JPH08206494A - Desiccant and use of desiccant - Google Patents

Abstract

PURPOSE: To provide a novel desiccant which is particularly suitable for drying HFC32. CONSTITUTION: The desiccant comprises a zeolite whose Si/Al ratio is in a range of 2 to 10, or a zeolite whose Si/Al ratio is in a range of 2 to 10 and a binder for connecting such zeolite, and in which a part or the whole of exchange ions comprises potassium ions, rubidium ions or a mixture of these ions. A part or the whole of material, which is dried by means of the desiccant, is a compound of fluorine, hydrogen, and carbon or a compound of fluorine, hydrogen, chlorine, and carbon, and particularly difluoromethane (HFC32).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a desiccant (dehydrating agent) capable of drying a compound which is chemically unstable and is easily decomposed without decomposing, for example, a desiccant for a CFC substitute refrigerant. Is. In particular, the present invention provides a desiccant that exhibits excellent performance with respect to an alternative CFC refrigerant containing at least difluoromethane (HFC32) as a part of its components.

[0002] The alternative chlorofluorocarbon is a general term for a substance which replaces the chlorine-containing chlorofluorocarbon, which has been pointed out to cause environmental damage due to ozone depletion, and is a fluorohydrocarbon containing only hydrogen, fluorine and carbon without containing chlorine. .

Specifically, HFC32, HFC125,
HFC134, HFC134a, HFC143, HFC
143a, HFC152a, HFC161, HFC22
7 is a promising one. Among such alternative CFCs, HFC32 has a high refrigerating capacity, but is known to be chemically unstable and easily decomposed.

[0004]

2. Description of the Related Art Conventionally, chlorine-based CFCs have been widely used as refrigerants for refrigeration systems.

However, in recent years, due to the environmental problem of global warming due to ozone depletion, elimination of chlorine-based CFCs and conversion to alternative refrigerants have been promoted.

As an alternative refrigerant for chlorine-based CFCs, attention has been paid to fluorohydrocarbons that do not contain chlorine and have a low ozone depletion potential. For example, tetrafluoroethane (HFC134).
a) has already been put to practical use. However, since HFC134a is inferior in refrigerating capacity, difluoromethane (HFC32) having a higher refrigerating capacity has recently been attracting attention.

Conventionally, in a refrigerating apparatus using a Freon refrigerant,
A desiccant has been used in order to eliminate the problem of mechanical troubles due to the deterioration of the refrigerating machine oil due to moisture and the blockage of the refrigerating machine line due to freezing of water.

Silica gel and synthetic zeolite are generally used as a desiccant for CFC refrigerants, and in particular, 4A type zeolite having sodium ion as a metal cation or 3A zeolite containing sodium ion and potassium ion is well known.

However, since the alternative CFCs shown above are chemically unstable, when a conventional zeolite desiccant is used,
There has been a problem that CFCs are decomposed by the catalytic action of zeolite. In particular, HFC32, which has a high refrigerating capacity, is prominently decomposed, so that conventional zeolite is immediately decomposed, and there has been earnestly desired to develop a desiccant applicable to this.

Difluoromethane having a high refrigerating capacity (hereinafter,
Since HFC32 is chemically unstable, it decomposes when a conventional desiccant is used, which causes a mechanical trouble of the refrigerator.

The present inventors have previously proposed a desiccant in which the pores of zeolite are controlled to be smaller than the molecular size of HFC32 as a desiccant in which HFC32 is hard to be adsorbed (Japanese Patent Application No. 6-265077). However, since the pore size of zeolite is constantly changing due to the lattice vibration of the crystal,
It has been difficult to control 32 HFC molecules so that they do not enter the zeolite at all.

Further, a known method of impregnating a zeolite desiccant in an alkali silicate to control the pore size (Japanese Patent Publication No. 38/38).
Although a desiccant (Japanese Patent Laid-Open No. 6-327968) using -18824, page 1, line 12) has been re-proposed, it is also possible to control HFC32 molecules so that they do not enter the zeolite at all. It was difficult.

[0013]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel desiccant which solves the above problems, particularly a novel desiccant suitable for drying HFC32.

[0014]

The present inventor has found that HFC32
As a result of intensive studies on the physical properties of zeolite and zeolite, it was found that the decomposition of HFC32 in zeolite was caused by exchange ions in zeolite, and Si /
It has been found that a zeolite (high silica zeolite) in which the number of exchange ions per unit weight is decreased by increasing the Al atomic ratio can reduce the decomposition of HFC32, and particularly potassium ions, rubidium ions, or a mixture thereof as exchange ions. The inventors have found that excellent characteristics can be obtained with ions, and have completed the present invention.

The desiccant zeolite of the present invention is Si / Al.
Any zeolite having an atomic ratio of 2 or more and 10 or less and capable of adsorbing water may be used, and synthetic zeolite or natural zeolite may be used.

Examples of general zeolites that can be used include analcime, bikitite, brewsterite, chabazite, clinoptilolite, epistilbite, erionite, faujasite, ferrierite, gallonite, gmelinite, harmonite, huran. Dite, L-type, Rumontite, Levinite, Mesolite, Mordenite, Natrite, Oferethite,
Ω type, P type, polingite, philipsite, scolesite, stillbite, T type, W type, Y type, yugawaralite, ZSM-5 and the like can be exemplified.

On the other hand, even if they belong to these zeolite species, the Si / Al atomic ratio is less than 2 or 10 depending on the synthesis conditions.
You cannot use more than. Because Si
When the / Al atomic ratio is 10 or more, the amount of exchanged ions per unit weight decreases, but the reactivity of each ion exchange site with HFC32 increases and the amount of decomposition of HFC32 increases, while Si / Al This is because if the atomic ratio is less than 2, the number of exchanged ions per unit weight increases and the amount of decomposition of HFC32 increases. A particularly preferable Si / Al atomic ratio is 4 or more and 8 or less.

The exchange ion of the zeolite species of the present invention is not particularly limited, but as the ion having low decomposability of HFC32, a part or all of it may be exchanged by potassium ion, rubidium ion, or a mixed ion thereof. preferable.

Since the use of the agent of the present invention is a desiccant, it is necessary to have a moisture adsorbing ability.
0.5% by weight of saturated moisture adsorption at 80 ℃ and 80% humidity
It is preferable to have the above. If the water adsorption amount is less than 0.5% by weight, the performance as a desiccant is insufficient. The upper limit of the amount of adsorbed water varies depending on the type of zeolite and the type of ion exchange. For example, K-exchanged L-type zeolite with a Si / Al atomic ratio of 6 is 9% and K-exchanged Y-type zeolite with a Si / Al atomic ratio of 5.5 is 16%, etc.

The method for measuring the saturated moisture adsorption amount at a temperature of 25 ° C. and a humidity of 80% is as follows. A weight after the desiccant of the invention was left for 16 hours or more after depressurization was reduced to A, and a weight after the desiccant adsorbing moisture was completely dehydrated at 900 ° C. was taken as B (calculation formula (AB)) It is represented by a value calculated by × 100 / B.

The desiccant of the present invention may be a zeolite alone or a zeolite molded product. It is general to use a clay-based binder or a silica binder as a binder for molding zeolite. Examples of clay-based binders include kaolin-based clays, kaolin minerals, serpentine minerals, chamosites, amesites, greenalite, clonstedite, hydrohalloysites, halloysites, kaolinite, dickite, nacrite, chrysotile, antigorite, Zet Ritz Kaolin,
Cornwall Kaolin, Georgia Kaolin, Hong Kong Kaolin, Chosen Kaolin, Fuzhou Clay, Wood Comb Clay, Frog Eye Clay, Soda Kaolin, Iwate Kaolin, Hijiori Kaolin, Ibusuki Kaolin, Kanhaku Kaolin, etc., or two selected from these The above mixture can be illustrated. Needless to say, the clay binder used is not limited to kaolin clay.

The shape of the desiccant is not particularly limited either, and it may be cylindrical,
Examples thereof include prismatic shapes and spherical shapes.

The mixing ratio of zeolite and clay is not particularly limited, but the ratio of clay to zeolite is 1% by weight.
To 40% by weight, especially about 20% to 40% by weight.

Although the natural clay may be used as the binder as the binder as it is, when the natural clay mineral is used as the binder, the clay may promote the decomposability of HFC32. It is preferred to impregnate and inactivate the clay surface for the decomposition of HFC32. It is a known method to impregnate a desiccant with an alkali silicate and use it (Japanese Patent Publication No. 38-18824).

Further, the desiccant is heat-treated in a steam atmosphere to reduce the pore size of the zeolite, and HFC3 to zeolite is reduced.
It is also possible to reduce the adsorption amount of 2.

[0026]

EFFECT OF THE INVENTION The desiccant of the present invention has a low degradability of HFC32 and has a sufficient water adsorption amount.
It exhibits excellent performance as a desiccant for a refrigerant containing 2. Further, the substance to be dried is not limited to HFC32 and can be a desiccant which can be used for all compounds that are chemically unstable and easily decomposed.

[0027]

EXAMPLES The present invention will now be described with reference to specific examples, but the present invention is not limited to these examples.

Example 1 1.0 g of zeolite L (trade name HSZ500KOA manufactured by Tosoh Corporation) powder having an Si / Al atomic ratio of 6 was added to a HFC32 gas partial pressure of 15 m in a helium atmosphere at 1 atm.
The decomposition rate (decrease in concentration) of HFC32 was measured by contacting in a quartz closed container at mHg and temperature of 300 ° C. for 1 hour. The HFC32 gas concentration was measured by the gas chromatography method. Since HFC32 decomposes slightly at 300 ° C. even without zeolite, the decomposition rate is the value obtained by subtracting the decomposition rate without zeolite. The powder has a moisture adsorption amount of 9
%, The decomposition rate of HFC32 was 7%. The powder was suitable as a zeolite for drying HFC32 because it had a sufficient water adsorption amount and had a low degradability of HFC32.

Example 2 20 parts of kaolin clay was added to zeolite L having an Si / Al atomic ratio of 6 used in the example, and a diameter of 2 was obtained by rolling granulation.
mm beads were prepared. Then, it was impregnated with an aqueous 20% potassium silicate solution, dried, and heat-treated at 600 ° C. to obtain a desiccant. Using this desiccant, a general shield tube test was conducted as a durability test of the desiccant for refrigerant.

1 g of desiccant beads and 4 g of HFC32 refrigerant were sealed in a closed glass tube having a volume of 35 cc and kept at 65 ° C. for 30 days. When the F concentration in the desiccant after the test was measured, it was 900 ppm, and HFC32 was hardly decomposed.

Example 3 1.0 g powder of zeolite Y (trade name HSZ320NAA manufactured by Tosoh Corporation) having an Si / Al atomic ratio of 5.5
Is ion-exchanged with a 1N potassium chloride aqueous solution to obtain an exchange rate of 5
A 0% potassium exchanged Y-zeolite was prepared. After the powder was dried and dehydrated at 600 ° C., the decomposition rate (decrease in concentration) of HFC32 was evaluated under the same conditions as in Example 1.

The powder had a moisture adsorption amount of 16% and a HFC32 decomposition rate of 6%. The powder was suitable as a zeolite for drying HFC32 because it had a sufficient water adsorption amount and had a low degradability of HFC32.

Example 4 Using the zeolite used in Example 3, desiccant beads were prepared in the same manner as in Example 2 and a shield tube test was conducted. The shield tube test conditions were the same as in Example 2.

After the test, the F concentration in the desiccant was measured and found to be 1000 ppm, indicating that HFC32 was hardly decomposed.

Example 5 1.0 g of a chabazite-type zeolite powder having an Si / Al atomic ratio of 2.0 was ion-exchanged with a 1N potassium chloride aqueous solution to obtain a potassium-exchanged chabazite-type zeolite having an exchange rate of 94.5%. Prepared. After the powder was dried and dehydrated at 600 ° C., the decomposition rate (decrease in concentration) of HFC32 was evaluated under the same conditions as in Example 1.

The powder had a water adsorption amount of 7% and a HFC32 decomposition rate of 15%. The powder was suitable as a zeolite for drying HFC32 because it had a sufficient water adsorption amount and had a low degradability of HFC32.

Example 6 Using the zeolite used in Example 5, desiccant beads were prepared in the same manner as in Example 2 and a shield tube test was conducted. The shield tube test conditions were the same as in Example 2.

After the test, the F concentration in the desiccant was measured and found to be 2000 ppm, and HFC32 was hardly decomposed.

Example 7 Ferrierite (trade name HSZ720KOA manufactured by Tosoh Corporation) powder having an Si / Al atomic ratio of 8.0 1.0
g was ion-exchanged with a 1N potassium chloride aqueous solution to prepare a potassium-exchanged ferrierite-type zeolite with an exchange rate of 60%. After the powder was dried and dehydrated at 600 ° C.,
The decomposition rate (concentration decrease) of HFC32 was evaluated under the same conditions as in Example 1.

The powder had a water adsorption amount of 8% and a HFC32 decomposition rate of 20%. The powder was suitable as a zeolite for drying HFC32 because it had a sufficient water adsorption amount and had a low degradability of HFC32.

Example 8 Using the zeolite used in Example 7, desiccant beads were prepared in the same manner as in Example 2 and a shield tube test was conducted. The shield tube test conditions were the same as in Example 2.

After the test, the F concentration in the desiccant was measured and found to be 3000 ppm, and HFC32 was hardly decomposed.

Comparative Example 1 Ferrierite having an Si / Al atomic ratio of 12 (trade name HSZ720KOA manufactured by Tosoh Corporation) was used, and Example 1 was used.
A HFC32 decomposition test was conducted in the same manner as in. The powder had a moisture adsorption amount of 7% and had a sufficient drying capacity, but HFC
The decomposition rate of 32 was 35%, which was unsuitable for drying HFC32.

Comparative Example 2 The powder of Comparative Example 1 was molded in the same manner as in Example 2 and a shield tube test was conducted. The test conditions were the same as in Example 2. The F concentration in the desiccant after the test was 1.3%,
A large amount of HFC32 was decomposed.

Comparative Example 3 Ferrierite having an Si / Al atomic ratio of 17 (trade name HSZ720KOA manufactured by Tosoh Corporation) was used and Example 1 was used.
A HFC32 decomposition test was conducted in the same manner as in. The powder had a moisture adsorption amount of 5% and had a sufficient drying capacity, but HFC
The decomposition rate of 32 was 30%, which was unsuitable for drying HFC32.

Comparative Example 4 The powder of Comparative Example 3 was molded in the same manner as in Example 2 and a shield tube test was conducted. The test conditions were the same as in Example 2. The F concentration in the desiccant after the test was 1.3%,
A large amount of HFC32 was decomposed.

Comparative Example 5 Using a K-exchanged A-type zeolite having an Si / Al atomic ratio of 1,
A HFC32 decomposition test was conducted in the same manner as in Example 1.
The powder had a moisture adsorption amount of 25% and a sufficient drying ability, but the decomposition rate of HFC32 was 45%, which was unsuitable for drying HFC32.

Comparative Example 6 The powder of Comparative Example 5 was molded in the same manner as in Example 2 and a shield tube test was conducted. The test conditions were the same as in Example 2.

The F concentration in the desiccant after the test was 1.5%
Then, a large amount of HFC32 was decomposed.

Comparative Example 7 A HFC32 decomposition test was conducted in the same manner as in Example 1 using K-exchanged X-type zeolite having an Si / Al atomic ratio of 1.25. The powder had a moisture adsorption amount of 33% and a sufficient drying ability, but the decomposition rate of HFC32 was 69%, and
Was not suitable for drying.

Comparative Example 8 The powder of Comparative Example 7 was molded in the same manner as in Example 2 and a shield tube test was conducted. The test conditions were the same as in Example 2.

The F concentration in the desiccant after the test was 1.5%
Then, a large amount of HFC32 was decomposed.

The results of Examples 1 to 8 and Comparative Examples 1 to 8 are summarized in Table 1 below.

[0054]

[Table 1]

Claims (5)

[Claims] 1. A desiccant comprising a zeolite having an Si / Al atomic ratio of 2 or more and 10 or less. 2. A desiccant comprising a zeolite having an Si / Al atomic ratio of 2 or more and 10 or less and a binder binding the zeolite. 3. The desiccant according to claim 1 or 2, wherein a part or all of the exchange ions consist of potassium ions, rubidium ions, or mixed ions thereof. 4. A part or all of the substance dried by the desiccant is fluorine, hydrogen and carbon, or a compound consisting of fluorine, hydrogen, chlorine and carbon. desiccant. 5. The desiccant according to claim 4, wherein the compound consisting of fluorine, hydrogen and carbon is difluoromethane (HFC32), or a mixture containing at least difluoromethane (HFC32).