DE102005053962A1 - Catalyst for the preparation of pentafluoro-ethane and process for its preparation - Google Patents

Abstract

A process for the production of a chromium oxide catalyst for the production of pentafluoroethane using a chloroethane compound is disclosed, which heat treatment of powdery chromium hydroxide at a temperature of not more than 300 ° C., whereby powdery chromium oxide is obtained, the heat treatment of metal hydroxide, which is made from magnesium hydroxide , Iron hydroxide, molybdenum hydroxide, vanadium hydroxide and aluminum hydroxide is selected at a temperature of not more than 300 ° C, thereby obtaining powdery metal oxide selected from magnesium oxide, iron oxide, molybdenum oxide, vanadium oxide and aluminum oxide, mixing 85 APPROX 99.5 % By weight of the powdery chromium oxide with 0.5 APPROX 15% by weight of the powdery metal oxide, whereby a mixture is obtained, the molding of the mixture into granules, the calcination of the granules at 200 APPROX 300 ° C. using nitrogen gas and fluorinating the granules at 300 APPROX 320 ° C using a gas mixture that includes N¶2¶ and HF, and then at 320 includes APPROX 380 ° C using HF gas. The fluorination catalyst prepared using this process of the present invention can be effectively used to produce pentafluoroethane in high yield using a chloroethane compound.

Description

General state of the technology

1. Field of the invention

The present invention generally relates to a catalyst for the production of pentafluoroethane and a process for its preparation. In particular, the present invention relates to a catalyst suitable for use in the preparation of pentafluoroethane (CF ₃ CHF ₂ , hereinafter referred to as "HFC-125") obtained by the reaction of perchloroethane (C ₂ Cl ₄ , hereinafter referred to as " PCE ") or 1,1-dichloro-2,2,2-trifluoroethane (CHCl ₂ CF ₃ , hereinafter referred to as" HCFC-123 ") with HF, and a process for producing such a catalyst.

2. Description of the relevant field

In general, HFC-125 contains no chlorine in the molecule and thus has a very low influence on global warming and the decrease of ozone. HFC-125, which is an alternative material for a chlorofluorocarbon or chlorofluorocarbon used as conventional refrigerants, foaming agents or blowing agents, is mixed with difluoromethane (CH ₂ F ₂ , hereinafter referred to as "HFC-32"), thereby serving as the Material for mixed coolant is used.

catalysts for the Use in the production of HFC-125 using Chloroethane compounds as starting material are known, almost all thereof include chromium oxides.

Japanese Laid-Open Patent Publication No. Hei. 2-178237 discloses a catalyst for the production of HFC-125 using a chloroethane compound, examples of which are 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.

The catalyst Cr ₂ O ₃ -Al ₂ O ₃ is prepared by dissolving Cr (NO ₃ ) ₃ .9H ₂ O and Al (NO ₃ ) ₃ .9H ₂ O in water, adding ammonia water with stirring to give a precipitate of Cr (OH) ₃ and Al (OH) _3, which is then washed with water, dried and then calcined at 450 ° C for 5 hours to obtain powdery Cr ₂ O ₃ -Al ₂ O ₃ , the powder is added Pellets or granules (hereinafter referred to as granules) molded and then the granules are fluorinated with a gas mixture of N ₂ and HF.

US-P-6,433,233 discloses the catalysts 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 and Cr ₂ O ₃ / ZnO.

Of these catalysts, the catalyst Cr ₂ O ₃ / Al ₂ O ₃ is prepared as follows.

First, ammonia water is added to an aqueous solution of Cr (NO ₃ ) ₃ , whereby a precipitate of Cr (OH ₃ ) _{3 is} obtained, which is then filtered and dried to give solid Cr (OH) ₃ , which is then converted into powdery Cr (OH ₃ ) _{3 is} ground. Subsequently, the powder is added to an aqueous solution of Al (NO ₃ ) ₃ , allowed to stand for 12 hours, dried and added with a small amount of graphite, thereby producing granules. The granules thus obtained are calcined with gaseous N _{2 for} 2 hours and then fluorinated, using a gas mixture of N ₂ + HF, whereby the desired catalyst Cr ₂ O ₃ / Al ₂ O _{3 is} obtained.

According to conventional methods for producing a binary chromium oxide catalyst, such as Cr ₂ O ₃ -Al ₂ O ₃ , or a ternary chromium oxide catalyst, in this way Cr (NO ₃ ) ₃ and Al (NO ₃ ) ₃ are dissolved in water, whereupon the resulting solution coprecipitates using ammonia to give a co-precipitated Cr (OH ₃ ) ₃ -Al (OH) ₃ , which is then calcined to give the catalyst Cr ₂ O ₃ -Al ₂ O ₃ (disclosed in U.S. Pat Japanese Patent Publication No. Hei. 2-178237). In addition, powdery Cr (OH) _{3 is} impregnated with an aqueous solution of Al (NO ₃ ) ₃ and then dried to obtain the composition Cr (OH) ₃ / Al (OH) ₃ , which is then calcined, whereby the catalyst Cr ₂ O ₃ / Al ₂ O _{3 is} obtained (US Pat. No. 6,433,233).

It is known that the activity of the chromium oxide catalyst is closely related to the crystal structure of the catalyst and the value of Cr is related.

in the active center of the chromium oxide catalyst disclosed in US Pat. No. 6,433,233 Chromium has a valence in the range of +3.5 to +5.0 and lies in an amorphous state.

It is also known that the activity of the catalyst Cr ₂ O ₃ / Al ₂ O ₃ depends on the valence of chromium and that aluminum oxide acts as a carrier.

The binary or ternary Chromium catalysts produced by impregnation or coprecipitation However, they have disadvantages because they have a low activity and selectivity for one Have conversion reaction of chloroethane. Thus, the above called catalyst for the use in commercial production processes unsuitable.

Especially when HFC-125 using PCE in the presence of the above said catalyst is the conversion and selectivity low. Furthermore show conventional catalysts not enough activity during fluorination.

The Use of the Chromium Oxide Catalyst (Japanese Patent Laid-Open Publication No. Hei. 2-178237), by Mitfall of binary or ternary Oxides arises, leads to the following conversion and selectivity, if PCE as starting material is used.

The Use of the chromium oxide catalyst (US Pat. No. 6,433,233) obtained by the impregnation from binary or ternary Oxides arises, leads to the following selectivity, when HCFC-123 is used as the starting material.

The is called, when the starting material is PCE, the selectivity is for HFC-125 less than 20%. The use of HCFC-123 as starting material leads to a contrast selectivity for HFC-125 of up to 70 %.

Consequently There is a need for the development of a catalyst that the Conversion of a chloroethane compound and an improvement of selectivity for HFC-125 during fluorination allows.

Short description the invention

For this invention, the present inventors have conducted intensive and thorough research on fluorination catalysts with the aim of avoiding the problems of insufficient activity of chromium oxide catalysts prepared from binary or ternary oxides by coprecipitation or impregnation processes, as the art the heterogeneous metal component mixed with chromium or the composition ratio of the catalyst is inappropriate to produce or maintain the active center of the catalyst, and also that the chromium catalyst, although the metal component is appropriately selected, becomes insufficient depending on the fluorination and production process may be activated or its active center may disappear by sintering, which occurs in the prior art, this has led to the finding that Cr (OH) _{3 is} heat treated in a temperature range which can maintain the amorphous state of chromium oxide, w is Cr ₂ O ₃ , which is then mixed mechanically with the selected heterogeneous metal oxide, followed by fluorination, thereby improving the activity of the chromium oxide catalyst.

consequently It is an object of the present invention to provide a catalyst for the Fluorinating, which in the production of HFC-125 both an increase in the Conversion as well as the selectivity allows when a chloroethane compound is used as starting material.

A Another object of the present invention is a method for preparing such a fluorination catalyst.

Short description the drawing

1 shows a process according to the invention for the stepwise preparation of a catalyst.

description of the preferred embodiments

The The present invention relates to a catalyst for fluorinating, the for the use in the production of HFC-125 by fluorination a chloroethane compound such as PCE or HCFC-123, and a method for its production.

Of the catalyst according to the invention is amorphous and a mixed chromium oxide catalyst, the chromium oxide as the main component and an oxide of a metal comprising magnesium, iron, molybdenum, Vanadium and aluminum selected is.

According to the present invention, the process for preparing the catalyst comprises heat treating the chromium hydroxide to be converted into chromium oxide, mixing the chromium oxide thus obtained with an oxide of magnesium, iron, molybdenum, vanadium or aluminum, and then fluorinating the mixture, thereby obtaining a chromium oxide Mixed catalyst is produced with a specific surface area of 10 ~ 30 m ² / g, wherein chromium has an average valence in the range of trivalent to pentavalent and is in the amorphous state. This catalyst is advantageous because it can improve the conversion of PCE and HCFC-123 and the selectivity for HFC-125. Since the activity of the catalyst changes with the conditions of the fluorination process of the catalyst, optimum fluorination treatment is required in the preparation of the catalyst.

The process according to the invention for the preparation of the catalyst is described below. First, an aqueous solution of chromium nitrate (Cr (NO ₃ ) ₃ .9H ₂ O) dissolved in water is added with ammonia water (NH ₄ OH), whereby a blue-gray precipitate of chromium hydroxide is obtained, which is then filtered. This filtered precipitate is sufficiently washed with hot water and dried. The drying process is carried out at 80-150 ° C in air for 24 ~ 72 hours, and preferably for 72 hours, and more preferably at about 100 ° C. When the precipitate of chromium hydroxide is heat-treated in an insufficiently washed and dried state, remaining therein nitrates and ammonium salts lead to the formation of excess NO _x, wherein a part thereof may remain. The sufficiently dried chromium hydroxide is placed in an oven or heater and then added for 2 hours 300 ° C heat treated. It is preferred that the temperature is gradually increased at intervals of 20 ° C to up to 300 ° C. In the temperature increasing process, when the temperature reaches about 200 ° C, a large amount of yellow gaseous NO _{x is} discharged, which circulates to a gas absorption column for disposal. When impurities (nitrates, ammonium salts, water, etc.) are removed from the catalyst, chromium oxide is produced in which the average valence of chromium is in the range of trivalent to pentavalent. In particular, if the residual impurities are not sufficiently removed, NO _{x is} undesirably produced upon fluorination of the catalyst, thereby decreasing the strength of the catalyst and generating large amounts of by-products. Therefore, the contaminants must be removed thoroughly. After the heat treatment, chromium hydroxide is finely ground and mixed with 0.5~15% by weight of another metal oxide obtained by the same method and then with a small amount of water, after which the mixture is shaped into granules. As such, water added in small amounts causes an increase in the degree of agglomeration and the strength of the granules. The granules are shaped to have a cylindrical structure with a diameter of about 12 mm and a height of 12 mm. The granulated catalyst is dried.

The catalyst prepared in the form of granules is placed in a reactor and then heat-treated at 200 ° C for 2 hours using nitrogen gas and then at 300 ° C for 3 hours using nitrogen gas. Thereafter, the temperature is raised to 320 ° C, and nitrogen gas and hydrogen fluoride gas are simultaneously supplied, thereby starting to fluorinate the catalyst. When the temperature is gradually raised to 380 ° C, only hydrogen fluoride gas without nitrogen gas is supplied, whereby the catalyst is completely fluorinated. The higher the temperature and pressure, the higher the fluorination rate. However, a significant change in temperature leads to a compromised catalyst. Thus, it is preferable that the temperature is gradually increased. The fluorinated catalyst has a specific surface area of 10 ~ 30 m ² / g.

For the synthesis of HFC-125 is in the presence of using the method of the invention prepared catalyst PCE or HCFC-123 as starting material used. The conversion of the used starting material and the selectivity for HFC-125 are changing with the molar ratios of Reactants, reaction temperatures, contact times, reaction pressure, the types of fluorination treatment, etc. The optimum reaction temperature is in the range of 350 to 400 ° C, and the optimum molar ratio between HF and PCE / HCFC-123 is in the range of 8/1 to 15/1. The contact time is preferably in the range of 2 ~ 20 s, wherein the maximum efficiency occurs at 5 s. Especially preferred Reaction results are obtained at atmospheric pressure. The selectivity for HFC-125 rises in proportion to an increasing reaction temperature and contact time. If the Reaction pressure, however, higher as atmospheric pressure is, the conversion rate to HFC-125 decreases.

The The present invention will be better understood from the following examples understandable, that are listed, to illustrate, but not limit, the present invention.

example 1

The fluorinated catalysts 1 ∽ 5 were prepared by the methods described in 1 are shown in steps. In 1 Catalyst 1 consisted of chromium oxide and magnesium oxide, catalyst 2 of chromium oxide and iron oxide, catalyst 3 of chromium oxide and molybdenum oxide, catalyst 4 of chromium oxide and vanadium oxide, and catalyst 5 of chromium oxide and aluminum oxide. Hereinafter, the method for producing the catalyst consisting of chromium oxide and magnesium oxide will be described.

To an aqueous solution of 1 kg of chromium (III) nitrate (Cr (NO ₃ ) ₃ .9H ₂ O) dissolved in distilled water was added dropwise 0.391 kg of ammonia water (NH ₄ OH), thereby giving a blue-gray precipitate Chromium hydroxide (Cr (OH) ₃ ) was obtained. This precipitate was sufficiently washed with hot distilled water, filtered and dried at about 100 ° C for 24 hours to prepare chromium hydroxide in the solid phase. The chromium hydroxide thus prepared was ground to powder with a ball mill or mortar, followed by heat treatment. The heat treatment was carried out by gradually raising the reaction temperature to 300 ° C at intervals of 20 ° C and maintaining the temperature at 300 ° C for 2 hours. During the heat treatment, if NO _{x was produced} by the nitrates remaining in chromium hydroxide, it was circulated to an absorption column for disposal. After completion of the heat treatment, the resulting material was ground with a mill. Separately, magnesium nitrate [Mg (NO ₃ ) ₂ .6H ₂ O] was treated in the same manner as in the above-mentioned processes to obtain magnesium hydroxide, which was then heat-treated as mentioned above to obtain powdery magnesium oxide (MgO).

98% by weight of chromium oxide was mixed with 2% by weight of magnesium oxide powder, after which water was added in an amount sufficient to mix the two oxides to obtain a reaction mixture, which was then granulated into a granule. The granules had a cylindrical shape with a diameter of about 12 mm and a height of 12 mm and were then dried at 100 ° C for about 48 hours before being placed in a reactor. Into a cylindrical reactor measuring 25.4 mm (1 inch) and 500 mm, about 150 g of the catalyst thus obtained was added and then calcined at 200 ° C for 2 hours in the presence of nitrogen and then at 300 ° C for 3 hours. Thereafter, the temperature was increased to 320 ° C, and hydrogen fluoride gas and nitrogen gas were supplied simultaneously to start the fluorination of the catalyst. The catalyst was reacted with the gas mixture containing hydrogen fluoride gas and nitrogen gas for about 30 minutes and then with hydrogen fluoride gas without nitrogen gas. The temperature was gradually increased to 380 ° C, and hydrogen fluoride gas was continuously supplied, whereby the catalyst was completely fluorinated. After completion of the fluorination, nitrogen gas was supplied to discharge unreacted hydrogen fluoride gas and gaseous impurities, thereby preparing the desired catalyst 1. It was confirmed by an X-ray diffractometer that the catalyst thus prepared was amorphous. In addition, the catalyst had a specific surface area in the range of 10 to 30 m ² / g, which was measured using a surface area analyzer (BET).

Example 2

Preparation of the catalyst 2 (chromium oxide-iron oxide catalyst)

Catalyst 2 was prepared in the same manner as in Example 1 except that iron nitrate [Fe (NO ₃ ) ₂ .6H ₂ O] was used in place of magnesium nitrate.

Example 3

Preparation of the catalyst 3 (chromium oxide-molybdenum oxide catalyst)

Catalyst 3 was prepared in the same manner as in Example 1 except that instead of magnesium nitrate, ammonium molybdate [(NH ₄ ) ₆ Mo ₇ O ₂₄ ] was used.

Example 4

Preparation of the catalyst 4 (chromium oxide-vanadium oxide catalyst)

Catalyst 4 was prepared in the same manner as in Example 1 except that ammonium vanadate (NH ₄ VO ₃ ) was used instead of magnesium nitrate.

Example 5

Preparation of the catalyst 5 (chromium oxide-alumina catalyst)

Catalyst 5 was prepared in the same manner as in Example 1 except that instead of magnesium nitrate, aluminum nitrate [Al (NO ₃ ) ₃ .9H ₂ O] was used.

The crystal structure and specific surface area of each of the catalysts prepared in Examples 2~4 were determined to be amorphous and 10 30 m ² / g, respectively, using an X-ray diffractometer or BET.

experimental example

Fluorinating PCE

PCE was obtained in the presence of each of those obtained in Examples 1-5 Catalysts 1 ~ 5 under the following reaction conditions with HF gas fluorinated.

Reaction conditions:

• Amount of catalyst: 150 g
• Reactor: 25.4 mm (ID), SUS 316L
• Reactive gas: PCE (6.9 g / min), HF (300 Ncm ³ )
• Contact time: 10 s
• Reaction temperature: 350 ° C, 300 ° C
• Reaction pressure: atmospheric pressure

After this PCE in the above Reaction conditions had been fluorinated, the resulting Gas through an aqueous potassium hydroxide solution outside passed the reactor, and then the gaseous reaction product was passed through Gas chromatography analyzed. The results at a reaction temperature of 300 ° C are listed in Table 1 below, and those at a reaction temperature of 350 ° C in the following Table 2.

Table 1

Table 2

If HFC-125 with PCE as the starting material in the presence of as above produced catalyst was the conversion of PCE at a reaction temperature of 350 ° C 94.9% or more, and the Conversion of PCE was at a reaction temperature of 300 ° C 80.1% or more. The selectivity for HFC-125 was at 350 ° C or 300 ° C 61% and 40.2% respectively. From these results it can be seen that the use of PCE as starting material in the presence of the catalyst according to the invention to a selectivity leads, the when using HCFC-123 as the starting material in Presence of a conventional Chromium mixed catalyst is similar. Given the fact that the synthesis of HFC-125 using PCE more problematic than the Use of HCFC-123, the activity of the catalyst of the invention however, are considered very high. The catalyst according to the invention, the chromium oxide and only 2 wt .-% of an oxide of Mg, Fe, Mo, V or Al includes, so he has a high catalyst activity may have activity and selectivity for HFC-125 improve on this reaction. Although the chromium oxide metal oxide is added in a small amount of 0.5 wt .-%, the selectivity be improved. The addition of metal oxide with more than 15 wt .-% on the other hand, however, reduces the activity and selectivity. Consequently For example, the amount of metal oxide relative to the amount of chromium oxide is preferably in the range of 0.5 ~ 15% by weight. In addition, the catalyst of the invention advantageous because it has an induction period during the initial Reaction to a uniform yield and selectivity to lead can be much shorter than that at the same reaction conditions in a pure chromium oxide catalyst. The catalyst activity of the used Metal oxide takes Mg> Fe> V> Mo> Al in the following order.

Test the catalyst activity by the type of fluorination treatment

Around the activity the catalyst in the reaction with changed types of fluorination treatment was subjected to fluorination with HF gas and HCFC-123 with the catalyst 2 is carried out under the following reaction conditions.

Reaction conditions:

• used catalyst: catalyst 2
• Contact time: 5 s
• Reactor: 25.4 mm (ID), SUS 316L
• Reactive gas: HCFC-123 (12.5 g / min), HF (590 Ncm ³ )
• Reaction temperature: 350 ° C
• Reaction pressure: atmospheric pressure

Type of fluorination treatment of the catalyst

The Test results are listed in Table 3 below.

Table 3

As is clear from the above results, the type of fluorination treatment of the catalyst greatly affects the activity and selectivity of the catalyst. In the type A fluorination treatment, since the fluorination is carried out at a high temperature not lower than 400 ° C for a long period of time, chromium oxide is deformed into a crystal structure of Cr ₂ O ₃ resulting in significantly lower catalyst activity and selectivity leads. On the other hand, in the types B, C and D of the fluorination treatment, it is found that the activity of the catalyst which has been fluorinated at a temperature of less than 400 ° C for a short time is excellent. Since the catalyst obtained by fluorinating at 380 ° C for 60~180 minutes is in the amorphous state, high conversion of PCE or HCFC-123 and high selectivity for HFC-125 can be found. In this way it is found that the activity of the catalyst is influenced by the treatment time as well as the treatment temperature during fluorination. That is, when the fluorination of the granules is carried out using HF gas at 380 ° C for a period not exceeding 3 hours, the maximum of the catalyst activity can be detected.

Around the influence of activity of the catalyst in dependence from the reaction temperature, the reaction was also with the catalyst 2 is carried out under the following reaction conditions.

Reaction conditions:

• used catalyst: catalyst 2
• Contact time: 10 s
• Reactor: 25.4 mm (ID), SUS 316L
• Reactive gas: PCE (6.9 g / min), HF (300 Ncm ³ )
• Reaction temperature: 300 ° C, 330 ° C, 350 ° C
• Reaction pressure: atmospheric pressure

The Results are shown in Table 4 below.

Table 4

As From Table 4, the selectivity for HFC-125 and the conversion are of PCE higher, The higher the reaction temperature is.

As As described above, the present invention provides a catalyst for the Preparation of HFC-125 and a process for its preparation ready. The prepared using the method according to the invention Catalyst for The fluorination can be effectively used to HFC-125 in high yield wherein starting material is a chloroethane compound is used.

Even though the preferred embodiments have been disclosed for illustration of the present invention, is it for the expert of course, that different Modifications, additions and substitutions possible are without departing from the scope and spirit of the invention they in the attached claims are disclosed.

Claims (5)

A process for producing a chromium oxide catalyst for the production of pentafluoroethane using a chloroethane compound, characterized by: heat-treating powdery chromium hydroxide at a temperature of not more than 300 ° C, thereby obtaining powdery chromium oxide; Heat-treating a metal hydroxide selected from magnesium hydroxide, iron hydroxide, molybdenum hydroxide, vanadium hydroxide and aluminum hydroxide at a temperature of not more than 300 ° C, thereby obtaining powdery metal oxide selected from magnesia, iron oxide, molybdenum oxide, vanadium oxide and alumina; Mixing 85 ~ 99.5% by weight of the powdered chromium oxide with 0.5 ~ 15% by weight of the powdered metal oxide to obtain a mixture; Shaping the mixture into a granulate; Calcining the granules at 200 ~ 300 ° C using nitrogen gas; and fluorinating the granules at 300 ~ 320 ° C using a gas mixture including N ₂ and HF and then at 320 380 ° C using HF gas. Method according to claim 1, characterized in that that the Chloroethane compound perchloroethane or 1,1-dichloro-2,2,2-trifluoroethane is. Method according to claim 1, characterized in that that the heat treatment the metal hydroxide is carried out at a temperature of not more than 300 ° C, for what Temperature for a period of not more than 2 h below atmospheric Conditions gradually elevated becomes. Method according to claim 1, characterized in that that this Fluorinate the granules using the HF gas for a Period of not more than 3 h at a temperature of not more than 380 ° C is performed. Chromium oxide catalyst for the preparation of pentafluoroethane, characterized in that the Application of the method has been prepared according to claim 1.