Technical Field of the Invention
The present invention relates to the field of saturated fluorocarbons. It more particularly relates to a manufacturing method of the l-chloro-2,2-difluoroethane from 1,1,2-trichloroethane.
BACKGROUND OF THE INVENTION
L-chloro-2,2-difluoroethane (HCFC-142) is known not only as a blowing agent in the manufacture of foams, but also as a raw material in the manufacture of pharmaceuticals or agrochemicals.

Is known from WO2015 / 082812 a method of l-chloro-2,2-difluoroethane from 1,1,2-trichloroethane and / or 1,2-dichloroethylene comprising at least one step during which the 1 , 1,2-trichloroethane and / or 1,2-dichloroethylene reacts or react with gas phase hydrofluoric acid to give a stream comprising l-chloro-2,2-difluoroethane, hydrochloric acid, hydrofluoric acid and 1,1-dichloroethylene. The presence of 1,1-dichloroethylene can be troublesome for subsequent reaction steps.

The applicant has developed a manufacturing method of the l-chloro-2,2-difluoroethane not have the drawbacks of the prior art, especially a method avoiding the formation of 1,1-dichloroethylene.

Summary of the Invention

The present invention relates to a manufacturing method of the l-chloro-2,2-difluoroethane from 1,1,2-trichloroethane comprising (i) at least one step in which 1,1,2-trichloroethane reacts with the gas phase hydrofluoric acid optionally in the presence of an oxidizing agent and in the presence or absence of a fluorination catalyst to give a stream comprising l-chloro-2,2-difluoroethane, the hydrochloric acid, hydrofluoric acid and at least one compound (s) chosen (s) among 1,2-dichloroethylenes (cis and trans), 1-chloro, 2-fluoroethylenes (cis and trans) 1, 2-dichloro-2-fluoroethane and unreacted 1,1,2-trichloroethane; (Ii) at least one step of separation of the compounds from the reaction step to give a first stream comprising hydrochloric acid and a second stream comprising hydrofluoric acid, l-chloro-2,2

difluoroethane, at least one compound (s) and 1, unreacted 1,2-trifluoroethane; (Iii) at least one step of separating the second stream to give an organic phase comprising 1-chloro-2,2-difluoroethane, at least one compound (s) and 1, unreacted 1,2-trichloroethane and inorganic phase comprising TH F; (Iv) at least one separation step of 1-chloro-2,2-difluoroethane from the organic phase obtained in (iii); (V) optionally recycling to step (i) of the organic phase after separation of step (iv); and (vi) optionally recycling to step (i) of the inorganic phase from step (iii), characterized in that step (iv) comprises:

a) purification of the organic phase obtained in step (iii) to form a first stream comprising l-chloro-2,2-difluoroethane, at least one compound (s) and hydrofluoric acid and a second stream comprising 1,1,2-trichloroethane;

b) removing the hydrofluoric acid from said first stream to form a third stream comprising l-chloro-2,2-difluoroethane and at least one compound (s);

c) purification, preferably a distillation, said third stream comprising l-chloro-2,2-difluoroethane.

According to a preferred embodiment, step a) purification of the organic phase obtained in (iii) is a distillation, preferably carried out at a temperature between 30 and 80 ° C and at an absolute pressure between 1 and 4 bar.

According to a preferred embodiment, the second stream comprising 1, 1,2-trichloroethane is recycled to step (i), preferably after distillation thereof at a temperature between 100 and 170 ° C and a pressure absolute between 1 and 4 bar absolute ..

According to a preferred embodiment, step b) comprises a step of washing said first stream to form an intermediate stream B comprising l-chloro-2,2-difluoroethane and said at least one compound A selected from the group consisting of cis-l, 2-dichloroethylene, trans-l, 2-dichloroethylene, cis-l-chloro-2-fluoroethylene, trans-1-chloro-2-fluoroethylene and 1,2-dichloro-l-fluoroethane and a current intermediate C comprising hydrofluoric acid.

According to a preferred embodiment, said intermediate stream B is dried to form said third current.

According to a preferred embodiment, the drying is implemented at a temperature of 0 to 30 ° C and an absolute pressure between 1 and 4 bar.

According to a preferred embodiment, the first stream obtained in step a) and the third stream obtained in step b) also include trans-l, 2-dichloroethylene and optionally at least one of A compounds selected from the group consisting of cis-1,2-dichloroethylene, cis-l-chloro-2-fluoroethylene, trans-l-chloro-2-fluoroethylene and 1,2-dichloro-l-fluoroethane.

According to a preferred embodiment, step c) comprises at least one distillation, preferably carried out preferably by distillation at a temperature between 35 and 79 ° C and at an absolute pressure between 1 and 4 bar.

According to a preferred embodiment, the first stream obtained in step a), the intermediate stream B and the third stream obtained in step b) comprise trans-1,2-dichloroethylene and at least one of the selected compounds A from the group consisting of cis-1,2-dichloroethylene, cis-l-chloro-2-fluoroethylene, trans-l-chloro-2-fluoroethylene and 1,2-dichloro-l-fluoroethane.

According to a preferred embodiment, the first stream obtained in step a), the intermediate stream B and the third stream obtained in step b) include l-chloro-2,2-difluoroethane, trans-2- dichloroethylene and at least one of a compounds selected from the group consisting of cis-l, 2-dichloroethylene, cis-l-chloro-2-fluoroethylene, trans-l-chloro-2-fluoroethylene and 1,2-dichloro- l-fluoroethane.

According to a preferred embodiment, step c) form a fourth stream comprising l-chloro-2,2-difluoroethane and trans-l, 2-dichloroethylene and a fifth stream comprising at least one of A compounds selected from the group consisting of cis-1,2-dichloroethylene, cis-l-chloro-2-fluoroethylene, trans-l-chloro-2-fluoroethylene and 1,2-dichloro-l-fluoroethane.

Detailed Description of the Invention

The present invention therefore relates to a method of manufacturing the l-chloro-2,2-difluoroethane from 1,1,2-trichloroethane. The method comprises the steps of:

(I) at least one step in which 1,1,2-trichloroethane reacts with hydrofluoric acid in the gas phase optionally in the presence of an oxidizing agent and in the presence or absence of a catalyst fluorination to give a stream comprising l-chloro-2,2-difluoroethane, hydrochloric acid, hydrofluoric acid and at least one compound (s) chosen (s) among 1,2-dichloroethylenes ( cis and trans), 1-chloro, 2-fluoroethylenes (cis and trans), the l, 2-dichloro-2-fluoroethane and unreacted 1,1,2-trichloroethane;

(Ii) at least one step of separation of the compounds from the reaction step to give a first stream comprising hydrochloric acid and a second stream comprising hydrofluoric acid, l-chloro-2,2-difluoroethane, at least one compound (s) and 1,1,2-trifluoroethane;

(Iii) at least one step of separating the second stream to give an organic phase comprising l-chloro-2,2-difluoroethane, at least one compound (s) and unreacted 1,1,2-trichloroethane and inorganic phase comprising HF;

(Iv) at least one step of separating the l-chloro-2,2-difluoroethane from the organic phase obtained in (iii);

(V) optionally recycling to step (i) of the organic phase after separation of step (iv); and

(Vi) optionally recycling to step (i) of the inorganic phase from step

(iii).

According to a preferred embodiment, step (iv) comprises:

a) purification, preferably distillation, from the organic phase obtained in step (iii) to form a first stream comprising l-chloro-2,2-difluoroethane, at least one compound (s) and the hydrofluoric acid and a second stream comprising 1,1,2-trichloroethane;

b) removing the hydrofluoric acid from said first stream to form a third stream comprising l-chloro-2,2-difluoroethane and at least one compound (s);

c) purification, preferably a distillation, said third stream comprising l-chloro-2,2-difluoroethane.

preferably a catalyst is used in step (i) and advantageously in the presence of an oxidizing agent. The temperature of the reaction step is preferably between 150 and 400 ° C, preferably between 200 and 350 ° C. The pressure at which the fluorination reaction is conducted is preferably between 1 and 30 bar absolute, advantageously between 3 and 20 bar absolute and more particularly between 3 and 15 bar.

The amount of hydrofluoric acid used in the reaction is preferably between 5 and 40 mol and advantageously between 10 and 30 mol per mol of HCC-140.

The contact time defined as the catalyst volume / debit total volumetric gas temperature and pressure of the reaction can be between 2 and 200 seconds, preferably between 2 and 100 seconds, preferably between 2 and 50 seconds .

The pure oxidizing agent or as a mixture with nitrogen can be selected from oxygen, and chlorine. We choose preferably chlorine.

The amount of oxidizing agent used is preferably 0.01 to 20 mol% per mole of F140, preferably between 0.01 to 0.2 mol% per mol of HCC-140.

An amount of oxidizing agent between 1 - 10 mol% relative to F140 gave very promising results.

The catalyst used can be bulk or supported. The catalyst may be based on a metal including a transition metal oxide or a derivative thereof, halide or oxyhalide of such a metal. For example, mention may be made FECU, chromium oxyfluoride, N1CI2, CrF.sub.3 and mixtures thereof.

By way of supported catalysts include those supported on carbon or magnesium base such as magnesium compounds in particular halides such as MgF2 or magnesium oxyhalides such as oxyfluorides or based on aluminum such as alumina, activated alumina or aluminum derivatives, in particular halides, such as AI F3 or oxyhalides such as aluminum oxyfluoride.

The catalyst may further comprise co-catalysts selected from Co, Zn, Mn, Mg, V, Mo, Te, Nb, Sb, Ta, P, Ni, Zr, Ti, Sn, Cu, Pd, Cd, Bi , rare earths and mixtures thereof. When the catalyst is based on chromium, Ni, Mg and Zn are advantageously selected as cocatalyst.

The atomic ratio cocatalyst / catalyst is preferably between 0.01 and 5.

The chromium-based catalysts are particularly preferred.

The catalyst used in the present invention can be prepared by coprecipitation of corresponding salts optionally in the presence of a support.

The catalyst may also be prepared by co-grinding of the corresponding oxides.

Prior to the fluorination reaction the catalyst is subjected to an activation step by THF at a temperature preferably between 100 and 450 ° C, preferably between 200 and 400 ° C for a period between 1 and 50 hours.

Furthermore THF by treatment, activation can be carried out in the presence of the oxidizing agent.

The activation steps can be carried out at atmospheric pressure or under pressure up to 20 bar.

According to a preferred embodiment of the invention, the support can be prepared from highly porous alumina. In a first step alumina is converted to aluminum fluoride or a mixture of aluminum fluoride and alumina, by fluorination using air and hydrofluoric acid, the alumina conversion rate aluminum fluoride mainly dependent on the temperature at which the fluorination is carried alumina (usually between 200 ° C and 450 ° C, preferably between 250 ° C and 400 ° C). The support is then impregnated with aqueous solutions of salts of chromium, nickel and optionally rare earth metal, or with the aid of aqueous solutions of chromic acid, nickel or zinc salt, and optionally salts or rare earth oxides and methanol (as a reducing agent to chromium). As chromium salts, nickel or zinc and rare earth metals can be employed, chlorides, or other salts such as, for example, oxalates, formates, acetates, nitrates and sulphates or nickel dichromate, and of rare earth metals, provided that such salts are soluble in the amount of water capable of being absorbed by the support.

The catalyst may also be prepared by direct impregnation of alumina (which is usually enabled) using solutions of the compounds of chrome, nickel or zinc, and optionally rare earth metals mentioned above. In this case, the conversion of at least part (e.g. 70% or more) of the alumina to aluminum fluoride or aluminum oxyfluoride is performed during the metal activation step of the catalyst.

The activated aluminas which may be used for catalyst preparation are well-known products available commercially. They are generally prepared by calcination of alumina hydrate (aluminum hydroxide) at a temperature between 300 ° C and 800 ° C. Aluminas (activated or not) can contain significant levels (up to 1000 ppm) of sodium without impairing the catalytic performance.

Preferably, the catalyst is conditioned or activated, that is to say converted into active and stable components (to reaction conditions) by activating said preliminary operation. This treatment may be carried out either "in situ" (in the fluorination reactor) or in a suitable apparatus designed to withstand activation conditions.

After impregnating the carrier, the catalyst is dried at a temperature between 100 ° C and 350 ° C, preferably 220 ° C to 280 ° C in the presence of air or nitrogen.

The dried catalyst is then activated in one or two steps with hydrofluoric acid, optionally in the presence of an oxidizing agent. The duration of this stage of activation by fluorination can be between 6 and 100 hours and the temperature between 200 and 400 ° C.

Preferably, the separation step (ii) comprises at least one distillation, preferably carried out at a temperature between -60 ° and 120 ° C and more particularly between -60 and 89 ° C and an absolute pressure of between 3 and 20 bar and preferably between 3 and 11 bar.

Addition of l-chloro-2,2-difluoroethane, hydrofluoric acid and 1,1,2-trichloroethane and the organic phase obtained in step (iii) also comprises at least one of A compound selected from the group consisting of cis-l, 2-dichloroethylene, trans-1,2-dichloroethylene, cis-l-chloro-2-fluoroethylene, 1,2-dichloro-l-fluoroethane and trans-l-chloro-2-fluoroethylene.

After separation of the second stream in step (iii), the inorganic phase obtained in (iii) preferably contains the majority of the HF initially present in the second stream with respect to the organic phase also obtained in step (iii ). The organic phase obtained in (iii) may contain hydrofluoric acid. The amount of hydrofluoric acid in the organic phase is less than the amount of hydrofluoric acid in the inorganic phase. The molar ratio of hydrofluoric acid present in the organic phase over hydrofluoric present in the inorganic acid phase is less than 1: 10, preferably less than 1: 50, especially 1: 100.

According to one embodiment, prior to recycling to step (i), the inorganic phase obtained in (iii) is purified so that the HF content is greater than or equal to 90% by weight. Preferably, this purification comprises at least one distillation, preferably carried out at a temperature between -23 and 46 ° C and an absolute pressure between 0.3 and 3 bar.

Preferably, the separation step (iii) comprises at least a decantation step, advantageously carried out at a temperature between -20 and 60 ° C and more particularly between -20 and 10 ° C.

Preferably, the separation step (iv) includes a step of purifying the organic phase obtained in (iii) for separating the l-chloro-2,2-difluoroethane and 1, 1,2-trichloroethane. Addition of l-chloro-2,2-difluoroethane and 1, 1,2-trichloroethane, the organic phase obtained in step (iii) also comprises at least two, three, four or all of the A compounds selected from the group consisting of cis-l, 2-dichloroethylene, trans-l, 2-dichloroethylene, cis-l-chloro-2-fluoroethylene, 1,2-dichloro-l-fluoroethane and trans-l-chloro-2-fluoroethylene; and optionally hydrofluoric acid. And the organic phase obtained in step (iii) may include trans-l, 2-dichloroethylene or trans-1,2-

dichloroethylene et cis-l-chloro-2-fluoroethylene ou trans-l,2-dichloroethylene, cis-l-chloro-2-fluoroethylene et 1,2-dichloro-l-fluorethane ou trans-l,2-dichloroethylene, cis-l-chloro-2-fluoroethylene, 1,2-dichloro-l-fluorethane et cis-l,2-dichloroethylene ou trans-1,2-dichloroethylene, cis-l-chloro-2-fluoroethylene, 1,2-dichloro-l-fluorethane, cis-1,2-dichloroethylene et trans-l-chloro-2-fluoroethylene.

Preferably, step a) purification of the organic phase obtained in (iii) is a distillation. In particular the distillation of the organic phase obtained in (iii) is carried out at a temperature of 10 to 100 ° C, preferably from 20 to 90 ° C, more preferably from 30 to 80 ° C, and a pressure absolute of 0.3 to 8 bar, preferably from 0.5 to 6 bar, more preferably from 1 to 4 bar.

According to a preferred embodiment, the first stream obtained in step a) and the third stream obtained in step b) comprise at least one compound A selected from the group consisting of cis-2- dichloroethylene, trans-l, 2-dichloroethylene, cis-l-chloro-2-fluoroethylene, trans-l-chloro-2-fluoroethylene and 1,2-dichloro-l-fluoroethane. Preferably, the first stream obtained in step a) and the third stream obtained in step b) comprise at least two, three, four or all of the compounds A selected from the group consisting of cis-2 -dichloroethylene, trans-l, 2-dichloroethylene, cis-l-chloro-2-fluoroethylene, 1,2-dichloro-l-fluoroethane and trans-l-chloro-2-fluoroethylene.

Thus, the first stream obtained in step a) and the third stream obtained in step b) may include trans-l, 2-dichloroethylene or trans-l, 2-dichloroethylene and cis-l-chloro-2-fluoroethylene or trans-l, 2-dichloroethylene, cis-l-chloro-2-fluoroethylene and 1,2-dichloro-l-fluoroethane or trans-l, 2-dichloroethylene, cis-l-chloro-2-fluoroethylene, 1,2 dichloro-l-fluoroethane and cis-l, 2-dichloroethylene or trans-l, 2-dichloroethylene, cis-l-chloro-2-fluoroethylene, 1,2-dichloro-l-fluoroethane, cis-2-dichloroethylene and trans-l-chloro-2-fluoroethylene.

According to a preferred embodiment, the second stream comprising 1, 1,2-trichloroethane is recycled to step (i), preferably after purification thereof, in particular the purification is distillation at a temperature of 20 to 300 ° C, preferably from 50 to 250 ° C, more preferably from 75 to 200 ° C, in particular 100 to 170 ° C and at an absolute pressure of 0.3 to 8 bar, preferably 0.5 to 6 bar, more preferably from 1 to 4 bar.

According to a preferred embodiment, the step removes the residual hydrofluoric acid present in the first stream. Thus, step b) comprises a step of washing said first stream to form an intermediate stream B comprising l-chloro-2,2

difluoroethane and said at least one of A compounds selected from the group consisting of cis-l, 2-dichloroethylene, trans-l, 2-dichloroethylene, cis-l-chloro-2-fluoroethylene, trans-1-chloro-2 -fluoroethylene and 1,2-dichloro-l-fluoroethane and an intermediate stream comprising C hydrofluoric acid. The intermediate stream may include B-chloro-2,2-difluoroethane and at least at least two, three, four or all of the A compounds selected from the group consisting of cis-l, 2-dichloroethylene, trans- 2-dichloroethylene, cis-l-chloro-2-fluoroethylene, 1,2-dichloro-l-fluoroethane and trans-l-chloro-2-fluoroethylene. Preferably, the intermediate stream B, in addition to l-chloro-2,2-difluoroethane may include trans-l, 2-dichloroethylene or trans-l, 2-dichloroethylene and cis-l-chloro-2-fluoroethylene or trans l, 2-dichloroethylene, cis-l-chloro-2-fluoroethylene and 1,2-dichloro-l-fluoroethane or trans-l, 2-dichloroethylene, cis-l-chloro-2-fluoroethylene, 1,2-dichloro- l-fluoroethane and cis-l, 2-dichloroethylene or trans-l, 2-dichloroethylene, cis-l-chloro-2-fluoroethylene, 1,2-dichloro-l-fluoroethane, cis-2-dichloroethylene and trans- l-chloro-2-fluoroethylene.

Preferably, the washing step is carried out at a temperature of 0 to 30 ° C. Preferably, the washing step is carried out at an absolute pressure between 1 and 4 bar.

Preferably, said intermediate stream B is dried to form said third current. In particular, the drying is implemented at a temperature of 0 to 30 ° C. Preferably, the drying is implemented at an absolute pressure between 1 and 4 bar.

According to a particular embodiment, the first stream obtained in step a), the intermediate stream B and the third stream obtained in step b) include l-chloro-2,2-difluoroethane, trans-2- dichloroethylene and at least one of a compounds selected from the group consisting of cis-l, 2-dichloroethylene, cis-l-chloro-2-fluoroethylene, trans-l-chloro-2-fluoroethylene and 1,2-dichloro- l-fluoroethane. Preferably, the first stream obtained in step a), the intermediate stream B and the third stream obtained in step b) include l-chloro-2,2-difluoroethane, trans-l, 2-dichloroethylene and at least one, two, three or all of the compounds a selected from the group consisting of cis-l, 2-dichloroethylene, cis-l-chloro-2-fluoroethylene, 1,2-dichloro-l-fluoroethane and trans-l- chloro-2-fluoroethylene.

Preferably, the intermediate stream comprising C hydrofluoric acid may be recycled to step (i).

According to a preferred embodiment, the third stream obtained in step b) is purified in step c). It is preferably a distillation. Thus, step c) can be a distillation carried out at a temperature between 35 and 79 ° C, preferably at an absolute pressure between 1 and 4 bar.

As mentioned above, the third stream obtained in step b) comprises 1-chloro-2,2-difluoroethane, trans-l, 2-dichloroethylene and at least one compound A selected from the group consisting of cis -l, 2-dichloroethylene, cis-l-chloro-2-fluoroethylene, trans-l-chloro-2-fluoroethylene and 1,2-dichloro-l-fluoroethane. Thus, step c) of this method enables to form a fourth stream comprising l-chloro-2,2-difluoroethane and trans-l, 2-dichloroethylene and a fifth stream comprising at least one of A compound selected from group consisting of cis-l, 2-dichloroethylene, cis-1-chloro-2-fluoroethylene, trans-l-chloro-2-fluoroethylene and 1,2-dichloro-l-fluoroethane.

According to a preferred embodiment, the fifth stream may include at least one, two, three or all of the compounds A selected from the group consisting of cis-1,2-dichloroethylene, cis-l-chloro-2-fluoroethylene, 1,2-dichloro-l-fluoroethane and trans-1-chloro-2-fluoroethylene, if the third stream comprises at least one, two, three or all of the compounds a selected from the group consisting of cis-2 -dichloroethylene, cis-l-chloro-2-fluoroethylene, 1,2-dichloro-l-fluoroethane and trans-l-chloro-2-fluoroethylene, as mentioned above.

According to a particular embodiment, said first current obtained in step a), the intermediate stream B, the third stream obtained in step b) and / or the fourth stream are devoid of 1, 1-dichloroethylene. The absence of 1, 1-dichloroethylene in said first stream obtained in step a) and / or said intermediate current B, and / or said third current obtained in step b) and / or the fourth current is thus obtained by the present invention.

claims
1. A method of manufacture of l-chloro-2,2-difluoroethane from 1,1,2-trichloroethane comprising (i) at least one step in which 1,1,2-trichloroethane reacts with the hydrofluoric acid in the gas phase optionally in the presence of an oxidizing agent and in the presence or absence of a fluorination catalyst to give a stream comprising 1-chloro-2,2-difluoroethane, hydrochloric acid, hydrofluoric acid and at least one compound (s) chosen (s) among 1,2-dichloroethylenes (cis and trans), 1-chloro, 2-fluoroethylenes (cis and trans), the l, 2-dichloro -2-fluoroethane and unreacted 1,1,2-trichloroethane; (Ii) at least one step of separation of the compounds from the reaction step to give a first stream comprising hydrochloric acid and a second stream comprising hydrofluoric acid, l-chloro-2,2-difluoroethane, at least one compound (s) and unreacted 1,1,2-trichloroethane; (Iii) at least one step of separating the second stream to give an organic phase comprising l-chloro-2,2-difluoroethane, at least one compound (s) and unreacted 1,1,2-trichloroethane and inorganic phase comprising HF; (Iv) at least one step of separating the l-chloro-2,2-difluoroethane from the organic phase obtained in (iii); (V) optionally recycling to step (i) of the organic phase after separation of step (iv); and (vi) optionally recycling to step (i) of the inorganic phase from step (iii), characterized in that step (iv) comprises:

a) purification of the organic phase obtained in step (iii) to form a first stream comprising l-chloro-2,2-difluoroethane, at least one compound (s) and hydrofluoric acid and a second stream comprising 1,1,2-trichloroethane;

b) removing the hydrofluoric acid from said first stream to form a third stream comprising l-chloro-2,2-difluoroethane and at least one compound (s);

c) purification, preferably a distillation, said third stream comprising l-chloro-2,2-difluoroethane.

2. Method according to the preceding claim characterized in that step a) purification of the organic phase obtained in (iii) is a distillation, preferably carried out at a temperature between 30 and 80 ° C and a pressure absolute between 1 and 4 bar.

3. A method according to any preceding claim characterized in that the second stream comprising 1,1,2-trichloroethane is recycled to step (i), preferably after distillation thereof at a temperature between 100 and 170 ° C and at an absolute pressure between 1 and 4 bar absolute.

4. A method according to any preceding claim characterized in that step b) comprises a step of washing said first stream to form an intermediate stream

B comprising l-chloro-2,2-difluoroethane and said at least one compound A selected from the group consisting of cis-l, 2-dichloroethylene, trans-l, 2-dichloroethylene, cis-l-chloro-2 -fluoroethylene, trans-l-chloro-2-fluoroethylene and 1,2-dichloro-l-fluoroethane and an intermediate stream comprising C hydrofluoric acid.

5. Method according to the preceding claim characterized in that said intermediate stream B is dried to form said third current.

6. Method according to the preceding claim characterized in that drying is implemented at a temperature of 0 to 30 ° C and an absolute pressure between 1 and 4 bar.

7. A method according to any preceding claim characterized in that the first stream obtained in step a) and the third stream obtained in step b) also include trans-l, 2-dichloroethylene and optionally at least one of compounds A selected from the group consisting of cis-l, 2-dichloroethylene, cis-l-chloro-2-fluoroethylene, trans-l-chloro-2-fluoroethylene and 1,2-dichloro-l-fluoroethane.

8. A method according to any preceding claim characterized in that step c) comprises at least one distillation, preferably carried out preferably by distillation at a temperature between 35 and 79 ° C and at an absolute pressure between 1 and 4 bar.

9. A method according to any preceding claim characterized in that the first current obtained in step a), the intermediate stream B and / or the third stream obtained in step b) comprises the trans-2 -dichloroethylene and at least one compound a selected from the group consisting of cis-l, 2-dichloroethylene, cis-l-chloro-2-fluoroethylene, trans-l-chloro-2-fluoroethylene and 1,2-dichloro- -fluoréthane.

10. Method according to the preceding claim characterized in that step c) form a fourth stream comprising l-chloro-2,2-difluoroethane and trans-l, 2-dichloroethylene and a fifth stream comprising at least one compound A selected from the group consisting of cis-l, 2-dichloroethylene, cis-l-chloro-2-fluoroethylene, trans-l-chloro-2-fluoroethylene and 1,2-dichloro-l-fluoroethane.