JPH10263365A - Decomposition of hydrofluoricarbon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst capable of efficiently decomposing hydroluorocarbons and long in life and to provide a decomposing method of hydrolufrocarbons using the catalyst. SOLUTION: In a reaction by which the hydroluorocarbons are decomposed in gas phase in the presence of steam or the steam and a molecular oxygen, the catalyst in which the total amount of alkali metals is <=300 wt.ppm and consisting of an oxide of phosphorus and the oxide of at least one kind element selected from a group consisting of aluminum, boron and alkaline earth metals is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for decomposing a hydrofluorocarbon. More specifically, the present invention relates to a method for decomposing a hydrofluorocarbon in a gas phase with steam or steam and molecular oxygen in the presence of a specific catalyst.

[0002]

2. Description of the Related Art With respect to the decomposition of hydrofluorocarbons, a combustion method, a cement kiln combustion method, a plasma decomposition method, a detonation method, a supercritical water method, a catalytic decomposition method and the like have been proposed. Each has its own problems, and the combustion method requires an expensive combustion furnace for high-temperature combustion and measures against dioxin.
The cement kiln combustion method is regional and not a general treatment facility. The plasma decomposition method generally has a problem with an increase in the size of the apparatus and utility costs. Although the detonation method is suitable for complete disassembly, there are problems with continuous high-volume processing. The supercritical water method is under high temperature and high pressure conditions, and has problems in terms of equipment and operation. The catalytic decomposition method has a relatively low temperature as compared with the combustion method, and is advantageous in terms of equipment. In addition, small-scale decomposition is possible and small-scale and easy, but improvement of performance represented by catalyst life is a major issue.

As a catalytic decomposition method, a photo decomposition method (Japanese Patent Laid-Open No.
JP-A-143630, JP-A-4-83515), a method using a catalyst carrying a carrier or a metal (JP-A-3-12220, JP-A-3-66388,
JP-A-3-106419, JP-A-3-42015
JP-A-3-249945), and a method using an alloy (JP-A-3-249945)
And Japanese Patent Application Laid-Open No. 4-122443). On the other hand, in a study using phosphoric acid as a catalyst, the Journal of the Chemical Society of Japan, 645 (1991) describes that the AlPO ₄ catalyst is immediately deactivated and the BPO ₄ catalyst has a life of about 10 hours. BPO ₄ decomposition catalyst (Ind. Eng. Chem. Res. 1
995, 34, 967-970) report a durability of about 35 hours by supplying 1% water. In addition, the same inventor describes the disappearance of chlorodifluoromethane using magnesium phosphate in Example 33 of JP-A-8-104656. However, regarding the type of decomposition product (degree of decomposition) and catalyst life, Not clear.

[0004]

The method for decomposing hydrofluorocarbon has the advantages that the temperature is relatively low and that small equipment is possible as compared with the combustion method, but the biggest problem is a catalyst having high activity and long life. In particular, long-life catalysts have been desired. In view of the above problems, as a result of intensive studies, the present invention has achieved a high activity and a long life of a hydrofluorocarbon decomposition catalyst under relatively low temperature conditions, and an object of the present invention is to propose a decomposition method using the same. .

[0005]

Means for Solving the Problems Hydrogen fluoride is by-produced in the decomposition reaction of hydrofluorocarbon. Many of the conventional catalysts used in the catalytic decomposition method mainly contain metal oxides, but the free energy of formation of metal fluoride is more negative than the free energy of formation of metal oxides. The metal oxide gradually changes to fluoride. The present invention has conducted intensive studies to solve the above-mentioned problems, and as a result, in a reaction of decomposing hydrofluorocarbon in a gas phase in the presence of water vapor or water vapor and molecular oxygen, the total amount of alkali metals is 300 ppm or less. A hydrofluorocarbon decomposition method characterized by using a catalyst comprising an oxide and an oxide of at least one element selected from the group consisting of aluminum, boron and alkaline earth metals has been found.

Hereinafter, the present invention will be described in detail. In the present invention, the hydrofluorocarbon refers to a hydrocarbon in which a part of hydrogen is replaced by fluorine. In addition, both saturated and unsaturated are included. Among them, a fluorinated hydrocarbon having 1 to 4 carbon atoms is preferable. For example, if the number of carbon atoms is 1, CH ₃
F, CH ₂ F ₂ , and CHF _{3.
2 H 5 F, C 2 H} 4 F 2, C 2 H 3 F 3, C 2 H 2 F
₄ , C ₂ HF ₅ alkanes; C ₂ H ₃ F, C ₂
Alkenes of H ₂ F ₂ and C ₂ HF ₃ , and similarly, C ₃ and C 4 can be easily exemplified.
These may be a single compound or a mixture. In addition, other H
CFC (hydrochlorofluorocarbon) or CFC
(Chlorofluorocarbon), an organic chlorine compound, an organic bromine compound, and hydrocarbons may be mixed.

The catalyst of the present invention will be described. A catalyst comprising an oxide of phosphorus having a total amount of alkali metal of 300 wtppm or less and an oxide of at least one element selected from the group consisting of aluminum, boron and alkaline earth metals. Specifically, aluminum phosphate, boron phosphate, magnesium phosphate, calcium phosphate, wherein the total amount of alkali metals is 300 wtppm or less,
Barium phosphate, strontium phosphate and mixtures thereof. Especially aluminum phosphate, boron phosphate,
Magnesium phosphate and calcium phosphate are preferred. More preferably, it is aluminum phosphate.

[0008] Among these catalysts, it is necessary to make the total amount of alkali metals not more than 300 wtppm, preferably not more than 70 wtppm. Alkali metal particularly refers to sodium, potassium, lithium and the like. As a raw material to be used, one containing as little alkali metal as possible is used.
In some cases, it is removed by purification. If the alkali metal is present in excess of 300 wtppm, the activity will be reduced, and even if the reaction temperature is increased, sufficient activity will not be achieved, and the catalyst life will be short.

The preparation method may be a general precipitation method. For example, a diluted aqueous ammonia is dropped into a mixed aqueous solution of nitrate and phosphoric acid to neutralize and precipitate, and the mixture is left to be aged if necessary. After that, wash with water and confirm that it was sufficiently washed with the conductivity of the washing water. In some cases, a portion of the slurry is taken and the contained alkali metal is measured. Further filter and dry. The drying temperature is preferably from 100 ° C to 130 ° C. The obtained dried product is crushed to make the particle size uniform, or further crushed and molded. afterwards,
Air calcination is performed at a temperature of 500 ° C. or more. Preferably 800
C. or higher, more preferably 900 to 1200.degree. The sintering time depends on the temperature, but is about 1 hour to about 50 hours, preferably about 2 hours to about 24 hours. Prolonged firing at high temperatures promotes crystallization and is economically insignificant. The effect is weak in a short time.

When preparing the catalyst or after calcination, the catalyst
At least one element selected from the group consisting of e, La, Y, Cr, Fe, Co, and Ni may be added and contained. Particularly, Ce, Fe, and Y are preferable. The added metal salt is preferably a nitrate, a chloride, an oxide, a phosphate, or the like, but a nitrate is easily prepared. The addition amount is 1 g atom or less, preferably 0.5 g atom or less per 1 g of phosphorus. It is more preferably at most 0.3 g atom.

The properties of the obtained catalyst differ depending on the kind of salt, the preparation method and the conditions. For example, in the case of aluminum phosphate, the BET surface area immediately after preparation is 50 m ² / g or more, preferably 80 m ² / g or more. When observed by XRD, an AlPO ₄ peak is partially visible in some cases in an amorphous state. Although this is a method usually used in the art, this catalyst may be used in a state of being supported on a carrier such as alumina, silicon carbide, silicon nitride, and activated carbon.

Next, the supply gas composition of the present invention will be described. First, the supply standard ratio of the supply gas containing hydrofluorocarbon (supply gas) is preferably 0.05 mol% to 50 mol%. More preferably 0.1 mol
% To 30 mol%. If the amount is too small, it is economically problematic, and if it is too large, catalyst deterioration is accelerated.

The supply gas (supply gas) containing hydrofluorocarbon requires steam, and its ratio is 5 mol% or more on a supply basis. More preferably 20 mo
1% or more and 70 mol% or less. If the amount is too small, the selectivity to carbon dioxide is reduced and the life is deteriorated quickly, while if it is too large, it is economically disadvantageous. In some cases, oxygen may be supplied. The type of supply gas (supply gas) containing hydrofluorocarbon depends on the composition, the amount of treatment, and the reaction temperature, but oxygen is preferably 30 mol% or less on a supply basis. If the amount is too large, crystallization of the catalyst is promoted, the specific surface area is reduced, and the activity is reduced.

When air is used as the oxygen source, nitrogen is entrained, but this is not a problem. In some cases, since it is an exothermic reaction, it is expected to exhibit an effect as a diluent gas.
Further, it is possible to circulate the carbon dioxide gas generated after the decomposition into the reaction system. In addition, helium and argon can be used. The supply ratio varies depending on the type and composition of the substrate, the processing amount, the temperature, etc., but generally, the supply gas: oxygen:
Water vapor (mol%) = 1: 1 to 50: 1 to 150, preferably supply gas: oxygen: water vapor (mol%) = 1: 1
-20: 1-50.

The decomposition reaction conditions in the present invention will be described. The decomposition reaction temperature depends on the type and composition of the hydrofluorocarbon to be decomposed, but decomposition at a high temperature is not economical because the catalyst life tends to be sharply reduced. On the other hand, if the temperature is too low, the ratio of raw materials that do not decompose increases, so
The temperature is preferably in the range of not lower than 600C and not higher than 600C. More preferably 200
° C to 550 ° C. The space velocity, which is the amount of gas supplied per catalyst, is from 100 liter GAS / liter catalyst · hr (hereinafter referred to as 50 / hr) to 100 liters.
00 / hr is appropriate, and more preferably 100 / hr to 5000 / hr.

The reaction is generally carried out in a fixed bed in a gas phase, but may be carried out in a fluidized bed. The material of the reactor depends on the processing amount and the kind of raw material.
Tubes are also possible, but preferably Inconel, Monel,
It is better to use Hastelloy C, nickel or the like. When the reaction is carried out for a long time in a continuous flow system, the activity of the catalyst is slightly reduced, and the conversion is reduced. In this case, it is an effective means to adjust the reaction temperature and the contact time to keep the conversion constant. There may be a way to control the amount of oxygen.

[0017]

The present invention will be described in more detail with reference to the following Examples, which by no means limit the present invention. Catalyst Preparation Examples 1 to 3 (Preparation method of aluminum phosphate) Aluminum nitrate nonahydrate (special grade reagent manufactured by Junsei Chemical Co., Ltd.)
Na 70 wtppm, K 2 wtppm) and 85% phosphoric acid (Junsei Chemical Co., Ltd., reagent special grade Na 4 wtppm, K 4
wtppm) was used without purification. First, at room temperature, aluminum nitrate and 85 were used in a 2 liter beaker.
Aqueous solution of 10% phosphoric acid and 10% aqueous ammonia were simultaneously added to 400 ml of pure water stirred in a 5 liter beaker.
It was dropped over time to adjust the pH to 7. The precipitate formed at this time was aged overnight. Thereafter, filtration and washing were repeated with pure water, and the conductivity of the filtrate was measured. The obtained solid was spread, placed in a drier, and dried at 120 ° C. Further, the mixture was calcined in air at a predetermined temperature for 5 hours and sized to 14 to 32 mesh. A part of the obtained catalyst was treated by the Belizerius method, and the alkali content was measured by the atomic absorption method.

Catalyst preparation example Firing temperature Na K Specific surface area XRD 1 1000 ° C 2 wtppm or less Detection limit or less 131 m ² / g Amorphous 2 800 ° C 2 wtppm or less Detection limit or less

Catalyst Preparation Example 3 Aluminum nitrate nonahydrate (Na 570 wt ppm, K
(50 wtppm) and 85% phosphoric acid (special grade Na 4 wtppm, K 4 wtppm, manufactured by Junsei Chemical Co., Ltd.) were used without purification. The catalyst was prepared in the same manner as in Catalyst Preparation Example 1, filtered, and washed only with an amount of water for facilitating handling. The obtained solid was spread, placed in a drier, and dried at 120 ° C. The mixture was further calcined in air at 1000 ° C. for 5 hours and sized to 14 to 32 mesh. When a part of the obtained catalyst was analyzed in the same manner as in Catalyst Preparation Example 1, Na 167 wtp
pm, K was 11 wtppm.

Catalyst Preparation Examples 4 to 6 (Preparation of Phosphate) As in Catalyst Preparation Example 1, Catalyst Preparation Example 4 was prepared from boric acid and phosphoric acid. In catalyst preparation example 5, Ca ₃ (PO ₄ ) ₂ was prepared from magnesium nitrate and phosphoric acid in catalyst preparation example 6 in the same manner.

Catalyst Preparation Examples 7 to 11 (Preparation of Adding Metal to Aluminum Phosphate) The following metals were added during preparation of aluminum phosphate in Catalyst Preparation Example 1. The amount added is 10% each.

[0022]

Examples 1 to 11 (Reaction Example) The reaction was carried out in a fixed-bed flow reactor under normal pressure. The reaction tube was used by connecting a stainless steel tube having an inner diameter of 13 mm to a stainless steel tube having an inner diameter of 16 mm. Nitrogen, oxygen, HFC134a
The three gases (CF ₃ CFH ₂ ) are mixed by a mixer,
It was sent to the catalyst layer in the reaction tube. Water was injected with a microfeeder. The gas after the reaction first captures the acid generated by decomposition with an acid trap (filled with water with a gas washing bottle),
The gas from which the acid was removed was analyzed by TCD gas chromatography.

The catalysts prepared in Catalyst Preparation Examples 1 to 13 were
3.5 g was charged, and the supply gas composition was HFC134a: O ₂ : N ₂ : H ₂ O = 0.5: 9.
3: 37.4: 57.8 (ml / min) (0.5 mol% for HFC134a, 55 mol for H ₂ O)
1%, the rest being air). The decomposition gas generated by the decomposition reaction at 500 ° C. in Example 1 was examined.
The conversion rate of 4a (the rate at which HFC134a decomposed and disappeared) was 100%, and only CO ₂ was detected as a decomposition product. The selectivity in the detected product is 100% for CO ₂ . Formally, when completely decomposed, C ₂ H ₂ F ₄ + H ₂ O + 1.5O ₂ → 2CO ₂ +4
HF

[0025]

[Table 1] Examples 1 and 3 show that a catalyst containing a large amount of alkali metal causes a decrease in activity.

[0026]

[Table 2]

Comparative Example 1 (Effect of Steam) 13.5 g of the catalyst prepared in Catalyst Preparation Example 1 was charged, and the supply gas composition was HFC134a: O ₂ : N ₂ : H ₂ O = 0.
5: 20.9: 83.6: 0 (ml / min). The reaction temperature and the results are shown. Conversion of 134a at 400 ° C. 1
0% or less.

Example 12 A catalyst in which the reaction of Example 7 (reaction temperature: 400 ° C.) was continued up to about 100 hours was taken out of the reactor, and the crystal state was examined by XRD. No significant change before and after the reaction
Peaks attributed to PO ₄ and CePO ₄ were observed. This indicates that the catalyst retained its activity without being fluorinated like AlF ₃ .

Example 13 A reactive decomposition was carried out in the same manner as in Example 7 except that a mixture of HFC134a, HCFC22 and CFC12 (composition: 50%, 30%, 20%) and carbon dioxide gas were used instead of nitrogen gas. At 400 ° C., the conversion of the mixture was 100%.

Example 20 HFC23, HFC143a, HCFC133a, CF
C134a mixture (composition: 10%, 60%, 15%,
15%) was decomposed in the same manner as in Example 7. At 400 ° C., the conversion of the mixture was 100%.

[0031]

According to the present invention, a hydrofluorocarbon or a gas containing a hydrofluorocarbon is used in the presence of water vapor and, in some cases, oxygen, in the presence of a specific catalyst, whereby the decomposition reaction can be carried out efficiently and with a long life. it can.

Claims (10)

[Claims] In a reaction for decomposing a hydrofluorocarbon in a vapor phase in the presence of water vapor or water vapor and molecular oxygen, a phosphorus oxide having a total amount of alkali metal of 300 wtppm or less and aluminum, boron and alkaline earth metal A method for decomposing a hydrofluorocarbon, comprising using a catalyst comprising an oxide of at least one element selected from the group consisting of: 2. The method for decomposing a hydrofluorocarbon according to claim 1, wherein the total amount of the alkali metal is 70 wtppm or less. 3. The method for decomposing a hydrofluorocarbon according to claim 1, wherein the water concentration in the supply gas is 5 mol% or more. 4. The method for decomposing a hydrofluorocarbon according to claim 3, wherein the water concentration in the supply gas is from 20 mol% to 70 mol%. 5. The method for decomposing hydrofluorocarbon according to claim 1, wherein a gas containing carbon dioxide, which is a main decomposition product gas, is returned to the supply gas. 6. The supply gas has a molecular oxygen concentration of 30 m.
The method for decomposing a hydrofluorocarbon according to any one of claims 1 to 5, which is not more than ol%. 7. The method for decomposing a hydrofluorocarbon according to claim 1, wherein the concentration of the supply gas containing the hydrofluorocarbon is from 0.05 mol% to 50 mol%. 8. The method for decomposing a hydrofluorocarbon according to claim 1, wherein the reaction temperature is 150 ° C. or higher and 600 ° C. or lower. 9. The catalyst according to claim 1, further comprising Ce, L.
9. The method for decomposing a hydrofluorocarbon according to claim 1, comprising at least one element selected from the group consisting of a, Y, Cr, Fe, Co, and Ni. 10. The decomposition method according to claim 1, wherein the hydrofluorocarbon has 1 to 4 carbon atoms.