Method for oligomerisation in a reactor comprising variable-diameter zones, including a step of recycling a pre-cooled solvent

Process for the oligomerization of an olefinic feedstock, comprising:

• a) a step of oligomerization of the olefinic feedstock, carried out at a temperature of between 30° C. and 200° C. and a pressure of between 0.1 and 10 MPa, in the presence of a homogeneous catalytic oligomerization system and of a solvent, in a reaction section comprising:
• an oligomerization reactor with zones of variable diameter and comprising a liquid phase, and
• at least one recirculation loop allowing the cooling of at least a part of a liquid-phase fraction to a temperature Tloop,
• b) a step of separating a reaction effluent resulting from the oligomerization step a), in a separation section so as to obtain a solvent fraction,
• c) a step of cooling the solvent fraction resulting from step b) to a temperature below the temperature Tloop to which the liquid-phase fraction is cooled in the recirculation loop(s),
• d) a step of introducing, into the reaction section of the oligomerization step a), the cooled solvent fraction resulting from step c).