Method for producing butadiene from ethanol with optimised in situ regeneration of the catalyst of the second reaction step

1. A process for producing butadiene from ethanol, comprising at least the following steps:

a) a step of converting ethanol into an effluent comprising ethanol and acetaldehyde, comprising at least one reaction section (A) fed with a stream comprising ethanol and operated in the presence of a catalyst (Ca) at a temperature of between 200 and 500° C., and at a pressure of between 0.1 and 1.0 MPa;

b) a butadiene conversion step comprising at least one reaction-regeneration section in which simultaneously implemented are a reaction step and a regeneration step in (n+n/2) fixed-bed reactors, n being an integer equal to 4 or a multiple thereof, said (n+n/2) fixed-bed reactors each comprising at least one fixed bed of a catalyst (Cb), said (n+n/2) fixed-bed reactors functioning in parallel and in sequence so that said reaction step starts in each of said reactors with a time shift equal to a quarter of the catalytic cycle time of said catalyst (Cb), said reaction-regeneration section comprising three regeneration loops, and wherein, at a given moment:

b1) said reaction step is operated in n of said fixed-bed reactors, n being an integer equal to 4 or a multiple thereof, fed at least with a fraction of said effluent obtained from step a), at a temperature of 300 to 400° C., at a pressure of between 0.1 and 1.0 MPa, and for a time equal to the catalytic cycle time of said catalyst (Cb), to produce a reaction effluent, and

b2) said regeneration step is operated in n/ 2 of said fixed-bed reactors for a total time equal to half of the catalytic cycle time of said catalyst (Cb), and comprises the following four successive phases:

i. a stripping phase operated at a temperature of 300 to 400° C., under a stream of inert gas, said phase i) starting on conclusion of the reaction step b1); and then

ii. a first combustion phase operated on conclusion of phase i) under a gas stream comprising said inert gas and oxygen in a content of less than or equal to 1 vol % relative to the total volume of said gas stream, at a temperature of 300 to 450° C.; and then

iii. a second combustion phase operated on conclusion of the first combustion phase ii) under a gas stream comprising said inert gas and oxygen in a content of greater than or equal to 2 vol % relative to the total volume of said gas stream, at a temperature of 390 to 550° C.; and then

iv. a final stripping phase operated at a temperature of 300° C. to 550° C., under a stream of said inert gas;

said three regeneration loops of said reaction-regeneration section comprising a regeneration loop for the inert gas of the stripping phases i) and iv), a regeneration loop for the gas stream of the first combustion phase ii) and a regeneration loop for the gas stream of the second combustion phase iii).

2. The process as claimed in claim 1 , wherein the reaction section of step a) is operated at a temperature of 250° C. to 300° C., and at a pressure of 0.1 to 0.5 MPa.

3. The process as claimed in claim 1 , wherein said fixed-bed reactors in said reaction step b1) are further fed with a supply of ethanol and/or a supply of acetaldehyde, and wherein a mole ratio of ethanol to acetaldehyde in said reaction step b1) is 1 to 5.

4. The process as claimed in claim 1 , wherein the integer n is equal to 4.

5. The process as claimed in claim 1 , wherein said reaction step b1) is operated at a temperature of 300 to 360° C.

6. The process as claimed in claim 1 , wherein said reaction step b1) is operated at a pressure of 0.2 to 0.4 MPa.

7. The process as claimed in claim 1 , wherein the catalytic cycle time of said catalyst (Cb) for the butadiene conversion step b) is greater than or equal to 1 day, and less than or equal to 20 days.

8. The process as claimed in claim 1 , wherein the inert gas of the regeneration step b2) is nitrogen, carbon dioxide (CO 2 ) or a mixture thereof.

9. The process as claimed in claim 1 , wherein said stripping phase i) is operated at a temperature of 330 to 370° C.

10. The process as claimed in claim 1 , wherein a flow rate of inert gas of said stripping phase i) is 0.5 to 1.5 Nm 3 /h/kg of catalyst.

11. The process as claimed in claim 1 , wherein the oxygen content of said first combustion phase ii) is 0.1 to 1 vol %.

12. The process as claimed in claim 1 , wherein said first combustion phase ii) is operated at a temperature of 330 to 430° C.

13. The process as claimed in claim 1 , wherein said first combustion phase ii) is operated at a flow rate of gas stream of 1.7 to 2.5 Nm 3 /h/kg of catalyst.

14. The process as claimed in claim 1 , wherein the oxygen content of said second combustion phase iii) is 2 to 20 vol %.

15. The process as claimed in claim 1 , wherein said second combustion phase iii) is operated at a constant temperature of 390 to 430° C. followed by a temperature increase ramp of 10 to 30° C/h and then a phase at a constant temperature of 460 to 510° C.

16. The process as claimed in claim 1 , wherein said second combustion phase iii) is operated at a flow rate of gas stream of 1.2 to 1.8 Nm 3 /h/kg of catalyst.

17. The process as claimed in claim 1 , wherein said final stripping phase iv) is operated on a temperature decrease ramp of 50 to 150° C/h followed by a phase at a constant temperature of 300 to 400° C.

18. The process as claimed in claim 1 , wherein said final stripping phase iv) is operated under a stream of said inert gas, at a flow rate of 0.5 to 1.5 Nm 3 /h/kg of catalyst.

19. The process as claimed in claim 1 , wherein the inert gas of the regeneration step b2) is nitrogen.

20. The process as claimed in claim 1 , wherein said first combustion phase ii) is operated at a constant temperature of 330 to 370° C. followed by a temperature increase ramp of 10 to 30° C/h and then a phase at a constant temperature of 390 to 430° C.