Simulated moving bed chromatographic separation

DETAILED DESCRIPTION What is claimed is: 1.
In a method for the separation of an extract component from a raffinate component contained in a fluid feed stream in a simulated moving bed chromatographic separation train having a plurality of serially connected sorbent containing beds and means for recycling fluid through said train, wherein single extract and raffinate concentration profiles are established across the entire train which advance downstream in said train in the direction of recycle flow in response to the rate of recycle flow, wherein there are means for introducing or withdrawing fluid streams at spaced points along the train, wherein the feed stream is introduced into the train at a feed point, a raffinate rich stream is withdrawn at a second point downstream of said feed point, a desorbent stream is introduced at a third point downstream of said second point and an extract rich stream is withdrawn at a fourth point downstream of said third point, and wherein the points of introduction and withdrawal of said streams are periodically shifted downstream of said train in the direction of recycle flow in a series of timed steps in response to the downstream advancement of said concentration profiles within said train, the improvement which comprises: continuously recycling fluid through all of the sorbent beds in the train, dividing each of the timed steps into an active period and a rest period, introducing the feed and desorbent streams and withdrawing the raffinate and extract streams throughout the active period of each step, and ceasing the introduction and withdrawal of said streams throughout the rest period of each step.
2.
A method in accordance with claim 1 wherein the feed stream is introduced adjacent the point of maximum total concentration of extract and raffinate components.
3.
A method in accordance with claim 1 wherein the desorbent stream is introduced adjacent the point of minimum total concentration of extract and raffinate components.
4.
A method in accordance with claim 1 wherein during the rest period of each step, the feed stream and the desorbent stream are introduced into and a raffinate rich stream and an extract rich stream are withdrawn from a second separation train