A process for separating an extract component from a raffinate component contained in a feed mixture comprising the steps of:
- (a) maintaining a unidirectional fluid flow system through a series of separating units in which said components have differential rates of travel due to selective retardation or acceleration of each of said components in each of said units, each of said units having a fluid inlet and a fluid outlet;
- (b) continuously passing said feed mixture into one of said fluid inlets and a displacement fluid into another of said fluid inlets, said displacement fluid being capable of displacing said components from said separating units;
- (c) establishing within a system comprising said fluid flow system a component concentration distribution, zones of which comprise, sequentially, the highest purity displacement fluid (zone I), extract component diluted with displacement fluid (zone II), concentrated extract component (zone III), extract and raffinate component mixture with the extract component being the major component (zone IV), extract and raffinate component mixture with the raffinate component being the major component (zone V), concentrated raffinate component (zone VI), and raffinate component diluted with displacement fluid (zone VII), certain of said zones being combinable to obtain one or two of the pairs of zones II and III or III and IV, and V and VI or VI and VII, whereby each pair is considered as one continuous zone, each zone may comprise part of only one pair, each of said zones II, IV, V and VII having associated with it, unless paired with another zone, one of said fluid inlets and one of said fluid outlets, zone I having the fluid inlet for displacement fluid associated with it, and each of zones III and VI, or zone pairs II and III or III and IV, and zone pairs V and VI or VI and VII having associated with it a fluid outlet for a product effluent stream, said feed mixture being passed through a fluid inlet, the locus of which is at least proximate to the point on said component concentration distribution where the relative proportions of the extract and raffinate components are the same as that occurring in the feed mixture;
- (d) continuously withdrawing an extract stream comprising the entire flow from the fluid outlet of zone III or one of zone pairs II and III or III and IV, and continuously withdrawing a raffinate stream comprising the entire flow from the fluid outlet of zone VI or one of zone pairs V and VI or VI and VII;
- (e) continuously passing the entire stream from each of the fluid outlets of each of said zones II, IV, V and VII, if not combined with another zone, to a corresponding fluid inlet, the locuses of each said outlet and corresponding inlet beng within the same zone of said component concentration distribution;
- and,
- (f) periodically simultaneously effecting the following shifting of said inlets and outlets:
- the feed mixture fluid inlet to what prior to the shift was the inlet of zone V or zone VII if zones V and VI are combined, the inlet of zone V, if uncombined, to what had been the inlet of zone VII or zone I if zones VI and VII are combined, the inlet of zone VII, if uncombined, to what had been the inlet of zone I, the inlet of zone I to what had been the inlet of zone II or zone IV if zones II and III are combined, the inlet of zone II, if uncombined, to what had been the inlet of zone IV, or to what had been the feed mixture inlet if zones III and IV are combined, the inlet of zone IV, if uncombined, to what had been the feed mixture inlet, the outlet of zone II, if uncombined, to what had been the outlet of zone III, or zone pair III and IV, the outlet of zone III or zone pair II and III to what had been the outlet of zone IV, if uncombined, the outlet of zone IV or zone pair III and IV to what had been the outlet of zone V or zone pair V and VI, the outlet of zone V, if uncombined, to what had been the outlet of zone VI or zone pair VI and VII, and the outlet of zone VI or zone pair V and VI to what had been the outlet of zone VII, if uncombined, and the outlet of zone VII or zone pair VI and VII, to what had been the outlet of zone II or zone pair II and III, said shifting being effected prior to the progression through said units of said component concentration distribution to the extent that the composition of the inlet or outlet streams to or from any zone or zone pair becomes inconsistent with the desired composition of that zone or zone pair.