Hydrated aluminum compounds, their preparation and use thereof

Details Hydrated aluminum compounds, their preparation and use thereof Hydrated aluminum compounds, their preparation and use thereof

1999-02-12

2001-03-06

Bos, Steven (Department: 1754)

Chemistry of inorganic compounds

Oxygen or compound thereof

Metal containing

C423S625000, C423S628000, C423S630000

Reexamination Certificate

active

06197276

ABSTRACT:

The invention concerns hydrated aluminium compounds, their preparation and the uses thereof.
During the course of research into aluminas with controlled porosity with a pore diameter of about 0.6 to 20 nm. we became interested in alumina precursors obtained from at least one inorganic aluminium source and at least one surfactant in an essentially aqueous medium at a controlled pH.
International patent WO 96/39357 describes a route using non-ionic surfactants such as polyethylene oxides and neutral precursors of inorganic oxides as sources of the reactants. That synthesis is carried out in an organic solvent. Porous inorganic oxides are prepared by this route from non-ionic surfactants.
Research carried out on the controlled hydrolysis of Al(OR′)
3
type organic alumina precursors, where R′ is a linear or branched alkyl group containing 1 to 5 carbon atoms, has distinguished the case where the template is a quaternary ammonium type, and the medium is a mixed water-alcohol, and the case where the template is a surfactant or an amphiphilic molecule, where the reaction is carried out in an organic solvent. Vaudry and Davis in Chem. Mater., 1996, p 1451 use fatty acid type surfactants. S. Bagshaw, T. J. Pinnavaia describe the production of lamellar phases in “Mesoporous alumina molecular sieves”, Angew. Chem. Intl. Ed. Engl. 1996, 35; 10, pages 1102-1105.
We have synthesised hydrated aluminium compounds from reactants in which the starting aluminium is in the Al
3+
and/or in the Al
13
form.
Hydrated aluminium compounds of the present invention are represented by the general formula (nS, mM, Al
2
O
3
, xH
2
O) where S is a surfactant or a group of surfactants, n is the number of moles of S, M is an alkaline cation, m is the number of moles of M and x is the number of moles of water.
In the present description, S represents a surfactant or possibly a group of surfactants; S never represents sulphur in the present case.
Hydrated aluminium compounds of the present invention are represented by the general formula (nS, mM, Al
2
O
3
, xH
2
O) where the number of moles n of surfactants S is about 0.1 to 2.2. the number of moles m of alkaline cation M is about 0.001 to 0.6, and the number of moles x of water is about 0.5 to 8.
When the starting aluminium is of type Al
3+
, the coefficients n, m and x in formula (nS, mM, Al
2
O
3
, xH
2
O) are such that n is about 0.1 to 1.8, m is about 0.001 to 0.6 and x is about 0.5 to 8.
When the starting aluminium is of type Al
13
, the coefficients n, m and x in formula (nS, mM, Al
2
O
3
, xH
2
O) are such that n is about 0.1 to 2.2, m is about 0.001 to 0.6 and x is about 0.5 to 6.
In the present description, the abbreviation “nm” will be used to represent a nanometer, i.e., 10
−9
meters.
These hydrated aluminium compounds can be used as precursors for aluminas with controlled porosity where the pore diameter is about 0.6 nm to 20 nm, preferably about 0.6 to 15 nm, more preferably about 0.6 to 10 nm. These aluminas obtained from these precursors can be used, for example, to obtain adsorbents and catalyst supports.
The preparation of oxides with controlled porosity is based on the fact that organic molecules classified as surfactants can combine together, in particular when subjected to the conditions used to synthesise controlled porosity oxides. They form micelles which have electrical charges on their surface and a geometry which varies depending on the conditions in the synthesis medium. Such micelles can then build around them polymeric species of mineral oxides such as silica, alumina or other metals such as titanium, and thus generate a solid framework with a controlled porosity.
The invention concerns hydrated aluminium compounds with general formula (nS, mM, Al
2
O
3
, xH
2
O) where the portion comprising the water and the surfactants represents about 40% to 80% by weight of the compound. The X ray diffraction diagram of the hydrated compounds of the present invention is characterized by a peak which corresponds to an interplanar distance “d” of about 1 to 15 nanometers.
The compounds of the invention are synthesised from inorganic aluminium sources which are in the form of cation-monomers and/or cation-oligomers, a cation-monomer being, for example, the ion [Al(H
2
O)
6
]
3+
where the aluminium is in the form Al
3+
, and a cation-oligomer being, foor example, an ion [Al
13
O
4
(OH)
24
(H
2
O)
12
]
7+
with a Keggin type structure, in which the aluminium is in the form Al
13
. The Al
13
aluminium form, also known as the Keggin ion, has a cluster structure in which octahedral sites are associated with tetrahedral sites, the tetrahedral sites representing about 1% to 20% of the sites, usually about 6% to 10% of the sites.
The hydrated aluminium compounds of the present invention exhibit octahedral sites associated with tetrahedral sites in which the percentage of tetrahedral sites represents about 0 to 20% of the total number of sites.
In the formula (nS, mM, Al
2
O
3
, xH
2
O), M is an alkaline cation, preferably selected from the group formed by Na
+
, K
+
, NH
4
+
; S is a group comprising at least one surfactant, these surfactants being anionic and/or non-ionic surfactants. When the group of surfactants comprises at least one anionic surfactant, at least one cationic surfactant can optionally be added such that the total charge on the ensemble of the surfactants remains negative.
The anionic surfactants are generally selected from the group formed by alkyl carboxylates, alkyl sulphates, alkyl sulphonates and alkylphenyl sulphonates.
The non-ionic surfactants are generally selected from the group formed by alkylpolyethylene oxides, alkylphenylpolyethylene oxides, alkylphosphine oxides and alkylamine oxides.
The cationic surfzactants are generally selected from the group formed by alkylammonium salts, alkylphosphonium salts, and alkylsulphonium salts.
The scope of the invention also encompasses the use of surfactants in which a plurality of functions co-exist, either amphoteric surfactants in which anionic and cationic functions co-exist, or surfactants in which anionic and non-ionic functions co-exist such as C-betaine, N-betaine, an alkylpolyoxyethylene sulphate or an alkylpolyoxyethylene sulphonate.
The advantages of the compounds of the invention are as follows: they are synthesised in a less contaminating, less expensive medium where the major solvent, and the only solvent, is water, using inorganic aluminium sources which are less expensive and easy to use.
Synthesis of the compounds of the invention is carried out using at least one inorganic aluminium source using a base, in the presence of at least one surfactant. The inorganic aluminium sources are cation-monomers and/or cation-oligomers. Synthesis is carried out in an essentially aqueous medium with a pH which is about 4.5 to 10.5.
The compounds of the invention are generally synthesised as follows: at least one inorganic aluminium source in the form of cation-monomers and/or cation-oligomers is reacted with at least one surfactant. The inorganic aluminium source is introduced into the mixture in the cationic form I
+
, the surfactants are anionic S
−
and/or non-ionic S. If the solution contains at least anionic surfactants S
−
, cationic surfactants S
+
can optionally be added, the quantity of added cationic surfactants being such that the total charge of the ensemble of surfactants is negative, the charge of the inorganic surface remaining positive, following a type S
−
I
+
mechanism. However, depending on the pH of the solution particularly when the pH is over 9, the negative charges on the surfaces of the alumina species I
−
can become the majority, and these micelles can then produce S
−
M
+
I
−
type interactions where M
+
is the compensating cation of the surfactant.
Without wishing to be bound to any particular theory, it can be considered that the surfactants control polycondensation of the compounds of the invention by multiple

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