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

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

• a) a step of converting ethanol into acetaldehyde, to produce an ethanol/acetaldehyde effluent, wherein the step of converting ethanol into acetaldehyde is carried out in at least one reaction section (A) fed with a stream comprising the ethanol and operated in the presence of a catalyst (Ca);
• b) a butadiene producing step carried out in at least one reaction-regenerative section in which are simultaneously performed a reaction step and a regeneration step in (n+n/2) fixed-bed reactors, n being an integer equal to 2 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 half of the catalytic cycle time of said catalyst (Cb), said reaction-regenerative section comprising a regeneration loop for inert gas and at least one regeneration loop for a gas stream comprising oxygen, and so that, at each instant:
• b1) said reaction step is operated in n of said fixed-bed reactors, n being as defined above, fed at least with a fraction of said ethanol/acetaldehyde effluent obtained from step a), at a temperature of between 300 and 400° C., at a pressure of between 0.1 and 1.0 MPa, for a time equal to the catalytic cycle time of said catalyst (b), to produce a reaction effluent comprising butadiene, 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 between 300 and 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 between 300 and 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 between 390 and 550° C.;
• and then
• iv) a final stripping phase operated at a temperature of between 550° C. and 300° C., under a stream of said inert gas.