Abstract: A process of the operation of simulated moving bed is disclosed in which said bed is packed with a solid sorbent and provided with a plurality of pipes acting as a feed stock inlet, a desorbent inlet, a sorbed component outlet and a non-sorbed component outlet and the upstream end and the downstream end of the bed are interconnected to form a loop path, and a fluid containing the sorbed component and the non-sorbed component, and a desorbent are supplied to the bed and the sorbed component and the non-sorbed component separated are recovered. An improvement comprises the flow rate of the fluid is controlled on the basis of the concentration distribution of the sorbed and the non-sorbed components whereby the separated components are recovered in high purity and in constant composition.