Process for the manufacture of dispersible alumino-silicates

Details Process for the manufacture of dispersible alumino-silicates Process for the manufacture of dispersible alumino-silicates

1999-08-19

2001-06-12

Griffin, Steven P. (Department: 1754)

Chemistry of inorganic compounds

Silicon or compound thereof

Oxygen containing

C423S328200, C516S079000

Reexamination Certificate

active

06245310

ABSTRACT:

The present invention relates to a process for the manufacture of high-purity alumino-silicates which are dispersible in aqueous or aqueous-acidic media by hydrolysis of aluminium compounds and silicic acid compounds and hydrothermal treatment.
There exists a large number and wide variety of natural alumino-silicates, including many compounds having defined crystalline structures, such as muscovite, nepheline, and chabasite. When exchanging part of the silicon atoms in the reticulation of silicates for aluminium atoms, while maintaining the reticulation, zeolites are obtained.
Besides natural alumino-silicates, there are many synthetic products of this kind. Such products may be those defined by crystal chemistry or may be physical mixtures of aluminium hydroxide and silicic acids with different quantities of water. Besides physical mixtures, alumino-silicate defined by crystal chemistry may be present as well.
A customary process for preparing such alumino-silicates is the conversion of clays, such as kaolin, using silicic acid and sodium hydroxide. Another synthesis route is the cogelation of aluminium hydroxide sols with silicic acid sols followed by precipitation [cf. GB 2166971-C]. Precipitation of an aluminium salt in a silicic acid sol is known as well [cf. CA 848966-A].
The aforesaid processes have the disadvantage that the desired sols or emulsions only exist at the instant they are prepared, while the powder obtained by subsequent drying can only incompletely be dispersed or requires solvent mixtures to achieve dispersion. Another disadvantage is that the sols or emulsions prepared in this way contain large quantities of alkali metals or alkaline earth metals used for stabilising the silicic acid. Subsequent purification, e.g. by ion exchange, is incomplete and results in typical concentrations of alkali metals or alkaline earth metals of 0.1% (equal to 1,000 ppm) after purification [cf. U.S. Pat. No. 3,933,6211].
Heterogeneous catalysis requires high-purity catalyst supports containing less than 100 ppm of alkali metals and/or alkaline earth metals, particularly less than 50 ppm of sodium oxide. The preparation of such high-purity alumino-silicates using ion exchanged ortho-silicic acid is described in German patent DE 38 39 580-C1. The resultant alumino-silicates have the desired high purities, but they cannot be dispersed.
Alumino-silicates are physically/chemically not comparable with aluminium hydroxides. For instance, their surfaces have higher acidities due to the stronger Lewis acid character of silicic acid. This property is utilized for a large number of catalytic processes, such as desulfurizing, denitrification, oxidation, hydrocracking, and mild hydrocracking.
Modern catalysts often consist of many different support materials [for instance, cf. GB 2166971-C]. It is essential that the catalyst support materials be homogeneously mixed to ensure uniform compositions. Therefore, dispersible alumino-silicates offer several advantages, e.g. when used for coating substrates. This method can be used in the field of catalysis and materials coating. The explanations given hereinabove show that there is a need for dispersible high-purity alumino-silicates.
It was the object of this invention to develop a synthesis for preparing dispersible alumino-silicates which offers the following advantages:
Even after drying and conversion into powder, the alumino-silicates prepared according to the present invention shall be dispersible in aqueous solutions without addition of or treatment with organic solvents.
The alumino-silicates prepared according to the present invention shall have high purities.
The starting materials used for preparing the aforesaid compounds shall be readily available.
The price of the starting materials shall allow an economic process.
The manufacturing process shall be feasible both as a continuous and discontinuous process.
It was surprisingly found that the process described hereinbelow provides alumino-silicates which solve the problems the present invention was based on.
The instant invention relates to a process for the continuous or discontinuous manufacture of high-purity alumino-silicates which can be dispersed in aqueous and/or aqueous-acidic media. The desired properties are obtained by the following process:
Process for the manufacture of alumino-silicates which are dispersible in aqueous and/or aqueous-acidic media wherein
(A) one or more hydrolyzable aluminium compound(s) is (are) hydrolyzed jointly or discontinuously in space or time, preferably jointly, and
(B) said compound(s) is (are) contacted with one or more silicic acid compound(s) prior to, during, or after hydrolysis, preferably prior to or during hydrolysis, and
(C) the combined compounds/reaction products are jointly subjected to hydrothermal ageing in an aqueous environment and in the presence of a monovalent organic C
1
to C
6
acid or a monovalent inorganic acid at temperatures of 40 to 220° C. for a period of more than 0.5 h during or after hydrolysis.
The hydrolysis may be carried out at 20 to 98° C., preferably 50 to 98° C., most preferably 85 to 98° C. Hydrolyzable aluminium compounds within the meaning of the instant invention are all the aluminium compounds forming Al—OH and/or Al—O—Al structures when reacted with water, e.g. aluminium alcoholates, aluminium hydroxyalcoholates, aluminium oxyalcoholates, aluminium acetyl acetonates, aluminium alkyl chlorides, or aluminium carboxylates. Preferably, the hydrolyzable aluminium compounds are compounds of the type Al(O-R-A-R′)
3−n
(O-R″)
n
, wherein independent of each other and, optionally, different for each residue
R″ is a branched or an unbranched, a cyclic or an acyclic, or an aromatic hydrocarbon residue having 1 to 30, particularly 2 to 12 carbon atoms,
R′ is a branched or an unbranched, a cyclic or an acyclic, or an aromatic hydrocarbon residue having 1 to 10 carbon atoms, particularly an alkyl residue having 4 to 8 carbon atoms,
R is a bivalent and branched or unbranched, cyclic or acyclic, or aromatic C
1
to C
10
hydrocarbon residue, particularly an alkyl residue having 1 to 5 carbon atoms, most preferably 1 to 3 carbon atoms, the latter one most preferably being unbranched and acyclic,
A represents a heteroatom of main group 6 (oxygen group) or main group 5 (nitrogen group) of the periodic system, preferably oxygen or nitrogen, wherein, if A represents an element of main group 5, A bears hydrogen or a C
1
to C
10
alkyl residue or a C
6
to C
10
aryl-/alkyl aryl residue as additional substituent(s) for the saturation of its valences, and
n is an index for the numbers 0, 1, 2, or 3.
Preferably, n is equal to 0 or equal to 3. In case n is equal to 0 and A is equal to oxygen, aluminium trisbutylene glycolates are preferred.
In case n is equal to 3, the aluminium alkoxy compounds are aluminium trisalcoholates which, with increasing preference, have C
2
to C
12
, C
4
to C
8
, or C
6
to C
8
hydrocarbon residues, the residues being saturated or unsaturated, cyclic or acyclic, branched or unbranched, or aromatic, preferably saturated. Saturated, linear C
6
to C
8
hydrocarbon residues are particularly preferred. For example, hydrolyzable aluminium alcoholates may be prepared according to the process disclosed in EP 0 111 115-A1.
Prior to use, the hydrolyzable metal compounds may be purified by distillation, filtration, or centrifugation. In the case of silicic acid, ion exchange of metal ions, particularly sodium, preferably on exchange resins containing ammonium ions, is an efficient purification method.
For the hydrothermal treatment, it is essential that an acid be present during or after hydrolysis. This acid is a monovalent organic C
1
to C
6
acid or a monovalent inorganic acid (or a monovalent mineral acid), such as HCl or HNO
3
. The acid may also be added after hydrolysis, as long as it is present during the hydrothermal treatment. According to the present invention, the acid or an acid-forming agent is added prior to the first

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