Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Reexamination Certificate
2000-06-09
2004-08-10
Bos, S J (Department: 1754)
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
C423S628000
Reexamination Certificate
active
06773690
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to crystalline boehmitic aluminas the crystallites of which exhibit unusual dimensional differences in the space directions 020 and 120. This invention further relates to a method for preparing such aluminas and the follow-up products obtained therefrom by calcination.
2. Description of the Prior Art
The structural relations of the various aluminium oxides and aluminium hydroxides are very complex. Main distinctions are made between &agr;-Al
2
O
3
(corundum), &agr;-AlO(OH) (diaspore), &agr;-Al(OH)
3
(occasionally also termed &bgr;-Al(OH)
3
, bayerite, or bauxite dihydrate), &ggr;-Al
2
O
3
, &ggr;-AlO(OH) (boehmite), and &ggr;-Al(OH)
3
(occasionally also termed &agr;-Al(OH)
3
, gibbsite, hydrargillite). In addition, there exist numerous modifications thereof, particularly modifications of different aluminium oxides obtained by thermal degradation of the aluminium hydroxides or aluminium oxide hydrates. For instance, it is generally believed that boehmitic alumina will undergo the following conversion under the influence of temperature:
Boehmite→&ggr;(gamma)-Al
2
O
3
→&dgr;(delta)-Al
2
O
3
→&thgr;(theta)-Al
2
O
3
→&agr;(alpha)-Al
2
O
3
In literature references there are no standardized designations for the various aluminium oxides, aluminium oxide hydrates (occasionally also termed aluminium oxide hydroxides), and aluminium hydroxides, particularly with respect to the preceding Greek characters. The term ‘boehmitic aluminas’ as used herein comprises boehmitic and pseudo-boehmitic aluminas.
Boehmitic aluminas are known. High-purity boehmitic aluminas can be prepared for example by controlled hydrolysis of aluminium alkoxides. The resultant aluminium hydroxide hydrogels crystallize for example in the form of the rhombic aluminium oxide hydrate crystallite (&ggr;-AlO(OH), boehmitic alumina).
DE 38 23 895-C1 discloses a process for producing boehmitic aluminas with pore radii which can be adjusted in a controlled way from 3 to 100 nm. According to said process, the boehmitic aluminas are subjected to hydrothermal aging at a steam pressure from 1 to 30 bar (corresponding to a temperature from 100 to 235° C.) for 0.5 to hours with agitation at a peripheral velocity from 1 to 6 s
−1
. Such aluminas and the boehmitic aluminas produced by other processes have crys-tallite sizes (measured on the 020 reflex) which are always smaller by at least 2 nm compared to the crystallite sizes measured on the 120 reflex. In U.S. Pat. No. 3,898,322, too, a process for producing hydrothermally aged alumina suspension is described. According to said process, the aqueous aluminium hydroxide/aluminium oxide hydrate suspension obtained by hydrolysis of the aluminium alkoxides is subjected to hydrothermal aging at room temperature for 2 to 60 hours.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide boehmitic aluminas having unusual morphologies. It is a further object of this invention to provide aluminium oxides with unusual high-temperature stabilities and, furthermore, with extraordinarily large surfaces and pore volumes after calcination.
The problem is solved by crystalline boehmitic alumina with a crystallite size measured in nm on the 020 reflex which is larger than the crystallite size which is smaller by 1.5 nm, preferably 0.5 nm, measured on the 120 reflex. It is particularly preferred that the crystallite size measured in nm on the 020 reflex be larger than the crystallite size measured in nm on the 120 reflex.
It is a further object of the present invention to provide methods for preparing the crystalline boehmitic aluminas of the instant invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The starting compounds employed for preparing the crystalline boehmitic aluminas of the present invention are conventional (i.e. crystalline, partially crystalline, or amorphous) aluminium-oxygen compounds, such as aluminium oxide hydrates, aluminium hydroxides, or mixtures thereof with aluminium oxides, preferably conventional pseudoboehmitic and/or boehmitic aluminas. When using commercial aluminium-oxygen compounds produced by other processes, or when the boehmitic alumina is not produced and is readily employed, for example as a hydrogel, it is preferred that the aluminium-oxygen compounds be subjected to grinding prior to aging according to this invention.
The starting compounds are aluminium oxide hydrates (or aluminium oxide hydroxides) which are preferably prepared by hydrolysis of aluminium alkoxides obtained from C
1
to C
24+
alcohols or mixtures thereof. The aluminium alkoxides can be prepared for example by the Ziegler process.
The aluminium alkoxides are hydrolyzed in an aqueous environment. Generally, the hydrolysis can be performed in a temperature range from 30 to 150° C., preferably 60 to 100° C. The resultant aluminium oxide hydrate suspension is then separated from the aqueous alcohol phase. The alumina-water phase may contain for example alumina hydrate with an Al
2
O
3
content from 5 to 12 wt. %, preferably 10 to 11 wt. %.
The aluminium-oxygen compounds employed as starting materials may also originate from natural resources or can be produced by other processes, e.g. the amalgam process.
The crystalline boehmitic aluminas of the present invention can be prepared by long-time hydrothermal aging of oxygen compounds of the aluminium, particularly aluminium oxide hydrates, in the presence of water at temperatures from 60 to 240° C., preferably 70 to 160° C., most preferably 70 to 110° C. for at least 10 hours, preferably at least 20 hours, most preferably at least 24 to 70 hours or 30 to 60 hours. It is desirable to keep the shear stress on the aluminium oxide hydrate suspension low during the production. The term ‘low shear stress’ used herein means the shear stress caused by an agitator, e.g. a propeller agitator, running at a peripheral velocity of 0.5 to 3 m/s. The particle size of the aluminium oxide hydrates in the suspension is preferably in the range from 1 to 12 microns, most preferably from 6 to 12 microns.
According to another embodiment of the present invention, the crystalline boehmitic aluminas of this invention can be prepared by hydrothermal aging in the presence of water and at least bidentate, preferably at least tridentate bases, which are preferably nitrogen bases, and at temperatures from 30 to 240° C., preferably 70 to 160° C., for 0.5 to 170 hours. Examples thereof are diethylene triamine, dipropylene triamine, triethylene tetramine (triene), tetraethylene pentamine (tetrene), and pentaethylene hexamine (pentrene).
According to yet another embodiment of the present invention, the crystalline boehmitic aluminas of this invention can be prepared by long-time hydrothermal aging in the presence of water and metallic or nonmetallic oxides, or oxide hydrates, except for aluminium oxide or aluminium oxide hydrates, and water at 40 to 240° C., preferably 70 to 160° C., for at least 8 hours, preferably 16 to 170 hours, most preferably 32 to 170 hours.
Preferably, said metallic or nonmetallic oxides or oxide hydrates are those of silicon, zirconium, titanium, lanthane, and/or boron. Examples thereof are SiO
2
, ZrO
2
, TiO
2
, and B
2
O
3
. Such oxides are added in quantities from 0.1 to 5 wt. %, preferably 0.2 to 2 wt. %, referring to A1
2
O
3
.
It is preferred that the crystalline boehmitic aluminas of the present invention or the aluminium oxides prepared therefrom be free from any foreign atoms, particularly other metal atoms (including silicon and phosphorus), i.e. said materials should exclusively consist of aluminium, oxygen, and/or hydrogen in quantities of greater than 99 atom %, preferably greater than 99.9 atom %.
Preferably, the crystalline boehmitic aluminas of the present invention, independently of one another, have the following characteristics: pore volumes of greater than 0.8 cm
3
/g, preferably greater than 0.9 cm
3
/g, crystallite sizes (measured on the 020 reflex) of greater than 10 nm, preferably greater than 12 nm, an
Bohnen Frank Michael
Glöckler Reiner
Juhl Jens
Meyer Arnold
Noweck Klaus
Bos S J
Browning & Bushman P.C.
SASOL Germany Gmb
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