A process for the production of middle distillates, comprising:
- subjecting a feed comprising olefins having 3 to 9 carbon atoms to catalytic oligomerization in a reaction section having a first position reactor and a second position reactor, wherein said reactors are positioned in series and can be permutated, each of said reactors containing at least one bed of oligomerization catalyst, said catalyst in each of said reactors being identical or different, wherein the second position reactor, which is the furthest downstream in the direction of movement of said feed, contains the catalyst with a period of service which is shorter than the period of service of the catalyst in the first position reactor and the second position reactor is operated at an average temperature, WBATn, which is lower than the average temperature, WBATn−1, of the first position reactor, the difference between WBATn and WBATn−1 being at least 35° C., WABTn−1−WABTn ≥35° C.,
- wherein in addition to said reaction section having said first position reactor and said second position reactor, a third reactor is provided in which the catalyst of said third reactor is being regenerated or replaced,
- wherein the reactors are used in a cyclic manner by:
- a step a) wherein the feed passes in succession through the first position reactor and the second position reactor,
- a step b) wherein the first position reactor, which has become deactivated, is short-circuited and the feed is introduced directly into the second position reactor, which has not been deactivated located immediately downstream of the first position reactor, whereby the second position reactor now becomes the new first position reactor, and said third reactor with fresh catalyst is connected downstream of the new first position reactor, whereby said third reactor with fresh catalyst becomes the second position reactor,
- a step b′), which is simultaneous with step b), during which said deactivated reactor becomes said third reactor and the catalyst of the deactivated reactor is regenerated or replaced,
- repeating steps a), b) and b′).