DE1048890B - Process for the production of acidic silicic acid hydroorganosols with an extremely low salt content - Google Patents

Description

Process for the production of acidic silicic acid hydroorganosols with extremely low salt content The invention relates to a method of production acidic silicic acid hydroorganosols, which are practically free from salts.

According to US Pat. No. 2,285,477, acidic silica alcohols are used prepared by first adding an acidic, aqueous, colloidal silica solution by mixing a mineral acid with an alkali silicate solution at a p $ from 1.8 to 4.5 and - before the resulting sol solidifies to form a gel - an organic solvent (e.g. alcohol) that is miscible with water for the purpose of Production of a mixed hydroorganisol adds. Addition of the organic solvent and cooling the sol caused a substantial proportion of the inorganic Salt precipitates; after removal of the precipitate, a sol is obtained whose Persistence depending on the pH of the sol and the temperature at which it is stored becomes, fluctuates. In any case, the brines are considerably less stable than alkaline ones Silica hydrosols.

These known hydroorganosols contain varying amounts of inorganic ones Salts depending on the acid and silicate used, the concentration of organic solvent and silica in the sol, the temperature of the sal and other folding doors. However, the minimum concentration is inorganic salt in the sol at about 0.1 to 0.3 percent by weight, which is suitable for certain uses of the sol is disadvantageous. The same goes for the acidic hydroorganosols that are after the method of U.S. Patent 2,285,449.

The objects of this invention are generally achieved by removal all or practically all remaining dissolved salts from an acidic silicic acid hydroorganosol achieved by such a sol with a strong cation exchanger that enables is to absorb metal cations from an acidic, aqueous-organic solution, and then with a weak anion exchanger loaded with a volatile organic acid, which contains a large number of salt-forming nitrogen atoms, under regulated pa Conditions is brought into contact. In practicing the present invention is it possible to mix the electrolyte-containing silicic acid hydroorganosol with the anionic and cation-exchanging material simultaneously or in any order contact as long as the pg conditions are properly monitored will.

Although it is known that salts from aqueous solutions are replaced by cationic and ammonium exchangers can be removed, could not be foreseen, that the removal of the salts from acidic silicic acid hydroorganosols in this way in the presence of an organic liquid - with the tendency of such brine, under relatively small increase in p11 to gel quickly, and also the tendency of silica, to be adsorbed in such sols by anion exchange resins - would be achieved. The invention proposes a method to make salts from such. Brines avoiding gelation of the brine and reducing adsorption colloidal silica through the anion exchanger. to be removed to a minimum.

The silicic acid hydroorganosols used here as starting materials can be prepared according to the procedures of the above U.S. patents. These Process first see the production of an acidic silicic acid hydrosol with a p1 'between 1.8 and 4.5 by adding a water-soluble alkali silicate, e.g. B. Sodium Silicate, with a mineral acid; z. B. sulfuric acid, acidified in a suitable amount and then a water-miscible organic solvent, such as ethanol, for precipitation of the salt formed by the reaction of silicate and acid is added, wherein .The brine can be cooled down to precipitate further quantities of salt. The salt will then completely separated from the Spl by filtration, centrifugation or the like. These . Brines still contain at least 0.1 percent by weight of salt, which is useful for certain purposes the brine, so z. B. in the production of films and also in the production of aerogels that are free or practically free of electrolytes must is unsatisfactory. The maximum salt content of the brine is below normal Circumstances at about 5 percent by weight.

According to a preferred embodiment of the invention, the starting silicic acid hydroorganosols by reacting an aqueous solution of sodium silicate with aqueous H2SO4 0 to 15 ° C and in such proportions and concentrations that a Acid silicic acid hydroso1 with a pH value of around 2 to 4 is formed, sodium sulfate and contains about 12 to 20 percent by weight Si 02 as silica. The hydrosols, which have a silica content over 17 percent by weight, must in general kept at 0 to 5 ° C to avoid rapid gel formation.

The silica hydrosol obtained in this way is kept at 0 to 1-5 ° C and with a water-miscible organic liquid such as ethanol Mixes formation of a silicic acid hydroorganosol which is about 25 to. 60 percent by weight of the organic liquid and about 4 to 11 percent by weight of S'02 as silica contains. The sodium sulfate is practically insoluble in the above sol and thus becomes precipitated in considerable quantities. When removing the Nag S 04 by centrifugation, Filtration or the like. A sol is obtained which has about 0.1 to 0.6 percent by weight Nag S contains 04, depending on the concentration of the organic liquid in the sol and the temperature of the sol.

The water-miscible liquid used can be used at atmospheric pressure have a boiling point below or above that of water when the sol z. B. to be used for treating textiles or paper. So can z. B. the higher-boiling, water-miscible liquids, such as diethylene glycol, Ethylene glycol, 2-ethoxyethanol, methoxyethanol, 2-butoxyethanol, monomethyl ether of diethylene glycol, the monoethyl ether of diethylene glycol or the monobutyl ether of diethylene glycol or the like., Can be used in such cases. However, if the Sole should be used for the production of aerogels, it is recommended that water-miscible organic liquids, preferably those made of carbon, Hydrogen and oxygen atoms are made to use that have a boiling point below that of water at atmospheric pressure. As examples of such liquids methanol, ethanol, isopropanol, tert-butyl alcohol, acetone or the like may be mentioned. The preferred organic liquids or diluents are ethanol and Acetone.

According to the invention, the remaining or dissolved salt is now from the above Silicic acid hydroarganosols described removed by being at a temperature under 15 '-C an acidic silicic acid hydroorganosol, the silicic acid, water, a with water, miscible organic liquid, a mineral acid -in a- quantity, which has a p, 1 value of 1.8 to 4.5, and contains an alkali with the hydrogen form one strong cation exchange insoluble in water and one with one volatile organic acid loaded water-insoluble-weak 'anion exchanger, which contains a variety of: salt-forming-'den substances, brings into contact, to .the hydroorganos oil practically free of the mentioned, .first mentioned salt is, the sol with the "mentioned anion and cation exchangers. The same ; is brought into contact in good time or in any order. That resulting sol contains less than 0.01 percent by weight of salt and also contains a volatile organic acid; which in the case of the manufacture of an airgel Expelled temperatures close to the critical temperature of the liquid phase of the sol will.

The reaction between the metal cations in the sol and the cation exchanger can be represented by the following equation: M + -1-- H R -> M R -f- H +, in which M + is a metal cation and R is the water-insoluble part of the cation exchanger is. The cation exchanger is therefore used in the hydrogen form - as soon as it is exhausted, it is removed by treatment with an acid, e.g. B. H2 S 04 or H Cl, regenerated. The cation exchanger must be a "strong cation exchanger", i.e. can remove metal cations from aqueous-organic solutions with a p $ value of 2. Examples of strong cation exchangers are water-insoluble phenolic methylene sulfonic acid resins, the z. B. by reacting phenol, formaldehyde and H2 S O4 or an alkali sulfite obtained; -water-insoluble polymerized vinyl aromatics, the nuclear Contain sulfonic acid or sulfuric acid groups on aliphatic parts of the polymers, and the like. In general, the cation exchangers that have a titration curve as shown in Fig. 1, p. 88, of "Analytical Chemistry", Vol. 21 (1949), well suited.

The reaction between the mineral acid anions in the sol and the volatile organic acid form of the weak anion exchanger can be grounded by the following equation: A- + R1 (NH2) x 'P -> Rz- (NH2) x'A + P- @ in the A- the anion of the mineral acid, e.g. B. Cl-, SO 4 - or PO4 ---, R1 - (N H2) x the water-insoluble part of an anion exchanger and P a volatile organic acid, e.g. B. formic or acetic acid. The equation explains the exchange of a mineral acid anion in the hydroorganosol for a volatile organic acid anion by using the salt of a volatile organic acid with a weakly basic anion exchanger which contains a large number of salt-forming nitrogen atoms, e.g. B. amino groups or imino groups contains. The anion exchanger must be in the form of a "salt of a fused base anion exchanger with a volatile organic acid," by which is meant a material which easily removes mineral acid anions from an aqueous-organic solution at a relatively low pH value, but which removes such anions only slowly, when the pH approaches 7.0. Strong anion exchangers cannot be used because they absorb silica as well as mineral acid anions from the sol. The base forms of some weak anion exchangers that have been investigated are not suitable for large-scale use because of the difficulty caused by gelation of the sol due to its relatively high p value when using such. Anion exchanger results. By using the form of a weak anion exchanger prepared with a volatile organic acid, it is possible to obtain the appropriate p values in the oil, and the resulting sol can be used for further operations such as pumping out. Temporary storage u..d - l - sufficient, sufficient - liquid. Examples of weak anion exchangers to be used here are the salts with volatile organic acids of weak anion exchangers, e.g. B. of water-insoluble copolymers of styrene and divinylbenzene containing nuclear amino groups or polyalkylamine groups, water-insoluble polymerized condensation products of an aromatic amine, eg. M-phenylenediamine, and formaldehyde and water-insoluble polymerized reaction products of a polyamine, e.g. B. ethylenediamine, diethylenetriamine and the like, with phenol and formaldehyde. In general, suitable weak anion exchangers are those which have a titration curve such as that of Fig. 6, p. 8 of the "Encyclopedia of Chemical Technology", Vol. 8 (1952), published by Interscience Encyclopedia, Inc. New York. Such substances contain a large number of -N H2-, - NH R-oter -NR.- groups, where R is an aliphatic radical. The volatile organic acids used to convert such materials to the salt form are formic, acetic, propionic and the like.

When the anion exchanger is exhausted, it can - z. B. by treatment regenerated with ammonia and then treated with a volatile organic Acid of the type described can be converted into the salt form of the weak acid.

In practicing the methods of this invention, it is important that the pH of the hydroorganosol be monitored during the cation and anion exchange in the sol in order to avoid gelling of the sol and to effectively and completely remove the cations and anions remove. The p11 conditions prevailing in the sol during the cation exchange and the anion replacement vary somewhat with the order in which the cation and anion exchange are used or when they are used simultaneously. If the starting hydroorganosol is brought into contact with the anion exchanger and then with the cation exchanger, the pH of the starting sol rises to about 4.4 to 4.8 during contact with the anion exchanger. This pH value would normally be too high because of the risk of gelation, but because the mineral acid anion in the sol is exchanged for the anion of the volatile organic acid, the resulting sol is more stable and does not gel as quickly as sols containing mineral acid anions. In fact, this sol has a stability of one hour or more at a temperature below 15 ° C. and is thus sufficiently fluid to be brought into contact with the cation exchanger before gelation. The subsequent contact of the sol with the cation exchanger lowers the pH of the sol with the removal of the metal cations to such an extent that it is below 4 and usually between about 1.8 and 3.3. This is a great advantage because the cation exchanger is initially used at the higher pH of the sol; which causes a more efficient removal of the metal cations than "in the case" where the cation exchange is initially reacted with a sol of a lower p $ value: Although this process causes the initial formation. of an S-ol with a relatively high PA value and thus the risk of rapid gelation, both the anion and cation exchangers are used with a pg value that is favorable for conversion: - According to the above process, the sol can can be used directly for specific purposes without further processing. If the sol is dried at temperatures up to about 140 ° C, the remaining silica drill is practically free of electrolyte because the volatile organic acid is driven off.

If the starting hydroorganosol is first used with the cation exchanger is brought into contact causes the removal of the metal cations. from it a drop in pH to about 1.8 to 2.0. The sol is at these pH values pretty -.d. 1i. about 1 week or more at temperatures below 15 ° C - resistant. There is therefore hardly any risk of gelation. However, it takes place at these lows pH values remove the last traces of metal cations relatively slowly, and the cation exchanger does not work with the greatest effectiveness. When that emerged As long as it is brought into contact with the anion exchanger, the pH value of the rises Sols with the removal of the mineral acid anions from the sol by the anion exchanger at. However, the sol should be separated from the anion exchanger before the pff exceeds the value 4.0, because otherwise the sol is relatively unstable and gels fairly quickly even at low temperatures.

The Au.sgarngshydroorganosol can also with a mixture of the cation and anion exchanger are brought into contact until all or practically all Ions of the salt in the sol have been removed by the exchangers. In the When this process is carried out, the pH of the sol is generally in the range from about 2.5 to 4.0, and the touch is continued for so long; until the sol littleor contains than 0.01 percent by weight of the salt. In this embodiment of the invention the starting hydroorganosol is preferably moved up or down through a mixed bed of the anion and cation exchangers, whereby the flow velocity is indi.gkeit so is regulated; that the pH of the outflowing sol is between 2.5 and 4.0, preferred but between 3.5 and 4.0, is taken to make both exchangers most effective to be let: In this way, the salt content of the starting sol is reduced so much; that it constitutes less than 0.01 percent by weight of the sol.

When the mixed bed is exhausted it can be regenerated by first the anion and cation exchangers are separated from one another. That can be done by hydraulic separation, which is dile differences in densities makes both materials usable. After the separation of the anion and cation exchangers As described above, these can be regenerated individually and again from one another be mixed for further treatment of the starting hydroorganosol. .

Regardless of the order of the exchangers who sell with If the starting sod is chosen, it is preferred to feed the sol through a. Bed -des Anion exchanger and a bed of the cation exchanger or a mixed bed to send both exchanges to remove the salt from the sol. -The flowing through the bed of the exchanger can look downwards or upwards. The easiest the sol is let down through the bed of the exchanger due to the force of gravity flow; .but this is not necessarily the most effective method. In each In case it is preferred, before: ... sending the exit, so through the - exchange bed any fixed ingredients, e.g. B. gel particles. or other Particles larger than colloidal in size to remove from the sol. That can go through Filtration or centrifugation or the like. Done; the sol is best sent a sand filter.

The invention is illustrated by the following examples. Parts and percentages are given in units of weight unless otherwise noted.

Example 1 7.51 of an acidic gravel @ elsäure Ethanol hydrosol with a temperature of 5 ° C and a content of colloidal silica of 9.7%; a sodium sulfate content of 0.3%, an ethanol content of 50%, a water content of 40% and so much free sulfuric acid that the pH was about 2.6, were first filtered through a sand filter and then downwards due to the gravity through a 140 ccm column of the hydrogen form of water-insoluble spheres of a mixed polymer of styrene and divinylbenzene containing granular sulfonic acid groups in an amount of approximately 10 ccm per minute. The cation exchange mixed polymerizate had a capacity of 4.25 meq / g. The pH of the ethanol hydrosol was lowered to about 2.0 by this treatment, and the effluent was practically free of sodium and iron ions, which was evident from the fact that there was negligible flame color for sodium and very faint color an acidic rhodanide solution when this was dripped into part of the draining sol.

3.751 of the sol drained from the cation exchange resin were placed in a glass container and vigorously stirred, while a total of 220 g of the acidic salt of "Amberlite IR-45" (weak anion exchanger, which consists of a water-insoluble styrene-divinylbenzene-Misdhpolymerisat with a large number of polyalkylamine groups) , which had a capacity of 6.0 meq / .g, were added. As soon as the pH of the sol had reached 3.7, the stirring was interrupted and the anion exchanger was quickly separated from the sol by filtering through a sieve with 525 meshes per square cm. The resulting sol gave no visible precipitate when part of it was tested with barium chloride solution and contained less than 0.01 percent by weight sodium sulfate. The amount of silica absorbed by the anion exchanger was negligible.

Example 2 9.751 of an acidic silicic acid-ethanol hydrosol with a temperature of 10 ° C. and a content of colloidal silicic acid of 9.70 / 0. a sodium sulfate content of 0.3% and an ethanol content of 50%, a water content of 401 / o and so much free sulfuric acid that the pH was about 3.0 were first filtered through a sand filter and Then due to the gravity down through a column of 17 mm Durehmess, he and 610 mm height of Kegelch, ai the hydrogen form of the cation exchange resin Amberlite IR-120, which is made of a water-soluble polymer of styrene and divinylbenzene with a large number of of nuclear sulfonic acid groups and a capacity of 4.20 meq / g, sent in an amount of 15 ccin per minute. The sol flowing off the cation exchange resin was collected until a pH of 2 was reached. A part of the drained sol was examined and resulted in negligible amounts of sodium in the flame; it was also tested by adding an acidic solution of rhodium and showed a very slight color and thus a negligible amount of iron.

The remainder of the drained sol was then down through a column 17 mm in diameter and 610 mm in height from beads of the formic acid salt of (above) "Amberlite IR-45" (capacity 6.0 meq /, g) in an amount of 15 ccm sent per minute. The pH of the sol drained from the anion exchanger hair was about 3.8, and its specific viability was 3. 10-5 reciprocal ohms at 25 ° C. The color of the flame showed negligible amounts of sodium ions, and no precipitate was observed and no turbidity was observed when a part of the flowing solution was admixed with a dilute aqueous barium chloride solution. The specific conductivity given above corresponded to a sodium sulfate content of less than 0.01%. Example 3 9.751 of an acidic silicic acid-ethanol hydrosol with a temperature of 5 ° C. and a silicon dioxide content of 9.4% as colloidal silicic acid, a sodium sulfate content of 0.60 / 0, an ethanol content of 45%, a water content of 45% and so much free sulfuric acid that the pH was about 2.3, was first filtered through a sand filter and then, due to the gravity, down through a column 17 mm in diameter and 1,220 mm in height from a thoroughly mixed bed of Particles sent that contained the same capacities of the hydrogen form of the cation exchanger "Amberlite IR-120" and the acetic acid salt of "Amberlite IR-45" :. The flow rate of the Ausgarngs sols through, the column was regulated so that a running sol with a pH between 3.5 and 4.0 was obtained. This draining sol contained less than 0.01% sodium sulfate and was rarely stable at 5 ° C for about 24 hours, during which time it could be pumped off or stored without any noticeable change in viscosity. EXAMPLE 4 An acidic silicic acid-ethanol hydrosol was prepared by gradually adding 630 g of an aqueous solution containing 201 / o sodium silicate with a Nag O: Si H2 ratio of 3.2: 1, with vigorous stirring, to 176 g of an aqueous solution containing 34.61 / o H2 S 04 contained. As soon as the pH of the mixture had reached 2.5, the addition of the sodium silicate solution was stopped and so much ethanol was gradually added that this accounted for 501 / o of the sol obtained. All of the above ingredients were in glass containers that were placed in an ice bath until the moment they were mixed. The sol obtained had a temperature of 6 ° C, and the at. The sodium sulfate crystals precipitated after the addition of the ethanol are filtered off from the sol at 6 ° C. The sodium sulfate content of this silica-ethanol hydrosol: s was 0.121 / o.

The above silica-ethanal hydrosol was used in an amount of 4 ccm is allowed to flow downwards through a column every minute due to the gravity, which was 1 cm in diameter and 28 cm in height and particles of formic acid salt of "Amberlifie IR-45" contained. The pH of the sol drained from this column was about 4.6 and the resistivity was 2500 ohms. A sample of 2 cc of running sol resulted with one drop of an 1 molar aqueous barium chloride solution no turbidity, indicating the effective removal of the Sttlfat ions.

The sol flowing out of the anion exchange column was in the State of rapid gelling ability and was therefore immediately down through the column sent, which had a diameter of 1 cm and a height of 28 cm, and made of particles of the hydrogen form from "Dowe -,;, 50", a strong clotionist resin, that consisted of a Misohpolymeris.at from Styroi and Divirtylbenzol with a variety of nuclear components Sulfonic acid groups and a capacity of 4.25 meq / g. The flow rate of the sol through the cation exchange bed was 4 cc per minute, and that of the The bed draining sol had a pH of about 3.0 and a resistivity of 6600 ohms, corresponding to a sodium sulfate gel content below 0.01%. This expiring Sol showed a negligible yellow coloration in the flame, which is practically the case indicated complete removal of the @tatrium ion. Example s Attempts were made as described in Examples 1 and 4, only the (otherwise same) starting brine acetone instead of alcohol. The Acid Ki, Eselsäure-Aceton-Hvdrosols contained less after treatment with the anion and cation exchange resins than 0.01% Nag S04.

Claims (6)

PATENT CLAIMS: 1. A process for the production of acidic silicic acid hydroorganosols with an extremely low salt content, characterized in that at a temperature below 15 ° C an acidic silicic acid hydroorganosol, the silicic acid, water, a water-miscible organic liquid, a mineral acid in an amount that adjusts a pH value of 1.8 to 4.5, and contains an alkali, with the hydrogen form of a water-insoluble, strong cation exchanger and a water-insoluble weak anion exchanger loaded with a volatile organic acid and containing a large number of salt-forming nitrogen atoms in Bringing contact until the hydroorganosol is practically free of the said, first-mentioned salt, the sol being brought into contact with the said anion and cation exchangers simultaneously or in any desired order. 2. Procedure according to Claim 1, characterized in that the organic liquid is ethanol or Acetone and the said, first mentioned salt is Na, S 04. 3. The method according to claim 1, characterized in that the acidic silicic acid hydroorganosal sodium sulfate, about 4 to 11 weight percent silica, about 25 to 60 weight percent one water-miscible organic liquid, water and a sufficient amount Contains sulfuric acid to produce an insane pH between 2 and 4. 4. Procedure according to claim 1, characterized in that at a temperature below 15 ° C a acidic silicic acid hydroorganosol, which contains about 0.1 to 0.6 percent by weight sodium sulfate, about 4 to 11 percent by weight of S "02 as silica, about 25 to 60 percent by weight a water-miscible organic liquid with a boiling point below the of water at atmospheric pressure, made up of oxygen, hydrogen and carbon atoms consists, contains and the rest of which consists practically of water and sulfuric acid in such Quantity consists that its pH is between 2 and 4, with the hydrogen form one water-insoluble, strong cationic static eliminator for the purpose of removing virtually all of them Natri.um ions of the sodium sulfate from the sol is brought into contact, whereby a hydroorganosol with a pH value between 1.8 and 3.3 is formed, and that the obtained sol then at a temperature below 15 ° C with a with a volatile organic acid-laden, water-insoluble weak anion exchanger, the contains a number of salt-forming nitrogen atoms becomes to practically all sulfate ions in the sol due to anions of the said volatile to replace organic acid, whereby a hydroorganosol is obtained, whose pH value is between about 3.3 and 4.0 and is practically free of sodium sulfate and others inorganic salts is. 5. The method according to claim 4, characterized in that that at a temperature below 15 ° C an acidic silicic acid hydroorganosoil, the about 0.1 to 0.6 percent by weight sodium sulfate, about 4 to 11 percent by weight silica, about 25 to 60 percent by weight of a water-miscible organic liquid with a boiling point below that of water at atmospheric pressure, consisting of carbon, Hydrogen and oxygen atoms consists, contains and the rest of which practically consists of Water and sulfuric acid exist in such an amount that its pH value between 2 and 4, with a volatile organic acid laden water-insoluble one weak anion exchanger containing a large number of salt-forming nitrogen atoms contains, is brought into contact until practically all of the sulfate ions in the said Sol has been exchanged for anions of the volatile organic acid mentioned are, wherein the pH of said sol increases to about 4.4 to 4.8, and that then said sol at a temperature below 15 ° C and before still considerable Change in viscosity takes place with the hydrogen form being water-insoluble strong cation exchanger brought into contact. until practically all sodium and other metal ions are removed from said sod by the cation exchange have been, the pH of the sol drops to about 2 to 3.3, and the sol is practically free from sodium sulfate and other inorganic salts. 6. Procedure according to any one of the preceding claims, characterized in that the volatile organic acid with which the anion exchanger forms the salt form, vinegar or Is formic acid. Documents considered: British Patent No. 701245.