JP4843292B2 - Fine particle cobalt trioxide containing acid component and method for producing the same - Google Patents

Description

  The present invention relates to particulate cobalt trioxide useful as an adsorbent and remover for harmful gases and malodorous gases including VOC and a method for producing the same.

  Cobalt tetroxide has been used in the past for catalysts and ceramic colorants. Cobalt tetroxide used in such applications has a large particle size and can be used at a size of several tens of micrometers. It is common. The above-described production of cobalt tetroxide is usually carried out by a dry method. For example, cobalt tetroxide is produced by pulverizing coarse particles of cobalt tetroxide to make fine particles.

  However, such a dry pulverization method cannot produce nanometer-sized fine particle cobalt tetroxide, and the particle size is large for applications requiring fine particle cobalt tetroxide. there were. As a means for solving this problem, the present inventors have found a method for producing a nanometer-sized cobalt tetroxide pigment by employing a wet method, and have already filed an application (Japanese Patent Application No. 2005-239450). .

However, in the above-mentioned application invention, the specific surface area of the pigment obtained for firing at a temperature of 300 ° C. or higher is at most 50 m ² / g or less. This size is too large for the purpose of use as an adsorbent or remover for harmful gases such as VOCs and odorous gases. Further, the pH value of the tribasic cobalt oxide pigment obtained by this method is 7 to 9 according to the method of JIS K5101-17-1. For the purpose of using it as an adsorbent or remover for harmful gases and odorous gases, Cobalt tetroxide exhibiting a pH value does not exhibit sufficient characteristics.

Accordingly, an object of the present invention is to provide a completely new fine particle having a small particle diameter and a BET specific surface area in the range of 125 to 300 m ² / g, and useful as an adsorbent or remover for harmful gases such as VOC and odorous gases. It is to provide cobalt oxide and a method for producing the same.

As a means for achieving the above object, the present invention employs a wet method for the production of cobalt tetroxide, thereby making it possible to reduce the particle size and using an alkali such as sodium carbonate as an alkaline precipitant In order to obtain fine particles of cobalt tetroxide having a large BET specific surface area in the range of 50 to 300 m ² / g and showing acidity, there is also generation of pores during heat treatment of basic carbonate. As a result, the present invention has been achieved.

That is, the present invention is a water-soluble salt of cobalt, sodium carbonate in an aqueous medium, with sodium or sodium bicarbonate hydroxide, cobalt hydroxide, carbonate Shioma other precipitating as their mixtures, the precipitate Provided is a method for producing fine particle cobalt tetraoxide containing an acid component, characterized in that after the heat treatment, the obtained fine particles are acid-treated in a pH range of 1 to 3 inclusive.

In the above-described present invention, the heat treatment temperature is preferably in the range of 200 to 400 ° C.. Moreover, before heat-treating the precipitate, it is preferable to oxidize the precipitate which is a hydroxide, carbonate or a mixture thereof with an oxidizing agent.

Further, the present invention is a nanometer size, the acidity is a pH value of 5.5 or less by the method of the pigment test method JIS K5101-17-1, and the BET specific surface area is 125 to 300 m ² / g. There is provided a particulate cobalt trioxide characterized by being.

  The particulate cobalt trioxide obtained by the present invention is very useful as an adsorbent or remover for harmful gases such as VOC and malodorous gases. Furthermore, the fine particles can be used as they are, or incorporated into various processed bodies.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments.
As the cobalt source of the fine particulate tribasic cobalt oxide of the present invention, cobalt salts such as cobalt nitrate, cobalt chloride, and cobalt sulfate can be used. It is also possible to use cobalt oxide or cobalt carbonate dissolved in a corresponding inorganic acid as an aqueous solution of a cobalt salt. As an alkaline substance for precipitating cobalt from the salt solution as an oxide, hydroxide or carbonate, sodium hydroxide, sodium carbonate, sodium hydrogen carbonate and the like can be used. Such an alkali is preferably used as an aqueous solution.

  Prepare the cobalt hydroxide aqueous solution (which may contain cobalt carbonate and cobalt oxide) by preparing both the cobalt salt aqueous solution and alkaline aqueous solution separately and dropping them into the precipitating water prepared in advance. Can be made.

  In this case, when sodium hydroxide is used as the alkali to be used, the precipitate formed is very fine, and as a result, very fine particles are aggregated to form a hard lump during drying. Dispersion is difficult and handling becomes difficult. However, the use of sodium hydroxide is easy to cause these states, and fine cobalt tetroxide having the desired properties in the present invention can be obtained. On the other hand, when sodium carbonate is used as the alkali source, the precipitated fine particles of cobalt tetroxide are less agglomerated and the fine particles of cobalt tetroxide are easily dispersed. preferable.

  In addition, since the carbon dioxide gas is released from the basic cobalt carbonate produced when sodium carbonate is used as an alkali during the subsequent heat treatment step, there is an effect of increasing the specific surface area of the particulate cobalt trioxide obtained by generating pores. Therefore, it is more preferable. The precipitation temperature at this time is preferably 50 to 70 ° C. If it is lower than that, it is difficult for cobalt ions to precipitate as an insoluble substance, and the amount of sodium carbonate during precipitation is much higher than the theoretical amount. It is difficult to wash.

  In addition, the pH at the time of alkali addition is suitably in the range of 6.0 to 8.0, and precipitation of cobalt hydroxide is not generated in a lower pH range. In addition, in the pH range higher than this, the bulk of the obtained fine cobalt tetroxide is large and easily scattered, so that the handling property is deteriorated.

  The particles produced by the addition of alkali precipitate as fine colloidal particles of several nm during this step, and gradually aggregate to adjust to a range of several nm to 100 nm. This particle size is basically kept at this size until the end of the final process, although there is some shrinkage during the heat treatment.

On the other hand, in the case of the conventional method for producing cobalt tetroxide particles by dry method, the particle size is adjusted by pulverizing coarse cobalt tetroxide particles, so that the pulverization is not uniform, and thus obtained. The particle diameter is about several tens of μm, and the size and shape of the particles are not uniform. Therefore, the production by the wet method is excellent for the preparation of fine cobalt trioxide having a fine particle diameter of several nm to 100 nm and a BET specific surface area having a large value of 50 to 300 m ² / g. The concentration of the precipitate slurry is suitably within 6% by mass (ratio of fine particles to be produced). If it is higher than this, the particles become larger and move away from the target fine particle cobalt trioxide.

  It is also an object of the present invention to oxidize divalent cobalt to a trivalent cobalt precipitate in a liquid phase in advance by adding an oxidizing agent such as hydrogen peroxide to the precipitate slurry synthesized as described above. Useful for the synthesis of particulate cobalt trioxide. Addition of an oxidizing agent such as hydrogen peroxide may be performed by dropwise addition of the salt solution and the alkali solution after the precipitation reaction is completed and during the reaction. In either case, good results can be obtained. The purpose of the addition of an oxidizing agent such as hydrogen peroxide is to oxidize cobalt ions. By this operation, the hydroxide or carbonate of cobalt is dehydrated to be converted into an oxide or slightly crystallized trivalent cobalt. Change to hydroxide. By such a process, the production | generation of the fine particle cobalt tetroxide in a heat treatment process becomes easy to produce | generate at low temperature.

  If the amount of hydrogen peroxide added is 10% by mass (35% hydrogen peroxide) with respect to the theoretically generated amount of the cobalt compound to be produced, the effect can be sufficiently exerted. When the amount is 10% by mass or more, there is almost no difference in effect, and when it is 50% by mass or more, hydrogen peroxide as a material is wasted.

  The cobalt compound produced as described above is washed with water by decantation or Nutsche in order to remove impurities contained therein, and sufficiently washed with water until the conductivity in the slurry is 300 μS / cm or less. Do. Insufficient washing with water will adversely affect the adsorption or removal performance of the toxic gas etc. of the final fine particle cobalt trioxide. The cobalt compound thus obtained can be dried at 100 to 110 ° C. for 12 hours or more in order to remove moisture and subjected to heat treatment.

  At this time, the dried product changes to a pink or slightly brown color. In order to obtain completely black fine particles of cobalt trioxide, it is necessary to further increase the temperature and perform heat treatment. At this time, the temperature gradually changes to black when the temperature is 200 ° C. or higher. However, since it has a considerably long time, 250 ° C. or higher, desirably 300 ° C. is appropriate. When the temperature exceeds 400 ° C., the specific surface area of the fine cobalt tetroxide is reduced and departs from the object of the present invention. The heat treatment time may be maintained for about 1 hour at about 300 ° C. depending on the temperature and amount. In addition, a hot air circulation type in which oxygen is forcibly sent to the fine cobalt tetroxide is suitable for this heat treatment operation.

  The cobalt trioxide obtained in this manner is washed again with water by decantation or Nutsche to remove impurities such as sodium ions generated by heat treatment, and until the conductivity of the slurry becomes 300 μS / cm or less. Wash out the ions. Insufficient washing with water will adversely affect the adsorption or removal performance of the toxic gas etc. of the final fine particle cobalt trioxide.

  The cobalt trioxide obtained in this way is subjected to acid treatment. The acid treatment may use dried cobalt tetroxide, but it is convenient to use the slurry after washing with water. The diluted acid aqueous solution is added to the slurry washed with decantation, and the pH is adjusted to 5 or less and mixed well. Desirably, the pH is adjusted to 1 to 3. If the pH value at this time is 5 or more, the resulting fine cobalt tetroxide does not show sufficient acidity, and if it is 1 or less, the acidity is too strong and the cobalt tetroxide is considerably dissolved. After mixing well, it is filtered and dried as it is without decanting once or decanting. Any kind of acid may be used as long as it generates protons. Sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, acetic acid, and the like can be used, but sulfuric acid is most suitable because of filterability and various characteristics.

The fine particles of cobalt tetroxide showing acidity obtained as described above have a high BET specific surface area of 50 to 300 m ² / g, and adsorbents of harmful gases such as VOC and malodorous gases, especially acetaldehyde. Very effective as a remover.

Next, the present invention will be described more specifically with reference to examples and comparative examples. In the text, “parts” and “%” are based on mass unless otherwise specified.
[Example 1]
543 parts of commercially available cobalt sulfate heptahydrate is dissolved in 1,000 parts of water to prepare a cobalt salt solution. Similarly, 269 parts of sodium carbonate as an alkali source is dissolved in 800 parts of water to prepare an alkaline solution. The obtained solution is simultaneously added dropwise to 2,000 parts of prepared water with stirring. The precipitation conditions at this time are pH 7.4, precipitation temperature 50 ° C., and dropping is completed over about 45 minutes. Next, the temperature of the precipitation slurry is raised to 70 ° C., and ripening is performed for 60 minutes in order to complete the precipitation.

  The precipitated slurry thus obtained is washed with water by decantation until the conductivity becomes 300 μS / cm or less, and the residual salt produced as a by-product is washed out. The slurry that has been washed with water is filtered with a Nutsche, and excess water is squeezed into a paste to be dried. The temperature at that time is 110 ° C., and drying is performed for 12 hours.

  The heat treatment is performed using a circulating hot air dryer, adjusted to 300 ° C., held at that temperature for 2 hours, and taken out after natural cooling. The microparticulate cobalt tetraoxide after heat treatment is alkaline with pH 11.2 when immersed in water, confirming that residual alkali has been discharged. Wash with water, and wash with water by decantation until the pH is around 8 and the conductivity is 300 μS / cm or less.

The fine particle cobalt trioxide slurry thus obtained is then acid treated. While stirring 3% dilute sulfuric acid solution prepared in advance, the slurry is added until the pH value of the slurry becomes 2.5. Since the pH value rises after stirring for a while, a small amount of 5% sulfuric acid solution is added to maintain the pH of 2.5, and the mixture is kept for 30 minutes. The obtained acidic slurry is filtered and dried as it is without being decanted. Drying is performed at 110 ° C. for 12 hours. The pH value measured by the pigment test method JIS K5101 17-1 of the obtained fine particle cobalt trioxide was 4.1. The BET specific surface area was 130 m ² / g.

  Moreover, in order to evaluate the adsorption | suction and removal capability of noxious gas and malodorous gas including VOC of the obtained fine particle cobalt tetroxide, it used for the next test. A 300 ml Erlenmeyer flask was charged with 1 μl of a 2% acetaldehyde aqueous solution and allowed to stand at 25 ° C. for gasification. 0.2 g of the obtained fine cobalt tetroxide was put in and sealed, and after a predetermined time, the residual concentration of acetaldehyde in the flask was measured using a Kitagawa gas detector. As a result, as shown in Table 1, it was found that acetaldehyde was adsorbed or removed very efficiently. In addition, a blank shows the case where fine particle cobalt trioxide is not thrown in.

[Example 2]
Synthesis was carried out in the same manner as in Example 1 except that 240 parts of sodium carbonate, precipitation condition pH 6.8, and temperature 60 ° C. were obtained to obtain fine-particle cobalt tetraoxide. The thus-obtained slurry pH value after soaking in water after 300 ° C. heat treatment was 4.9, and the amount of treatment with 3% sulfuric acid was less than that in Example 1.
The fine cobalt tetroxide obtained in this manner was evaluated by the same test as in Example 1. As a result, it had a BET specific surface area of 160 m ² / g, and the adsorption or removal ability of toxic gases and the like is also shown in Table 1. The result was good.

[Example 3]
When 290 parts of sodium carbonate is added and a cobalt salt aqueous solution and an aqueous alkali solution are dropped simultaneously, a solution obtained by dissolving 60 parts of 35% hydrogen peroxide in 120 parts of water is dropped simultaneously to oxidize cobalt to trivalent in advance. Except for the above, synthesis was performed in the same manner as in Example 1 to obtain fine-particle cobalt tetraoxide. The fine particle cobalt trioxide obtained in this way was subjected to the same test as in Example 1, and the pH value measured by the pigment test method JIS K5101 17-1 was 4.0. The BET specific surface area was 125 m ² / g. Moreover, as shown in Table 1, the acetaldehyde adsorption / removal ability was good.

[Comparative Example 1]
Commercially available copper sulfate pentahydrate 105.6 parts, manganese sulfate monohydrate 133.3 parts and cobalt sulfate heptahydrate 55.4 parts are dissolved in water 800 parts to prepare a mixed solution. Similarly, 125 parts of sodium hydroxide as an alkali source is dissolved in 800 parts of water to prepare an alkaline solution. Similarly, a solution is prepared by diluting 80 parts of hydrogen peroxide with 200 parts of water as an oxidant solution. The obtained solution is simultaneously dropped into 1000 parts of prepared precipitation water with stirring at three points. Under the present circumstances, dripping is complete | finished over 45 minutes at pH10.7 and the precipitation temperature of 25-30 degreeC. All excess alkali is added. Next, the temperature of the precipitation slurry is aged at 30 ° C. to complete the precipitation.

  The resulting precipitated slurry is washed with water by decantation, washing to an electric conductivity of 300 μS / cm or less, and residual salt produced as a by-product is washed out. The slurry after washing with water is filtered through a Nutsche and dried. Drying is performed at 110 ° C. for 12 hours and used for the test sample.

The obtained copper, manganese, cobalt hydroxide or oxide mixture has a BET specific surface area as large as 240 m ² / g and is known to efficiently adsorb various gaseous substances.

  The test results of various samples obtained as described above are shown in Table 1. As can be seen from the table, the fine cobalt tetroxide containing the acid component has the ability to efficiently adsorb or remove acetaldehyde gas, which is very difficult to deodorize.

  Conventionally, activated carbon has been generally used as an adsorbent or remover for malodorous gases such as VOC and harmful gases. On the other hand, as a deodorizer such as hydrogen sulfide, copper, cobalt, and manganese-based composite oxides have high adsorption ability and removal characteristics and have been used in various fields. However, there has been no adsorbent or deodorant exhibiting good performance in VOC gas such as acetaldehyde. The particulate cobalt trioxide containing the acid component of the present invention has the ability to adsorb or remove acetaldehyde very efficiently, and can be used as a deodorizing agent for these gases. It can also be used as a deodorizer for various VOCs.

Claims (4)

Nanometer sized, pH values by the method of pigment test method JIS K5101-17-1 as acidity is 5.5 or less, and, BET specific surface area, characterized in that it is a 125 ~300m ² / g Fine cobalt trioxide. A method of manufacturing a particulate tricobalt tetroxide according to claim 1, the water-soluble salts of cobalt, sodium carbonate in an aqueous medium, with sodium or sodium bicarbonate hydroxide, cobalt hydroxide, carbonate or is precipitated as mixtures thereof, after heat treatment of the precipitate, resulting microparticles and the pH is fine tricobalt tetroxide containing an acid component, characterized in that the acid treatment with 3 or less in the range greater than 1 Production method. The method for producing particulate cobalt trioxide according to claim 2 , wherein the heat treatment temperature is in the range of 200 to 400 ° C. The method for producing fine-particle cobalt trioxide according to claim 2 or 3, wherein the precipitate, which is a hydroxide, carbonate or a mixture of cobalt, is oxidized with an oxidizing agent before heat-treating the precipitate.