Claims
- 1. A method of preparing silica gel which comprises electrolyzing an aqueous anolyte solution of an alkali metal silicate and a salt of a non-siliceous anion in a concentration of at least about 0.01 normal in a cell having a cation permselective membrane separating the anolyte and an aqueous catholyte solution to deposit silica hydrogel on an anode of the cell and recovering the silica hydrogel from the anode.
- 2. The method of claim 1 in which the silica concentration of the anolyte solution is from about 5 to about 30 weight percent.
- 3. The method of claim 1 in which the silica concentration of the anolyte solution is from about 8 to about 28 weight percent.
- 4. The method of claim 1 in which the pH of the anolyte solution is at least about 10.
- 5. The method of claim 1 in which the pH of the anolyte solution is at least about 12.
- 6. The method of claim 1 in which the anolyte solution has a silica to alkali metal oxide weight ratio of from about 1:1 to about 4:1.
- 7. The method of claim 1 in which the anolyte solution has a silica to alkali metal oxide weight ratio of about 3.25:1.
- 8. The method of claim 1 in which the salt is a neutral salt of a strong acid, a basic salt of a weak acid, or an acidic salt of a weak base.
- 9. The method of claim 8 in which the salt is a salt of the same alkali metal as is present in the alkali metal silicate.
- 10. The method of claim 1 in which the anion is nitrate, nitrite, carbonate, bicarbonate, sulfate, sulfamate, borate, acetate, citrate, oxalate, silicofluoride, sulfosalicylate, fluoride, phosphate, or mixtures thereof.
- 11. The method of claim 1 in which the anion is sulfate, nitrate, or carbonate.
- 12. The method of claim 1 in which the anion is an anion of a strong acid.
- 13. The method of claim 11 in which the anion is sulfate or nitrate.
- 14. The method of claim 1 in which the salt is an ammonium salt or alkali metal salt.
- 15. The method of claim 1 in which the salt is a sodium or potassium salt.
- 16. The method of claim 1 in which the salt has a concentration of from about 0.01 to about 0.25 normal.
- 17. The method of claim 1 in which the aqueous catholyte is an aqueous solution of at least one alkali metal hydroxide.
- 18. The method of claim 1 in which the aqueous catholyte is an aqueous solution of a hydroxide of the same alkali metal as is present in the alkali metal silicate.
- 19. The method of claim 1 in which the anode comprises a conductive coating of a platinum group metal, metal oxide, or mixture thereof on a metal substrate of titanium, tantalum, zirconium, niobium, hafnium, or mixtures thereof.
- 20. The method of claim 1 in which the cathode comprises iron, steel, stainless steel, nickel, or a nickel alloy.
- 21. The method of claim 1 in which the anolyte solution is electrolyzed at a current density of from about 0.1 to about 2 amperes per square inch of anode area.
- 22. The method of claim 1 in which the temperature of the anolyte solution is from about 10.degree. to about 100.degree. C.
- 23. The method of claim 1 in which the temperature of the anolyte solution is from about 25.degree. to about 45.degree. C.
- 24. The method of claim 1 in which the recovered hydrogel is aged at about 32.degree. to about 82.degree. C. for from about 5 to about 48 hours.
- 25. The method of claim 1 further comprising washing the recovered hydrogel with water, an acidic aqueous medium, or an alkaline aqueous medium.
- 26. The method of claim 25 in which the hydrogel is washed with an acidic aqueous medium.
- 27. The method of claim 26 further comprising drying the washed hydrogel.
- 28. The method of claim 25 in which the hydrogel is washed with an aqueous alkaline medium.
- 29. The method of claim 28 further comprising drying the washed hydrogel.
- 30. The method of claim 25 further comprising drying the washed hydrogel.
- 31. The method of claim 1 further comprising drying the recovered hydrogel.
- 32. The method of claim 1 in which the silica concentration of the anolyte solution is from about 8 to 15 weight percent, the temperature of the anolyte solution is from about 10.degree. to about 50.degree. C., and the anolyte solution is electrolyzed at a current density of from about 0.1 to about 0.4 amperes per square inch of anode area.
- 33. The method of claim 1 in which the silica concentration of the anolyte solution is from about 15 to about 28 weight percent, the temperature of the anolyte solution is from about 10.degree. to about 80.degree. C., and the anolyte solution is electrolyzed at a current density of from about 0.1 to about 2 amperes per square inch of the anode area.
- 34. The method of claim 1 further comprising removing the anolyte solution from the cell and electrolyzing an aqueous acid anolyte solution in the cell for at least about one hour to purify the hydrogel.
- 35. The method of claim 34 in which the acid anolyte is an aqueous solution of the non-siliceous anion.
- 36. The method of claim 35 in which the acid anolyte is an aqueous solution of nitric acid or carbonic acid.
- 37. The method of claim 35 in which the electrolysis is effected for about one to about three hours at a current density of from about 0.01 to about 0.4 amperes per square inch.
- 38. A method of preparing a silica xerogel which comprises electrolyzing in the substantial absence of agitation an aqueous anolyte solution of sodium silicate and a salt selected from the group consisting of sodium nitrate and sodium sulfate, said solution having a silica concentration of from about 8 to about 28 weight percent, a salt concentration of from about 0.01 to about 0.25 normal, a temperature of from about 25.degree. to about 45.degree. C., and a pH of at least about 12, in a cell having a cation permselective membrane separating the anolyte and an aqueous sodium hydroxide catholyte solution to deposit silica hydrogel on an anode of the cell, recovering the hydrogel from the anode, and drying the hydrogel to provide the silica xerogel.
Parent Case Info
This is a division of application Ser. No. 80,485, filed Oct. 1, 1979, now U.S. Pat. No. 4,279,879.
US Referenced Citations (16)
Foreign Referenced Citations (2)
Number |
Date |
Country |
816581 |
Jul 1959 |
GBX |
1545702 |
May 1979 |
GBX |
Non-Patent Literature Citations (1)
Entry |
Policard and Collet, "Etude Experimentale des Lesions Renales Provoquees par Elimination de la Silice", 60, J. Urol. 164-171, (Paris, France, 1954). |
Divisions (1)
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Number |
Date |
Country |
Parent |
80485 |
Oct 1979 |
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