Process for the selective hydrogenation of olefinic feeds with a single principal reactor and a guard reactor of reduced size

A process for the selective hydrogenation of a feed of hydrocarbons containing polyunsaturated molecules comprising at least 3 carbon atoms, in which said feed and a gaseous phase comprising hydrogen are passed, under hydrogenation conditions, over a hydrogenation catalyst in a single principal fixed bed reactor containing at least two catalytic beds and a fixed bed guard reactor which is smaller in size containing at least one catalytic bed, said reactors being disposed in series for use in a cyclic manner by repeating the steps a), b), c), c′), d) and d′) defined below in succession:

• a step a), during which the feed passes in succession through all of the catalytic beds of the principal reactor,
• when the first catalytic bed of the principal reactor starts to become deactivated, a step b), during which the feed is introduced into the guard reactor then, by short-circuiting the first partially deactivated catalytic bed of the principal reactor, into the next non-deactivated catalytic bed of said principal reactor located immediately downstream with respect to the direction of movement of the feed,
• a step c), during which the feed passes uniquely and successively through all of the catalytic beds of the principal reactor,
• a step c′), simultaneously with step c), during which the deactivated catalyst of the catalytic bed or beds of the guard reactor is regenerated and/or replaced with fresh catalyst,
• a step d), during which the feed only passes through the guard reactor,
• a step d′), simultaneously with step d), during which the deactivated catalyst of the at least two catalytic beds of the principal reactor is regenerated and/or replaced with fresh catalyst.