Method for the production and purification of 2,3,3,3-tetrafluoropropene

1. A process for the production and purification of 2,3,3,3-tetrafluoropropene (HFO-1234yf) carried out starting from a starting composition comprising at least one compound of formula (I) CH (n+2) (X) m —CH p (X) (n+1) —CX (3+p−m) , where X independently represents F or Cl; n, m and p are, independently of one another, 0 or 1 with n+m=0 or 1, n+p=0 or 1 and m−p=0 or 1, at least one X being Cl; said process comprising the stages of:

a) bringing the starting composition into contact, in the presence of a catalyst, with HF under conditions effective in producing a composition A comprising HCl, a part of the unreacted HF, 2,3,3,3-tetrafluoropropene (HFO-1234yf), intermediate products B comprising 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf), 1,1,1,2,2-pentafluoropropane (HFC-245cb) and trans-1,3,3,3-tetrafluoro-1-propene (HFO-1234zeE) and byproducts C comprising trans-1-chloro-3,3,3-trifluoro-1-propene (HCFO-1233zdE), cis-1-chloro-3,3,3-trifluoro-1-propene (HCFO-1233zdZ), cis-1,3,3,3-tetrafluoro-1-propene (HFO-1234zeZ), 1,1,1,3,3-pentafluoropropane (HFC-245fa), 2-chloro-1,1,1,3,3-pentafluoropropane (HCFC-235da), 1,2-dichloro-3,3,3-trifluoropropene (HCFO-1223xd), 2-chloro-1,3,3,3-tetrafluoropropene (HCFO-1224xe), 1,1,1,3,3,3-hexafluoropropane (HFC-236fa) and optionally one or more compounds of formula (II) C n H x F y Cl z in which n=4, 5 or 6, x is an integer from 0 to 6, y is an integer from 4 to 12, z is an integer from 0 to 6, with 2n=x+y+z if w is 1 or 2n−2=x+y+z if w is 2 or 2n+2=x+y+z if w is 0, w being the number of unsaturations in the compound of formula (II) considered;

b) recovering and purifying said composition A in order to form and recover a gas stream G1 comprising HCl, 2,3,3,3-tetrafluoropropene (HFO-1234yf), a part of the unreacted HF, a part of the intermediate products B and a part of the byproducts C; and a stream, which is liquid, L1 comprising a part of the unreacted HF, a part of the intermediate products B and a part of the byproducts C;

wherein said gas stream G1 is purified by the following stages:

b1) distilling the gas stream G1 in order to recover a stream G1a comprising HCl and a stream G1b comprising 2,3,3,3-tetrafluoropropene (HFO-1234yf), a part of the unreacted HF, said a part of the intermediate products B and said a part of the byproducts C;

b2-1) distilling said stream G1b obtained in stage b1) under conditions effective in forming a gas stream G1c comprising 2,3,3,3-tetrafluoropropene (HFO-1234yf), a portion of said part of said unreacted HF, a portion of said part of the intermediate products B and a liquid stream G1d comprising a portion of said part of the intermediate products B and said part of the byproducts C and a portion of said part of said unreacted HF; and

b2-2) distilling said stream G1d obtained in stage b2-1) under conditions effective in forming a stream G1d′ comprising said portion of said part of the intermediate products B, said portion of said part of said unreacted HF and a portion of said part of the byproducts C comprising cis-1,3,3,3-tetrafluoro-1-propene (HFO-1234zeZ), 1,1,1,3,3,3-hexafluoropropane (HFC-236fa) and a part of trans-1-chloro-3,3,3-trifluoro-1-propene (HCFO-1233zdE) and 1,1,1,3,3-pentafluoropropane (HFC-245fa); and a stream G1d″ comprising a portion of said part of the byproducts C comprising cis-1-chloro-3,3,3-trifluoro-1-propene (HCFO-1233zdZ), 2-chloro-1,1,1,3,3-pentafluoropropane (HCFC-235da), 1,2-dichloro-3,3,3-trifluoropropene (HCFO-1223xd), 2-chloro-1,3,3,3-tetrafluoropropene (HCFO-1224xe), and optionally one or more compounds of formula (II) C n H x F y Cl z in which n=4, 5 or 6, x is an integer from 0 to 6, y is an integer from 4 to 12, z is an integer from 0 to 6, with 2n=x+y+z if w is 1 or 2n−2=x+y+z if w is 2 or 2n+2=x+y+z if w is 0, w being the number of unsaturations in the compound of formula (II) considered.

2. The process as claimed in claim 1 , wherein at least 90% of the 1,1,1,2,2-pentafluoropropane and of the trans-1,3,3,3-tetrafluoropropene contained in the stream G1d are recovered in the stream G1d′.

3. The process as claimed in claim 1 , wherein the stream G1d′ comprises from 60% to 70% by weight of 1,1,1,2,2-pentafluoropropane, from 1% to 5% by weight of trans-1,3,3,3-tetrafluoropropene and from 10% to 15% by weight of 2-chloro-3,3,3-trifluoropropene, based on the total weight of the stream G1d′.

4. The process as claimed in claim 1 , wherein at least 85% of the cis-1,3,3,3-tetrafluoro-1-propene (HFO-1234zeZ) and of the 1,1,1,3,3,3-hexafluoropropane (HFC-236fa) contained in the stream G1d are recovered in the stream G1d′.

5. The process as claimed in claim 1 , wherein the stream G1d′ comprises from 0.1% to 0.5% by weight of cis-1,3,3,3-tetrafluoro-1-propene (HFO-1234zeZ), from 1.0% to 5.0% by weight of 1,1,1,3,3,3-hexafluoropropane (HFC-236fa), from 0.5% to 2.0% by weight of trans-1-chloro-3,3,3-trifluoro-1-propene (HCFO-1233zdE) and from 0.1% to 1.0% by weight of 1,1,1,3,3-pentafluoropropane (HFC-245fa), based on the total weight of the stream G1d′.

6. The process as claimed in claim 5 , wherein the stream G1d′ further comprises 2-chloro-1,1,1,3,3-pentafluoropropane (HCFC-235da), 1,2-dichloro-3,3,3-trifluoropropene (HCFO-1223xd) and 2-chloro-1,3,3,3-tetrafluoropropene (HCFO-1224xe) in a total content of less than 5% by weight, based on the total weight of G1d′.

7. The process as claimed in claim 1 , wherein the stream G1d′ is recycled in stage a).

8. The process as claimed in claim 1 , further comprising the stages:

b3) bringing the stream G1c into contact with an aqueous hydrofluoric acid solution with a concentration of greater than 40% in order to form a two-phase stream G1c′ comprising 2,3,3,3-tetrafluoropropene (HFO-1234yf), hydrofluoric acid, a portion of said part of the intermediate products B and a portion of said part of the byproducts C,

b4) storing said two-phase stream G1c′ in a holding tank, said second two-phase stream comprising a liquid phase and a gas phase,

b5) passing the gas phase of said stream G1c′ into an absorption column fed countercurrentwise with an aqueous flow in order to form a stream G1c″ comprising 2,3,3,3-tetrafluoropropene (HFO-1234yf), a portion of said part of the intermediate products B and a portion of said part of the byproducts C and a stream G1c′″ comprising HF;

and optionally the stages:

b6) neutralizing said stream G1c″ obtained in stage b5) with an aqueous alkaline solution in order to form a neutralized stream, and

b7) drying said neutralized stream obtained in stage b6) in order to form a neutralized and dried stream G1c″″.

9. The process as claimed in claim 8 , wherein the aqueous hydrofluoric acid solution used in stage b3) is at a temperature of between 0 and 30° C. before it is brought into contact with the stream G1c.

10. The process as claimed in claim 8 , wherein the process comprises a stage c), subsequent to stage b5) or to stage b7), in which the stream G1c″ obtained in stage b5) or the stream G1c″″ obtained in stage b7) comprises 2,3,3,3-tetrafluoropropene (HFO-1234yf), 1,1,1,2,2-pentafluoropropane (HFC-245cb) and trans-1,3,3,3-tetrafluoro-1-propene (HFO-1234zeE); and said stream G1c″ or G1c″″ is distilled in order to form a stream G1e′ comprising 2,3,3,3-tetrafluoropropene (HFO-1234yf) and 1,1,1,2,2-pentafluoropropane (HFC-245cb) and a stream G1h′ comprising trans-1,3,3,3-tetrafluoro-1-propene (HFO-1234zeE).

11. The process as claimed in claim 1 , wherein said liquid stream L1 comprises a part of the intermediate products B and all or part of the byproducts C, and a part of the liquid stream L1 is brought to low temperature, in order to form a first phase L1a comprising a part of the unreacted HF and a second phase L1b comprising said intermediate products B and said byproducts C; optionally, said stream G1d formed in stage b2) is mixed with the liquid stream L1 before the latter is brought to low temperature.

12. The process of claim 10 , wherein the stream G1c″ or G1c″″ is distilled by extractive distillation.

13. The process of claim 12 , wherein the stream G1c″ or G1c″″ is distilled by extractive distillation by the stages:

c1′) bringing said stream G1c″ or G1c″″ into contact with an organic extraction agent in order to form a stream G1g′, and

c2′) extractive distillation of the stream G1g′ in order to form the flow G1e′ comprising 2,3,3,3-tetrafluoropropene (HFO-1234yf) and 1,1,1,2,2-pentafluoropropane (HFC-245cb), and the stream G1h′ comprising trans-1,3,3,3-tetrafluoro-1-propene (HFO-1234zeE) and said organic extraction agent.

14. The process of claim 11 , wherein said second phase L1b is distilled in order to recover a stream L1c comprising 1,1,1,2,2-pentafluoropropane (HFC-245cb) and trans-1,3,3,3-tetrafluoro-1-propene (HFO-1234zeE), and a stream L1d comprising 2-chloro-3,3,3-trifluoro-1-propene (HCFO-1233xf), E-1-chloro-3,3,3-trifluoro-1-propene (HCFO-1233zdE) and 1,1,1,3,3-pentafluoropropane (HFC-245fa), and said stream L1c is recycled in stage a).

15. The process of claim 14 , wherein said stream L1d is separated by extractive distillation in order to form a flow comprising 2-chloro-3,3,3-trifluoro-1-propene (HCFO-1233xf) and a stream comprising E-1-chloro-3,3,3-trifluoro-1-propene (HCFO-1233zdE) and 1,1,1,3,3-pentafluoropropane (HFC-245fa).