Method for the simulated moving bed (SMB) separation of a feedstock (F), in which: at least one zone (1, 2, 3, 4) contains fewer than three beds, if the stream (D, E, F, R) delimiting said zone and situated upstream of said zone is injected or withdrawn at the plate P.sub.i via the bypass line L.sub.i/i+1, then the stream delimiting said zone and situated downstream of said zone is injected/withdrawn at the plate P.sub.j via the bypass line L.sub.j/j+1, and if the stream delimiting said zone and situated downstream of said zone is injected or withdrawn at the plate P.sub.i via the bypass line L.sub.i−1/i, then the stream delimiting said zone and situated upstream of said zone is injected/withdrawn at the plate P.sub.j via the bypass line L.sub.j−1/j.

Method for the simulated moving bed (SMB) separation of a feedstock (F), in which: at least one zone (1, 2, 3, 4) contains fewer than three beds, if the stream (D, E, F, R) delimiting said zone and situated upstream of said zone is injected or withdrawn at the plate P.sub.i via the bypass line L.sub.i/i+1, then the stream delimiting said zone and situated downstream of said zone is injected/withdrawn at the plate P.sub.j via the bypass line L.sub.j/j+1, and if the stream delimiting said zone and situated downstream of said zone is injected or withdrawn at the plate P.sub.i via the bypass line L.sub.i1/i, then the stream delimiting said zone and situated upstream of said zone is injected/withdrawn at the plate P.sub.j via the bypass line L.sub.j1/j.

Method for the simulated moving bed separation of a feedstock (F), in which when a fluid/effluent (feedstock F, desorbent D, extract E, raffinate R) is injected/withdrawn into/from a chosen plate (P.sub.i) using an external bypass line (L.sub.i1/i, L.sub.i+1/i) connected to said chosen plate (P.sub.i), the flow rate within the said external bypass line (L.sub.i1/i, L.sub.i+1/i) is controlled in such a way that: a major proportion of the fluid/effluent (F, D, E, R) is injected/withdrawn into/from the chosen plate (P.sub.i); and a minor proportion of the fluid/effluent (F, D, E, R) is injected/withdrawn into/from the adjacent plate (P.sub.i1, P.sub.i+1) connected to the said external bypass line (L.sub.i1/i, L.sub.i+1/i).