Process for separation of a feedstock F by adsorption in a simulated moving bed in an SMB device that comprises a zone 1 for desorption of compounds produced by extraction, a zone 2 for desorption of compounds produced with a raffinate, a zone 3 for adsorption of compounds produced by extraction, and a zone 4 that is located between the draw-off of the raffinate and the supply of the desorbent,whereby the device comprises external bypass lines Li/i+1 directly joining two successive plates Pi, Pi+, that are equipped with non-automated means for adjusting flow rate and closing means, in which the degree of opening of the restriction means of the scavenging flow rate of the bypass lines Li/i+1 is adjusted so as to obtain the best performance of the SMB.