Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Reexamination Certificate
1998-09-04
2001-01-09
Dunn, Tom (Department: 1754)
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
C423S625000, C423S628000, C502S355000
Reexamination Certificate
active
06171573
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an alumina sol, a process for producing the same, a process for producing an alumina forming product using the same, and an alumina supported catalyst obtained by the use of the alumina forming product. More particularly, the invention relates to an alumina sol comprising fibrous boehmite of high monodispersibility which contains a small amount of water of crystallization and is composed of thin and long boehmite fibers. The invention also relates to a process capable of producing the alumina sol in a high concentration. The invention further relates to a process for producing an alumina forming product, wherein the above alumina sol is used without subjecting it to a special concentration operation to produce an alumina forming product that is optimum for alumina adsorbent or alumina carrier which has excellent mechanical strength and sharp pore distribution and is useful in fields of catalyst industry, exhaust gas purification and petroleum chemistry. The invention furthermore relates to an alumina supported catalyst which is obtained by supporting an active metallic component on the alumina forming product and thereby shows desired properties, which has excellent mechanical strength and sharp pore distribution, and which is favorable for heavy oil treatment in the petroleum refining.
Processes for producing alumina sols, alumina methods having &rgr;- and &khgr;-crystal structures, hydrolyses of aluminum salts, metal supporting methods, forming methods and hydrogenation catalysts, etc. of the prior art, all relating to the present invention, are described below.
With respect to an aqueous alumina sol obtained by hydrolysis of aluminum alkoxide, Japanese Patent Laid-Open Publication No. 10535/1995 (referred to as “Publication No. 1” hereinafter) discloses a process wherein hydrated alumina is deflocculated under heating in the presence of an acid to produce a transparent low-viscosity alumina sol. With respect to needle-like colloidal boehmite, a process wherein aluminum alkoxide is hydrolyzed to produce boehmite having a length of 100 to 500 nm is disclosed in J. Am. Cera. Soc., 74(6) 1,303-1,307 (1991) (referred to as “Publication No. 2” hereinafter).
With respect to a process for producing an aqueous alumina sol using metallic aluminum, Japanese Patent Laid-Open Publication No. 166220/1985 (referred to as “Publication No. 3” hereinafter) discloses a process wherein an amorphous fibrous alumina sol is produced from metallic aluminum and an organic acid; and Japanese Patent Laid-Open Publication No. 24824/1993 (referred to as “Publication No. 4” hereinafter) discloses a process wherein hydrochloric acid is added in the presence of silicic acid ion and sulfuric acid radical to produce an amorphous alumina sol of bunchy fibers having a diameter of 20 to 100 &mgr;m and a length of 200 to 500 &mgr;m.
As examples of the processes using a starting material analogous to that of the present invention, that is, the processes for producing alumina forming products wherein ultrafine boehmite or bayerite is synthesized from alumina having &rgr;- and &khgr;-crystal structures obtained by the contact of aluminum hydroxide with hot gas and the boehmite or bayerite is used to produce alumina forming product, the following ones can be mentioned. Japanese Patent Publication No. 21319/1975 (referred to as “Publication No. 5” hereinafter) discloses a process for producing an active alumina forming product. Japanese Patent Laid-Open Publication No. 74994/1976 (referred to as “Publication No. 6” hereinafter) discloses a process for producing a forming product carrier for a high-purity, thermally stable, active alumina supported catalyst. Japanese Patent Publication No. 13446/1984 (referred to as “Publication No. 7” hereinafter) discloses a process for producing alumina in the form of flaky or bunchy ultrafine boehmite. Japanese Patent Laid-Open Publication No. 72624/1986 (referred to as “Publication No. 8” hereinafter) discloses a process for producing dispersible hydrated aluminum oxide having a low bulk density.
In the general process for producing an alumina forming product, aluminum salt, aluminate or the like is hydrolyzed to produce an alumina hydrogel in the presence of a salt as a by-product, and the hydrogel is subjected to washing of the salt and concentration to obtain an alumina forming product. In the forming product obtained by the process, the surface area and the pore volume can be made large, but the pore structure and the strength are insufficient. In such circumstances, Japanese Patent Laid-Open Publication No. 26512/1986 (referred to as “Publication No. 9” hereinafter) describes improvement of the pore structure. With respect to industrial forming, Japanese Patent Laid-Open Publications No. 7164/1971 and No. 16395/1972 (referred to as “Publication No. 10” and “Publication No. 11”, respectively, hereinafter) disclose a process comprising washing an alumina hydrogel obtained by hydrolysis over a filter to remove a salt as a by-product, subjecting the hydrogel filter cake containing a large amount of water to spray drying in a hot gas to obtain a dry product, pulverizing the product, adjusting the water content and forming. Japanese Patent Laid-Open Publication No. 104568/1994 (referred to as “Publication No. 12” hereinafter) discloses a process comprising washing a hydrogel obtained by hydrolysis, drying the hydrogel, mixing the dry gel in a mixer in the presence of a deflocculating agent, and extruding the mixture.
The hydrogenation catalyst carrier for use in the petroleum refining industry is produced by the hydrolysis method capable of making the pore volume large, but the strength of the resulting catalyst is insufficient. In the petroleum refining industry, the insufficient strength of the catalyst may cause such a serious problem that powdering of the catalyst takes place in the reactor to mainly cause a biased stream, whereby a local abnormal high temperature is brought about.
In the three way catalysts for the automobile exhaust gas purification, catalyst carriers wherein materials mainly made of alumina are supported on honeycombs made of cordierite or stainless steel are employed. The corrugated catalyst carriers having a laminated structure are ideal in other catalytic reactions, but they have not been commercialized yet.
In the process for producing an alumina sol using aluminum alkoxide, that is described in Publication No. 1, an alumina sol is synthesized in an alumina concentration of 5 to 10%, and the alumina sol is concentrated by heating to have a concentration of up to 20%. The fiber form is not described, but from the viscosity formula of the colloidal solution, it is easily presumed that the resulting boehmite particle in the low-viscosity alumina sol is extremely short. The alumina forming product obtained from the particles has a three-dimensional network with narrow voids even when the alumina sol is converted to a hydrogel, and therefore it becomes difficult to ensure a sufficient pore volume. In the process of Publication No. 2, colloidal boehmite in the form of needles of 200 to 500 nm and having a low content of water of crystallization is obtained, but there remain problems such as that plural kinds of aluminum alkoxides are used, the synthesized alumina sol has only a low alumina concentration of not more than 1%, and because of the too low alumina concentration, extensive equipment and a large number of steps are necessary for conducting concentration. Moreover, there is a commercial problem such that the use of the special aluminum alkoxide and the synthesis conditions within the low-concentration region make it impossible to mass produce alumina sols at low costs.
In each of the processes of Publications No. 3 and No. 4 to produce a fibrous alumina sol from metallic aluminum, an alumina sol of amorphous fibrous particles is obtained. In the fibrous alumina sol obtained by the process described in Publication No. 4, the fibers are in the form of bunches. In such alumina sol of bunchy f
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