight of 45,000 and a degree of saponification of 97 - 99.5% (Polyviol der Company Wacker) a solution of 16 wt. The solution was stored for a week at 50 ° C before being made into a film on a V2A plate about 1 mm thick.

After the film had been pulled, it was left to stear in the air for 5 minutes then precipitated the membrane by dipping it in an acetone tape at 20 ° C. After completion the precipitation was the membrane: rzt a saturated solution of potassium chrome alum Treated at 40 0C for a few hours. After that, the membrane was rinsed with water at 2, to remove excess chrome. To study their properties were corresponding areas are removed from the 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 were water flow through the membrane and phenol retention measured. The feed consisted of a solution of 0.2% by weight phenol in water. It Tests were carried out on solutions with a pH of 12 and 5. The following results were obtained: pH of the solution phenol retention product flow.

12 86% 0.1 m / d 5 61% 0.1 m / d Example 3 A polyvinyl butyral with the degree of polymerization 60 and a content of 12 - 16% of alcoholic groups and a content of 1% of acetate groups, the remainder was butyral with a concentration of 25 wt. in a mixture of dimethylformamide and ethanol with stirring and heating solved. The solution was poured onto a V2A steel plate at room temperature a filv about 1 mm thick. After waiting 5 minutes it was the membrane is precipitated by immersion in ice water. After the completion of the precipitation was the membrane with a saturated solution of potassium chrome alum at 40 0C for a few hours treated.

The membrane was then rinsed with water at 20 ° C. to remove excess Remove chrome. To investigate their properties in the process of the reverse Osmosis, pieces of appropriate size were separated from the membrane and placed in clamped a test apparatus.

At a pressure of 50 bar on the inflow side and a pressure of 1 bar on the product side were 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 the pH 11ert 12.

The following results were obtained: pH of the solution phenol retention $ Product flow 12 33 t 3.29 m / d Example 4 polyvinyl acetate of molecular weight 110 00O (Ftowilith 30 from Farbwerke Hoechs-t) were used with one concentration of 20 wt. 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 waiting 5 minutes, the membrane was dipped in ice water pleases. After the completion of the precipitation, the membrane was saturated with a solution Treated by potassium chrome alum at 40 oC soaking hours. After that, the membrane was rinsed with water at 20 ° C. to remove excess chromium. For examination Pieces became more appropriate to their properties in the reverse osmosis process 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 were water flow through the Mcmbran and phenol retention measured. The inflow consisted of a solution of 0.2 wt had a pH of 5.

The product flow under these conditions was 0.75 m / d; the phenol retention 32%.

Example 5 A polyvinyl alcohol having a molecular weight of 80,000, corresponding to 86 up to 89 t was saponified (residual acetate groups) was explained in accordance with example 1 Appropriately esterified with boric acid.

With the exception of a small remainder of about 1 to 2%, the free esterified alcoholic groups. The product became one containing 7.5% by weight Solution made in a mixture of 60% DMSO, 30% ethanol and 10% water. The solution was closed at a slightly elevated temperature on a plate made of V2A steel a film about 1 mm thick pulled out-. After waiting 5 minutes it was the membrane is precipitated by immersion in methyl ethyl ketone at 20 ° C. After completion After precipitation, the membrane was coated with a saturated solution of potassium chrome alum treated in water at 40 0C for a few hours. After that, the membrane was using water Rinsed from 20 0C to remove excess chromium.

To study their properties in the process of repentance Osmosis, pieces of the appropriate size were separated from the membrane and placed in clamped a test apparatus.

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

pH value of the solution salt content phenol retention product flow 12 0 82% 0.15 m / d 5 0 46% 0.2 m / d 5 0.02% by weight 69 8 0.18 m / d Example 6 A polyvinyl alcohol the molecular weight of 45,000 with the degree of saponification 97 to 99.5% was that in the example 1 described procedure esterified accordingly with boric acid. There were about 75% of the free alcoholic groups are esterified. The product was in a mixture dissolved from 60% DMSO, 30% ethanol and iO% water, so that a clear, viscous Solution with a concentration of 10% by weight was formed. The solution obtained was at a slightly elevated temperature on a plate made of V2A steel to a film of about 1 mm thick. After a waiting time of 5 minutes, the membrane was broken Immersion in acetone at 20 0C precipitated. After the completion of the precipitation, the membrane was with a saturated solution of potassium chrome alum in water at 40 0C for some time treated. The membrane was then rinsed with water at 20 ° to remove excess Remove chrome. To study their properties in the process of repentance Osmosis, pieces of the appropriate size were separated from the membrane and placed in clamped a test apparatus.

At a pressure of 50 bar on the inflow side and a pressure of 1 bar on the product side was the water flow through the membrane and the phenol retention measured. The inflow consisted of a solution of 0.2 parts by weight of phenol in water. the DH values of the solution were 12 and 5. In one experiment, a phenol solution of pH 5 0.02% by weight of sodium chloride was added. The following results were obtained: pH value of the solution Salt content Phenol content Product flow 12 - 91% 0.07 m / d 5 - 46% 0.12 m / d 5 0.02 60% 0.12 m / d% by weight Example 7 Polyvinyl alcohol by weight 100,000 with a degree of saponification of 86 to 89% was that described in Example 1 Appropriately esterified with boric acid. About 25% of the free esterified alcoholic groups. The product was in a mixture of 60% DMSO, 30% ethanol and 10 t water dissolved so that a clear. viscous solution with a Concentration of 5% by weight resulted. The solution obtained was increased at a little Temperature drawn out on a plate made of V2A steel to form a film about 1 mm thick. After waiting about 5 minutes, the membrane was immersed in acetone at 20 0C. After completion of the precipitation, the membrane was saturated with a Solution of potassium alum CK Al (SO4) 2) in water at 40 0C for some time. The membrane was then rinsed with water at 20 ° C. to remove excess aluminum to remove. To study their properties in the process of the reverse Osmosis, pieces of appropriate size were separated from the membrane and placed in clamped a test apparatus.

At a pressure of 50 bar on the inflow side and a pressure of The water flow and the phenol retention were measured at 1 bar on the product side. The feed consisted of a solution of 0.2% by weight phenol in water. There were solutions used with tHt.Ter th 12 and 5. The following results were obtained: PH value of the solution phenol retention $ product flow 12 75% 0.12 r: / d 5 43-87 0> 15 mxtd.

Example 8 Cellulose acetate of molecular weight 24,000 with an acetalization degree of 39.8% is in a mixture of 60% by weight of acetone and 40% by weight of formamide dissolved at a concentration of 25% by weight. The resulting solution was on a Plate made of V2A steel drawn out into a film about 1 mm thick. After a wait The membrane was precipitated from about 1 minute by immersion in ice water. To At the end of the precipitation, the membrane was coated with a saturated solution of potassium chromium alum (K. Cr (S04) 2) treated at 40 0C for about 4 hours. After that, the membrane was made to Remove excess chromium, rinse with water at 20 0C. For examination Pieces became more appropriate to their properties in the reverse osmosis process 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 The water flow and the phenol retention were measured at 1 bar on the product side. The feed consisted of a solution of 0.2% by weight phenol in water at pH 5. With a product flow of 0.5 m / d, the phenol retention was 58%. %.

Claims (10)

Expectations 1. Process for the production of membranes for reverse osmosis by solidifying or precipitating a polymer-containing casting solution and optionally Application of the solidified membrane to a carrier material, characterized in that that the casting solution is based on polyvinyl alcohol or its derivatives, Cellulose esters, polyamides or polyimides used and after onset or termination the solidification or precipitation of the membrane formed at least on one side a metal ion of II. and / or III. Main group and / or the VI. and / or VIII. Subgroup of the periodic system containing solution treated. 2. The method according to claim 1, characterized in that the Treatment with a barium salt or hydroxide or an aluminum salt or chromium (III) salt solution performs. 3. The method according to claim 1 and 2, characterized in that one the treatment is carried out at temperatures of 20 to 800C. 4. The method according to claim 1 to 3, characterized in that one a casting solution used, the esters or ketals of polyvinyl alcohols, in particular with more than 5% free OH groups. 5. The method according to claim 4, characterized in that as Casting solution used a boric acid esterified polyvinyl alcohol. 6. The method according to claim 1 to 3, characterized in that one a polyvinyl alcohol having a molecular weight of 20,000 to 100,000 as a casting solution containing solution used. 7. The method according to claim 1 to 3, characterized in that one a casting solution containing polyvinyl butyral is used. 8. The method according to claim 1 to 7, characterized in that one the membranes during or after their production on a carrier material of the same or of a different kind. 9. The method according to claim 1 to 8, characterized in that one treated the membrane from only one side with the solution containing metal ions. 10. Use of membranes according to claim 1 to 9 for water purification especially for the removal of phenol from wastewater.