Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Reexamination Certificate
2000-08-07
2001-07-17
Langel, Wayne (Department: 1754)
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
C423S630000
Reexamination Certificate
active
06261533
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns aluminum oxide masses with very narrow pore radius distribution which are particularly suited for production of catalysts and/or adsorption agents.
2. Description of Related Art
It is normally desirable that catalysts have a large surface. Since the surface can be increased only slowly and expensively by size reduction, an attempt is made to give a catalyst material a large “internal surface” by formation of very fine channels, so-called pores. The following relation applies to cylindrical pores:
Internal surface=2×pore volume/pore radius.
For pores having a radius of 4 nm and a pore volume of 1 cm
3
g
−1
, an internal surface area of 1000 m
2
g
−1
. is obtained. Such materials are already commercially available.
However, the size of the internal surface area is not the only thing that matters, but also that the walls of the catalyst pores have the correct appropriate structure. Wall structures of catalyst pores (acid, basic centers, openings, metal clusters, etc.) are considered the cause for active sites.
The pores of now common catalysts, except for the special case of zeolites, are not uniform in pore size and pore shape. Pores with more than 25 nm radius are referred to as macropores, pores with a radius from 1 to 25 nm are called mesopores. Pores with a radius smaller than 1 nm are the so-called micropores.
The macro- and mesopores are generally caused by the spacing between primary particles. The micropores are attributed to cracks with almost atomic dimensions within the primary particles. In the zeolites, which occur in nature, but can also be synthesized, cuboctahedral structures are present. Their structural elements are Si—O—Al structures. Their peculiarities consist of the fact that they surround relatively large cavities (cages) that are accessible via comparatively narrow openings. They have a very large internal surface area in the form of their pores with fixed symmetry.
BRIEF SUMMARY OF THE INVENTION
The underlying object of the invention is to prepare aluminum oxide masses or high specific surface area and a narrow pore radius distribution.
DETAILED DESCRIPTION OF THE INVENTION
The subject of the invention are therefore aluminum oxide masses characterized by a specific surface area of ≧70 m
2
/g and a narrow pore radius distribution of ≧90% between about 1.7 and 2.2 nm.
The specific surface is preferably ≧100 m
2
/g, the pore radius distribution with equal to or greater than 95% is between about 1.8 and 2.1 nm.
These masses can also contain limited fractions of aluminum oxocarbide structures related to production. They can also be doped with —Si—O— structures and/or catalytically active substances, especially with catalytically active metals.
The masses can be present in piece form so that they can be used for a fluidized bed process, optionally after further size reduction. Moreover, the masses can be bonded to at least one zeolite.
The aluminum-containing masses according to the invention can be produced by initially subjecting an aluminoxane with a basic structural element —Al—O—Al— and/or an oligomeric structure based on Al—O—Al—O—Al—O—Al, in which the free bonds are occupied by organic residues, preferably alkyl residues, to mild hydrolysis and to thermolysis at temperatures of about 300 to 900° C.
Hydrolysis is preferably run in a fluidized bed, especially at temperatures of about 10 to 100° C.
One preferably starts from an aluminoxane in which the free bonds are occupied by lower alkyl groups, especially methyl groups.
One can also start from an aluminoxane that was produced in higher hydrocarbons, like toluene or in polar compounds, like dioxane or diethyl ether.
One can also start from aluminoxanes that were doped with siloxanes (silanols) and/or catalytically active substances, like metals.
When it is desirable to incorporate Si—O groups, the aluminoxanes are converted in known fashion with silanol before treatment according to the invention. If dopants, especially heavy metals, are desired, heavy metal compounds like acetylacetonates, can be added to the solutions or suspensions of aluminoxanes, during which these heavy metals are reduced and precipitate in a very fine distribution in the aluminoxane.
To produce zeolite-containing masses reaction of aluminoxanes, optionally together with the dopants, can be carried out in the presence of at least one zeolite and the reaction product which may be obtained in piece form, can be optionally subjected to size reduction.
Powdered zeolites can be stirred into the solution of aluminoxane. After treatment of the aluminoxane according to the invention the obtained masses contain the zeolites with unaltered activity. Since the mass produced according to the invention is in coarse pieces, this is of particular interest when very fine-grain zeolites are to be used in fluidized beds, which require a specific particle size, since the coarse-piece material can be reduced as desired.
The aggregates have a bimodal pore structure, which is caused, on the one hhand, by the pores structure of the aluminum oxide masses and, on the other hand, by the pore structure of the zeolite. It was possible in this fashion to influence the selectivity of catalysts or adsorption agents produced from the masses.
The object of the invention is also the use of the aforementioned masses to produce catalysts and/or adsorption agents.
The aluminoxanes used according to the invention were investigated in the course of research work on Ziegler-Natta catalysts. The basic structural element is an Al—O—Al structure. Oligomeric Al—O—Al—O—Al—O—Al structural elements are also present to a significant extent, in which the free bonds of Al in the aluminoxane are occupied by organic groups, especially alkyl groups. In special cases, especially in methylaluminoxane, cuboctahedral structures are also formed with a composition [Al
16
O
12
(CH
3
)
24
] H 2Al(CH
3
)
3
, which can be understood based on coordinative saturation of a base unit. For this purpose the literature source “Macromolecular Symposia Aluminoxanes”, Macromol. Symp., Vol. 97; especially A. R. Barron, pages 15-25; H. Sinn, pages 27-52 is referred to.
It was initially investigated whether large internal surface areas can be formed during elimination of the alkyl groups by hydrolysis or thermolysis. During hydrolysis with large amounts of water vapor or liquid water, however, the —Al—O—Al—O—Al— structures were destroyed upon formation of aluminum hydroxide, whereby aluminum oxides with a larger surface area but with a very broad pore radius distribution were obtained. Mild hydrolysis with limited amounts of water vapor led to products of a low surface area and a broad pore radius distribution. If thermolysis was used instead of hydrolysis, then aluminum oxocarbides were obtained with a limited specific surface area and a broad pore radius distribution.
Only with the combination according to the invention of mild hydrolysis and thermolysis could masses with the stated high internal specific surface and narrow pore radius distribution be obtained. Mild hydrolysis is preferably run in a fluidized bed, in which the aluminoxane is preferably fluidized with nitrogen or argon, in which very small amounts of gaseous water are added to the inert gas with the stipulation that the dew point limit is always fallen short of. This will be achieved, for example, if the fluidizing gas absorbed water vapor over cooled ice at low temperature (water vapor partial pressure about 0.5 to 5 mbar) and then was brought to higher temperature before contact with the fluidized product during hydrolysis (about 0 to 100° C., preferably about 20° C. above the saturation temperature).
The pore radius distribution of the obtained products primarily (>95%) lies between about 1.8 and 2.1 nm. The obtained aluminum oxide masses therefore have pore radii that are much higher than those of zeolites, which generally lie between 0.3 and 1 nm.
The surface area determinations were carried out according to B
Sinn Hansjorg
Von Thienen Norbert
Cox Scott R.
Ildebrando Christina
Langel Wayne
Sud-Chemie AG
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