Oligomerization process implementing the recycling of the gas headspace

A process for the oligomerization of ethylene, carried out at a pressure of between 0.1 and 10 MPa, at a temperature of between 30 and 200° C., in a sequence of at least two gas/liquid reactors placed in series, said process comprising the following steps:

• a) a step of introducing a catalytic oligomerization system comprising at least one metal precursor, optionally at least one activating agent and optionally at least one additive into at least the first reactor of the sequence comprising a reaction chamber comprising a liquid phase in a lower zone and a gas phase in an upper zone,
• b) a step of introducing gaseous ethylene into the lower part of the reaction chamber of at least the first reactor of the sequence,
• c) for each reactor, a step of withdrawing a fraction of liquid phase from the lower part of the reaction chamber of the reactor, the liquid fraction being separated into two streams:
• a first stream corresponding to a first portion of the liquid fraction, termed main liquid fraction, which is sent to the cooling step c);
• a second stream corresponding to the second portion of the liquid fraction which constitutes the liquid feed of the reactor, located downstream in the sequence, unless the liquid fraction withdrawn is from the final reactor of the sequence, and for the final reactor of the sequence, the second stream corresponds to the effluent obtained at the end of the oligomerization process,
• d) a step of introducing said second portion of the liquid fraction withdrawn from the reactor located upstream into the reaction chamber of the reactor located downstream in the direction of flow,
• e) a step of cooling said main liquid fraction withdrawn from the reactor located upstream in step c) by passing said first portion of the liquid fraction into a heat exchanger in order to obtain a cooled liquid fraction,
• f) a step of introducing said liquid fraction cooled in step e) at the top of the reaction chamber of said reactor, steps a) to f) being carried out for each reactor of the sequence, and
• g) a step of recycling a gas fraction, withdrawn from the upper zone of the reaction chamber and introduced at the lower part of said reaction chamber into the liquid phase, said recycling step g) being carried out in at least the first reactor of the sequence.