Process and device for improving the purity of a product in a simulated moving bed that comprises forced fluid recirculation

A process for chromatographic separation of a feedstock in a simulated moving bed device that comprises at least one column (1) that is filled with an adsorbent, whereby the column comprises a number of adsorbent beds (A1 to An), a fluid distributor plate (P.sub.i) between each bed, each distributor plate is divided into a number of sectors, each distributor plate sector comprises at least two distribution chambers (CH.sub.i, CH.sub.j) that are pierced with orifices (18) and a fluid circulation space (8) near said orifices of said chambers, whereby each chamber (CH.sub.i, CH.sub.j) of the plate is connected to a transfer line (LT.sub.i, LT.sub.j) that extends between said chamber and a point that is located outside of the column;

• during at least a fraction of a period T of the cycle and on at least one of the plates of the column are carried out injection of the feedstock, draw-off of a raffinate, injection of desorbent, and draw-off of an extract into and from a distribution chamber, characterized in that a volume of the fluid that circulates in the column is circulated at a suitable flow rate in a bypass line (L.sub.i,j) that connects all of chambers CH.sub.j of distributor plate P.sub.i toward all of chambers CH.sub.i of this same distributor plate, for at least a fraction of period T of the cycle and on at least one of the plates of the column, whereby the flow rate of fluid that circulates in the bypass line is at least equal to the volume of all of chambers CH.sub.i and CH.sub.j of the distributor plate and lines that comprise the bypass line via which the transfer of fluid is carried out, divided by said fraction of the period of the cycle.