JPH07149580A - Calcium oxide porous material having high activity and its production - Google Patents

Abstract

PURPOSE:To obtain a calcium oxide porous material having a large specific surface area and high activity, and at the same time having large particle diameters and accordingly easy handleability by granulating fine powder of calcium hydroxide or calcium carbonate followed by calcining under specified heating conditions at a relatively low temperature. CONSTITUTION:This high-active calcium-oxide porous material has a specific surface area of >=5m<2>/g and particle diameters of >=1mm. For producing this material, at first calcium hydroxide powder or calcium carbonate powder having particle diameters of <=300mum is granulated to granules having particle diameter of >=1mm. Subsequently, (1) in the case of calcium hydroxide, the obtained granules are heated under a normal pressure and calcined while the temperature is increased from 390 deg.C to 480 deg.C taking at least 5min. And, (2) in the case of calcium carbonate, the granules are heated under a normal pressure and calcined while the temperature is increased from 700 deg.C to 780 deg.C taking at least 5 min. Optionally in both cases, the granules are further calcined up to 950 deg.C within the period of the time in which the CO2 reaction ratio does not decrease to and below 40%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly active calcium oxide porous body having a large specific surface area, a large particle size and easy handling, and a method for producing the same.

[0002]

2. Description of the Related Art Calcium oxide is usually produced by calcining calcium carbonate, which is known to have different activity depending on the calcining temperature.
That is, what is obtained at a firing temperature close to the decarbonation temperature of calcium carbonate is called soft-calcined quick lime and is rich in activity, whereas that obtained at a higher temperature is called hard-calcined quick lime and has low activity. This is because the open porosity, in other words, the specific surface area, decreases due to the growth and compaction of calcium oxide crystals. For example, in the case of a pure product, the open porosity of soft burned lime is about 50% and the specific surface area is about 2 m ² / g, whereas the open porosity of hard burned lime is about 10% and the specific surface area is about 0. It is very small at 04 m ² / g.

Up to now, attempts have been made to reduce the fineness of powder and increase the specific surface area in order to obtain highly active calcium oxide, but there is a limit to reducing the size of calcium carbonate powder. As long as calcium carbonate is used as a raw material, the specific surface area cannot be increased so much, and the maximum specific surface area of the calcium oxide powder obtained by firing at normal pressure is about 3 m ² / g. Further, it has been proposed to increase the activity by firing in a vacuum, but there are many problems in the equipment and it has not been put into practical use ["Gypsum & Lim (Gypsum & Lim
e) ", No. 178, pages 31-40].

On the other hand, there is also known an example in which a fine powder of calcium hydroxide is used as a raw material, and this is fired at a temperature of 300 to 390 ° C. under vacuum to produce a calcium oxide powder having a large specific surface area of 110 to 133 m ² / g. However, the [Journal of the American Ceramic
Society (J. Am. Ceramic So
c. ) ", Vol. 64, No. 2, pp. 74-80],
The powder obtained by this method has a fine particle size of 1 to 10 μm even though it is highly active, and therefore it is difficult to handle and the field of use thereof is inevitably limited.

[0005]

DISCLOSURE OF THE INVENTION The present invention has a large specific surface area, therefore has a high activity, is large in particle size and is easy to handle, and has a wide range of catalysts, exhaust gas adsorbents, heat insulating materials for steelmaking, flux for steelmaking The purpose of the present invention is to provide a highly active calcium oxide porous body that can be used throughout.

[0006]

Means for Solving the Problems As a result of intensive studies to obtain highly active calcium oxide, the present inventors have granulated calcium hydroxide or calcium carbonate fine powder and then, under predetermined heating conditions. It was found that the calcium oxide porous body obtained by firing at a relatively low temperature exhibits high activity despite having a large particle size, and the present invention has been completed based on this finding.

That is, the present invention is at least 5 m ² /
A highly active calcium oxide porous body comprising a calcined product of calcium hydroxide or calcium carbonate granules having a specific surface area of g and a particle size of at least 1 mm.

According to the present invention, such a highly active calcium oxide porous body is obtained by granulating calcium hydroxide powder having a particle size of 300 μm or less into granules having a particle size of at least 1 mm, and heating the granulated body under normal pressure. Then, the temperature is raised between 390 and 480 ° C over at least 5 minutes, or the particle size is 300μ.
Calcium carbonate powder having a particle size of m or less is granulated into granules having a particle diameter of at least 1 mm, and the granules are heated under normal pressure to 700 to 7
The temperature is raised between 80 ° C over at least 5 minutes, and if necessary, the CO ₂ reaction rate is 40% at a temperature up to 950 ° C.
It can be produced by firing for a time within the range not lowering below.

At this time, as the calcium hydroxide used as a raw material, commercially available calcium hydroxide (slaked lime) may be used as it is, or a hydrated product of commercially available calcium oxide (quick lime) may be used. When calcium is mixed, the activity of the obtained calcium oxide is lowered, so that it is preferable to use the one having the highest purity. This calcium hydroxide is used as a powder having an average particle size of 10 to 300 μm.

The calcium carbonate may be light or heavy, and a commercially available product may be used as it is, or a product produced by passing carbon dioxide in an aqueous solution of calcium hydroxide may be used.

Next, in the granulation of calcium hydroxide powder or calcium carbonate powder, water is added to this and kneaded, and a minimum diameter of at least 1 mm, for example 3 to 6 mm, long length is obtained by using a conventional granulator. It is carried out by extrusion molding into cylindrical granules having a size of about 3 to 6 mm. The amount of water added at this time is 5 to 5 based on the weight of calcium hydroxide.
A range of 25% by weight is suitable. In this granulation,
If desired, an organic binder may be added to improve the shape retention. As the organic binder, a water-soluble polymer substance such as carboxymethyl cellulose (CMC) or polyvinyl alcohol is used. The amount of the organic binder added is appropriately in the range of 0.5 to 5% based on the weight of calcium hydroxide.

The granules thus obtained are then calcined using, for example, an electric furnace. The calcining conditions are, in the case of calcium hydroxide, a temperature in the range of 390 to 480 ° C. for at least 5 minutes. , 700 for calcium carbonate
It is necessary to raise the temperature in the range of ˜780 ° C. for at least 5 minutes. When firing under other conditions, it is not possible to obtain a highly active material having a specific surface area of 5 m ² / g or more.

In this case, the rate of temperature rise is preferably in the range of 1 to 10 ° C./minute, and in the case of calcium hydroxide, 480.
In case of calcium carbonate and calcium carbonate, when the upper limit of 780 ° C. is reached, it is preferable to stop heating as soon as possible. When the pore distribution spectrum was measured, at this point,
A peak is recognized around 02 to 0.2 μm.

In the case of large-scale treatment, it is necessary to further raise the temperature in order to complete the firing of the charged raw material, but in this case, the temperature does not exceed 950 ° C. and C
Care must be taken so that the O ₂ conversion does not fall below 40%. This is carried out, for example, by extracting a sample at regular time intervals and measuring the CO ₂ reaction rate for the sample.

This heating time is too long and the CO ₂ reaction rate is 4
When the state is reduced to 0% or less, once the highly active calcium oxide obtained is condensed, the activity begins to decrease and the time increases, and this tendency becomes remarkable.

[0016] CO ₂ reaction rate in the present invention, a mixed gas of CO ₂ and _{N 2} which are known beforehand CO ₂ concentration in the sample, is contacted for 1 minute at 20 ° C., the difference between the CO ₂ concentration before and after contact Is divided by the CO ₂ concentration before contact to obtain 10
Defined as multiplied by zero.

At the time of firing, by adding a reducing agent that decomposes at a low temperature, such as calcium fluoride,
The firing time can be shortened. Further, according to the method of the present invention, by selecting the above production conditions, it is possible to obtain calcium oxide whose activity is adjusted to a desired degree.

[0018] In this way, a specific surface area of ^{5 m} 2 / g or more, usually calcium oxide porous body having a high activity of 10 to 60 m ² / g is obtained as granules of diameter 1 to 6 mm. If necessary, this porous body is further finely pulverized to be used for various purposes.

[0019]

INDUSTRIAL APPLICABILITY The calcium oxide of the present invention has a large specific surface area of at least 5 m ² / g, and therefore exhibits very high activity. Moreover, since it is a porous body, it has a particle size larger than that of conventional calcium oxide. Since it can be used as a product such as a catalyst, an exhaust gas adsorbent, a heat retaining agent for steelmaking, a flux for steelmaking, it has an advantage of being extremely easy to handle. Further, according to the method of the present invention, there is an advantage that calcium oxide having an activity depending on the purpose of use can be obtained by selecting the production conditions.

[0020]

EXAMPLES Next, the present invention will be described in more detail by way of examples. The CO ₂ reaction rate and specific surface area in each example are obtained as follows. (1) CO ₂ reaction rate; sample 5 g, inner diameter 20 mm, length 6
The mixture was charged in a 00 mm cylindrical reactor, and a mixture of CO ₂ gas and N ₂ gas was passed at a rate of 100 ml / min at a temperature of 20 ° C., and the CO ₂ concentration in the mixture before and after contacting with the sample was measured according to JIS R6124. It was measured by the combustion capacity method and calculated from the obtained results according to the following formula.

[0021]

[Equation 1]

(2) Specific surface area: 0.5 g of each sample was measured by a BET common point method using a monosoap specific surface area measuring device (manufactured by Yuasa Ionics), and the obtained measured value was doubled. The surface area per gram was calculated.

Example 1 Calcium hydroxide powder [manufactured by Suzuki Kogyo Co., Ltd., industrial slaked lime, purity 95.9%, particle size 300 μm or less] was added with 25% by weight of water to prepare a disk pelleter [Fuji Paudal Co., Ltd.]. Manufactured] to granulate into granules having a diameter of 3 mm and a length of 3 mm.

This granule was placed in an electric furnace and the temperature rising rate was 1 ° C.
The temperature was increased to 470 ° C./min, and when the temperature reached 470 ° C., the sample was immediately taken out of the electric furnace and allowed to cool. 390 at this time
The temperature rising time from ° C to 480 ° C was 90 minutes.

The pore distribution of this product was measured using a pore distribution meter (PORESIZER9310 manufactured by Micromedix Co.), and the highest peak was observed at a position of 0.06 μm. The CO ₂ reaction rate of this product is 97.
%, The specific surface area was 57.67 m ² / g.

Example 2 Calcium carbonate powder [manufactured by Bihoku Powder Co., Ltd., purity 98%,
Granules of 150 μm or less] are granulated into granules having a diameter of 3 mm and a length of 3 mm, and the granules are placed in an electric furnace and heated from room temperature to 780
The sample was heated up to 0 ° C at a temperature rising rate of 1 ° C / min, and at the same time when it reached 780 ° C, it was taken out of the electric furnace and allowed to cool. 70 at this time
The heating time from 0 ° C. to 780 ° C. was 80 minutes. This product has a CO ₂ reaction rate of 95% and a specific surface area of 35.86.
m was ² / g.

Examples 3 to 6 Calcium hydroxide powder [manufactured by Suzuki Kogyo KK, industrial slaked lime, purity 95.9%] was 45 μm or less, 45 to 75 μm.
m, 75-150 μm and 150-300 μm, and powdered each fraction with water 2
5% by weight was added and the mixture was granulated into a granule having a diameter of 3 mm and a length of 3 to 4 mm using a disk pelleter (manufactured by Fuji Paudal Co., Ltd.), and the granule was heated at 700 ° C. at a temperature rising rate of 10 ° C./min. And then calcined at a heating temperature of 900 ° C. for 1 hour. Regarding the calcium oxide porous body thus obtained, C
The O ₂ reaction rate and the specific surface area were measured. The results are shown in Table 1.

[0028]

[Table 1]

As is apparent from this table, the particle size is 300 μm.
Calcium hydroxide powder of m or less has a specific surface area of 5 m
Gives ² / g or more of calcium oxide.

Example 7 The calcium hydroxide used in Example 1 was granulated to have a diameter of 3 mm and a length of 3 mm, and the granules were placed in an electric furnace and the temperature rising rate was 10
It was heated to 700 ° C. at a rate of ° C./min and calcined at this temperature for 30 minutes. At this time, the temperature rising time from 390 ° C to 470 ° C was 8 minutes. The pore distribution of the calcium oxide porous body thus obtained was measured. As a result, the product of the present invention is
It was found to have pores in the range 0.02-0.2 μm.

Examples 8 to 13 and Comparative Example 1 The same calcium hydroxide powder as that used in Example 6 was granulated to have a diameter of 3 mm and a length of 3 mm, and it was heated at room temperature at a heating rate of 10 ° C./min. To 400 to 1100 ° C. and baked for 30 minutes each. 39 at this time
The heating time from 0 ° C. to 470 ° C. was 8 minutes. The CO ₂ reaction rate and the specific surface area of the thus obtained porous calcium oxide body were measured, and the results are shown in Table 2.

[0032]

[Table 2]

Examples 14 to 16 and Comparative Example 2 The same calcium carbonate powder as used in Example 2 and having a particle size of 150 μm or less was granulated to a diameter of 3 mm and a length of 3 to 4 mm, and this granulated product was heated in an electric furnace. Charge from room temperature to 8 each
The temperature is raised to 00 ° C, 900 ° C, 950 ° C and 1100 ° C at a rate of 10 ° C / min, and after reaching the maximum temperature, 30
Bake for minutes. Then, each sample was taken out from the electric furnace and cooled to obtain a calcium oxide porous body. C of this thing
The O ₂ reaction rate and the specific surface area were measured, and the results are shown in Table 3.

[0034]

[Table 3]

Claims (5)

[Claims] 1. A highly active calcium oxide porous body comprising a calcined product of granulated calcium hydroxide or calcium carbonate having a specific surface area of at least 5 m ² / g and a particle size of at least 1 mm. 2. A calcium hydroxide powder having a particle size of 300 μm or less is granulated into granules having a particle size of at least 1 mm, and the granulated body is heated under normal pressure to raise the temperature between 390 to 480 ° C. over at least 5 minutes. The method for producing a highly active calcium oxide porous body according to claim 1, wherein the method is followed by firing. 3. Calcium hydroxide powder having a particle size of 300 μm or less is granulated into granules having a particle size of at least 1 mm, and the granulated body is heated under normal pressure to raise the temperature between 390 and 480 ° C. over at least 5 minutes. After making it, 480-950 ℃
CO ₂ conversion rate is 40% at any temperature within the range of
The method for producing a highly active calcium oxide porous body according to claim 1, wherein the firing is performed for a time within a range not lowering below. 4. Calcium carbonate powder having a particle size of 300 μm or less is granulated into granules having a particle size of at least 1 mm, and the granulated body is heated under normal pressure, and the temperature between 700 and 780 ° C. is at least 5.
The temperature is raised over a period of time and the firing is performed.
A method for producing the highly active calcium oxide porous body described. 5. Calcium carbonate powder having a particle size of 300 μm or less is granulated into granules having a particle size of at least 1 mm, and the granulated body is heated under normal pressure, and a temperature between 700 and 780 ° C. is at least 5.
The temperature is raised over a period of one minute, and then the firing is further performed at an arbitrary temperature within a range of 780 to 950 ° C. for a time within a range in which the CO ₂ conversion does not decrease to 40% or less. 1. A method for producing a highly active porous calcium oxide body.