Title of Invention

A PROCESS FOR THE MANUFACTURE OF DIFLUOROMETHANE

Abstract The invention relates to the manufacture of difluoromethane by gas-phase catalytic fluorination of methylene chloride. According to the invention, the operation is carried out in the presence of chlorine. The presence of chlorine assists to lengthen the lifetime of the catalyst.
Full Text The present invention relates to a process for the manufacture of difluoromethane (F32) by catalytic fluorination of methylene chloride.
Difluorociethane, known under the designation 32, is considered harmless to the ozone layer. It is herefore particularly preferred for the replacement of FCs. As a mixture with other hydrofluoroalkanes such s 1,1,1-trifluoroethane (F143a), 1,1,1,2-etrafluoroethane (F134a) or pentafluoroethane (F125), t is proposed to use F32 to replace in particular F22 2hlorodifluoromethane) and F502 (azeotropic mixture of 22 and of chloropentafluoroethane) in refrigeration, Lr conditioning and other applications.
There are various known processes for the tnufacture of F32. The hydrogenolysis of F12 Lichlorodifluoromethane) or of F22 (Japanese patent ' 60-01731 and European Patent Specification » 508 660) has the disadvantage of being generally not sry selective and of producing worthless methane as '-product. It has recently been proposed to produce 2 by fluorination of bis(fluoromethyl) ether luropean Patent Specification EP 518 506).
It is also known to produce F32 by uorination of methylene chloride (F30) with anhydrous . Many patents describe this reaction, claiming the e of catalysts such as Cr203, CrF3, A1F3, Cr/carbon, /A1F3 etc.
The difficulty of this reaction lies in the


stability of the catalyst, which tends either to coke rapidly or to crystallize. The problem becomes very tricky if it is intended to combine a high space time yield and a good selectivity while maintaining good stability of the catalyst.
To reduce this deactivation it has been proposed to employ specific catalysts such as a mechanical mixture of alumina and chromium oxide (British Patent Specification GB 821 211). This specification gives an example for the fluorination of methylene chloride but the F32 space time yields obtained on this catalyst are low ( More generally, during fluorination reactions, it is very often envisaged to inject oxygen or air continuously in order to lengthen the lifetime of the catalysts. Thus, Japanese patent JP 51-82206 describes the use of 0.001 to 1 % of oxygen to maintain the activity of catalysts prepared from chromium oxide. The examples in this patent relate only to reactions of fluorination of perhalogenated molecules (CC14, C2C13F3) .
The major disadvantage of this process is the appearance of a Deacon reaction. In fact, chromium oxide, well known as a fluorination catalyst, is also a good catalyst for the oxidation of HCl (US patents 4 803 065 and 4 822 589). The oxygen introduced during the fluorination reacts with the HCl formed to produce

1
water and chlorine. Because of corrosion problems, the presence of water is particularly undesirable in a fluorination process.
Continuous introduction of a small quantity of chlorine has already been proposed in Japanese patent JP 49-134612, in order to stabilize the activity of the catalysts employed for the disproportionation of perhalogenated molecules; in this case the use of chlorine does not result in a decrease in the selectivity.
More recently the use of chlorine as an inhibitor of deactivation has been described in the fluorination of CF3CH2C1 (US Statutory Invention Registration H1129). The examples which are presented clearly show that the use of chlorine makes it possible to maintain a stable space time yield of CF3CH2F (F134a). On the other hand, no indication is given as to the effect of chlorine on the selectivity of the reaction.
However, in the case of hydrogenated molecules and in particular in the case of the fluorination of CF3CH2C1 (F133a) , the presence of chlorination reactions has been demonstrated, resulting in the formation of worthless by-products. Thus, in the case of the fluorination of F133a, by-products of the F120 series (C2HClnF5_n) are chiefly formed.
Given that the Deacon reaction produces chlorine, this loss in selectivity is also observed

during the fluoridation of hydrogenated molecules in the presence of oxygen on chromium catalysts. This is why some patents (see, for example, European patent EP 546 883) have described the preparation of specific catalysts which limit the oxidation of HC1 and the by-production of chlorine.
It could be assumed that the behaviour of methylene chloride would be similar to that of F133a, and this would make the use of chlorine not very advantageous for maintaining the activity of the catalyst. However, it has been surprising to find that, in the case of the methylene chloride fluorination, even with relatively high contents (Cl2/F30 = 3 mol%) , chlorine undergoes very little reaction with the compounds of the F30 series (CH2ClnF2_n) , and this allows it to be employed without any significant decrease in the selectivity of the reaction.
In addition, in Japanese patent JP 51-82206 it is indicated that oxygen enables the catalyst activity to be maintained even in concentrations that are lower than that employed with chlorine. However, it has been found that, during the fluorination of methylene chloride, the continuous introduction of chlorine is, at an equal concentration, a more effective means than the addition of oxygen in stabilizing the activity of the catalysts. In fact, in high space time yield conditions, oxygen addition is not sufficient to maintain the activity of the

catalysts even at high temperature, whereas the addition of chlorine enables their lifetime to be significantly lengthened from a temperature of 250° upwards and therefore the fluorination of methylene chloride to be carried out in a temperature range in which an irreversible deactivation of the catalyst by crystallization is not very probable.
Accordingly the present invention provides a process for the manufacture of difluoromethane by gas-phase catalytic fluorination of methylene chloride by means of anhydrous hydrofluoric acid, which operation is carried out in the presence of chlorine, the CI2/CH2CI2, molar ratio being between 0.01 % and 10 % at a temperature of between 200 and 450°C and in the presence of a catalyst selected from bulk catalysts and supported catalysts.
Our co-pending Indian Patent Application No. 1072/MAS/96 relates to synthesis of difluoromethane.
In accordance with the process according to the invention, chloride (pure or diluted in an inert gas such as nitrogen or helium) may be introduced into the reactor at the same time as methylene chloride and HF.
A C12/CH2C12 molar ratio of between 0.05 and 5 % is preferably employed and, more particularly, a molar ratio of between 0.1 % and 3 %. It is also possible to introduce chlorine by dissolving it in methylene chloride.
The reaction temperature is generally between 200 and 450°C. However, the operation is preferably carried out at a temperature of between 250 and 380°C in order to obtain a high space time yield without

risking a deactivation of the catalyst due to crystallization.
The fluorination catalysts to be employed for making use of the process according to the invention may be bulk catalysts or supported catalysts, the support which is stable in the reaction mixture being, for example, an active carbon, an alumina, a partially fluorinated alumina, aluminium trifluoride or aluminium phosphate. Partially fluorinated alumina is intended to mean a composition which is rich in fluorine and contains chiefly aluminium, fluorine and oxygen in proportions such that the quantity of fluorine expressed as A1F3 constitutes at least 50 % of the total weight.
Among the bulk catalysts it is possible to mention more particularly chromium(III) oxide prepared according to methods known to a person skilled in the art (sol-gel process, precipitation of the hydroxide from chromium salts, reduction of chromic anhydride, and the like) and chromium trifluoride. Derivatives of metals such as nickel, iron, vanadium (in the oxidation state III), manganese, cobalt or zinc may also be suitable by themselves or in combination with chromium, in the form of bulk catalysts, as well as in the form of supported catalysts. Alkaline-earth metals, rare earths, graphite or alumina can also be incorporated in these catalysts or in their support in order to increase the thermal or mechanical stability thereof.

During the preparation of catalysts using a number of metal derivatives in combination, the catalysts may be obtained by mechanical mixing or by other techniques, such as coprecipitation or a coimpregnation.
The supported or bulk catalysts can be employed in the form of beads, extrudates, tablets, or even, if operating in a stationary bed, in the form of fragments. When the operation is carried out in a fluid bed it is preferred to employ a catalyst in the form of beads or extrudates.
As nonlimiting examples of catalysts there may be mentioned:
- chromium oxide microbeads obtained by the sol-gel process as described in French patent FR 2 501 062,
- catalysts with chromium oxide deposited on active carbon (US patent 4 474 895), on aluminium phosphate (European patent EP 55 958) or on aluminium fluoride (US patents 4 579 974 and 4 579 976) ,
- mixed chromium oxide and nickel chloride catalysts deposited on aluminium fluoride (European patent application EP 0 486 333),
- bulk catalysts based on crystallized chromium oxide
(European patent application EP 657 408),
- bulk catalysts based on nickel and chromium oxide
(European patent application EP 0 546 883),
- bulk catalysts based on vanadium and chromium oxide
(European patent application EP 0 657 409).

The abovementioned patent specifications, the content of which is incorporated here by reference, describe broadly the preparation of these catalysts, as well as their activation, that is to say preliminary conversion of the catalyst into stable active species by fluorination by means of gaseous HF diluted with compounds which are inert (nitrogen) or not (air or l,l,2-trichloro-l,2,2-trifluoroethane). During this activation the metal oxides serving as active material (for example chromium oxide) or as support (for example alumina) may be partially or completely converted to corresponding fluorides.
Mixed catalysts based on chromium and nickel, which are described in European patent applications EP 0 486 333 and EP 0 546 883 are more particularly preferred.
The contact time, defined as the ratio of the total flow rate of the reactants (measured in the reaction conditions) to the volume of catalyst, may vary within wide limits and is generally between 0.01 and 20 seconds. In practice it is preferable to work with contact times of between 0.1 and 5 seconds.
This reaction may be carried out at atmospheric pressure or at a higher pressure. A pressure of between 1 and 20 bar absolute is preferably chosen.
The following examples illustrate the invention without limiting it.

a) Preparation and activation of a catalyst based on nickel and chromium which are supported on fluorinated alumina
250 ml of partially fluorinated alumina (containing, in all, 83 mass% of aluminium fluoride and 16 % of alumina) obtained beforehand by fluorination of alumina at about 300°C with the aid of nitrogen and hydrofluoric acid are placed in a rotary evaporator. Before impregnation, this fluorinated support exhibits the following physicochemical characteristics:
form : beads 1-2 mm in diameter
apparent density : 0.57 g/ml
BET surface : 67 m2/g
pore volume : 0.72 ml/g (for pores with
radius between 4 nm and 63 fim)
An aqueous solution containing 12.5 g of chromic acid Cr03 and 29 g of nickel chloride hexahydrate in 40 g of water, and a methanolic solution made up of 17.8 g of methanol in 50 g of water are added simultaneously onto the support, with stirring. The impregnation is performed over 45 minutes, at ambient temperature and at atmospheric pressure, on the support, with stirring.
After drying for 4 hours, under a stream of nitrogen, in a fluidized bed at about 110°C, the

catalyst is next charged into a reactor made of Inconel 600 and activated as a stationary bed with a nitrogen/HF mixture according to the procedure described in European patent EP 0 486 333. After this treatment the physicochemical characteristics of the Ni-Cr/A1F3 catalyst activated in this way are the following: Chemical composition (by weight):
fluorine : 58.6%
aluminium : 25.9%
nickel : 6.4%
chromium : 6.0%
Physical properties;
volume of the pores
with a radius of
between 4 ran and 63 /im: 0.4 ml/g
BET surface : 23 m2/g
b) Fluorination of methylene chloride
4 ml of this Ni-Cr/A1F3 catalyst are charged into a tubular reactor made of Inconel 600, with an internal diameter of 1 cm and a volume of 40 ml and then, in a first stage, HF and chlorine are introduced at respective flow rates of 0.45 mol/h and 0.005 mol/h. Methylene chloride, vaporized in a preheater the temperature of which is set at 150°C, is next introduced in gaseous form into the reactor at a flow

rate of 0.15 mol/h. The temperature of the reactor is maintained at 300°C and the contact time in these conditions is 0.5 seconds.
On leaving the reactor, the reaction products are washed, dried and analysed by gas chromatography. The following table summarizes the results obtained after 48, 171, 338 and 527 hours' continuous operation.

Despite a large addition of chlorine (3 mol%), the chlorination by-products remain in a minority in these reaction conditions. These by-products are chiefly F20 (trichloromethane), F21 (fluorodichloromethane), F22 (chlorodifluoromethane) and F23 (trifluoromethane).
In these reaction conditions the addition of chlorine allows a stable activity to be maintained with an F32 space time yield higher than 1100 g/h and a selectivity for F31+F32 higher than 99.5 %. EXAMPLE 2 (comparative)
The operation is carried out as in Example 1



It is concluded that oxygen does not enable the catalyst activity to be maintained. At the end of the fluorination test the solid is coked; its carbon weight content is 2.5 %.
EXAMPLE 4
The catalyst is a bulk chromium oxide which has a specific surface of 209 m2/g and a pore volume (4 nm The activated catalyst has the following physicochemical properties:
fluorine weight content : 27%
chromium weight content : 53%
Volume of the pores with
a radius of between
4 nm and 63 fim : 0.13 ml/g
BET surface : 101 m2/g«
The fluorination of methylene chloride is carried out on this catalyst in the conditions of Example 1. After washing and drying, the analysis of the reaction products by gas chromatography gave the

results which are brought together in the following table:

As in Example 1 and in these reaction conditions, the chlorination products remain in a I minority (selectivity for F31+F32 > 98 %). The
by-products are chiefly F20 (trichloromethane), F21 (fluorodichloromethane), F22 (chlorodifluoromethane) and F23 (trifluoromethane) and are formed with respective average selectivities of 0.5 %, 0.1 %, 0.1 % and 1.3 %. EXAMPLE 5
55 ml of the Ni-Cr/A1F3 catalyst described in Example 1-a) are charged into a tubular reactor made of Inconel 600, with an internal diameter of 21 mm and a volume of 150 ml, and then the reactants (HF, F30 and Cl2) are fed at 300°C and at a pressure of 1.5 MPa (absolute) at the following flow rates:

- HF: 3 mol/hour
- F30: 1 mol/hour
- Cl2: 0.02 mol/hour
In these conditions the contact time on the catalyst is 15 seconds. On leaving the reactor the crude reaction gases are analysed by gas chromatography.
The following table summarizes the results obtained after 346 and 376 hours of continuous operation.

The by-products of the F20 series remain in a minority. In these reaction conditions the continuous addition of chlorine allows a stable activity to be maintained with an F32 space time yield of 470 g/h per litre of catalyst and a selectivity for F31+F32 of 97 %. EXAMPLE 6 (comparative)
The operation of Example 5 is continued but with the chlorine feed cut off for 4 hours.
The results obtained after 383, 385 and 3 87 hours of continuous operation appear in the following table:


It is found that the absence of chlorine, even for a few hours of operation, results in an appreciable drop in catalyst activity (approximately 13 % in 4 hours), which causes a drop in the space time yield of F32 from 421 to 366 g/h per litre of catalyst. EXAMPLE 7
The operation is carried out under pressure (1.5 MPa absolute) as in Example 5, but on a fresh charge (35 ml) of the same Ni-Cr/A1F3 catalyst and with a contact time of 5 seconds at 250°C. The reactant feed flow rates are the following:
- HF: 6.6 mol/hour
- F30: 2.2 mol/hour
- Cl2: 0.04 mol/hour
The results obtained after 119, 500 and 785 hours of continuous operation in these conditions are collated in the following table:





WE CLAIM:
1. A process for the manufacture of difiuoromethane by gas-phase catalytic fluorination of methylene chloride by means of anhydrous hydrofluoric acid, which operation is carried out in the presence of chlorine, the C12/CH2C12, molar ratio being between 0.01 % and 10 % at a temperature of between 200 and 450°C and in the presence of a catalyst selected from bulk catalysts and supported catalysts.
2. The process according to claim 1, in which the CI2/CH2CI2 molar ratio is between 0.05 and 5 %.
3. The process according to claim 1, in which the Cl2/CH2Cl2 molar ratio is between 0.1 and 3 %.
4. The process according to any one of claims 1 to 3, in which the operation is carried out at a temperature of between 250 and 380°C.
5. The process according to any one of the preceding claims, in which a bulk or supported mixed catalyst based on chromium and nickel is employed.
6. The process according to any one of the preceding claims, in which the contact time is between 0.01 and 20 seconds.
7. The process according to any one of claims 1 to 5 in which the contact time is between 0.1 and 5 seconds.

8. The process according to any one of the preceding claims, in which the operation is carried out at a pressure of between 1 and 20 bar absolute.
9. A process for the manufacture of difluoromethane substantially as herein described and exemplified.


Documents:

1073-mas-1996 abstract.pdf

1073-mas-1996 claims.pdf

1073-mas-1996 correspondence-others.pdf

1073-mas-1996 correspondence-po.pdf

1073-mas-1996 description (complete).pdf

1073-mas-1996 form-2.pdf

1073-mas-1996 form-26.pdf

1073-mas-1996 form-4.pdf

1073-mas-1996 form-6.pdf

1073-mas-1996 petition.pdf


Patent Number 196304
Indian Patent Application Number 1073/MAS/1996
PG Journal Number 20/2006
Publication Date 19-May-2006
Grant Date 03-Feb-2006
Date of Filing 18-Jun-1996
Name of Patentee ELF ATOCHEM SA
Applicant Address 4 & 8 COURS MICHELET LA DEFNESE 10, F-92800, PUTEAUX
Inventors:
# Inventor's Name Inventor's Address
1 BENOIT REQUIEME NE225 CHEMIN DE LA CROIX BOURGUIGNON, 69390 CHARLY
2 SYLVAIN PERDRIEUX 707 RUE DE LA MACONNIERE-CHARLY, 69390 VERNAISON
3 BERNARD CHEMINAL LES IRIS-11 CHEMIN DE CHAUCHERE 69510 SAUCIEU-EN-JARREST
4 ERIC LACROIX LE BOURG 69480 AMBERIEUX D'AZEGUES,
5 ANDRE LANTZ DOMAINE DE LA HETRAIE 69390 VERNAISON,
PCT International Classification Number C07C17/08
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 95.07821 1995-06-29 France