This application is the national phase under 35 U.S.C. xc2xa7371 of PCT International Application No.
PCT/JP99/00391 which has an International filing date of Jan. 29, 1999, which designated the United States of America.
The present invention relates to a method for manufacturing a pseudo-boehmite powder as a raw material for producing a carrier for a catalyst for hydrogenation refining. In particular, the present invention relates to a method for manufacturing pseudo-boehmite by effectively utilizing waste water and sludge discharged from the aluminum surface-processing steps, and the present invention also relates to a method for producing a catalyst carrier and a method for producing a hydrogenation catalyst.
In the petroleum refining, a catalyst, in which a metal component having a hydrogenation ability is carried on an alumina carrier, is used as catalyst for hydrogenation refining in many cases. The alumina carrier can be produced by mixing, kneading, and forming a fine powder of pseudo-boehmite as an alumina hydrate, followed by calcination. The pseudo-boehmite powder, which is used as a raw material for the alumina carrier as described above, is produced by using a first method (1) in which an aluminic acid or aluminum salt is formed from gibbsite (aluminum hydroxide) followed by performing a reaction therewith, or a second method (2) in which aluminum alkoxide is hydrolyzed to synthesize the pseudo-boehmite powder. The characteristics of the obtained catalyst are greatly affected by the quality and the characteristics of the alumina carrier and the pseudo-boehmite. Therefore, in general, a high purity aluminum source is used as the raw material of the pseudo-boehmite powder.
When an aluminum product to be used for building materials such as sashes made of aluminum is produced, a treatment is performed in which an aluminum oxide coating forms on the formed aluminum by means of an electrochemical method to improve the corrosion resistance, the abrasion resistance, and the appearance of beauty. This treatment uses a process comprising the steps of, for example, anodization, etching, and washing with water, and it is called the alumite treatment. FIG. 1 shows a series of aluminum surface treatment process including the alumite treatment.
As shown in FIG. 1, the aluminum material is first subjected to the surface degreasing, and it is washed with water. After that, the material is subjected to the alkaline etching step. In the alkaline etching step, the surface of aluminum is dissolved with caustic soda or sodium hydroxide in an amount of several xcexcm to several tens xcexcm. Subsequently, the steps of washing with water, neutralization, and washing with water are performed, and then the material is subjected to anodization or an anodic oxidation step. In the anodization, an oxide coating is formed on the surface of the aluminum material in an electrolytic solution such as sulfuric acid. After the anodization, the washing step is further performed with water, optionally followed by coloring and sealing steps to obtain the product.
A large amount of alkaline waste liquid, in which metal aluminum is dissolved at a dense concentration, is produced in the alkaline etching step. In order to effectively utilize the alkaline waste liquid, aluminum hydroxide is deposited from the alkaline waste liquid. On the other hand, the resultant recovery liquid is reused by returning it as caustic soda to the alkali etching step. The deposited aluminum hydroxide has its water concentration of 12 to 15%, and it is a crystalline aluminum hydroxide called gibbsite. This product has been hitherto used as a material for cement and ceramic industries.
In the anodization step described above, an acidic waste liquid (sulfate waste liquid) dissolved with metal aluminum is also produced. In order to treat the acidic waste liquid, diffusion dialysis method has been hitherto used so that sulfuric acid and aluminum sulfate are recovered. In other cases, an alkaline waste liquid, which is produced by the alkaline etching, has been hitherto mixed with the acidic waste liquid to recover aluminum hydroxide.
Further, aluminum dissolved in a washing liquid also exists in the step of washing with water after the alkaline etching and the steps of washing with water before and after the anodization. The washing liquids are gathered and neutralized, followed by solid-liquid separation to obtain sludge or slime containing aluminum hydroxide. The aluminum hydroxide in the sludge has a high water content, and it is an amorphous aluminum hydroxide in a form of gel. Therefore, the aluminum hydroxide sludge has troubles concerning the treatment and disposal. The sludge contains a large amount of other metal components which are components of the aluminum alloy other than aluminum, and it has been hitherto processed by reclamation, or it has been hitherto processed by dissolving it in a by-product of aluminum sulfate. The aluminum sulfate contains colored ions such as those of copper and nickel having been contained in the aluminum alloy. Therefore, the aluminum sulfate is inferior in added value as compared with the high purity aluminum sulfate produced by dissolving gibbsite. As a result, for example, a problem arises in that the aluminum sulfate can be merely used for usage as a neutralizing aggregation treatment agent for processing the waste water.
The effective utilization and the problems, which relate to the waste liquid and the aluminum hydroxide sludge in the alumite processing as described above, are disclosed in detail in xe2x80x9cTechnology for Processing Waste (Aluminum Hydroxide Sludge) and Reproducing Resource from Wastexe2x80x9d issued by the juridical foundation of Clean Japan Center (February, 1981). Factories for processing and treating alumite are present at not less than 1000 sites only in Japan. The amount of produced sludge exceeds 5000 tons per year. Therefore, the waste liquid, which is produced by the alumite processing or treatment, contains a large amount of valuable components. However, in the present circumstances, it is difficult to consider that such valuable components are sufficiently reused. Further, it is demanded to reuse aluminum scrap and aluminum waste produced from the alumite treatment and from other aluminum-processing sites.
An object of the present invention is to provide a method for reproducing a resource from waste, in which a waste liquid or a sludge containing aluminum as described above is utilized as a raw material for producing a catalyst carrier.
Another object of the present invention is to provide a novel process for producing pseudo-boehmite which serves as a raw material for a catalyst carrier. Still another object of the present invention is to provide a method for producing the catalyst carrier and a method for producing a hydrogenation refining catalyst based on the use of the novel process.
Still another object of the present invention is to provide a novel method for treating alumite including the process of effectively utilizing a waste liquid and an aluminum hydroxide sludge produced from the alumite treatment.
According to a first aspect of the present invention, there is provided a method for producing pseudo-boehmite, comprising the steps of dissolving metal aluminum in an acidic or alkaline aqueous solution to prepare an acidic or alkaline aluminum aqueous solution, and producing the pseudo-boehmite from the acidic or alkaline aqueous solution.
As described in the column of the background art, the pseudo-boehmite, which is the material for producing the alumina carrier for the catalyst, is generally produced by forming aluminic acid by using high purity gibbsite as a starting material, and then reacting the obtained product. The present inventors have found out that the pseudo-boehmite can be produced by reacting, under a predetermined condition, the alkaline aqueous solution or the acidic aqueous solution dissolved with a large amount of metal aluminum discharged in a large amount as a waste liquid from the aluminum-processing site such as those for the alumite treatment. The use of this method makes it possible to reuse aluminum as a resource which would be otherwise dealt with as a waste. Further, the use of this method makes it possible to produce, at low cost, the pseudo-boehmite as well as the catalyst carrier and the catalyst based on the use of the same. The method has not been hitherto known, in which the pseudo-boehmite is produced from the starting material of the acidic or alkaline aqueous solution of aluminum obtained by dissolving metal aluminum (metallic aluminum) as described above. In this specification, the phrase xe2x80x9cmetal aluminumxe2x80x9d of the phrase xe2x80x9cdissolve metal aluminumxe2x80x9d is intended to include oxide or hydrate formed by oxidation of metal aluminum is dissolved.
In order to form the pseudo-boehmite, an acidic aluminum aqueous solution may be mixed with an aluminate aqueous solution obtained from the alkaline aluminum aqueous solution described above. Alternatively, an aluminate aqueous solution may be mixed with the acidic aluminum aqueous solution described above. Those usable as the aluminate aqueous solution include, for example, an aluminate aqueous solution produced from the alkaline etching step for aluminum in the alumite treatment. Those usable as the acidic aluminum aqueous solution include an acidic waste liquid produced from the anodization step for aluminum in the alumite treatment, i.e., an acidic aluminum aqueous solution. The acidic aluminum aqueous solution may contain metal components other than aluminum in a molar ratio of 0.001 to 0.02 with respect to total aluminum contained in the aqueous solution.
Those intended as the metal aluminum may include an aluminum material to be used in the aluminum-processing site such as those for the alumite treatment, because of the following reason. That is, a part of such an aluminum material is dissolved in alkali or acid in the following step such as the etching step to produce the acidic or alkaline aluminum aqueous solution which may serve as the material for producing the pseudo-boehmite.
The material may include an aluminum material used for any usage other than the alumite treatment.
According to a second aspect of the present invention, there is provided a method for producing pseudo-boehmite, comprising the steps of dissolving metal aluminum in an alkaline aqueous solution to prepare an aluminate aqueous solution, dissolving metal aluminum in an acidic aqueous solution to prepare an acidic aluminum aqueous solution, and mixing the prepared aluminate aqueous solution with the prepared acidic aluminum aqueous solution to form the pseudo-boehmite. According to this method, for example, the pseudo-boehmite can be produced only by mixing, under a predetermined condition, the aluminate aqueous solution produced from the alkaline etching step for aluminum in the alumite treatment and the acidic aluminum aqueous solution produced from the anodization step for aluminum in the alumite treatment. Therefore, it is possible to establish an extremely low cost process for producing pseudo-boehmite by utilizing the waste liquid. This process can be carried out in the alumite treatment factory. Accordingly, this process provides the by-product for the alumite treatment factory.
According to a third aspect of the present invention, there is provided a method for producing pseudo-boehmite, comprising the step of maturing or aging, in an alkaline solution, an aluminum hydroxide sludge produced from an alumite treatment. The present inventors have succeeded in producing the pseudo-boehmite only by treating the aluminum hydroxide sludge under a predetermined condition, while being limited to the waste liquid produced from the alumite treatment. According to this method, it is possible to effectively utilize a huge amount of aluminum hydroxide sludge discharged from the aluminum-processing sites existing in Japan as well as all over the world. Especially, when an alkaline waste liquid, which is produced from the alkaline etching step in the alumite treatment, is utilized as the alkaline solution described above, it is possible to produce the pseudo-boehmite in a closed system established at the alumite-processing site. The aluminum hydroxide sludge may be matured, for example, in the alkaline solution at a temperature of 50 to 90xc2x0 C. under a condition of pH 8 to 12. In general, the aluminum hydroxide sludge is produced from the alkaline etching step for aluminum, and the washing steps performed before and after the anodization step in the alumite treatment.
According to a fourth aspect of the present invention, there is provided a method for treating alumite comprising the steps of alkaline etching for aluminum, anodization, and washing performed thereafter, the method further comprising the step of producing pseudo-boehmite by using an alkaline waste liquid produced from the alkaline etching step, an acidic waste liquid produced from the anodization step, or an aluminum hydroxide sludge produced from the washing step. In the alumite treatment method according to the present invention, the pseudo-boehmite, which serves as a raw material for a catalyst carrier, can be provided as a by-product. Especially, the pseudo-boehmite can be produced in the alumite treatment factory by mixing the alkaline waste liquid produced from the alkaline etching step and the acidic waste liquid produced from the anodization step. In addition to this process, or separately from this process, the pseudo-boehmite may be produced by maturing, in an alkaline solution, the aluminum hydroxide sludge produced from the washing step. The added value may be provided for the alumite treatment factory only by installing, at the alumite-processing site, the equipment for carrying out the process for producing the pseudo-boehmite as described above.