JPH07118018A - Production of manganese dioxide - Google Patents

Abstract

PURPOSE:To produce manganese dioxide having a large surface area without using a large amt. of a mineral acid and to industrially advantageously produce manganese dioxide having stable catalytic performance and high reliability. CONSTITUTION:A slurry contg. manganese hydroxide prepd. by mixing an aq. soln. of a divalent manganese compd. with an aq. soln. of an alkali metal hydroxide is subjected to oxidation treatment with a permanganate and further treated with an aq. soln. of a mineral acid to produce the objective manganese dioxide.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing manganese dioxide having a high specific surface area.

[0002]

2. Description of the Related Art Manganese dioxide as a dry battery material has titanium or the like as an anode, and a cathode is placed through the electrolyte of a manganese salt aqueous solution such as manganese sulfate, manganese chloride or manganese nitrate, and a voltage is applied between these electrodes. Applying electrolysis to remove manganese dioxide deposited on the anode, pulverize,
Most of them are neutralized, washed with water and dried. Manganese dioxide, which is used as the main component of the catalytic oxidation catalyst for carbon monoxide, which is known as an air pollutant contained in automobile exhaust gas, is a divalent manganese compound that is an oxidizing agent such as potassium permanganate. It is prepared by various chemical reaction methods that oxidize. For example, JP-A-51-71299
JP-A-54-10 discloses a method of adding potassium permanganate to a nitric acid acidic aqueous solution of a divalent manganese compound to oxidize it.
No. 6099, a method of oxidizing manganese carbonate prepared from manganese sulfate and sodium carbonate with an oxidizing agent such as potassium permanganate, J. Am. Chem. Soc., Vol. 43, 1982 (1921).
Discloses a method of oxidizing a slurry of manganese sulfate produced by adding sulfuric acid to an aqueous solution of manganese sulfate with potassium permanganate.

However, these known methods are, for example, J. Am.
The method of Chem. Soc., Vol. 43, 1982 (1921) uses a large amount of sulfuric acid and requires a step for neutralizing the sulfuric acid. Therefore, the step is very complicated or a large amount of ammonium sulfate is by-produced. There was a problem such as doing. Further, in the known method of oxidizing manganese hydroxide or manganese carbonate to obtain manganese dioxide, decomposition takes a long time at a low temperature and oxidation does not proceed sufficiently, so that at a high temperature manganese dioxide having a large surface area is obtained due to particle growth. There was a defect such as not being. Manganese dioxide is known to take various crystal forms, and the crystal form is one of the determinants of the surface area. That is, control of the crystal form was required to obtain manganese dioxide having a high specific surface area. However, since it is difficult to control the crystal form by the known method, manganese dioxide having a large surface area could not be prepared with good reproducibility. Therefore, there was a problem that the catalyst performance was not satisfactory in practice.

[0003]

[Means for Solving the Problems] The present inventors have completed the present invention as a result of extensive studies to solve the above problems. That is, the present invention is
First step of adding an alkali metal hydroxide aqueous solution to a water-soluble manganese compound solution to precipitate crystals of manganese hydroxide, and a second step of oxidizing the resulting slurry with permanganate to produce manganese dioxide The method for producing manganese dioxide is characterized by comprising the third step of aging the slurry of manganese dioxide by adding an aqueous solution of a mineral acid.

The present invention has solved the above-mentioned problems, and as a result of detailed examination of conditions and phase changes in preparing manganese dioxide from a divalent manganese compound and permanganate, It has a high specific surface area from the manganese hydroxide crystals and permanganate precipitated by controlling the pH of the divalent manganese compound aqueous solution, and has a high specific surface area for the above-mentioned catalytic oxidation reaction of carbon monoxide. On the other hand, they have found that manganese dioxide having an extremely high catalytic activity can be prepared, and have completed the present invention.

The divalent manganese compound used in the present invention is manganese sulfate, manganese carbonate, manganese nitrate, manganese chloride, manganese phosphate and the like, and either anhydrous salt or hydrate can be used. You may use together 2 or more types. The concentration of the divalent manganese compound aqueous solution is not particularly limited, but is usually 0.1 to 6.0 mol / l. The pH at the time of precipitating crystals of manganese hydroxide is usually 7 to 10, preferably 8 to 9, and is similar to the divalent manganese compound aqueous solution in which oxygen is removed by introducing an inert gas such as nitrogen. What is prepared by pouring an aqueous solution of alkali metal hydroxide without oxygen is used. The alkali metal hydroxide used is usually a lithium, sodium, potassium, rubidium or cesium hydroxide.

The permanganate used in the present invention is potassium permanganate, sodium permanganate, barium permanganate and the like, and two or more of these permanganates may be used in combination. The molar ratio of the permanganate to the divalent manganese compound is 0.5 to 2.0, preferably 0.6 to
It is 1.5. If it is less than 0.5, sufficient oxidation does not occur and manganese dioxide with high activity is not produced. If it is more than 2.0, the amount of permanganate used is too large, which is uneconomical. The oxidation treatment with permanganate may be performed by adding the permanganate to the manganese hydroxide slurry as a solid or as an aqueous solution. When using an aqueous solution of permanganate, a slurry of the aqueous solution of permanganate may be added.

In the present invention, the pH when treating the slurry after the oxidation treatment with the aqueous solution of mineral acid is usually 3 or less, preferably 1 or less. The mineral acid used is usually sulfuric acid, nitric acid, phosphoric acid or hydrochloric acid. The treatment time and aging time are 0.1 to 48 hours, preferably 0.5 to 24 hours, depending on the temperature or pH.

In the present invention, the temperature at which the divalent manganese compound aqueous solution and the alkali metal hydroxide aqueous solution are mixed to precipitate the crystals of manganese hydroxide may be either room temperature or warming, ~ 90 ° C, preferably 10
℃ ~ 70 ℃. The temperature at which such a slurry is oxidized with permanganate is 20 ° to 150 ° C, preferably 40 ° to 90 ° C. If it is lower than 20 ° C, the oxidation treatment does not proceed at a sufficient rate, and if it is higher than 150 ° C, it does not become a highly active manganese oxide. Furthermore, the temperature when treating the slurry after such an oxidation treatment with a mineral acid aqueous solution is
Usually, it is carried out within the temperature range in which the oxidation treatment is carried out. In the present invention, the manganese dioxide after the treatment with the aqueous solution of mineral acid may be subjected to a treatment of washing with water or neutralization with an alkali followed by washing with water in order to remove residual mineral acid ions.

[0009]

EXAMPLES The present invention will be described in more detail below with reference to examples. Example 1 To an aqueous solution in which 129 g of manganese sulfate 4-5 hydrate was dissolved in 1 liter of water and nitrogen was introduced to remove dissolved oxygen, an aqueous potassium hydroxide solution of pH = 11 from which dissolved oxygen was removed by introducing nitrogen was added. Thus, a white manganese hydroxide slurry having a pH of 8.5 was obtained. This slurry was heated to 80 ° C., 0.56 l of 0.76 mol / l potassium permanganate aqueous solution was added, and after the addition was completed.
The mixture was stirred at 80 ° C for 2 hours. Next, add dilute sulfuric acid to adjust the pH.
Adjust to 0.5 and stir for 1 hour, then filter with 5 l of water.
Wash twice, dry at 110 ° C for 15 hours, and dry with manganese dioxide.
I got 78g. The specific surface area was 300 m ² / g.

Comparative Example 1 Manganese dioxide was prepared in the same manner as in Example 1 except that the treatment with dilute sulfuric acid was omitted. Specific surface area is 183 m ² /
It was g.

Example 2 An oxidation catalyst was prepared by a known method using Example 1, Comparative Example 1 and commercially available electrolytic manganese dioxide. Copper sulfate Cu
SO ₄ · 5H ₂ 0 50g solution pH of a 30% aqueous sodium hydroxide solution in a copper sulfate aqueous solution obtained by dissolving in water 250ml (0.79mol / l) is approximately
Add to 10 to obtain a copper hydroxide precipitate. The precipitate is thoroughly washed until the pH of the filtrate is 7.5 or less. Next, water was added to the copper hydroxide thus obtained to make a slurry, and water was added to 10 g each of Example 1, Comparative Example 1 or commercially available electrolytic manganese dioxide to make a slurry. Add g and stir to mix well, then filter, wash, 120
A manganese dioxide-copper oxide-based oxidation catalyst was manufactured by drying at 15 ° C for 15 hours. Hereinafter, these catalysts will be referred to as catalysts A, B or C, respectively. Put 1 g of these powdery catalysts in a 300 ml glass container, introduce air containing 20% carbon monoxide, seal it, and contact it at 70 ° C to reduce the rate of carbon monoxide accompanying the reaction by FT-IR.
It was determined by measuring the absorption intensity of carbon monoxide at 2200 cm ^-1 using a spectrophotometer. As a result, the time required for carbon monoxide to reach 1/10 of the initial concentration is
C were 14 min, 18 min and 33 min respectively. It can be seen that the manganese dioxide-copper oxide-based oxidation catalyst mainly composed of manganese dioxide according to this example has excellent performance for removing carbon monoxide.

[0012]

From the viewpoint of the production method, the method for producing manganese dioxide of the present invention is advantageous in terms of cleanness and cost, since the amount of mineral acid used is small and the by-products such as ammonium sulfate due to neutralization are small. There are advantages such as. On the other hand, the manganese dioxide produced also has a large specific surface area, which is a fundamentally important factor for the catalytic performance, and exhibits excellent performance in removing oxidization of carbon monoxide and the like. As described above, according to the present invention, manganese dioxide having stable catalytic performance and high reliability can be industrially advantageously produced.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location // B01J 23/84 ZAB 8017-4G 23/889 8017-4G B01J 23/84 311 A (72) Inventor Keiichi Ikeda 1190 Kasama-cho, Sakae-ku, Yokohama, Kanagawa Mitsui Toatsu Chemical Co., Ltd. (72) Masahiro Tokuman 1190, Kasama-cho, Sakae-ku, Yokohama, Kanagawa Mitsui Toatsu Chem., Ltd.

Claims (1)

[Claims] 1. In the method for producing manganese dioxide, the first step of adding an aqueous solution of an alkali metal hydroxide to an aqueous solution of a divalent manganese compound to precipitate crystals of manganese hydroxide, the obtained slurry being permanganate. A method for producing manganese dioxide, which comprises a second step of oxidizing manganese dioxide with a salt to produce manganese dioxide and a third step of adding an aqueous mineral acid solution to the slurry of the manganese dioxide and aging.