Simulated moving bed separation method and device with bypass fluid flow

Method for the simulated moving bed separation of a feedstock (F) in a simulated moving bed separation device,

• the device comprising:
• at least one column comprising a plurality of beds of adsorbent (Ai) which are separated by plates (Pi) each comprising a distribution/extraction system;
• and
• external bypass lines (Li/i+1) directly joining two successive plates (Pi, Pi+1), each external bypass line comprising fluid (F, D) feed points and effluent (E, R) withdrawal points,
• in which method:
• the at least one column is fed with the feedstock (F) and a desorbent (D) and at least one extract (E) and at least one raffinate (R) is withdrawn from the at least one column, the feed and withdrawal points being shifted during the course of time by an amount corresponding to one adsorbent bed with a changeover period (ST) and determining a plurality of operating zones of the device, and notably the following main zones:
• a zone 1 for the desorption of the compounds from the extract, this zone being comprised between the feed for the desorbent (D) and the withdrawal of the extract (E),
• a zone 2 for the desorption of the compounds from the raffinate, this zone being comprised between the withdrawal of the extract (E) and the feed for the feedstock (F),
• a zone 3 for the adsorption of the compounds from the extract, this zone being comprised between the feed for the feedstock (F) and the withdrawal of the raffinate (R), and
• a zone 4 situated between the withdrawal of the raffinate (R) and the feed for the desorbent (D);
• when a fluid (F, D) is injected towards a chosen plate (Pi) via an external bypass line (Li−1/i, Li/i+1) connected to the said chosen plate (Pi), the flow rate within the said external bypass line (Li−1/i, Li/i+1) is controlled in such a way that a major proportion of the fluid (F, D) is injected towards the chosen plate (Pi), and that a minor proportion of the fluid (F, D) is injected towards the adjacent plate (Pi−1, Pi+1) connected to the said external bypass line (Li−1/i, Li/i+1);
• and/or
• when an effluent (E, R) is withdrawn from a chosen plate (Pi) via an external bypass line (Li−1/i, Li/i+1) connected to the said chosen plate (Pi), the flow rate within the said external bypass line (Li−1/i, Li/i+1) is controlled in such a way that a major proportion of the effluent (E, R) is withdrawn from the chosen plate (Pi), and that a minor proportion of the effluent (E, R) is withdrawn from the adjacent plate (Pi−1, Pi+1) connected to the said external bypass line (Li−1/i, Li/i+l).