JPH08206493A - Desiccant and its use - Google Patents

Abstract

PURPOSE: To provide a novel desiccant which is suitable for drying a compound comprising fluorine, hydrogen, and carbon, prticularly such as difluoromethane (HFC32). CONSTITUTION: The desiccant comprises P-type zeolite and/or HS-type zeolite, or P-type zeolite and/or HS-type zeolite and a binder for connecting such zeolite, and in which a part or the whole of zeolite is ion-exchanged by means of potassium ion and/or rubidium ion. The whole or part of material which is dried by means of the desiccant is a compound comprising fluorine, hydrogen, and carbon, or a compound comprising fluorine, hydrogen, chlorine, and carbon.

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 which exhibits excellent performance with respect to an alternative fluorocarbon refrigerant containing at least difluoromethane (HFC32) as a part of its components.

The alternative chlorofluorocarbon is a general term for a substance replacing the chlorine-containing chlorofluorocarbon, which has been pointed out to cause environmental damage due to ozone layer depletion, and is a fluorohydrocarbon which does not contain chlorine but is composed of only hydrogen, fluorine and carbon. .

Specifically, HFC32, HFC125,
HFC134, HFC134a, HFC143, HFC
143a, HFC152a, HFC161, HFC22
7 etc. are mentioned.

Among them, HFC32 is known to have a high refrigerating capacity, but is chemically unstable and easily decomposed.

[0006]

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 environmental problems such as 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 coefficient. For example, tetrafluoroethane (HFC134).
a) has already been put to practical use.

However, tetrafluoroethane (HFC13
Since 4a) is inferior in refrigerating capacity, difluoromethane (HFC32), which has a higher refrigerating capacity, has recently attracted 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.

Difluoromethane (H
Since FC32) is remarkably decomposed, conventional zeolite is decomposed immediately, and development of a desiccant applicable to this has been eagerly awaited.

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 already proposed a desiccant in which the pores of zeolite are smaller than the molecular size of HFC32 as a desiccant in which HFC32 is less likely to be adsorbed. (Japanese Patent Application No. 6-265077) However, in reducing the pore diameter of zeolite by heat treatment in steam, the pore diameter of the zeolite slightly changes depending on the heat treatment conditions. Therefore, precise control is required for producing zeolite having the same pore diameter. Was requested.

Further, a known method of impregnating a zeolite desiccant in an alkali silicate to reduce the pore size (Japanese Patent Publication No. 38/38).
A desiccant (JP-A-6-327968) using 18824, page 1, line 12) has been re-proposed, but it was not sufficient.

[0016]

DISCLOSURE OF THE INVENTION The object of the present invention is suitable for drying a novel desiccant which solves the above-mentioned problems, in particular, a compound composed of fluorine, hydrogen and carbon such as difluoromethane (HFC32). Another object is to provide a novel desiccant.

[0017]

Means for Solving the Problems The present inventor has found that P-type zeolite or HS-type zeolite has a sufficiently small pore size by itself, and therefore does not adsorb and decompose HFC32 without complicated operations. We have found that it can be used as a desiccant, and by suitable ion exchange
We found that the degradability of FC32 was further reduced,
The present invention has been completed.

The basic skeleton structure of the desiccant zeolite of the present invention must be P-type or HS-type zeolite.

It is known that P-type zeolite and HS-type zeolite have the chemical formulas shown below. (Zeoli
te Molecular Sieves D.E. W. B
reck al P155, P168 other) P-type zeolite _{Na 2 O · Al 2 O 3} · 2~5SiO 2 · 5H 2 O HS -type zeolite _{Na 2 O · Al 2 O 3} · 2~5SiO 2 · 2.5H 2 O These Since the zeolite has smaller pores than the commonly used A-type zeolite and X-type zeolite, it has not been industrially used so far, and recently P-type zeolite has been used as a detergent carrier ( The use as a builder) is only proposed.

According to Breck et al., The pore size of P-type zeolite and HS-type zeolite is estimated to be 2.6 angstroms, which is larger than that of the conventionally known 3A zeolite (potassium-exchanged A-type zeolite) of 3.3 angstroms. It has a small pore size.

Since the molecular diameter of HFC32 is estimated to be about 3.3 Å, the pore diameter is 2.6.
Water can be adsorbed by the Angstrom P-type zeolite and HS-type zeolite, but almost no HFC32 molecule is adsorbed, and it can be used as a desiccant for HFC32.

The pore size is about 2.6 Å,
Other zeolites having a water adsorption capacity include edingtonite, epistilbite, dysmondite, harmonite, hurlandite, rumontite, levinite, natrite, phillipsite, scolesite, tomsonite, etc., but all are natural zeolites. It is not industrial because the synthesis requires a high temperature of 100 ° C. or higher. The zeolite of the present invention, or the desiccant composed of zeolite and a binder, has a sufficient water adsorption capacity to be used as a desiccant.

The water adsorption amount of zeolite is generally indicated by the equilibrium adsorption amount at room temperature (25 ° C.) and humidity of 80%.

The saturated water adsorption amount at a temperature of 25 ° C. and a humidity of 80% is measured by placing the sample in an atmosphere of a temperature of 25 ° C. and a humidity of 80%, for example, in a vacuum desiccator containing a saturated vapor pressure of a supersaturated ammonium chloride aqueous solution. 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 P-type zeolite and the HS-type zeolite of the present invention should basically not adsorb HFC32, but since the pore size of the zeolite is constantly changing due to thermal vibration, the HFC32 molecule has a slight pore size. There is a probability of invading.

Therefore, it is more preferable that the exchange ions in the P-type zeolite and the HS-type zeolite are hard to decompose the HFC32 molecule. For example, it is preferable that some or all of the exchanged ions are ion-exchanged with potassium ions and / or rubidium ions.

The content of these exchange ions is not particularly limited, but a higher exchange ratio is preferable, and 0.1% or more, particularly 33% or more of the total exchange ions is preferable. The upper limit of ion exchange is 100%.

The desiccant of the present invention may be a zeolite alone or a zeolite molded. 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 a cylindrical shape,
Examples thereof include prismatic shapes and spherical shapes. Further, the kneading ratio of zeolite and clay is not particularly limited, but the ratio of clay to zeolite is generally 1% by weight to 40% by weight, particularly about 20% by weight to 40% by weight.

Next, an example of a method for producing the desiccant of the present invention will be described.

The method for producing P-type zeolite and HS-type zeolite is described in D. W. Zeolite Mole by Breck
are described in detail by Clar Sieves et al.

In the desiccant of the present invention, it is preferable that the P-type zeolite and the HS-type zeolite are ion-exchanged with potassium ions, rubidium cations, or a mixed ion thereof. This can be achieved by ion exchange with a solution containing ions.

As the solution containing potassium ions, rubidium ions, or mixed ions thereof, an aqueous solution of these salts can be used, and examples thereof include chlorides, sulfates, nitrates and organic acid salts.

The higher the ion concentration in the ion exchange solution, the higher the efficiency, and it is preferable that the ion concentration is 0.1 N or more.

The ion exchange method is not particularly limited, either.
Examples include batch immersion with stirring and flow-type exchange method in an ion exchange tower. The higher the temperature of ion exchange, the better the efficiency, from room temperature (20 ° C) to 100 ° C, especially 30 ° C to 90 °
The range of ° C is preferred. The ion exchange time varies depending on the concentration of the ion exchange solution, the exchange temperature, and the exchange method,
Generally 1 to 100 hours, especially 4 to 20 hours
It is a range of time. The ion exchange may be carried out in the state of zeolite powder or may be carried out after molding.

The zeolite powder may be molded by pressing only the zeolite, but it is generally molded by using the above-mentioned molding binder (clay) in order to maintain the strength. The molding method is not particularly limited, and examples thereof include rolling granulation, extrusion molding, and press molding.

The desiccant may be used as it is, but when natural clay mineral is used as a binder, the clay itself may decompose HFC32. Therefore, the desiccant is impregnated with alkali silicate and the clay surface is treated. It is preferable to inactivate the degradability of HFC32. It is a known technique to impregnate a desiccant with an alkali silicate. (Japanese Examined Patent Publication No. 38-18824) Ion exchange, or a desiccant which has been subjected to ion exchange and alkali treatment is dried to obtain a desiccant by heat treatment at 300 ° C. or higher and dehydration.

The heat treatment temperature is 300 ° C. or higher and 800 ° C. or lower,
Particularly, 350 ° C or higher and 700 ° C or lower are preferable. When the heat treatment temperature is 800 ° C. or higher, the pores of zeolite are clogged and water is not adsorbed, so that it cannot be used as a desiccant. On the other hand, if the temperature is lower than 300 ° C, it takes a long time for dehydration, which is not economical.

The heat treatment atmosphere is also not particularly limited, and in the air,
Although oxygen or an inert atmosphere can be used, it is also possible to introduce water (steam) into the heat treatment atmosphere to slightly reduce the pore size of the zeolite and further reduce the amount of HFC32 adsorbed on the zeolite.

[0040]

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 that can be used for all compounds that are chemically unstable and easily decomposed.

[0041]

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 [Zeolite preparation] Water glass, sodium aluminate,
P-type zeolite and HS-type zeolite were synthesized using caustic soda and water as raw materials.

The composition of the zeolite synthesis and the reaction conditions are shown in Table 1.

[0044]

[Table 1]

The reaction product was filtered, washed with water and dried, and then analyzed by X-ray diffraction.
It was confirmed to be S-type zeolite and P-type zeolite. Next, these zeolites were ion-exchanged with rubidium and potassium. The ion exchange was carried out by ion-exchange with a chloride aqueous solution of each metal (concentration 1N each) at 70 ° C. for 16 hours, followed by washing with water and drying. The ion exchange rate was measured by the ICP method.

[Evaluation of Moisture Adsorption Amount] The prepared zeolite powder was dehydrated at 600 ° C. for 2 hours, then at 25 ° C. and humidity 80%.
Under the conditions described above, moisture was absorbed for 16 hours and the amount of adsorbed water was measured.

The amount of adsorbed water was calculated by the method described in the specification.

[Evaluation of HFC32 Decomposition Characteristics] 1.0 g of dehydrated powder was brought into contact with a HFC32 gas partial pressure of 15 mmHg and a temperature of 300 ° C. in a quartz closed container in a helium atmosphere of 1 atm to decompose HFC32 after 1 hour. (Lower concentration)
Was measured. The HFC32 gas concentration was measured by the gas chromatography method.

Since HFC32 is slightly decomposed at 300 ° C. even without zeolite, the decomposition rate is a value obtained by subtracting the decomposition rate without zeolite. Table 2 shows the exchanged metal ions, the ion exchange rate, the water adsorption amount, and the HFC32 decomposability.

[0050]

[Table 2]

Example 2 Among the zeolites prepared in Example 1, 20% of kaolin clay was mixed with K-exchanged HS zeolite having a particularly low degradability of HFC32, and beads having a diameter of 2 mm were prepared by rolling granulation.

Next, the obtained beads were impregnated with a 20% potassium silicate aqueous solution, dried, and heat-treated at 600 ° C. The beads were subjected to a general shield tube test as a durability test of a desiccant for refrigerant. 1.0 g of beads and 4.0 g of HFC32 refrigerant were enclosed in a sealed glass container having an internal volume of 35 cc and kept at a temperature of 65 ° C. for 30 days.

After the test, the desiccant was taken out and the F concentration in the desiccant was measured and found to be 800 ppm.
32 was hardly decomposed.

Comparative Example 1 A type zeolite (Na ion exchange (4A) type and K ion exchange (3A) type) and X type zeolite were evaluated in the same manner as in the example, and the results are shown in Table 3. .

[0055]

[Table 3]

Degradability of HFC32 was higher than that of P-type zeolite and HS-type zeolite.

Comparative Example 2 The K-exchanged A-type zeolite of Comparative Example 1 was molded in the same manner as in Example 2 and a shield tube test was conducted, and the test conditions were the same as in Example 2.

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

Claims (5)

[Claims] 1. A desiccant comprising P-type zeolite and / or HS-type zeolite. 2. A desiccant comprising a P-type zeolite and / or an HS-type zeolite and a binder that binds the zeolite. 3. The desiccant according to claim 1, wherein the ion exchange metal of the P-type zeolite and / or the HS-type zeolite is partly or wholly ion-exchanged with potassium ions and / or rubidium ions. 4. The drying according to claim 1, wherein the substance dried by a desiccant or a part thereof is fluorine, hydrogen and carbon, or a compound consisting of fluorine, hydrogen, chlorine and carbon. Agent. 5. The desiccant according to claim 4, wherein the compound consisting of fluorine, hydrogen and carbon according to claim 4 is difluoromethane (HFC32) or a mixture containing at least difluoromethane (HFC32).