Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Silicon containing or process of making
Reexamination Certificate
1998-10-14
2001-03-20
Hendrickson, Stuart (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Silicon containing or process of making
C423S326000, C502S237000, C502S238000, C516S111000
Reexamination Certificate
active
06204217
ABSTRACT:
The present invention relates to a process for the preparation of a micro-mesoporous gel, consisting of a silica matrix in which one or more metal oxides having a catalytic activity are possibly dispersed.
More specifically, the present invention relates to a process for the preparation of a micro-mesoporous gel consisting of a silica matrix in which one or more metal oxides selected from transition metals or metals belonging to groups IIIA, IVA and VA, characterized by a monomodal pore distribution, are possibly uniformly dispersed.
Among materials known in the art which can be used in various fields such as heterogeneous catalysis, the separation of liquids or gases, ion exchange, zeolites should be mentioned, which are porous crystalline alumino-silicates of a natural or synthetic nature.
The particular characteristic of zeolites is the presence of a controlled microporosity, with channels having dimensions of between about 3 Å and 7 Å. In some particular zeolitic structures, there are cavities with greater dimensions, up to about 13 Å. On the basis of the average dimensions of the channels, zeolites are classified as small, medium or large pores, the latter having an average pore diameter of about 7 Å.
The preparation of zeolites with channels having an average diameter of more than 7 Å is still of great interest in the field of heterogeneous catalysis as the use of these materials could be extended to reactions involving sterically hindered organic molecules, which are not possible with the microporous systems known at present. These materials could be used in industrial processes for the production of intermediates for the chemical industry, of fine chemicals and, above all, for the transformation of heavy refinery feeds and for the process called “Fluid Catalytic Cracking” (FCC). Attempts at synthesizing zeolites of this type have so far had no success even though an aluminium phosphate called VPI-5, with an average pore diameter of about 12.1 Å has been prepared, as described by M. E. Davis, C. Saldarriaga, C. Montes, J. Garces and C. Crowder, Nature (1988), Vol. 331, page 698 and also Cloverite, a gallium phosphate characterized by pores with a diameter of between 6 Å and 13.2 Å as described by M. Estermann, L. B. McCusker, Ch. Baerlocher, A. Merrouche and H. Kessler, Nature (1991), Vol. 352, page 320.
The practical use in acid-catalyzed reactions of the products described above is however jeopardized by the weak acid force, low thermal stability and limited resistance to hydrothermal treatment.
The possibility of synthesizing an amorphous silica-alumina with a high surface area characterized by a narrow distribution of mesoporosity (with pore dimensions within the range of 37 Å and 150 Å) has been described by M. R.Manton and J. C. Davidtz, Journal of Catalysis (1979), Vol. 60, pages 156-166. These materials however have not found practical application.
More recently, European patent 463.673 and U.S. Pat. Nos. 4,992,608 and 5,049,536 describe the possibility of obtaining amorphous alumino-silicates with a rather narrow pore distribution (average diameter of about 10 Å or less, basic absence of pores with a diameter of more than 30 Å) and excellent catalytic properties in acid-catalyzed reactions. These properties probably derive from the fact that the preparation method used allows a uniform distribution of the aluminium in tetrahedric coordination. This enables the amorphous alumino-silicates described above to be classified as zeolite-like materials.
The process for the synthesis of the above materials is similar, in fact, to that which is typically used for some zeolites and differs from this in the basic absence of hydrothermal treatment. The process involves the mixing of a silica source (preferably tetraethylorthosilicate) and an aluminium source (a trialkoxide, preferably tri-n-propoxide or tri-isopropoxide) with an aqueous solution of a tetraalkylammonium hydroxide (R
4
N—OH, with R=ethyl, n-propyl, n-butyl). The solution obtained is subsequently gelified by heating to a temperature of between 50° C. and 70° C. In this way, a partial evaporation of the alcohols produced by the hydrolysis of the reagents, is obtained. The gel obtained is then dried and calcined to give the final product.
Even more recently, Italian patent application MI 93 A 002696 describes amorphous alumino-silicates characterized by a dimensionally very narrow distribution of the micro-mesoporosity, obtained by a process in which the gelification is carried out at the boiling point (or slightly higher) of the alcohols produced by the hydrolysis of the reagents, without eliminating the alcohols themselves from the reagent mixture. This process can be easily carried out in a reactor equipped with a reflux condenser or in a closed autoclave, operating at autogenous pressure. The ammonium bases claimed are still of the R
4
N—OH type (with R =ethyl, n-propyl, n-butyl, n-pentyl). The positive effect of the presence of alcohol on the porous characteristics of the above amorphous alumino-silicates has also been verified by adding an alcohol, preferably ethanol, to the reaction mixture, in a quantity of up to a maximum of the molar ratio between alcohol added and SiO
2
of 8/1. It should be pointed out that the presence of alcohol makes the reaction mixture homogeneous right from the beginning. Under these conditions, the hydrolysis and gelification rate is much higher than under heterogeneous conditions. In addition, the gelification can also take place at temperatures lower than the boiling point of the alcohols produced by the hydrolysis of the reagents, even at room temperature, with times which are not necessarily higher than those used in the analogous process carried out at 60° C. in a heterogeneous phase.
Patent application WO 91/11390 describes the possibility of obtaining a new group of mesoporous alumino-silicates (called M41S) having an average pore diameter of between 20 Å and 100 Å and regularly organized in the material according to a hexagonal structure (MCM-41) or cubic structure (MCM-48).
These materials can be prepared starting from a mixture containing at least a silica source, an alumina source, an organic compound having formula R
1
R
2
R
3
R
4
Q—OH wherein Q is nitrogen or phosphorous, at least one among R
1
, R
2
, R
3
and R
4
, represents an aryl or alkyl group containing from 6 to 36 carbon atoms, and each of the remaining R
1
, R
2
, R
3
and R
4
is selected from hydrogen and an alkyl group containing from 1 to 5 carbon atoms. Examples of cations having formula R
1
R
2
R
3
R
4
Q* which can be used according to WO 91/11390 are: cetyltrimethylammonium, cetyltrimethylphosphonium, octadecyltrimethylphosphonium, benzyltrimethylammonium, cetylpyridinium, myristyltrimethylammonium, decyltrimethylammonium, dodecyltrimethylammonium and dimethyldidodecylammonium.
A quaternary ammonium base can also be present, having the above formula R
1
R
2
R
3
R
4
N—OH wherein, however, R
1
, R
2
, R
3
and R
4
are selected from hydrogen and a C
1
-C
5
alkyl group or, two among the alkyl groups, can be jointly considered as forming a cyclic compound.
The mixture is subjected to hydrothermal treatment at a temperature of between 25° C. and 250° C. for a time of between 5 minutes and 14 days.
The product obtained is characterized by an X-ray diffraction spectrum from powders (XRD) having a hexagonal structure with a bidimensional order or a symmetrical cubic structure. Analyses carried out with high resolution transmission electronic microscopy (HREM) show, in the case of mesoporous alumino-silicates with a hexagonal symmetry (called MCM-41), the presence of monodimensional mesoporosity regularly organized according to a honeycomb hexagonal structure. In these aluminium materials there is a tetrahedric coordination which gives acidity to the material. In addition, these materials are extremely stable to thermal treatment.
In Italian patent application MI 94 A 01399 it has been found that, by means
Bassi Gianluca
Bellussi Giuseppe
Millini Roberto
Pazzucconi Giannino
Perego Carlo
Eni Tecnologie S.p.A.
Hendrickson Stuart
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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