the head of column 7 i e regenerant from this perspective again the composition of the head of column 8 has not varied what varied during this second displacement are the compositions in columns 5 and 1 since raffinate was obtained at the foot of column 5 and extract at the foot of column 1 during this second displacement the water u201c buffer u201d was reformed between the two parts of the production regeneration process to avoid the contamination of different species in the third embodiment the displacement of the fronts is asynchronous since all of the entering fronts do not move synchronously with the exiting fronts in the example the entering fronts are first displaced then the exiting fronts are displaced but it is also possible to do the reverse in the third embodiment the subsequence without injection of the load corresponds to subsequence 1 3 or 2 3 depending on the considered sequence the number of columns in a displacement zone or in a zone corresponding to zones a b c and d is not necessarily constant it can be beneficial to vary the number of columns in each zone to take full advantage of each column for example it is possible to have a first set of columns in elution displacement columns whereof the number.