JP2008037681A - Desiccant raw material and production method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a desiccant raw material capable of suppressing rapid reaction with water and generation of high heat while retaining high hygroscopicity, and to provide a method for producing the same. <P>SOLUTION: A mixture is prepared which contains 80-93 mass% of calcium carbonate and 7-20 mass% of an alkaline earth metal salt or an alkaline earth metal salt and an alkali metal salt, and then the mixture is burned. The resulting desiccant raw material retains high hygroscopicity, and when the desiccant raw material having a mass of 100 g or more at 30°C is allowed to react with 18 mass% of water based on the mass, the exothermic maximum temperature resulting from the reaction is 65°C or less. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a desiccant raw material obtained by firing a mixture containing calcium carbonate and a method for producing the same.

  A desiccant containing quicklime (CaO; calcium oxide) has been widely used for food preservation because it has a high drying capacity and is inexpensive. However, since quick lime contained in this desiccant may generate high heat due to a rapid reaction with water, a safer one is required particularly when used for food preservation. In addition, when the desiccant is discarded as general waste, it is also required to improve handling properties such that it is necessary to discard the desiccant so as not to generate heat.

In addition, as a method for suppressing the reactivity of quicklime with water, for example, a method in which quicklime is baked at a high temperature to transform into crystals with a small porosity and a large particle size, and a method in which the surface of the quicklime particles is coated with oils Or there is a method of adding salts to quicklime. Especially, in the method of adding salts to quicklime, it is said that the generation of high heat can be suppressed by using alkali metal salts as the salts (for example, see Non-Patent Documents 1 and 2).
Junichi Kasai, Seiji Tsukada, Study on hydration of quicklime containing alkali metal oxides, “Gypsum and lime”, 1956, No. 21, p. 1113-1116 A. H. White (AHWhite), Earl. M. RMTrue, “INDUSTRIALAND ENGINEERING CHEMISTRY”, 1925, Vol. 17, No. 5, p. 520-521

  However, although quick lime modified by such a method has been improved with respect to rapid reaction with water and generation of high heat, it is not yet sufficient as a desiccant raw material, and further improved exothermic characteristics. Is required. In addition, when used as a desiccant raw material, a certain level of hygroscopicity is required, and the production of a desiccant raw material (quick lime) that can greatly improve heat generation characteristics while maintaining at least the current level of hygroscopicity It is desired.

  The present invention has been made in view of such problems, and an object thereof is to provide a desiccant raw material that retains high hygroscopicity while suppressing rapid reaction with water and generation of high heat, and a method for producing the same. It is in.

  The desiccant raw material according to the present invention contains calcium carbonate in an amount of 80% by mass to 93% by mass, an alkaline earth metal salt, or an alkaline earth metal salt and an alkali metal salt in an amount of 7% by mass to 20% by mass. By firing the mixture, when the mass is 100 g or more in an environment of 30 ° C., the maximum exothermic temperature due to reaction with 18% by mass of water is 65 ° C. or less.

  The method for producing a desiccant raw material according to the present invention comprises calcium carbonate in an amount of 80% by mass to 93% by mass, an alkaline earth metal salt, or an alkaline earth metal salt and an alkali metal salt in an amount of 7% by mass to 20% by mass. It includes a mixture production process for producing a mixture including the following, and a firing process for firing the mixture.

  Examples of alkaline earth metal salts include magnesium carbonate, magnesium chloride, magnesium oxide, magnesium silicate, magnesium nitrate, magnesium sulfate, magnesium fluoride, magnesium phosphate, magnesium hydroxide, calcium chloride, calcium nitrate, calcium sulfate, Calcium fluoride, calcium phosphate, strontium carbonate, strontium chloride, strontium nitrate, strontium sulfate, strontium fluoride, strontium phosphate, strontium hydroxide, barium carbonate, barium chloride, barium nitrate, barium sulfate, barium fluoride, barium phosphate, It contains at least one selected from the group consisting of barium hydroxide.

  Examples of alkali metal salts include sodium carbonate, sodium bicarbonate, sodium sesquicarbonate, sodium chloride, sodium nitrate, sodium sulfate, sodium hydroxide, sodium silicate, sodium fluoride, sodium phosphate, sodium borate, sodium sulfide. , Potassium carbonate, potassium hydrogen carbonate, potassium chloride, potassium nitrate, potassium sulfate, potassium silicate, potassium hydroxide, potassium fluoride, potassium sulfide, lithium carbonate, lithium chloride, lithium sulfate, lithium nitrate, lithium hydroxide, lithium fluoride And at least one selected from the group consisting of lithium nitride.

  According to the desiccant raw material of the present invention, calcium carbonate is 80% by mass or more and 93% by mass or less, an alkaline earth metal salt, or an alkaline earth metal salt and an alkali metal salt are 7% by mass or more and 20% by mass or less. When the mass is 100 g or more in an environment of 30 ° C. while maintaining high hygroscopicity, the maximum exothermic temperature due to the reaction with 18% by mass of water is 65% by mass. It can be suppressed to a low temperature of ℃ or less. Therefore, for example, it can be suitably used for food storage requiring high safety.

  According to the method for producing a desiccant raw material of the present invention, calcium carbonate is 80% by mass or more and 93% by mass or less, an alkaline earth metal salt, or an alkaline earth metal salt and an alkali metal salt are 7% by mass or more and 20% by mass. After preparing a mixture containing less than mass%, this mixture was baked, so that while maintaining high hygroscopicity, a rapid reaction with water was suppressed and a desiccant raw material having a low exothermic temperature was obtained. Can do.

  Hereinafter, the manufacturing method of the desiccant raw material which concerns on this Embodiment is demonstrated.

  First, a calcium carbonate powder, an alkaline earth metal salt, and an alkali metal salt are mixed to prepare a mixture. At that time, the content of the calcium carbonate powder is 80% by mass to 93% by mass with respect to the mixture, and the total content of the alkaline earth metal salt and the alkali metal salt is 7% by mass with respect to the mixture. It is 20 mass% or less, More preferably, it is 10 mass% or more and 20 mass% or less. This is because the heat generation temperature can be further lowered in the range of 10% by mass or more and 20% by mass or less. At this time, the mixture may be adjusted without mixing the alkali metal salt. This is because if at least calcium carbonate and an alkaline earth metal salt are contained, the exothermic temperature of the desiccant raw material to be produced can be suppressed.

  Next, the mixture is stirred to be uniform. At that time, only the mixture may be stirred by a dry method without using a solvent or the like, or may be stirred by a wet method in which a solvent is added to this mixture.

  Examples of the alkaline earth metal salt include magnesium carbonate, magnesium chloride, magnesium oxide, magnesium silicate, magnesium nitrate, magnesium sulfate, magnesium fluoride, magnesium phosphate, magnesium hydroxide, calcium chloride, calcium nitrate, and calcium sulfate. , Calcium fluoride, calcium phosphate, strontium carbonate, strontium chloride, strontium nitrate, strontium sulfate, strontium fluoride, strontium phosphate, strontium hydroxide, barium carbonate, barium chloride, barium nitrate, barium sulfate, barium fluoride, barium phosphate One containing at least one of the group consisting of barium hydroxide can be preferably used.

  Examples of the alkali metal salt include sodium carbonate, sodium bicarbonate, sodium sesquicarbonate, sodium chloride, sodium nitrate, sodium sulfate, sodium hydroxide, sodium silicate, sodium fluoride, sodium phosphate, sodium borate, sulfide. Sodium, potassium carbonate, potassium bicarbonate, potassium chloride, potassium nitrate, potassium sulfate, potassium silicate, potassium hydroxide, potassium fluoride, potassium sulfide, lithium carbonate, lithium chloride, lithium sulfate, lithium nitrate, lithium hydroxide, fluoride What contains at least 1 sort (s) among the group which consists of lithium and lithium nitride can be used suitably.

  Next, the produced mixture is baked at a temperature of 900 ° C. or higher. This is because calcium oxide contained in the desiccant is substantially generated at a temperature of 900 ° C. or higher. For example, when a small raw material having a particle size of about 1 to 3 mm is baked by a rotary kiln or the like in mass production, calcium oxide can be generated in a short baking time even at a temperature of about 900 ° C.

  Moreover, it is preferably 1050 ° C. or higher, more preferably 1050 ° C. or higher and 1300 ° C. or lower. By baking at 1050 ° C. or higher, the rapid reaction of the produced desiccant raw material with water and the maximum exothermic temperature can be more easily reduced. On the other hand, when the firing temperature is higher than 1300 ° C, the heat generation temperature tends to easily exceed 100 ° C. Note that “calcination” is a heat treatment method of a mixture of calcium carbonate and an alkaline earth metal salt. As such a firing method, a known method such as an atmosphere firing method or a reaction firing method can be used.

  The desiccant raw material produced in this way is a non-calcium lime (CaO) crystal produced by firing a mixture containing calcium carbonate and an alkaline earth metal salt at a predetermined content and calcium. Contains crystalline.

  Thereby, a rapid reaction with water is suppressed while maintaining high hygroscopicity, and when the mass is 100 g or more in an environment of 30 ° C., heat is generated due to the reaction with 18% by mass of water with respect to the mass. The maximum temperature can be kept below 65 ° C. In the conventional desiccant raw material, the higher the environmental temperature or the greater the amount (mass) of the desiccant raw material that reacts with water, the higher the exothermic temperature. However, the desiccant raw material of the present embodiment has a mass of 100 g or more. In addition, the exothermic temperature can be kept low even in an environment of 30 ° C. Therefore, as a matter of course, the exothermic temperature can be kept lower under the condition of 30 ° C. or less or the amount of the desiccant raw material is small.

  The desiccant raw material has pores having an average pore diameter of 1.7 μm or more and 4.2 μm or less in a state where the particle diameter is 75 μm or less after passing through a 200 mesh sieve. The average pore diameter is obtained by a mercury intrusion (porosimeter) method, and is obtained from the amount of mercury that is intruded into the pores of the desiccant raw material. In this desiccant raw material, the average pore size is larger than that of conventional calcined lime obtained by firing only calcium carbonate or a mixture of calcium carbonate and an alkali metal salt (such as quick lime). Is getting bigger. This is because the alkaline earth metal salt has a lower melting point than the alkali metal salt, etc., so that the solid changes from a lower temperature to a liquid, and the growth of crystal grains and the modification of the grain surface are promoted. This is probably because of this.

Furthermore, the desiccant material is in the following state particle diameter 75μm to pass through a 200 mesh sieve, and has the following specific surface area 0.04 m ² / g or more 1.87m ² / g. This specific surface area is also determined by the mercury intrusion method and can be measured together with the average pore diameter. Since this desiccant raw material has a predetermined average pore diameter and specific surface area in a state where the particle diameter is 75 μm or less after passing through a 200 mesh sieve, for example, the desiccant raw material is further granulated. Even what was produced can be specified as the same by making it into the above state.

  Having such a predetermined average pore diameter and specific surface area is advantageous for rapid reaction with water, suppression of exothermic temperature, and retention of high hygroscopicity. It can be assumed that each particle has a solid structure and a smooth surface. Water permeates from the outside of the particle to cause a hydration reaction, and the hydration reaction generates heat. This is because the balance between heat dissipation and air heat dissipation is maintained. “Solid” represents a state in which the smaller fine particles constituting the particles are in close contact with each other to the extent that it is difficult for water molecules to enter.

  In the desiccant raw material prepared as described above, calcium carbonate and at least an alkaline earth metal salt of alkaline earth metal salt and alkali metal salt are mixed at a predetermined content to prepare a mixture. After that, since this mixture was prepared by firing, rapid reaction with water was suppressed while maintaining high hygroscopicity, and the exothermic temperature was reduced. In addition, during mass production, firing can be performed at a lower temperature and in a shorter time, so that the efficiency and handling properties in the manufacturing process are improved. Therefore, for example, by granulating and then enclosing it in a packaging material made of a moisture permeable film or the like, it can be suitably used as a desiccant for food preservation requiring high safety.

  Hereinafter, specific examples will be described in detail.

(Examples 1-1 to 1-5, Comparative Example 1-1)
As Examples 1-1 to 1-5, the desiccant raw material was prepared as follows.

First, calcium carbonate (CaCO ₃ ) powder, magnesium hydroxide (Mg (OH) ₂ ) powder, and sodium carbonate (Na ₂ CO ₃ ) powder were mixed to prepare a mixture. At that time, the contents of calcium carbonate, magnesium hydroxide, and sodium carbonate were 90.5 mass%, 1.5 mass%, and 8 mass% in Example 1-1 with respect to the mixture, respectively. 2 is 90.5% by mass, 3.5% by mass, 6% by mass, Example 1-3 is 90.5% by mass, 1.5% by mass, 8% by mass, and Example 1-4 is 93% by mass. %, 3.5% by mass, and 3.5% by mass, and adjusted to be 93% by mass, 1.5% by mass, and 5.5% by mass in Example 1-5.

  Next, these mixtures were mixed so as to be uniform, then fired at a temperature of 1050 ° C. in Example 1-1 and 1100 ° C. in Examples 1-2 to 1-5, and cooled to room temperature. As a result, a desiccant raw material was obtained.

  With respect to the produced desiccant raw materials of Examples 1-1 to 1-5, the hygroscopic property 1 and the hygroscopic property 2 were evaluated. At that time, the produced desiccant raw material was granulated to a particle size of 1 to 3 mm (hereinafter referred to as a granulated product in this example). FIG. 1 shows the hygroscopic property 1 and FIG. 2 shows the hygroscopic property 2.

<Hygroscopic property 1>
A desiccant package was prepared by enclosing 10 g of the granulated material in a packaging material (8 cm × 10 cm) made of a moisture permeable film, and the mass (g) (mass before charging) at this time was measured. That is, this desiccant package is put into a constant temperature and humidity chamber at a temperature of 25 ° C. and a humidity of 80%, and the mass (g) of the desiccant package is measured every 24 hours. Hygroscopic property 1 was evaluated by determining the change with time in the amount of moisture absorption (g) obtained by subtracting.

<Hygroscopic property 2>
A desiccant package in which 10 g of the granulated material was wrapped with Japanese paper and a data logger for measuring temperature and humidity were placed in a polypropylene wrapping material (15 cm × 21 cm) and sealed. Next, this packaging material was put into a thermo-hygrostat at a temperature of 25 ° C. and a humidity of 80%, and the moisture absorption characteristic 2 was evaluated by determining the change in humidity (% RH) in the packaging material over time.

  From the results of FIG. 1 and FIG. 2, the granulated product of Examples 1-1 to 1-5 produced by firing a mixture of calcium carbonate, magnesium hydroxide, and sodium carbonate has good moisture absorption characteristics over time. The results are shown, and it can be seen that the desiccant material has high hygroscopicity.

  Further, the exothermic characteristics of the desiccant raw materials of Examples 1-1 to 1-3 and Comparative Example 1 were evaluated. At that time, the same one used for the evaluation of the moisture absorption characteristics 1 and 2, that is, a granulated product having a particle diameter of 1 to 3 mm was used. The results are shown in FIG. 3, and in particular, the maximum temperature during heat generation (heat generation maximum temperature) is shown in Table 1.

<Heat generation characteristics>
In an environment of 30 ° C., 100 g of the granulated product and 18 g of water having a water temperature of 30 ° C., that is, 18% by mass of water with respect to 100 g of the granulated product (desiccant raw material) are placed in a 350 ml steel can and used as a desiccant. The temperature of the raw material was measured. After that, the temperature of the granulated material was measured every 5 minutes until 12 hours passed, and the heat generation characteristics were evaluated by obtaining the change with time.

  From the results shown in FIG. 3, in the granulated product of Examples 1-1 to 1-5 prepared by firing a mixture in which calcium carbonate, magnesium hydroxide, and sodium carbonate were mixed at a predetermined content, the measurement was always started from the start of measurement. It can be seen that the exothermic temperature stays below 65 ° C., and in any of the examples, an average low temperature is maintained.

  Furthermore, the average pore diameter and specific surface area of the produced desiccant raw materials of Examples 1-1 to 1-5 were measured by mercury porosimetry. At that time, the produced desiccant raw material was passed through a 200-mesh sieve and a particle size of 75 μm or less (hereinafter referred to as a sized product in this example) passed through this sieve was used. These results are also shown in Table 1.

<Mercury intrusion method>
1 g of the granulated product was put in a container, and the container was set in a measuring apparatus (Amco, Porosimeter 2000 type), and the pressure was reduced until the inside became almost vacuum. Next, the average pore size and specific surface area were determined by mercury porosimetry. In addition, as a measuring apparatus, the thing whose hole diameter range which can be measured is 3.7 nm-7,500 nm was used.

  Moreover, as Comparative Example 1-1 of Examples 1-1 to 1-5, a calcium carbonate powder was fired at a temperature of 1100 ° C. to prepare a desiccant raw material. For the desiccant raw material of Comparative Example 1-1, the heat generation characteristics were evaluated in the same manner as in Examples 1-1 to 1-5, and the average pore diameter and specific surface area were measured by the mercury intrusion method. These results are shown in Table 1 together with the results of Examples 1-1 to 1-5. As for the heat generation characteristics, only the maximum temperature during heat generation is shown.

  As shown in Table 1, with respect to the desiccant raw material of Comparative Example 1-1 produced without mixing the alkaline earth metal salt, the average pore size of the desiccant raw material of Examples 1-1 to 1-5 The specific surface area is within a predetermined range, and the maximum temperature during heat generation is 65 ° C. or lower under predetermined conditions. This is because the area where water and the desiccant material are in direct contact with each other is appropriately sized, and the rapid hydration reaction between the desiccant material and water is suppressed. This is considered to be maintained.

  As described above, a mixture containing calcium carbonate in an amount of 80% by mass to 93% by mass, an alkaline earth metal salt, or an alkaline earth metal salt and an alkali metal salt in an amount of 7% by mass to 20% by mass. The desiccant raw materials of Examples 1-1 to 1-5 obtained by firing have high moisture absorption characteristics due to having a predetermined average pore diameter and specific surface area, and also have rapid absorption with water. It has been found that it is possible to suppress the reaction and the generation of high heat. Specifically, it was found that when the mass of the desiccant raw material is 100 g or more in an environment of 30 ° C., the exothermic temperature due to the reaction with 18% by mass of water can be suppressed to 65 ° C. or less. .

It is the figure showing the moisture absorption characteristic 1 of the desiccant raw material which concerns on the Example of this invention. It is a figure showing the moisture absorption characteristic 2 of the desiccant raw material which concerns on the Example of this invention. It is a figure showing the heat_generation | fever characteristic of the desiccant raw material which concerns on the Example of this invention.

Claims (7)

By calcining a mixture containing calcium carbonate in an amount of 80% by mass to 93% by mass, an alkaline earth metal salt, or an alkaline earth metal salt and an alkali metal salt in an amount of 7% by mass to 20% by mass,
A desiccant raw material characterized in that when the mass is 100 g or more in an environment of 30 ° C, the maximum exothermic temperature by reaction with 18% by mass of water is 65 ° C or less with respect to the mass. The desiccant raw material according to claim 1, wherein the desiccant raw material has pores having an average pore size of 1.7 µm or more and 4.2 µm or less in a state where the particle size passes through a 200 mesh sieve and is 75 µm or less. In the following state particle diameter 75μm to pass through a 200 mesh sieve, desiccant material according to claim 1, characterized in that it comprises the following specific surface area 0.04 m ² / g or more 1.87m ² / g. A mixture preparation step of preparing a mixture containing calcium carbonate in an amount of 80% by mass to 93% by mass, an alkaline earth metal salt, or an alkaline earth metal salt and an alkali metal salt in an amount of 7% by mass to 20% by mass; ,
And a baking step of baking the mixture. The alkaline earth metal salt includes magnesium carbonate, magnesium chloride, magnesium oxide, magnesium silicate, magnesium nitrate, magnesium sulfate, magnesium fluoride, magnesium phosphate, magnesium hydroxide, calcium chloride, calcium nitrate, calcium sulfate, and fluoride. Calcium fluoride, calcium phosphate, strontium carbonate, strontium chloride, strontium nitrate, strontium sulfate, strontium fluoride, strontium phosphate, strontium hydroxide, barium carbonate, barium chloride, barium nitrate, barium sulfate, barium fluoride, barium phosphate, water It contains at least 1 sort (s) among the group which consists of barium oxide. The manufacturing method of the desiccant raw material of Claim 4 characterized by the above-mentioned. The alkali metal salt is sodium carbonate, sodium bicarbonate, sodium sesquicarbonate, sodium chloride, sodium nitrate, sodium sulfate, sodium hydroxide, sodium silicate, sodium fluoride, sodium phosphate, sodium borate, sodium sulfide, Potassium carbonate, potassium bicarbonate, potassium chloride, potassium nitrate, potassium sulfate, potassium silicate, potassium hydroxide, potassium fluoride, potassium sulfide, lithium carbonate, lithium chloride, lithium sulfate, lithium nitrate, lithium hydroxide, lithium fluoride, And at least one selected from the group consisting of lithium nitride. The method for producing a desiccant material according to claim 4. The said mixture is baked at the temperature of 1050 degreeC or more. The manufacturing method of the desiccant raw material of Claim 4 characterized by the above-mentioned.

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