Chemistry of inorganic compounds – Silicon or compound thereof – Oxygen containing
Patent
1987-02-11
1988-06-21
Doll, John
Chemistry of inorganic compounds
Silicon or compound thereof
Oxygen containing
423338, 423339, C01B 3312
Patent
active
047524588
DESCRIPTION:
BRIEF SUMMARY
This invention concerns the preparation of microspherical silica particles which can be formed into porous solids within which the interstitial pore structure can be controlled. Such materials are of value as supports for catalysts and biocatalysts, as chromatographic packing, as adsorbents and as supports for polymers used as chromatographic packing, adsorbents or ion exchange media.
Porous silica microspheres have been made by spray drying sols containing colloidal silica as disclosed in U.S. Pat. No. 3,301,635 and in U.S. Pat. No. 4,131,542. In another process for the production of microspheres in the 0.5 to 20 micron range disclosed in U.S. Pat. No. 4,010,242 colloidal silica particles are formed into microspheres by coacervation of urea or melamine formaldehyde resins which must be burned out later. The processes of the prior art do not provide silica microspheres which can be prepared in solution over a broad range of particle sizes by alteration of the process conditions and which can be formed into larger solid masses containing a controlled macropore structure.
The present invention provides a method of preparing microparticles of silica comprising adding an acid solution to a solution of a soluble silicate, and also adding an organic polymer solution comprising an alkali metal alginate, ammonium alginate, starch, gelatin, pectin or a mixture thereof.
The acid solution may be added to the silicate solution before or after addition of the polymer, that is to say the alkali metal alginate, ammonium alginate, starch, gelatin, pectin or mixtures thereof.
The microparticles produced by the invention may be substantially spherical having diameters of from 0.5 to 250 microns. The microparticles can be used to produce macroporous materials preferably having controlled pore structures.
Any soluble silicate such as sodium, potassium or ammonium silicate may be used and the solution should contain between 3% and 25% SiO.sub.2 and preferably from 10% to 20% w/v SiO.sub.2. The concentration of the polymer solution containing a soluble alginate, starch, gelatin, pectin or mixtures thereof should be between 0.1% and 25% w/v and preferably between 0.5% and 10% w/v. Any suitable acid may be used such as sulphuric, hydrocloric, nitric, acetic or phosphoric acid and the solution should contain from 1% to 10% by volume of the acid selected.
According to a preferred embodiment of the present invention an acid solution is added with stirring to a solution of a soluble silicate such that the pH remains above a value of 7. To this is added a solution containing a soluble alginate, starch, gelatin, pectin or mixtures thereof whereafter stirring may be discontinued and the mixture allowed to stand for between 1 and 24 hours. Each of the solutions is adjusted to and the mixture held at a constant temperature of between 0.degree. and 100.degree. C. The silica microspheres which form are separated from the liquor supernatent thereto, preferably by filtration, and are washed thoroughly using first hot and then cold water until largely free of organic matter followed by a dilute acid solution until largely free of any alkali metal ion present, and finally with cold water. The supernatent liquor may be recovered to allow extraction and reuse of the organic polymer. The filter cake may be masticated to break up any microsphere aggregates. If desired the microspheres may be dried at this stage by heating for example at 100.degree. C. Alternatively the microspheres may be consolidated into a solid by for example pressing the filter cake. Consolidation is improved if after washing the microspheres are suspended in water and flocculated with polyethylene oxide for example using between 0.1% and 1.0% by weight of polyethylene oxide on the weight of silica. The macroporous solid formed is dried for example by heating at between 30.degree. and 60.degree. C. in a current of air. During drying little shrinkage occurs.
Before drying the filter cake may be shaped and will retain this shape after drying. Thus the moist microspheres may be fo
REFERENCES:
patent: 4564556 (1986-01-01), Lange
patent: 4621936 (1986-11-01), Hansson
Doll John
Freeman Lori S.
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