JPS61149240A - Molded catalyst for decomposing hypochlorite and preparation thereof - Google Patents

Abstract

PURPOSE:To eliminate the generation of NOX gas, by molding a catalyst from a mixture consisting 60-90wt% of nickel sesquioxide, 1-30wt% of SiO2 or 1-15wt% of Al2O3 and 0.1-10wt% of a molding aid. CONSTITUTION:10-100pts.wt. of a silica sol or alumina sol is added to 100pts. wt. of nickel sesquioxide and both of them are mixed and dried. Subsequently, the resulting mixture is baked at 300-500 deg.C and 0.1-10wt% of a molding aid is added to the baked mixture before press molding. The molded one is baked at 300-500 deg.C to obtain a molded catalyst for decomposing hypochlorite containing 60-90wt% of nickel sesquioxide, 1-30wt% of SiO2 or 1-15wt% of Al2O3 and 0.1-10wt% of the molding aid. As the molding aid, sodium stearate, magnesium stearate or boric acid can be used.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a catalyst for decomposing hypochlorite in an aqueous solution, and more specifically to a catalyst for decomposing hypochlorite ions in an aqueous solution of hypochlorite. The present invention relates to a molded catalyst that decomposes chloride into chlorine ions and molecular oxygen, and has a high decomposition ability that is stable for a long time even in high-concentration hypochlorite aqueous solutions, and a method for producing the same.

Wastewater containing hypochlorite ions is generated from processes in factories that manufacture chlorine and caustic soda, bleaching disinfectants such as bleaching powder and chlorinated cyanuric acid, and pulp bleaching processes.

Hypochlorite ions in aqueous solutions are toxic to fish, shellfish, and aquarium plants, and corrode many metals.

For this reason, wastewater containing hypochlorite ions is usually reduced and discharged into public rivers, lakes, the sea, etc.

(Prior art) As a chemical decomposition method for removing hypochlorite from an aqueous solution, for example, H, O□, NaSHNag SO
2. NaH3O5, Na, s, 03, NaN0□, etc. are used, but the treatment cost is high for large amounts of wastewater, and Na5H and Na25O1 make the treated water cloudy, so they are not used in secondary or tertiary wastewater treatment. Is required. Therefore, all of these chemical treatments require a large amount of expense for wastewater treatment.

A catalytic decomposition method has been proposed as a method for economically treating large amounts of highly concentrated hypochlorite aqueous solutions.

Heavy metals, particularly cobalt, nickel, copper, iron, etc., and their salts, oxides, and hydroxides are known as catalysts for decomposing hypochlorite in an aqueous solution.

For example, it is known that certain transition metals act as catalysts for decomposing hypochlorite into chloride ions and oxygen (Japanese Patent Application Laid-Open No. 115002/1982).

However, since this method uses transition metal ions, it is not economical because it requires dissolution loss and complicated steps to prevent the loss, and it also has the possibility of contaminating wastewater with heavy metals.

Further, a hypochlorite decomposition catalyst consisting of oxides or hydroxides of iron, copper, magnesium, nickel, and cobalt has been reported. Among the metals mentioned above, cobalt is reported to have the highest decomposition ability, but cobalt is expensive and therefore uneconomical.

These catalysts are used in the form of powder, granules, or pellets. Powdered catalysts float due to molecular oxygen produced in the decomposition reaction, resulting in loss of useful catalyst. To prevent this, a complicated catalyst recovery process is required. For this reason, shaped catalysts are preferred. When producing this shaped catalyst, in most cases, the nitrate is neutralized with an alkali, filtered with a hydroxide, and washed with water, or a carrier such as ceramic is impregnated with the nitrate and fired to obtain an oxide catalyst. An oxide catalyst is produced by impregnating a molded carrier with nitrate, drying it, and then calcining it. At this time, a large amount of harmful NO, 1 is generated, so a NOx gas abatement device is required.

(Problems to be Solved by the Invention) In producing a catalyst for decomposing hypochlorite, the present inventors have developed a method that does not generate the above-mentioned NOX, and moreover, fills a fixed bed reactor with the catalyst for a long period of time. The present invention was completed through intensive research into a catalyst that does not disintegrate even when waste fluid containing hypochlorite is treated and has a very long catalyst life.

(Means for solving the problem) That is, the molding for decomposing hypochlorite of the present invention contains 60 to 90% by weight of nickel sesquioxide, and 1 to 30% by weight of SiO2 or 1 to 15% by weight of AlzO3. %, and 0.1 to 10% by weight of a molding filler.

The manufacturing method is per 100 parts by weight of nickel sesquioxide,
10 to 100 parts by weight of silica sol or alumina sol is added, mixed, dried, and fired at 300 to 500°C. To this fired product, 0°1 to 10% by weight of a molding agent is added, and pressure molded to 300 to 500°C. It is characterized by being fired at 500°C.

Nickel oxide, which is the catalyst of the present invention, is obtained by calcining nickel carbonate or basic nickel carbonate, and compositionally corresponds to nickel sesquioxide.

However, ordinary nickel sesquioxide is a fine particle of about 0.1 μm in size, and it is extremely difficult to mold the powder.

In molding the present invention, nickel sesquioxide powder is kneaded using water-soluble high concentration silica sol or alumina sol as a binder, and dried at 100-110°C to remove moisture. As the high-concentration silica sol, "Snow Typhoid" manufactured by Nissho Kagaku Co., Ltd., and as the high-concentration alumina sol, "Alumina Sol-100J" and "Alumina Sol-200" can be suitably used. These binders include nickel sesquioxide 10
Add 10 to 100 parts by weight to 0 parts by weight and knead. Preferably, by adding and kneading 20 to 30 parts by weight, less water can be removed by drying.

The kneaded and dried composition containing di-nokel sesquioxide as a main component is heated to 300 to 500°C, preferably 380 to 400°C.
Heat treatment at 20°C. At temperatures above 500°C, sintering of nickel sesquioxide occurs, resulting in a significant loss of activity as a hypochlorite decomposition catalyst.

Further, at temperatures below 300°C, silica and alumina do not form stable alkali-resistant compounds and therefore do not function as binders. Heating time varies depending on the processing temperature, but from IO minutes to
Heat treatment for 3 hours. This heat treatment imparts alkali resistance to the binder.

Next, the heat-treated powder or granules are shaped and subjected to a re-firing treatment. Molding is carried out by adding 0.1 to 10% of ordinary molding additives such as sodium stearate, magnesium stearate, aluminum stearate, boric acid, and talc. Preferred molding agents are boric acid and talc.

Furthermore, high concentration silica sol and high concentration alumina sol used as binders are most suitable as binders that can be fired in a state with a large specific surface area, which is preferable for decomposing hypochlorite. This binder retains a large specific surface area even when it is powdered by firing at 4.degree.

The firing temperature of the molded product is 300-5, the same as the initial firing temperature.
00°C, preferably 380-420°C.

Various shapes are possible for the shaped catalyst, but a cylindrical or ring shape is preferred. The size of the catalyst is such that the diameter of the catalyst is less than 1/4 of the inner diameter of the fixed bed filled in the fixed bed reactor. If the diameter of the catalyst is 1/4 or more of the inner diameter of the fixed bed, liquid permeation will be poor and catalyst utilization efficiency will be poor.

As mentioned above, the catalyst composition of the present invention is preferably used as a molded product in a fixed bed reactor, but even if it is in granular form, if a reactor suitable for the catalyst form is used, Can be used as a chlorate decomposition catalyst.

(Effect of the invention) The shaped catalyst of the present invention efficiently decomposes hypochlorite contained in a high concentration in an aqueous solution, does not disintegrate the catalyst, and does not require a catalyst separation process, so it can be used in industrial applications. It is a shaped catalyst for hypochlorite decomposition that is extremely excellent in terms of performance. Furthermore, the method for producing the shaped catalyst allows the above-mentioned shaped catalyst to be produced without generating NOx during the production process.

EXAMPLES Hereinafter, the method for producing the shaped catalyst of the present invention and the decomposition of an aqueous hypochlorite solution using the catalyst will be explained in more detail with reference to Examples.

Example 1 [Production method of catalyst] Nickel sesquioxide powder (commercial product, purity 95% min)
To 100 parts, 30 parts of high concentration silica sol (Snowtex-〇, SiO, containing 30%) is added and mixed with a mixer. This mixture was dried at 10θ to 110°C for about 16 hours to obtain granules, which were calcined at 400°C for 1 hour. Talc (980g of the granules thus obtained) (
Add 20 g of talc, hydrated magnesium silicate) and form into a cylindrical pellet with a diameter of 3/16 inches and a length of 3/16 inches using a tablet machine.

〔Example of use〕

A packed tower with an inner diameter of 25 mm was filled with 100 g of catalyst, and an aqueous solution of sodium hypochlorite (available chlorine 3.5%) was passed through the top of the packed tower at a flow rate of 7.5 mlZ at 50°C. The available chlorine in the effluent was 0.175%, and the hypochlorite was 9.
Indicates that 5% has been decomposed. Further, no nickel was detected in the effluent, and no loss of catalyst was observed.

Example 2 A shaped catalyst was produced in the same manner as in Example 1 except that the pellets had a diameter of 5/8 inch and a length of 5/16 inch.

40 kg of this catalyst was placed in a packed column with a cross-sectional area of 0.049 rrr.
Filled with hypochlorite (available chlorine 3.0-3°5%)
An aqueous solution containing 200! ! The liquid was passed continuously at a rate of /hour. The catalyst did not disintegrate even after being used for more than 4 months, the available chlorine in the effluent remained below 0.2%, and the decomposition rate of hypochlorite was 94% to 98%.

Comparative Example 1 A commercially available molecular sieve 5A (4 mm spherical product) was immersed in nickel nitrate, dried and calcined at 400° C. for 1 hour to obtain a catalyst supporting 30% of nickel sesquioxide.

100g of this catalyst was packed into a packed tower with an inner diameter of 25mm, and a hypochlorite aqueous solution (available chlorine 2.6%) was added at 70℃ for 4 hours.
．． The liquid was passed at a rate of 3 mρ/min. The available chlorine of the effluent is 0.65
%, and the decomposition rate of available chlorine was 75%. Also,
The effluent was colored reddish-purple, and nickel elution was 50 ppm.
The leakage of nickel was quite large.

Comparative Example 2 Commercially available nickel molded catalyst (Nissan Girdler Catalyst Co., Ltd. G
-53D) was packed into a packed tower with an inner diameter of 25 mm in the same manner as in Example 1, and sodium hypochlorite (available chlorine 3.5%
) at 50℃7. When 5 ml of liquid was passed through the solution, the catalyst collapsed in about 10 minutes.

Further, the available chlorine at the outlet immediately after the start of liquid passage was 1.4%, which was inferior to that in Example 1.

Comparative Example 3 No graphite was added to a commercially available nickel oxide granular catalyst.
．． Added 5% by weight and made into tablets with a diameter of 3/16 inches and a length of 3
/16 inch cylinder shape and baked at 400°C for 1 hour. Example 1 100 g of the shaped catalyst obtained in this way was
Similarly, 100g was packed into a packed tower with an inner diameter of 25mm,
4. Sodium hypochlorite (available chlorine 2.6%) at 70°C.
When the liquid was passed for 3 m7!7 minutes, the catalyst collapsed in about 20 minutes and the liquid could no longer be passed. Further, the available chlorine at the outlet immediately after the start of liquid passage was 0.65%, which was inferior to that in Example 1.

Claims (1)

[Scope of Claims] 1) A shaped catalyst for decomposing hypochlorite in an aqueous solution, wherein the shaped catalyst contains 60 to 90% by weight of nickel sesquioxide.
Contains SiO_21-30% by weight or Al_2O_
A shaped catalyst for decomposing hypochlorite, characterized in that it contains 1 to 15% by weight of C.3 and 0.1 to 10% by weight of a shaping filler. 2) Add 10 to 100 parts by weight of silica sol or alumina sol per 100 parts by weight of nickel sesquioxide, mix, dry, and sinter at 300 to 500°C, and add 0.1 to 10 % by weight of a molding agent to this baked product. Added, pressure molded,
By firing at 300-500℃, 60% of nickel sesquioxide
-90% by weight, 1-15% by weight of SiO_21-30% by weight or Al_2O_3, and 0.5% by weight of molding filler.
A method for producing a shaped catalyst for decomposing hypochlorite containing 1 to 10% by weight.