High surface area silica solid

Details High surface area silica solid High surface area silica solid

1998-07-27

2001-05-22

Kight, John (Department: 1612)

Chemistry of inorganic compounds

Silicon or compound thereof

Oxygen containing

C424S404000, C502S232000, C502S407000, C556S400000

Reexamination Certificate

active

06235258

ABSTRACT:

The present invention relates to a high specific surface area silica solid, to process for preparing it and to the use of polyethyleneimines as templates.
The preparation of silica solids, for example silicic acids and silica gels, is known per se. A survey of the processes currently in industrial use is given in Ullmann's Enzykl. Techn. Chem. 4th ed., vol. 21, 1982, pp. 439-476.
Silica thus prepared has a specific surface area in the range from 200 to 800 m
2
/g and pore diameters of from 8 to 20 nm, with large-pore silicas generally having smaller surface areas. Such large-pore silicas have a broad pore size distribution extending over a range from 5 to 30 nm.
High surface area MCM-41 type aluminosilicates having a narrow pore size distribution have been described by Kresge et al. in Nature 359 (1992), 710-712, but with pore size limited to a range from 2 to 4 nm. This reference describes the use of, for example, cetyltrimethylammonium ions as pore-formers and states that it is possible to vary the pore size by varying the long-chain alkyl group.
Mesoporous oxides have likewise been described, for example in DE-A 44 07 326 and DE-A 195 43 638. According to these references, mesoporous oxides are prepared by adding a cationic, anionic or nonionic surfactant as a structure-directing reagent, or template, to the oxide precursors (monomers or oligomers) in the course of the polycondensation process to give an inorganic oxide. According to these references, the actual synthesis is followed by thermal removal of the template surfactants, for example by calcining in air at from 350 to 600° C., giving rise to a mesoporous, purely inorganic oxide.
The pore sizes of prior art mesoporous oxides are predominantly confined to the range of about 2 nm to about 6 nm.
However, oxide solids which have smaller pores and which are inexpensive to produce are desirable for some applications, for example for use as adsorbents, to be able to generate strong forces of adsorption and hence to obtain the substrate to be purified in high purity after use of the oxide as adsorbent. This aim is in fact achieved with some of the commercially available silicas, which, however, have broad pore diameter distributions and comparatively small specific surface areas.
It is an object of the present invention to provide a silica solid which is suitable for a multiplicity of applications, in particular for use as adsorbent, and a process for preparing this solid in an economically favorable, ie. inexpensive, way.
We have found that, surprisingly, this object is achieved by using a template comprising a polyethyleneimine in the preparation of the silica solid.
The present invention accordingly provides a process for preparing a silica solid, which comprises the step of contacting in a liquid medium at least one silica precursor with at least one template comprising a polyethyleneimine or a mixture of two or more thereof.


REFERENCES:
patent: 015132 (1980-09-01), None
patent: 775520 (1997-05-01), None
patent: 814059 (1997-12-01), None
Le Febre et al.,Zeolites, vol. 8, No. 1, Jan. 1988, pp. 60-67.
Gunawardane et al.,Zeolites, vol. 8, No. 2, Mar. 1988, pp. 127-131.
Corma et al.,Zeolites, vol. 15, No. 1, Jan. 1995, pp. 2-8.
Ullmann's Enc. of Techn. Chem.4th Ed., vol. 21, pp. 439-476.
Kresge et al.,Nature, vol. 359, pp. 710-712, 1992.
Derwent Abstracts of DE 44 07 326.
Derwent Abstracts of DE 195 43 638.

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