JP4410782B2 - Catalyst for producing pentafluoroethane and method for producing the catalyst - Google Patents

Description

The present invention relates to a catalyst for producing pentafluoroethane and a method for producing the catalyst, more specifically, perchloroethane (C ₂ Cl ₆ , hereinafter referred to as “PCE”) or 1,1-dichloro-2,2, Catalyst useful for producing pentafluoroethane (CF ₃ CHF ₂ , hereinafter referred to as “HFC-125”) by reacting 2-trifluoroethane (CHCl ₂ CF ₃ , hereinafter referred to as “HCFC-123”) with HF And a method for producing the catalyst.

HFC-125 has almost no global warming and ozone depletion index because it does not contain chlorine in the molecule, and has been used as an existing refrigerant, blowing agent, propellant, etc. It is an alternative to hydrogen chlorofluorocarbon and is used as a raw material for mixed refrigerants by mixing with difluoromethane (CH ₂ F ₂ , hereinafter referred to as “HFC-32”).

A catalyst used to produce HFC-125 using a chloroethane compound as a raw material is already known, and a typical example thereof is chromium oxide.
In Patent Document 1, as a catalyst for producing HFC-125 using a chloroethane compound as a raw material, Cr ₂ O ₃ —BaO—Al ₂ O ₃ , Cr ₂ O ₃ —MgO—Al ₂ O ₃ , Cr ₂ O ₃ —SrO— Al ₂ O ₃ , Cr ₂ O ₃ —CaO—Al ₂ O ₃ , Cr ₂ O ₃ —Fe ₂ O ₃ , Cr ₂ O ₃ —Al ₂ O ₃ , and Cr ₂ O ₃ —MgO are described.
Here, the Cr ₂ O ₃ —Al ₂ O ₃ catalyst is prepared by dissolving both Cr (NO ₃ ) ₃ · 9H ₂ O and Al (NO ₃ ) ₃ · 9H ₂ O in water, and putting this in ammonia water. By stirring, a precipitate of Cr (OH) ₃ and Al (OH) ₃ was obtained. The precipitate was washed with water and dried, then calcined at 450 ° C. for 5 hours, and Cr ₂ O ₃ —Al ₂ O ₃ The powder is obtained, and the powder is formed into a pellet and fluorinated with a mixed gas of N ₂ and HF.

In Patent Document 2, Cr ₂ O ₃ / Al ₂ O ₃ , Cr ₂ O ₃ / In ₂ O ₃ , Cr ₂ O ₃ / Ga ₂ O ₃ , Cr ₂ O ₃ / CoO, Cr ₂ O ₃ / NiO, Cr _{A 2} O ₃ / ZnO catalyst is described.
Here, the Cr ₂ O ₃ / Al ₂ O ₃ catalyst is produced by the following method.
Ammonia water is added to an aqueous Cr (NO ₃ ) ₃ solution to obtain a precipitate of Cr (OH) ₃ , which is filtered and dried to pulverize solid Cr (OH) ₃ to obtain Cr (OH) ₃ After obtaining the powder, it was placed in an Al (NO ₃ ) ₃ aqueous solution and allowed to stand for 12 hours and then dried. A small amount of graphite was added thereto to form a pellet, and this was formed in N ₂ gas for 2 hours. It is fired and fluorinated with a mixed gas of N ₂ + HF.

That is, in the conventional method for producing a binary or ternary chromium oxide catalyst such as Cr ₂ O ₃ —Al ₂ O ₃ , both Cr (NO ₃ ) ₃ and Al (NO ₃ ) ₃ are used in water. dissolved coprecipitated with aqueous _{ammonia, Cr (OH 3) 3 -Al} (OH) 3 coprecipitate (coprecipitate) by firing whether obtain _Cr 2 _{O 3 -Al} 2 _O 3 catalyst (Patent Reference 1), or a Cr (OH) ₃ powder impregnated in an Al (NO ₃ ) ₃ aqueous solution and then dried to obtain a composition of Cr (OH) ₃ / Al (OH) ₃ , which is fired A Cr ₂ O ₃ / Al ₂ O ₃ catalyst is obtained (see Patent Document 2).

On the other hand, it is known that the activity of a chromium oxide catalyst is closely related to the crystal structure of the catalyst and the valence of Cr atoms.
According to Patent Document 2, chromium on a chromium oxide-based catalyst has a valence of +3.5 to +5.0, and an amorphous state is an active site of the catalyst. is there.
In the Cr ₂ O ₃ / Al ₂ O ₃ fluorination catalyst, the activity is related to the valence of chromium, and alumina is known to function as a supporter.
However, the two-component and three-component chromium catalysts produced by the impregnation method or coprecipitation method are suitable for industrial production processes due to the low conversion rate and selectivity to HFC-125 in the conversion reaction of chloroethane. There is no problem.

In particular, conversion and selectivity are low in the process of producing HFC-125 using PCE as a raw material, and existing catalysts do not exhibit sufficient activity in the fluorination reaction.
Conversion rate and HFC-125 when a chromium oxide catalyst (Patent Document 1) produced by a coprecipitation method using a two-component or three-component oxide starts with PCE (perchloroethylene) The selectivity to (pentafluoroethane) is as shown in Table 1.

（注）HFC―１２５：ペンタフルオロエタン
HFC―１２４：テトラフルオロエタン
HFC―１２３：トリフルオロエタン
HFC―１２２：ジフルオロエタン

(Note) HFC-125: Pentafluoroethane
HFC-124: Tetrafluoroethane
HFC-123: trifluoroethane
HFC-122: Difluoroethane

  On the other hand, HFC-125 in the case where a chromium oxide catalyst (Patent Document 2) produced by impregnation using a binary or ternary oxide starts with HCFC-123 (dichlorotrifluoroethane). Table 2 shows the selectivity.

（注）HFC―１２５ ：ペンタフルオロエタン
HCFC―１２４：クロロテトラフルオロエタン
HCFC―１２３：1,1−ジクロロ−2,2,2−トリフルオロエタン
HCFC―１１５：クロロペンタフルオロエタン
すなわち、出発物質がＰＣＥの場合には、ＨＦＣ−１２５に対する選択率が２０％未満であり、出発物質がＨＣＦＣ−１２３の場合にも、ＨＦＣ−１２５選択率は７０％を超えていない。
したがって、この分野では、クロロエタン化合物のフッ素化においてより高い転換率と特にＨＦＣ−１２５に対する選択率が高い触媒の開発が必要な実情にある。

(Note) HFC-125: Pentafluoroethane
HCFC-124: Chlorotetrafluoroethane
HCFC-123: 1,1-dichloro-2,2,2-trifluoroethane
HCFC-115: Chloropentafluoroethane That is, when the starting material is PCE, the selectivity for HFC-125 is less than 20%, and even when the starting material is HCFC-123, the selectivity for HFC-125 is 70 % Is not exceeded.
Therefore, in this field, it is necessary to develop a catalyst having a higher conversion rate and particularly a high selectivity for HFC-125 in the fluorination of chloroethane compounds.

Japanese Patent Laid-Open No. 02-178237 US Pat. No. 6,433,233

The present inventors have mixed chromium with the reason why chromium oxide-based catalysts prepared by conventional coprecipitation or impregnation methods using two-component or three-component oxides do not exhibit sufficient activity. Even if different metal components and their composition ratios do not help to achieve or maintain the active site of the catalyst, or even when the metal component is appropriately selected, the active site of chromium is activated by the production method and the fluorination method. When producing a two-component chromium oxide considering that it can easily disappear by sintering or the like, the chromium oxide is mixed before the chromium oxide and the metal oxide are mixed. After the Cr (OH) ₃ is heat-treated to form Cr ₂ O ₃ within a temperature range in which an amorphous state can be maintained, it is simply mechanically bonded to the selected dissimilar metal oxide. Fluorinated after mixing with As a result, it was confirmed that the activity of the chromium oxide catalyst could be increased, and the present invention was completed.
An object of the present invention is to provide a fluorination catalyst exhibiting high conversion and selectivity in a method for producing HFC-125 using a chloroethane compound as a raw material, and a method for producing the catalyst.

The present invention for solving the above object provides a fluorination catalyst useful for producing HFC-125 by fluorinating a chloroethane compound such as PCE or HCFC-123, and a method for producing the catalyst.
The catalyst of the present invention is an amorphous chromium oxide mixed catalyst containing an oxide of a metal selected from magnesium, iron, molybdenum, vanadium and aluminum in the main component chromium oxide.

In the catalyst production method of the present invention, chromium hydroxide is heat-treated to convert to chromium oxide, mixed with magnesium, iron, molybdenum, vanadium or aluminum oxide, and then subjected to a fluorination process. , A method for producing a chromium-based mixed catalyst having a specific surface area of 10 to 30 m ² / g while maintaining an amorphous state with an average chromium valence of 3 to 5, and having a high conversion rate of PCE and HCFC-123. The effect of improving selectivity to HFC-125 was brought about. Since the catalytic activity varies depending on the conditions of the catalyst fluorination step during the production of the catalyst, the fluorination treatment under the optimum conditions is essential.

  The fluorination catalyst produced by the method of the present invention has an effect that pentafluoroethane can be produced in a high yield using a chloroethane compound as a raw material.

Hereinafter, the catalyst production method of the present invention will be described.
First, chromium nitrate _{(Cr (NO 3) 3 ·} 9H 2 O) to give the ammonia water to an aqueous solution obtained by dissolving in water _(NH 4 OH) was added to blue-gray chromium hydroxide precipitate with hot water The filtered precipitate is washed thoroughly and dried. The drying process is preferably performed in air at a temperature of 80 to 150 ° C, and particularly about 100 ° C is appropriate. The drying time is 24 to 72 hours, preferably 72 hours. If heat treatment is performed without sufficient cleaning and drying, an excessive amount of NO _x is generated due to the nitrate and ammonium salt components remaining inside, and a part of the NO _x may remain. The sufficiently dried chromium hydroxide is put in an oven or a heater, slowly heated to 300 ° C., and then subjected to a heat treatment for 2 hours. In this process, when reaching about 200 ° C., a large amount of yellow NO _x gas is released, and this gas is sent to the gas absorption tower for processing. At this time, impurities (nitrate, ammonium salt, moisture, etc.) remaining inside the catalyst are removed, and at the same time, chromium oxide having an average valence of 3 to 5 is formed. In particular, if the residual impurities is not sufficiently removed, after which the strength of the catalyst is weakened by the occurrence of the NO _x in the catalyst fluorination process, since many products are produced must be removed thoroughly impurities. Finely pulverize heat-treated chromium hydroxide, add other metal oxides made through the same process at a weight ratio of 0.5-15%, mix with a small amount of water and form into pellets . Here, the addition of a small amount of water plays an important role in increasing the cohesiveness and strength of the pellets. The pellet has a cylindrical structure with a diameter of about 12 mm and a height of 12 mm. The catalyst produced in pellet form is dried.

The catalyst formed into a pellet is put into a reactor and nitrogen gas is passed through at a temperature of 200 ° C. for 2 hours, then the temperature is raised to 300 ° C., and then heat treatment is performed while the nitrogen gas is passed through for 3 hours. Thereafter, the temperature is raised to 320 ° C., and the fluorination reaction of the catalyst is started by simultaneously flowing nitrogen gas and hydrogen fluoride gas. Nitrogen gas is shut off while the temperature is gradually raised to 380 ° C., and pure fluorinated hydrofluoric acid gas is passed to completely fluorinate the catalyst. The higher the temperature and pressure, the faster the fluorination rate, but since a too rapid temperature change causes damage to the catalyst, it is preferable to raise the temperature slowly. The fluorination catalyst has a specific surface area in the range of 10 to 30 m ² / g.

  When HFC-125 is synthesized using PCE and HCFC-123 as starting materials using the catalyst produced by the method of the present invention, the conversion rate of the starting materials and the selectivity of HFC-125 are expressed as the molar ratio of the reactants, the reaction It varies depending on temperature, contact time, reaction pressure and fluorination treatment method. The optimum reaction temperature was 350 to 400 ° C., and the optimum molar ratio of HF and PCE / HCFC-123 was 8/1 to 15/1. The contact time was 2 to 20 seconds, and the maximum efficiency was exhibited at 5 seconds or more. The best results were obtained when the reaction pressure was atmospheric pressure. The selectivity of HFC-125 showed a tendency to increase with increasing reaction temperature and contact time. On the other hand, when reaction pressure became higher than atmospheric pressure, the conversion rate to HFC-125 showed the tendency to become low.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.

  The fluorination catalysts 1 to 5 are produced according to the sequence shown in FIG. In FIG. 1, catalyst 1 is a catalyst made of chromium oxide and magnesium oxide, catalyst 2 is a catalyst made of chromium oxide and iron oxide, and catalyst 3 is a catalyst made of chromium oxide and molybdenum oxide. The catalyst 4 is a catalyst composed of chromium oxide and vanadium oxide, and the catalyst 5 is a catalyst composed of chromium oxide and aluminum oxide.

Next, a method for producing a catalyst composed of chromium oxide and magnesium oxide will be described.
Added dropwise and chromium nitrate _{(Cr (NO 3) 3 ·} 9H 2 O) 1kg aqueous solution to 0.391kg of ammonia water dissolved in distilled water _(NH 4 OH), chromium hydroxide (Cr _{(OH) 3)} A blue-grey precipitate can be obtained. The precipitate is thoroughly washed with hot distilled water, filtered, and dried at about 100 ° C. for 24 hours to produce solid chromium hydroxide. The chromium hydroxide thus produced is pulverized using a ball mill or a mortar to form a powder and heat-treated. In the heat treatment, the temperature is slowly increased to 300 ° C. at intervals of 20 ° C. and held at 300 ° C. for 2 hours. During the heat treatment process, NO _x is generated by nitrate remaining in the chromium hydroxide, and this gas is sent to an absorption tower for treatment. When the heat treatment is completed, it is sufficiently pulverized using a pulverizer. After producing each hydroxide using magnesium nitrate [Mg (NO ₃ ) ₂ .6H ₂ O] by the above method, heat treatment is performed by the same method to obtain a magnesium oxide (MgO) powder.
After mixing 2% by weight magnesium oxide powder with 98% by weight chromium oxide, add enough water to mix each of the two oxides, and then use a tablet machine. Mold into pellets. The pellets are dried at 100 ° C. for about 48 hours before being formed into a cylindrical shape with a diameter of about 12.5 mm and a height of 12 mm and charged into the reactor. About 150 g of a catalyst is packed in a cylinder type reactor having an inner diameter of 1 inch and a length of 500 mm, and calcined while bubbling nitrogen at 200 ° C. for 2 hours and at 300 ° C. for 3 hours. Thereafter, the temperature is raised to 320 ° C., and hydrofluoric acid and nitrogen gas are simultaneously supplied to start the fluorination reaction of the catalyst. After reacting with a mixture of hydrofluoric acid gas and nitrogen gas for about 30 minutes, the nitrogen gas is shut off and only pure hydrofluoric acid gas is vented. The temperature is raised stepwise to 380 ° C., and a hydrofluoric acid gas is continuously passed to fully fluorinate the catalyst. After completion of the fluorination reaction, nitrogen gas is supplied to discharge unreacted fluorinated hydroacid gas and impurity gas. Catalyst 1 was produced in this way, and the produced catalyst was measured with an X-ray diffractometr. As a result, it was confirmed to be amorphous. The specific surface area of the catalyst measured with a specific surface area measuring apparatus by the BET method was between 10 and 30 m ² / g.

<Production of catalyst 2 (chromium oxide-iron oxide catalyst)>
Catalyst 2 was produced in the same manner as in Example 1 except that iron nitrate [Fe (NO ₃ ) ₂ .6H ₂ O] was used instead of magnesium nitrate.

<Production of catalyst 3 (chromium oxide-molybdenum oxide catalyst)>
Catalyst 3 was produced in the same manner as in Example 1 except that molybdenum ammonium salt [(NH ₄ ) ₆ Mo ₇ O ₂₄ ] was used instead of magnesium nitrate.

<Production of Catalyst 4 (Chromium Oxide-Vanadium Oxide Catalyst)>
Catalyst 4 was produced in the same manner as in Example 1, except that vanadium ammonium salt (NH ₄ VO ₃ ) was used instead of magnesium nitrate.

<Manufacture of catalyst 5 (chromium oxide-aluminum oxide catalyst)>
Except using aluminum nitrate _{[Al (NO 3) 3 ·} 9H 2 O] in place of the magnesium nitrate was prepared catalyst 5 in the same manner as in Example 1.
As a result of measuring the catalysts produced in Examples 2 to 4 with an X-ray diffractometer and the BET method, all the crystal structures were amorphous, and all the specific surface areas were in the range of 10 to 30 m ² / g.

(Experimental example)
<Fluorination reaction of PCE>
The gas phase fluorination reaction of PCE by HF was performed using the catalysts 1 to 5 obtained in the examples under the following reaction conditions.
(Reaction conditions)
Catalyst amount: 150g
Reactor: 25.4 mm (ID), SUS316L
Reaction gas: PCE (6.9 g / min), HF (300 cm ³ )
Contact time: 10 seconds Reaction temperature: 350 ° C, 300 ° C
Reaction pressure: atmospheric pressure After fluorination of PCE under the above-mentioned conditions, the obtained gas was passed through a potassium hydroxide aqueous solution outside the reactor, and then the reaction product gas was analyzed using a gas chromatograph. Table 3 shows the reaction results when the fluorination reaction temperature is 350 ° C, and Table 4 shows the reaction results when the fluorination reaction temperature is 300 ° C.

（注）ＨＣＦＣ−１２２；トリクロロジフルオロエタン
ＣＦＣ−１１４；ジクロロテトラフルオロエタン
ＣＦＣ−１１３；トリクロロトリフルオロエタン

(Note) HCFC-122; trichlorodifluoroethane CFC-114; dichlorotetrafluoroethane CFC-113; trichlorotrifluoroethane

（注）ＨＣＦＣ−１１３；クロロトリフルオロエタン
Ｆ−１１１１；フルオロトリクロロエタン（Ｃ_２ＦＣｌ_３）

(Note) HCFC-113; Chlorotrifluoroethane F-1111; Fluorotrichloroethane (C ₂ FCl ₃ )

  When synthesizing HFC-125 using PCE as a starting material using the catalyst produced by the method of the present invention, when the reaction temperature is 350 ° C., the conversion rate of PCE is 94.9% or more, and the reaction temperature is In the case of 300 ° C., the PCE conversion was 80.1% or more. And the selectivity of HFC-125 showed 61% and 40.2% or more, respectively. This shows that the catalyst of the present invention has the same selectivity as a conventional chromium oxide-based mixed catalyst using HCFC-123 as a starting material while using PCE as a starting material. In view of the fact that the reaction to HFC-125 is much more difficult when PCE is the starting material than when HCFC-123 is the starting material, it can be seen that the activity of the catalyst of the present invention is very high.

  The catalyst of the present invention improves the reaction activity and selectivity to HFC125 even when only 2% by weight of Mg, Fe, Mo, V, and Al oxides are added to highly active and pure chromium oxide. I understand that. The selectivity is improved even when the amount of the metal oxide mixed with the chromium oxide is a small amount of about 0.5% by weight. However, even if it exceeded 15%, there was almost no change in the improvement of selectivity. Therefore, it is appropriate that the amount of the metal oxide mixed with the chromium oxide is determined in the range of 0.5 to 15% by weight. The invented catalyst is characterized by a shorter induction period under the same reaction conditions, which shows a certain yield and selectivity at the beginning of the reaction than a pure chromium oxide catalyst. The increase in the catalytic activity of the added metal oxide is in the order of Mg> Fe> V> Mo> Al.

<Test of catalyst activity by catalyst fluorination method>
On the other hand, in order to investigate the characteristics of the reaction activity according to the fluorination treatment method of the catalyst, fluorination gas phase reaction of HF and HCFC-123 was carried out using the catalyst 2 under the following reaction conditions.
(Reaction conditions)
Catalyst used: Catalyst 2
Contact time: 5 seconds Reactor: 25.4 mm (ID), SUS316L
Reaction gas: HCFC-123 (12.5 g / min), HF (590 cm ³ )
Reaction temperature: 350 ° C
Reaction pressure: atmospheric pressure

試験結果は、次の表７に記載した。

The test results are listed in Table 7 below.

It can be seen that the fluorination treatment method of the catalyst greatly affects the reaction activity and selectivity of the chromium oxide catalyst. When the fluorination process is performed for a long time at a high temperature of 400 ° C. or more as in the fluorination process A, the chromium oxide is transformed into a crystal structure of Cr ₂ O ₃ , which greatly increases the activity and selectivity of the catalyst. With reduced results. On the other hand, the activity of the catalyst fluorinated for a short time at a temperature of less than 400 ° C. as in the fluorination steps B, C, and D is good, and the catalyst that has undergone the fluorination step for about 60 to 180 minutes at 380 ° C. It can be seen that it is in an amorphous state and is excellent in the conversion rate of PCE and HCFC-123 and the selectivity of HFC-125. As can be seen from this test, the activity of the catalyst is influenced not only by the treatment temperature during the fluorination process, but also by the treatment time as well as the treatment temperature. That is, it can be seen that the most excellent catalytic activity is exhibited when the step of fluorinating the molded pellets with HF gas is performed at a temperature of 380 ° C. within a range of 3 hours.

Next, the influence of the activity of the produced catalyst by the reaction temperature using the catalyst 2 was examined.
(Reaction conditions)
Catalyst used: Catalyst 2
Contact time: 10 seconds Reactor diameter: 25.4 mm (ID), SUS316L
Reaction gas: PCE (6.9 g / min), HF (300 cm ³ )
Reaction temperature: 300 ° C, 330 ° C, 350 ° C
Reaction pressure: atmospheric pressure The results are shown in Table 8 below.

上記の結果より、反応温度が高くなるほど生産されるＨＦＣ−１２５への選択性とＰＣＥの転換率が増加することが分かる。

From the above results, it can be seen that the selectivity to HFC-125 produced and the conversion rate of PCE increase as the reaction temperature increases.

It is a flow sheet which shows the catalyst manufacturing process of this invention.

Claims (5)

In the method for producing a chromium oxide-based catalyst for producing pentafluoroethane using a chloroethane compound as a raw material,
85 to 99.5% by weight of chromium oxide powder obtained by heat-treating chromium hydroxide powder at 300 ° C. or less, and metal hydroxide selected from magnesium, iron, molybdenum, vanadium and aluminum hydroxides Pellets formed by mixing 0.5 to 15% by weight of a metal oxide powder selected from magnesium oxide, iron oxide, molybdenum oxide, vanadium oxide and aluminum oxide, obtained by heat treatment at 300 ° C. or lower Is baked at 200 to 300 ° C. in nitrogen gas, and then fluorinated with a mixed gas of N ₂ + HF at 300 to 320 ° C. and HF gas at 320 to 380 ° C. to produce a chromium oxide catalyst.   The method for producing a chromium oxide-based catalyst according to claim 1, wherein the chloroethane compound is perchloroethane or 1,1-dichloro-2,2,2-trifluoroethane.   The method for producing a chromium oxide-based catalyst according to claim 1, wherein the heat treatment of the metal hydroxide is performed at a temperature of 300 ° C or less within 2 hours by slowly raising the temperature in the atmosphere. .   The method for producing a chromium oxide-based catalyst according to claim 1, wherein the step of fluorinating the formed pellets with HF gas is performed at a temperature of 380 ° C or less within 3 hours.   A chromium oxide-based catalyst for producing pentafluoroethane produced by the method according to claim 1.

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