JP2018030122A - Method for producing desiccant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a desiccant which is excellent in a moisture absorption rate and can be regenerated at low temperature.SOLUTION: A production method includes: a step of firing a silicic acid plant at 400°C or higher in an inert atmosphere to prepare a silica-carbon composite body; a step of preparing a mixture of the silica-carbon composite body and an Al compound and an alkali metal compound or an alkali earth metal compound and water so that an aluminosilicate in a molar ratio of Si:Al=1:0.1 to 1.2 is produced; a step of subjecting the mixture to a hydrothermal reaction to obtain a porous aluminosilicate-carbon composite body; and a step of subjecting the porous aluminosilicate-carbon composite body to inert gas treatment at 600-800°C to obtain a desiccant.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a desiccant.

  A desiccant is a substance that absorbs water vapor from the air.

  As the performance of the desiccant, the moisture absorption capacity that represents the mass of water that can absorb moisture, the moisture absorption that is the amount of moisture remaining after the desiccant is applied, and the moisture absorption rate that represents the amount of moisture absorption per unit time are important.

  The desiccant can be reused by heating or reducing the pressure. In recycling, the desorption rate of water molecules absorbed by the desiccant, that is, the regeneration rate is important.

  The desiccant is roughly classified into a chemical desiccant and a physical desiccant.

  A chemical desiccant is a desiccant that utilizes chemical reaction or deliquescence. As a chemical desiccant, for example, calcium chloride used in a storage space having a certain volume such as a close-in / closet is known. When calcium chloride absorbs water, it becomes an aqueous solution due to deliquescence. Calcium chloride can be regenerated by evaporating water, but is generally disposable.

  The physical desiccant utilizes the property that water molecules are easily adsorbed on the porous surface. Physical desiccants are used to store a small amount of an object in a dry state. Physical desiccants are, for example, silica gel and zeolite. The regeneration of silica gel and zeolite is generally performed at a high temperature of 80 ° C. or higher.

Silica gel is a xerogel obtained by dehydrating a white amorphous gel produced by adding an acid to an alkali silicate solution such as sodium silicate and drying the gel at 500 ° C., for example. The composition of silica gel is expressed as SiO ₂ · nH ₂ O. There is no combination of a certain amount of water with respect to 1 mol of silicon dioxide in silica gel. Silica gel is considered to contain orthosilicic acid (H ₄ SiO ₄ ) and metasilicic acid (H ₂ SiO ₃ ). In order to regenerate the moisture-absorbed silica gel, heat treatment is necessary to break the chemical bond between SiO ₂ and H ₂ O. Silica gel can be regenerated by heat treatment at 80 to 100 ° C. or heat treatment using a microwave oven.

  A distinction is made between zeolites, natural zeolites, artificial zeolites and synthetic zeolites. Natural zeolite is a mineral, and artificial zeolite is mainly hydrothermally synthesized from coal ash as a raw material. Synthetic zeolite is also referred to as molecular sieve. Synthetic zeolite is, for example, hydrothermally synthesized from a mixture of silicon, aluminum, and an alkali compound.

However, for example, there is a report that the DTA endothermic peak for desorbing H ₂ O adsorbed on zeolite 4A is 130 to 230 ° C.

  Thus, the conventional desiccant composed of silica gel or zeolite has a relatively high regeneration temperature.

  Patent Document 1 describes an adsorbent that simultaneously adsorbs carbon dioxide gas and water vapor, which includes a porous aluminosilicate-carbon composite material produced from rice husk. However, Patent Document 1 does not consider the use as a desiccant for the purpose of dehumidification, and naturally does not consider the regeneration of the desiccant.

Japanese Patent No. 5487483

  An object of the present invention is to provide a method for producing a desiccant that has a high moisture absorption rate and can be regenerated even at low temperatures.

  According to the first aspect of the present invention, a silicic acid plant is baked at 400 ° C. or higher in an inert atmosphere to produce a silica-carbon composite, Si: Al = 1: 0.1 to 1. A step of preparing a mixture containing the silica-carbon composite, an Al compound, an alkali metal compound or an alkaline earth metal compound, and water so that an aluminosilicate in the range of 2 is formed, and a hydrothermal reaction to the mixture And a step of obtaining a porous aluminosilicate-carbon composite, and a step of applying an inert gas treatment to the porous aluminosilicate-carbon composite at 600 to 800 ° C. to obtain a desiccant. A method for producing a desiccant is provided.

  According to the present invention, there is provided a method for producing a desiccant which has a high moisture absorption rate and can be regenerated even at a low temperature of 40 ° C. or higher.

The graph which shows the result of having absorbed the water | moisture content in a container using the desiccant obtained by the manufacturing method which concerns on this invention. The graph which shows the result of having regenerated the desiccant obtained by the manufacturing method which concerns on this invention once, and having absorbed the moisture in the container. The graph which shows the result of having dried the desiccant obtained by the manufacturing method which concerns on this invention twice, and absorbed the moisture in a container. The graph which shows the result of having absorbed the water | moisture content in a container by regenerating | regenerating the desiccant obtained by the manufacturing method which concerns on this invention 3 times. The graph which shows the result of having absorbed the water | moisture content in a container by regenerating | regenerating the desiccant obtained by the manufacturing method which concerns on this invention four times. The graph which shows the result of having absorbed the water | moisture content in a container by regenerating the desiccant obtained by the manufacturing method which concerns on this invention 5 times. The graph which shows the result of having absorbed the water | moisture content in a container by regenerating the desiccant obtained by the manufacturing method which concerns on this invention seven times.

  Hereinafter, embodiments of the present invention will be described.

<Method for producing desiccant>
Below, the manufacturing method of the desiccant which concerns on one Embodiment of this invention is demonstrated.

First, a silicate plant is prepared as a raw material for the desiccant.
The silicate plant is, for example, a gramineous plant. Gramineae plants are, for example, rice, wheat, barley, rye, pearl barley, millet, millet, millet, corn and Japanese pampas grass. Silicic plants are preferably rice husks and rice husks having a high silicic acid content, with rice husks being particularly preferred.

Rice husk comprises about 20% by mass of an inorganic component and about 80% by mass of an organic component such as cellulose. Of the inorganic component of about 20% by mass, 85 to 95% by mass is active silica (SiO ₂ ).

  Silica in rice husks is deposited between the cell walls of rice husks. Silica in rice husks is outside the epidermal cells when water-soluble silicate ions in irrigation water pass through rice roots, through stem conduits, reach the epidermis, and moisture evaporates from the rice husk epidermis Deposited in the cuticle. Silica is dispersed in an organic cuticle, and silica and silica are in very close proximity (Takeshi Okutani, Material Analysis and Characterization Science, 6, 24-50 (1993)).

  In addition, the silicic acid plant may remove foreign substances such as stone and soil by wind selection or sieving as necessary. Silicate plants may be leached with, for example, dilute hydrochloric acid to elute and remove iron, alkali metal compounds, and alkaline earth metal compounds contained in trace amounts in inorganic materials.

  Hereinafter, an embodiment of the present invention will be described assuming that the silicate plant is rice husk.

  Next, the rice husk is fired at 400 ° C. or higher in an inert atmosphere to produce a silica-carbon composite. When the rice husk is fired in an inert atmosphere, the organic matter in the rice husk is carbonized to form a silica-carbon composite. The silica-carbon composite is a composite in which silica and carbon are very close to each other, and is also called rice husk carbide or rice husk charcoal. The silica and carbon contained in the silica-carbon composite are very fine, homogeneous at the molecular level, and have a small distance from each other compared to a simple silica-carbon mixture.

  The inert atmosphere is, for example, an atmosphere of nitrogen or argon.

  The firing temperature is 400 ° C. or higher, preferably within the range of 450 to 1000 ° C., more preferably within the range of 500 to 1000 ° C., and even more preferably within the range of 500 to 900 ° C. . When the firing temperature is lower than 400 ° C., carbonization of the rice husk is insufficient, or a long time is required until the carbonization is completed.

  The firing time is preferably from several minutes to several tens of hours, more preferably from several tens of minutes to several hours. Specifically, it is preferably 10 minutes to 30 hours, more preferably about 30 minutes to 3 hours.

  In addition, it is preferable to measure the component of a silica-carbon composite, and it is especially preferable to measure the silicon content of a silica-carbon composite. When the silicon content of the silica-carbon composite is measured, it is easy to determine, for example, the blending amount of the Al compound based on the silicon content when preparing the mixture in the subsequent step. The component of the silica-carbon composite can be measured using, for example, atomic absorption spectrometry. You may measure content, such as silicon and Al, Na, K, and Ca, as needed.

  However, if the same rice husk is used as a raw material, the component content of the silica-carbon composite does not change greatly. Therefore, the component of the silica-carbon composite is always measured every time the desiccant is produced. There is no need.

  Next, a silica-carbon composite, an Al compound, and an alkali metal so that an aluminosilicate having a molar ratio of Si: Al = 1: 0.1 to 1.2 is generated by a hydrothermal reaction described later. A mixture containing the compound or alkaline earth metal compound and water is prepared.

For example, the Al compound is Al (OH) ₃ , NaAlO _2, and Al ₂ O ₃ , and the Al compound is preferably Al (OH) ₃ .

  The alkali metal compound or alkaline earth metal compound is preferably one or a mixture of two or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide.

Next, the mixture is subjected to a hydrothermal reaction.
When the mixture is subjected to a hydrothermal reaction, a porous aluminosilicate-carbon composite is obtained. In the hydrothermal reaction, the mixture is treated under hot water at high temperature and pressure. The hydrothermal reaction is performed, for example, in an autoclave.

  When the silica in the silica-carbon composite is reacted with the added Al compound and the alkali metal compound or alkaline earth metal compound by a hydrothermal reaction, a porous aluminosilicate is formed, and the porous aluminosilicate together with the carbon not involved in the reaction. An acid-carbon complex is obtained.

The porous aluminosilicate produced by this reaction is preferably a zeolite. The composition of zeolite is represented by the following general formula.
(M ^I , M ^II _1/2 ) _m (Al _m Si _n O _{2 (m + n)} ) · xH ₂ O
In the above formula, M ^I and M ^II are alkali metal and alkaline earth metal exchange cations, respectively. M ^I is, for example, Na ⁺ , K ⁺ or Li ⁺ , and M ^II is, for example, Ca ²⁺ , Mg ²⁺ or Ba ²⁺ .

  The zeolite is preferably A-type zeolite, X-type zeolite, or Y-type zeolite.

  In order to obtain A-type zeolite, it is desirable to adjust the components in the range of Si: Al: Na = 1: 0.8 to 1.2: 2.5 to 4.0 (molar ratio).

  In order to obtain X-type zeolite, it is desirable to adjust the components in the range of Si: Al: Na = 1: 0.2 to 0.3: 3.5 to 5.0 (molar ratio).

  In order to obtain Y-type zeolite, it is desirable to adjust the components in the range of Si: Al: Na = 1: 0.1 to 0.3: 0.8 to 1.0 (molar ratio).

Zeolites are distinguished by their crystalline framework. For example, zeolite 4A is a Na-A type zeolite having Na ⁺ as an exchange cation, and has a unit cell composition (Na ₁₂ [Al ₁₂ Si ₁₂ O ₄₈ ] · 27H ₂ O). Its _{crystals, (SiO} ^{4) 4} 4 one around _{^{(AlO 4) 5-, (AlO}} 4) 4 single _(SiO ⁴⁾ around the ^{5-4-organizational} assembled are arranged, equilateral A tetrahedron (sodalite cage) having a four-membered ring cut off from each vertex of the face piece connects the four-membered rings of the cut face to form a three-dimensional skeleton. A cavity surrounded by eight sodalites is formed, and the adjacent cavities are connected via six eight-membered ring entrances. Since the exchange cation Na ⁺ exists in the vicinity of the entrance, the pore entrance diameter is 4.1 mm.

Different kinds of exchange cations have different pore entrance diameters. For example, when the exchange cation is K ⁺ , the pore entrance diameter is about 3 mm. When the exchange cation is divalent Ca ²⁺ , since Ca ²⁺ does not exist at the pore entrance, the pore entrance diameter is about 5 mm (“Zeolite Chemistry and Industry”, Yoshio Ono, Kenaki Yashima, Kodansha Scientific) Fick, 2000, ISBN 4-06-153389-4).

H ₂ O has a van der Waals diameter of 4.82 mm and does not enter the pores of zeolite 4A, but the polar molecule H ₂ O is strongly strengthened by the electrostatic action with the exchange cation Na ⁺ at the pore entrance. Adsorbed. There is a report that the peak of DTA endothermic peak for desorbing H ₂ O adsorbed on zeolite 4A is 130-230 ° C. (Aomura et al., Hokkaido University Engineering Report, 76, 155-162 (1975)). ).

  The temperature of the hydrothermal reaction is preferably in the range of 50 to 200 ° C, and particularly preferably in the range of 80 to 120 ° C. When the temperature is too low, the hydrothermal reaction hardly occurs. If the temperature is too high, the shape and diameter distribution of the zeolite crystals may be affected, and other crystalline zeolites may be produced.

  The hydrothermal reaction is preferably performed within a range of several minutes to several tens of hours, and particularly preferably performed within a range of tens of minutes to several hours. Specifically, it is preferably 10 minutes to 30 hours, more preferably about 30 minutes to 5 hours.

  The produced porous aluminosilicate-carbon composite may be washed with water or the like.

  Next, the porous aluminosilicate-carbon composite is subjected to an inert gas treatment at 600 to 800 ° C. to obtain a desiccant. The temperature of the inert gas treatment is preferably 650 to 750 ° C.

  When the porous aluminosilicate-carbon composite is treated with an inert gas, the adsorption sites of the zeolite and carbon are fused.

  The inert gas is preferably, for example, nitrogen or argon, and particularly preferably nitrogen.

  When the inert gas treatment is performed at a temperature lower than 600 ° C., there are many functional groups such as —COOH and —OH remaining on the activated carbon surface, and this functional group tends to inhibit the fusion of the aluminosilicate and the activated carbon. large. On the other hand, when the inert gas treatment is performed at a temperature higher than 800 ° C., the carbonization of the activated carbon proceeds excessively and the activated carbon shrinks, so the number of contact points between the aluminosilicate and the activated carbon decreases, and the fusion tends to decrease. Become.

  The desiccant produced by the above-described method is, for example, granular or flakes reflecting the shape of the raw material such as rice husk. The desiccant may be crushed into granules or powder as necessary. An appropriate binder such as an organic adhesive and an inorganic adhesive may be added to the desiccant, put into a mold, the binder may be cured, and molded into various shapes. Examples of the shape of the desiccant include a pellet shape, a porous columnar shape, a block shape, a tubular shape, a honeycomb shape, and a plate shape. The desiccant can be used, for example, by filling a container with high air permeability.

  According to the above-described method, a desiccant having a high adsorption rate and reproducible at a low temperature can be obtained. This is considered to be due to the following reason.

  By the inert gas treatment, the aluminosilicate and carbon are fused and brought closer together, and the carbon is located very close to the adsorption site of water molecules consisting of exchange cations near the pore entrance of the aluminosilicate. . If oxygen in the air is adsorbed on the carbon or oxygen remaining in the carbon is present, as a result of attracting electrons, the electron density at the adsorption site is lowered, and the adsorbing power of water molecules is lowered. Accordingly, water molecules are easily desorbed from the adsorption site, so that the desiccant can be regenerated at a low temperature.

  Moreover, since the desiccant obtained by the manufacturing method mentioned above has a low bulk density and is easy to touch an atmosphere, it is also known that the adsorption speed at the initial stage of adsorption is fast.

<Moisture absorption and regeneration method for desiccant>
The desiccant moisture absorption / regeneration method according to the embodiment of the present invention will be described below.

First, moisture absorption is started using the desiccant obtained by the manufacturing method described above, and moisture absorption is stopped before the water adsorption amount reaches saturation. The desiccant obtained by the manufacturing method described above has a higher adsorption rate than the conventional desiccant in the period until the water adsorption amount reaches saturation, but the adsorption rate decreases near saturation. Take advantage of the characteristics of adsorption speed. In other words, moisture is absorbed within a range in which a high adsorption rate is maintained.
Next, the desiccant is regenerated at a temperature of 40 ° C. or higher. When the desiccant is regenerated, the moisture adsorbed on the zeolite is released. As described above, the desiccant according to the present invention can be regenerated in a short time because the absorbed water molecules are easily detached. The regeneration temperature range is 40 to 100 ° C., but 50 to 90 ° C. is preferable and 50 to 80 ° C. is more preferable from the viewpoint of low temperature regeneration.

  By performing the regeneration time within a range of 15 to 30 minutes, it is expected that the regeneration temperature is low and the adsorption power can be recovered at low energy. The regeneration may be performed under conditions of reduced pressure in the range of atmospheric pressure or atmospheric pressure to vacuum.

  Next, moisture absorption and regeneration described above are repeated at least once, and moisture absorption by the desiccant and regeneration of the desiccant are performed.

  According to the method described above, it is possible to efficiently dehumidify. The desiccant can absorb a large amount of moisture in a short time. This is because the desiccant produced by the above-described method has a high moisture absorption rate. Further, according to the above-described method, the desiccant can be regenerated with a small energy. This is because the desiccant produced by the above-described method can be regenerated at a low temperature and in a short time because water molecules are easily detached. Therefore, it is possible to efficiently dehumidify by repeatedly performing moisture absorption and regeneration using this desiccant.

  According to the method described above, the desiccant can be regenerated to have a high moisture absorption rate. Therefore, moisture can be absorbed while the moisture absorption rate of the desiccant is always high. For example, moisture in the circulating gas can be absorbed sufficiently and efficiently.

  The method described above can be advantageously applied to continuously dehumidify a relatively closed space with a relatively small volume. Such a space is, for example, a space station. In space stations, desiccants are used to remove water that is discharged during human activities and to collect water. In space stations, the available resources and energy are limited, so it is advantageous to use a desiccant that has a high moisture absorption rate and can be regenerated at low temperatures.

<Drying agent production system>
Next, a system for manufacturing the desiccant described above will be described.

  The desiccant production system includes a silica-carbon composite production part, a mixture production part, a porous aluminosilicate-carbon composite production part, and a desiccant production part.

  First, in a silica-carbon composite preparation part, a silicic acid plant is baked at 400 degreeC or more in inert atmosphere, and a silica-carbon composite is produced.

  Next, in the mixture preparation part, an aluminosilicate having a molar ratio of Si: Al = 1: 0.1 to 1.2 is generated in the porous aluminosilicate-carbon composite preparation part described later. A mixture containing a silica-carbon composite, an Al compound, an alkali metal compound or an alkaline earth metal compound, and water is prepared.

  Next, in the porous aluminosilicate-carbon composite preparation part, the mixture is subjected to a hydrothermal reaction to obtain a porous aluminosilicate-carbon composite.

  Next, in the desiccant production department, the porous aluminosilicate-carbon composite is subjected to an inert gas treatment at 600 to 800 ° C. to obtain a desiccant.

  The desiccant production system may be configured integrally with a silica-carbon composite preparation unit, a mixture preparation unit, a porous aluminosilicate-carbon composite preparation unit, and a desiccant production unit. May be configured in a separated state. In addition, the desiccant production system may include other functional units as long as the present invention is not hindered.

Below, a test example is demonstrated.
<Production of desiccant A composed of porous aluminosilicate-carbon composite>
First, 25 g of rice husk was washed with distilled water and dried. The dried rice husk was subjected to reflux treatment (leaching) for 2 hours at 100 ° C. using 0.5 L of 3% v / v hydrochloric acid solution. The refluxed rice husk was filtered, the rice husk was washed until the filtrate had a pH of about 7.0, and vacuum dried at 80 ° C. for 1 hour to remove impurities such as potassium in the rice husk. The vacuum-dried 12 g of rice husk was treated at 100 mL / min in a nitrogen stream at 500 ° C. for 1 hour to obtain a silica-carbon composite (chaff carb).

  Next, the components of the silica-carbon composite were examined by inductively coupled high-frequency plasma spectroscopy. Table 1 shows the components of the silica-carbon composite. In Table 1, LOI (Loss Of Ignition) indicates ignition loss. The loss on ignition was determined based on the difference between the weight after heating in air at 600 ° C. for 3 hours from the weight before heating. The component of ignition loss is almost carbon.

Next, a stirrer, 4.4 g of NaOH (Wako reagent special grade purity 97%) and 4.4 mL of distilled water were placed in a 300 mL beaker, and NaOH was completely removed using a heating magnetic stirrer (IKA, RH basic 1). Until dissolved. In this beaker, 2.7 g of Al (OH) ₃ (Wako reagent) was added and stirred for about 10 minutes until the solution became homogeneous. In addition, when Al (OH) ₃ was not easily dissolved, the beaker was heated at a temperature of 100 ° C. or less.

Next, 35.6 mL of distilled water, 4.12 g of silica-carbon composite (2.0 g as SiO ₂ ), and 0.02 g of synthetic zeolite (A-4 manufactured by Tosoh Corporation 200 mesh) were added to this beaker, Mix for approximately 20 minutes to obtain a mixture.

Since the molecular weight of SiO ₂ is 60.0, the molecular weight of Al (OH) ₃ is 78.0, and the molecular weight of NaOH is 40.0, the molar ratio of Si: Al: Na is 2.0 / 60.0: 2. 7 / 78.0: 4.4 / 40.0 = 1.00: 1.04: 3.30.

  Next, the mixture was placed in an approximately 200 mL Teflon (registered trademark) autoclave containing four iron cored Teflon (registered trademark) balls and stirred at a rate of 100 reciprocations / min. The temperature was raised to 0 ° C. and held at 100 ° C. for 4 hours to carry out hydrothermal synthesis. After allowing the autoclave to cool to 35 ° C. or lower, the obtained hydrothermal composition was suction filtered and washed with warm water. The hydrothermal composite was washed until the filtrate had a pH of 9 or less and then dried at 60 ° C. overnight to obtain a porous aluminosilicate-carbon composite. The aluminosilicate constituting the porous aluminosilicate-carbon composite was zeolite 4A.

When the specific surface area of the porous aluminosilicate-carbon composite was measured by the BET method, the specific surface area was 182 m ² / g. The porous aluminosilicate-carbon composite had a micropore volume by the t-plot method of 0.047 mL / g.

  The porous aluminosilicate-carbon composite was 57.6 wt% zeolite and 35.6 wt% carbon. The remaining 6.8 wt% excluding zeolite 4A and carbon is considered to be unreacted silica or zeolite that did not crystallize.

Next, the porous aluminosilicate-carbon composite was treated with an inert gas at 700 ° C. for 1 hour in a nitrogen stream to fuse the aluminosilicate and carbon. The specific surface area of the porous aluminosilicate-carbon composite was 199 m ² / g, and the micropore volume was 0.055 mL / g. Thus, the desiccant A of the Example was obtained.

<Test Example 1>
A moisture absorption test was performed using the desiccant A, silica gel, and zeolite 4A of the examples. The test method is as follows.

  First, 1 g of desiccant A was put in a container having an internal volume of 2 L, a temperature of 24 to 28 ° C., and a relative humidity of 62 to 77% RH.

  Next, using a temperature / humidity sensor, the change in relative humidity in the container was measured from the time when the desiccant A was added to 60 minutes, with the time when the desiccant A was added to the container being 0 minutes.

  The change in the relative humidity of the container was measured in the same manner as described above except that zeolite 4A or silica gel having a particle size in the range of 2 to 4 mm was used in place of the desiccant A. The results are shown in FIG. A blank is a change in relative humidity in a container without a desiccant.

  The following can be understood from the results of FIG. The amount of water adsorbed after 60 minutes is smaller for the desiccant A than for silica gel, but the adsorption rate up to 30 minutes is greater for the desiccant A than for silica gel. Despite the zeolite amount of the desiccant A being 57.6% by mass, the water adsorption amount is larger than that of the zeolite 4A. Thus, the desiccant A has a larger amount of water adsorption than the zeolite 4A, and has a higher adsorption rate up to 30 minutes than the silica gel.

<Test Example 2>
A moisture absorption test was performed after regenerating the desiccant A, silica gel, and zeolite 4A in the examples. The test method is as follows.

  First, the desiccant A was exposed to an atmosphere having a temperature of 26 ° C. and a relative humidity of 96% RH for 36 hours to sufficiently absorb moisture.

  Next, the desiccant A absorbed in moisture was treated at 50 ° C. for 3 hours under atmospheric pressure to regenerate the desiccant A.

  Next, the change in relative humidity in the container was measured using the desiccant A once regenerated by the same method as in Test Example 1.

  Further, except that zeolite 4A or silica gel having a particle size in the range of 2 to 4 mm was used in place of the desiccant A, these were absorbed and regenerated by the same method as described above, and the relative humidity in the container was The change of was measured. The results are shown in FIG.

  The following can be understood from the results of FIG. The desiccant A decreased in relative humidity from 70% to 45% in about 15 minutes, and showed a substantially constant relative humidity in an elapsed time of 15 minutes or more. In zeolite 4A, the relative humidity decreased only by 3% after 60 minutes, and it was found that water was strongly adsorbed at the adsorption site in the first moisture absorption test. In the case of silica gel, the relative humidity decreased by 30% after 60 minutes, and the relative humidity was still decreasing. As shown in FIG. 2, the desiccant A reached saturation adsorption in 15 minutes, and the adsorption rate up to that time was higher than that of silica gel.

<Test Example 3>
The adsorption test was performed after regenerating the desiccant A, silica gel and zeolite 4A in the examples twice. The test method is as follows.

  First, the desiccant A used in Test Example 2 was treated at 50 ° C. under atmospheric pressure for 86 hours to regenerate the desiccant A.

  Next, the change in relative humidity in the container was measured using the desiccant A regenerated twice by the same method as in Test Example 1.

  These were regenerated in the same manner as above except that zeolite 4A or silica gel after use in Test Example 2 was used instead of desiccant A after use in Test Example 2, The change in relative humidity was measured. The results are shown in FIG.

  The following can be understood from the results of FIG. The second regeneration time was longer than the first regeneration time, but both the desiccant A and the silica gel exhibited substantially the same moisture absorption behavior as in FIG. In zeolite 4A, a decrease in relative humidity of 10% was observed, and the relative humidity became constant in 15 minutes. As shown in FIG. 3, the desiccant A reached saturation adsorption in 15 minutes, and the adsorption rate until then was larger than that of silica gel.

<Test Example 4>
An adsorption test was conducted after regenerating the desiccant A, silica gel and zeolite 4A of the Examples three times. The test method is as follows.

  First, the desiccant A after being used in Test Example 3 was treated at 70 ° C. under atmospheric pressure for 3 hours to regenerate the desiccant A.

  Next, the change in relative humidity in the container was measured using the desiccant A regenerated three times by the same method as in Test Example 1.

  Moreover, these were regenerated by the same method as described above except that zeolite 4A or silica gel after use in Test Example 3 was used instead of desiccant A after use in Test Example 3, and in the container The change in relative humidity was measured. The results are shown in FIG.

  The following can be understood from the results of FIG. As a result of increasing the regeneration temperature from 50 ° C. for the first and second regenerations to 70 ° C. for the third regeneration, the relative humidity is reduced by 27% in FIG. 4, compared with FIGS. It was observed. Also in this test, the amount of water adsorbed was higher for the desiccant A than for the zeolite 4A. As shown in FIG. 4, the desiccant A reached saturation adsorption in 30 minutes, and the adsorption rate until then was larger than that of silica gel.

<Test Example 5>
An adsorption test was conducted after regenerating the desiccant A, silica gel and zeolite 4A of the examples four times. The test method is as follows.

  First, the desiccant A after being used in Test Example 4 was treated at 50 ° C. for 3 hours under reduced pressure 0.02 to 0.03 MPa lower than the atmospheric pressure to regenerate the desiccant A.

  Next, the change in relative humidity in the container was measured using the desiccant A regenerated four times by the same method as in Test Example 1.

  Moreover, these were regenerated by the same method as described above except that zeolite 4A or silica gel after use in Test Example 4 was used instead of desiccant A after use in Test Example 4, and The change in relative humidity was measured. The results are shown in FIG.

  The following can be understood from the results of FIG. When the regeneration treatment was performed under reduced pressure, neither the desiccant A nor the silica gel had an effect of increasing the water adsorption amount. On the other hand, as shown in FIG. 5, even when the regeneration treatment was performed under reduced pressure, the desiccant A reached saturated adsorption in 15 minutes, and the tendency that the adsorption rate until then was larger than that of silica gel was recognized. .

<Test Example 6>
An adsorption test was conducted after regenerating the desiccant A, silica gel, and zeolite 4A of the Examples five times. The test method is as follows.

  First, the desiccant A used in Test Example 5 was treated at 70 ° C. for 16 hours under atmospheric pressure to regenerate the desiccant A.

  Next, the change in relative humidity in the container was measured using the desiccant A regenerated five times by the same method as in Test Example 1.

  Moreover, these were regenerated by the same method as described above except that zeolite 4A or silica gel after use in Test Example 5 was used instead of desiccant A after use in Test Example 5, and The change in relative humidity was measured. The results are shown in FIG.

  The following can be understood from the results of FIG. When the adsorption test after the third regeneration with the same regeneration temperature of 70 ° C. and the regeneration time of 3 hours (FIG. 4) is compared with the adsorption test after the fifth regeneration with the regeneration time of 16 hours (FIG. 6) Although the desiccant A showed almost the same behavior, the silica gel had a relative humidity difference of 43% after 60 minutes, and the effect of time was great. Still, the adsorption rate up to 15 minutes was greater for desiccant A than for silica gel.

<Test Example 7>
After drying the desiccant A of the example seven times, an adsorption test was conducted. The test method is as follows.

  First, 1 g of desiccant A was put in a container having an internal volume of 2 L, a temperature of 26 to 27 ° C., and a relative humidity of 60 to 70% RH, and was exposed to this atmosphere for 15 minutes to absorb moisture. Next, the moisture-absorbing desiccant A was regenerated by treating it at 80 ° C. for 15 minutes under atmospheric pressure. By repeating these operations, desiccant A regenerated seven times was obtained.

  Next, using a temperature / humidity sensor, the change in relative humidity in the container was measured from the time when the desiccant A was added to 15 minutes with the time when the desiccant A regenerated seven times was set to 0 minutes. did. The results are shown in FIG.

  The following can be understood from the results of FIG. The desiccant A, which was absorbed for 15 minutes and regenerated seven times under the conditions of a regeneration temperature of 80 ° C. and a regeneration time of 15 minutes, decreased in relative humidity from 65% to 35% in about 10 minutes, and over 15 minutes. It showed an almost constant relative humidity over time. Therefore, the desiccant A can be regenerated to a high adsorption rate even when regenerated at 80 ° C. for 15 minutes.

The above results can be summarized as follows.
The desiccant produced by the method of the present invention has an advantage that the moisture absorption rate is higher than that of silica gel before the water adsorption amount reaches saturation. Further, the desiccant produced by the method of the present invention could be regenerated when treated at a temperature of 50 to 80 ° C.
Therefore, after using the desiccant according to the present invention to start moisture absorption, when the water adsorption amount reaches saturation, the moisture absorption is stopped, and regeneration at a temperature of 40 to 100 ° C. is repeated to efficiently remove moisture. Those skilled in the art will fully understand that this is possible.
Further, the regeneration may be performed under conditions of reduced pressure in the range of atmospheric pressure or atmospheric pressure to vacuum.

Claims (7)

A step of producing a silica-carbon composite by firing a silicate plant at 400 ° C. or higher in an inert atmosphere;
The silica-carbon composite and the Al compound and the alkali metal compound or alkaline earth metal compound and water so that an aluminosilicate having a molar ratio of Si: Al = 1: 0.1 to 1.2 is formed. Producing a mixture comprising:
A hydrothermal reaction is performed on the mixture to obtain a porous aluminosilicate-carbon composite, and the porous aluminosilicate-carbon composite is treated with an inert gas at 600 to 800 ° C. to obtain a desiccant. A method for producing a desiccant comprising the step of:   The method for producing a desiccant according to claim 1, wherein the silicic acid plant is rice husk or straw.   The aluminosilicate constituting the porous aluminosilicate-carbon composite is any one or a mixture of two or more of A-type zeolite, X-type zeolite, and Y-type zeolite. Item 3. A method for producing a desiccant according to Item 1 or 2.   The Al compound is aluminum hydroxide, and the alkali metal compound or the alkaline earth metal compound is any one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide. Item 4. A method for producing a desiccant according to any one of Items 1 to 3.   Moisture absorption is started using the desiccant obtained by the production method according to any one of claims 1 to 4, and the moisture absorption is stopped before the water adsorption amount reaches saturation, at a temperature of 40 to 100 ° C. A moisture absorption / regeneration method using a desiccant, characterized by repeating the regeneration of the desiccant.   6. The moisture absorption / regeneration method using a desiccant according to claim 5, wherein the regeneration is performed under reduced pressure. A silica-carbon composite preparation section for producing a silica-carbon composite by firing a silicic acid plant at 400 ° C. or higher in an inert atmosphere;
The silica-carbon composite and the Al compound and the alkali metal compound or alkaline earth metal compound and water so that an aluminosilicate having a molar ratio of Si: Al = 1: 0.1 to 1.2 is formed. A mixture preparation section for preparing a mixture including:
A porous aluminosilicate-carbon composite preparation part that performs a hydrothermal reaction on the mixture to obtain a porous aluminosilicate-carbon composite;
A desiccant production system comprising: a desiccant production unit that obtains a desiccant by subjecting the porous aluminosilicate-carbon composite to an inert gas treatment at 600 to 800 ° C.