EP1274668A1

EP1274668A1 - Method for preparing a hydro(chloro)fluoroalkane and catalyst

Info

Publication number: EP1274668A1
Application number: EP01927906A
Authority: EP
Inventors: Vincent Wilmet; Francine Janssens
Original assignee: Solvay SA
Current assignee: Solvay SA
Priority date: 2000-04-12
Filing date: 2001-04-09
Publication date: 2003-01-15
Also published as: AU5480301A; US7067706B2; JP2003530374A; FR2807751B1; FR2807751A1; WO2001077048A1; US20040024271A1

Abstract

The invention concerns a method for preparing a hydro(chloro)fluoroalkane which consists in reacting a halogenated hydro(chloro)fluoroalkane precursor with a hydrogen fluoride in the presence of a catalyst comprising chromium (Cr) and at least another metal selected from the group consisting of aluminium, barium, bismuth, calcium, cerium, copper, iron, magnesium, strontium, vanadium and zirconium.

Description

Process for the preparation of a hydro (chloro) fluoroalkane and catalyst

The present invention relates to a process for the preparation of a hydro (chloro) fluoroalkane and a catalyst.

When a halogenated precursor of a hydro (chloro) fluoroalkane is reacted in the presence of hydrogen fluoride under fluorination conditions, it is difficult to selectively obtain a desired hydro (chloro) fluoroalkane. The formation of other reaction products, which are often not recyclable or usable, such as unwanted isomers or disproportionation products decreases the productivity of hydro (chloro) fluoroalkane.

It is, for example, known from JP-A-02/178237 to carry out hydrofluorination of perchlorethylene with hydrogen fluoride in the presence of a catalyst comprising oxides of chromium, magnesium and aluminum. This process has an unsatisfactory pentafluoroethane (HFC-125) productivity. Nor is the method satisfactory with regard to the selectivity for 1,1,1-trifluoro-2,2-dichloroethane (HCFC-123).

It was therefore desirable to find a process which would allow controlled and selective access to a particular hydro (chloro) fluoroalkane.

The invention therefore relates to a process for the preparation of a hydro (chloro) fluoroalkane according to which a halogenated precursor of rhydro (chloro) fluoroalkane is reacted with hydrogen fluoride in the presence of a catalyst comprising chromium (Cr ) and at least one other metal (M) selected from aluminum, barium, bismuth, calcium, cerium, copper, iron, magnesium, strontium, vanadium, and zirconium, process in which the catalyst is poor in ammonium ions.

It has been found, surprisingly, that the method according to the invention allows access with high selectivity to a particular hydro (chloro) fluoroalkane with high overall selectivity for hydro (chloro) fluoroalkane and hydrochlorofluorinated precursors of said hydro ( chloro) fluoroalkane.

In the process according to the invention, the catalyst typically contains at most 1% by weight of ammonium ions. Preferably, it has an ammonium ion content of at most 0.5% by weight. Preferably, the ion content ammonium in the catalyst is at most 0.2% by weight. Excellent results are obtained with a catalyst whose ammonium ion content is at most 0.1% by weight. Particularly interesting results are obtained with a catalyst whose ammonium ion content is at most 0.05% by weight.

The catalyst can be a bulk or supported catalyst. A mass catalyst is preferred.

The M / Cr atomic ratio between the metal M and the chromium in the catalyst is generally at least 0.01. The atomic ratio is preferably at least 0.05, advantageously at least 0.1. Generally, the atomic ratio is at most 100. More often it is at most 20. Preferably, it is at most 10.

The catalyst generally has a specific surface area determined according to the BET method with nitrogen of at least 15m ² / g, preferably at least 25m ² / g. The specific surface is generally at most 200 m ² / g. Preferably it is at most 100 m ² / g.

In the process according to the invention, the catalyst is preferably obtained by fluorination of a mixed chromium and metal oxide M. The fluorination is carried out, preferably with hydrogen fluoride optionally diluted with an inert gas such than nitrogen or helium. The duration of the fluorination is generally from 1 to 100 h. The fluorination temperature is generally between 150 and 400 ° C. Preferably, it is at most 350 ° C. Fluorination can be carried out, for example, directly before the reaction of the halogenated precursor with hydrogen fluoride, preferably in the reactor used for this latter reaction.

The preparation of the mixed oxide preferably comprises a step of co-precipitation by reaction of an aqueous solution of soluble salts of metal and chromium which is reacted with an aqueous solution of ammonia.

The preparation of the mixed oxide can advantageously comprise one or more stages of drying or calcination. The calcination temperature is generally from 150 ° C to 400 ° C. Preferably, the calcination temperature is at most 350 ° C. A calcination temperature of at most 340 ° C. is more particularly preferred. Calcination is often carried out at a temperature of at least 200 ° C. After calcination, the mixed oxide generally has a specific surface determined according to the BET method with nitrogen of at least 150m ² / g, of preferably at least 180 m / g. The specific surface area of the mixed oxide is generally at most 450 m ² / g.

The preparation of the catalyst generally includes a treatment to reduce, preferably eliminate essentially the content of ammonium ions in the catalyst. This treatment can be, for example, at least one wash, preferably with water or a heat treatment or a combination of these treatments. Generally, the effectiveness of the treatment intended to reduce the content of ammonium ions is verified by methods known in themselves. One can for example use the reagent of Nessler to analyze the content of ammonium ions. Preferably, this treatment is applied to the precursor mixed oxide of the catalyst, before subjecting it to the fluorination step.

In a particularly preferred variant, the preparation of the catalyst comprises the following stages: (a.) A preparation of a mixed oxide of metal M and of chromium by co-precipitation from an aqueous solution of soluble salts of metal and of chromium which is reacted with an aqueous ammonia solution; (b.) washing the mixed oxide to reduce, preferably to essentially eliminate, the content of ammonium ions in the catalyst;

(c.) calcining the washed mixed oxide;

(d.) a fluorination treatment of the calcined mixed oxide.

The catalyst and mixed oxide are generally essentially amorphous. Preferably they are completely amorphous. In the process according to the invention, the reaction between hydrogen fluoride and the chlorinated precursor is usually carried out at a temperature of 150 to 450 ° C. The reaction is preferably carried out in the gas phase. The reaction pressure is usually 0.5 to 30 bar. The molar ratio between hydrogen fluoride and the halogenated precursor is usually 1 to 100. The residence time is usually 1 to 1000 s.

Halogen precursors which can be used in the process according to the invention are known. Preferably the halogen precursor is a chlorinated precursor. Examples include dichloromethane, trichloromethane, trichlorethylene, perchlorethylene and pentachloroethane. In a variant, the method according to the invention applies to the synthesis

• a hydrochlorofluoroalkane. In this variant, the metal M is advantageously selected from barium, bismuth, copper, iron, magnesium and strontium. The metal is preferably selected from barium, bismuth, magnesium and strontium. This variant of the process according to the invention has proved to be advantageous for preparing chlorofluoromethane, chlorodifluoromethane, 2-chloro-1,1,1, -trifluoroethane or 2,2-dichloro-1,1,1 -trifluoroethane.

This variant has been found to be particularly advantageous for preparing 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123). In this case, the halogen precursor advantageously comprises at least one chlorinated organic compound selected from perchlorethylene, l, l, 2-trichloro-2-fluoroethylene, l, l, 2-trichloro-2,2-difluoroethane and l , l, 2,2-tetrachloro-2-fluoroethane. Preferably, the chlorinated organic compound is selected from 1,1,2-trichloro-2,2-difluoroethane and perchlorethylene.

In another variant, the method according to the invention applies to the synthesis of a hydrofluoroalkane. In this variant, the metal is advantageously selected from aluminum, calcium, cerium, vanadium, and zirconium. Zirconium and aluminum are preferred. Aluminum is particularly preferred.

In order to reduce the cost of the catalyst in the process according to the invention, it is advantageous to use a catalyst with a high aluminum content compared to the more expensive chromium. It has been found that, in the process according to the invention, hydrofluoroalkanes can be synthesized in a particularly selective and economical manner when a catalyst comprising chromium and aluminum is used in an Al / Cr atomic ratio of at least 0.5. Preferably, this ratio is at least 1. In a particularly preferred manner, this ratio is at least 2. The Al / Cr atomic ratio is advantageously at most 20. Preferably this ratio is at most 10. In a particularly preferred manner, it is at most 5.

This second variant has proven to be advantageous for preparing difluoromethane, 1,1,1,2-tetrafluoroethane or pentafluoroethane.

This variant has proved to be particularly advantageous for preparing pentafluoroethane. In this case, the halogen precursor is advantageously perchlorethylene or 2,2-dicMoro-1,1,1 l-trifluoroethane. The pressure is advantageously in this case at most 15 bar, preferably less than 10 bar. The pressure is advantageously at least 1 bar. Lower pressure allows further increase in selectivity to pentafluoroethane while higher pressure increases the overall productivity of the process.

The invention also relates to the mixed oxide and the catalyst described above. The examples given below are intended to illustrate the invention without, however, limiting it. In the examples, the conversion rate of the halogen precursor is the ratio, expressed in percent, between, on the one hand, the quantity used minus the quantity not converted and, on the other hand, the quantity used. artwork; the selectivity for hydro (chloro) fluoroalkane is the ratio, expressed in percent, between the quantity of hydro (chloro) fluoroalkane formed and the quantity which would have formed if all the converted halogen precursor had generated hydro (chloro) fluoroalkane; the overall selectivity is the sum of the selectivity of all the intermediate products which can be upgraded to the desired hydro (chloro) fluoroalkane; the yield of hydro (chloro) fluoroalkane is the product of the conversion rate by the selectivity in this hydro (chloro) fluoroalkane. Examples 1-7

1.6 l of an aqueous solution were prepared containing 0.56 mol / l of chromium nitrates and of other metal M and having the desired atomic ratio between chromium and metal M. To this solution was added under stirring, at room temperature, 0.7 1 of aqueous ammonia having an NH ₄ OH concentration of 4 mol / 1. The precipitate was centrifuged. The pellet was washed several times with water at approximately 65 ° C, until at least 80% of the initial content of ammonium ion in the pellet, verified using the Nessler reagent, was eliminated. The washed pellet was dried for 2 days at 105 ° C. The agglomerates obtained after drying were ground to obtain grains with a size less than 5 mm. The grains were subjected to calcination for a total period of 69 h under nitrogen sweeping. The temperature was maintained first at 215 ° C and then at 330 ° C. The specific surface (SS) of the mixed oxide obtained is shown in Table 1. It was determined according to the BET method with nitrogen, measured on a CARLO ERBA Sorptomatic® 1990 device after degassing of the samples for 12 h at room temperature under a vacuum of 10 ^"5 torr. the ammonium ion content in the mixed oxide is also shown in table 1.

The mixed oxide was introduced into a Hastelloy C tubular reactor. A fluorination treatment was carried out for 8 hours at a temperature of 200 to 350 ° C. with gaseous hydrogen fluoride (10 g / h per 100 cm of oxide mixed) mixed with nitrogen. The specific surface (SS) of the catalysts obtained is indicated in Table 1. 10 cm of the catalyst and a hydrogen fluoride / perchlorethylene mixture (PER) in a molar ratio of 10 mol / mol were introduced into a tubular reactor with an internal diameter of 15 mm. The reaction pressure was maintained at 1 bar and the temperature at 350 ° C. The residence time was 12.5 seconds.

The results are collated in Table 1 below. It appears that the process according to the invention makes it possible to obtain a high yield of HFC-125. The process gives high overall selectivity at high transformation rates. Table 1

Claims

1. Process for the preparation of a hydro (chloro) fluoroalkane according to which a halogen precursor of the hydro (chloro) fluoroalkane is reacted with hydrogen fluoride in the presence of a catalyst comprising chromium (Cr) and at at least one other metal (M) selected from aluminum, barium, bismuth, calcium, cerium, copper, iron, magnesium, strontium, vanadium, and zirconium, a process in which the content of NH4 + ammonium ions in the catalyst is at most 1% by weight.

2. The method of claim 1, wherein the content of ammonium ions in the catalyst is at most 0.2% by weight.

3. Method according to claim 1 or 2, wherein the catalyst has a specific surface area determined according to the BET method of at least 15m ² / g.

4. Method according to any one of claims 1 to 3, wherein the catalyst was obtained by fluorination of a mixed oxide of chromium and metal M.

5. Method according to claim 4 wherein the mixed oxide was obtained by co-precipitation by reaction of an aqueous solution of soluble salts of metal and chromium which is reacted with an aqueous solution of ammonia.

6. The method of claim 4 or 5 wherein the mixed oxide has before fluorination a specific surface determined by the BET method of at least 150m ² / g.

7. Method according to any one of claims 1 to 6, applied to the synthesis of a hydrofluoroalkane.

8. The method of claim 7 wherein the metal is selected from aluminum, calcium, cerium, vanadium, and zirconium.

9. The method of claim 8 wherein the metal is aluminum.

10. The method of claim 9 wherein the Al / Cr atomic ratio is 0.5 to 20.

1 1. Process according to any one of claims 7 to 10, in which the hydrofluoroalkane obtained is pentafluoroethane.

12. Method according to any one of claims 1 to 6, applied to the synthesis of a hydrochlorofluoroalkane.

13. The method of claim 12 wherein the metal is selected from barium, bismuth, copper, iron, magnesium and strontium.

14. Catalyst comprising chromium (Cr) and at least one other metal (M) selected from aluminum, barium, bismuth, calcium, cerium, copper, iron, magnesium, strontium, vanadium , and the catalyst zirconium in which the content of ammonium ions NH4 + is at most 1% by weight.

15. The catalyst according to claim 14, in which the content of ammonium ions NH4 + is at most 0.2% by weight.

16. Mixed oxide comprising chromium (Cr) and at least one other metal selected from aluminum, barium, bismuth, calcium, cerium, copper, iron, magnesium, strontium, vanadium, and zirconium mixed oxide in which the content of ammonium ions NH4 + is at most 1% by weight.

17. Mixed oxide according to claim 16 wherein the content of NH4 + ammomum ions is at most 0.2% by weight.