There are 18 commutations between different types of control. An interesting fact is that with time, zero arcs become longer, whereas the final one becomes the greatest of all existing arcs. In Table , it is noted that the tray hold-up is set at 0.1 mol, however, the influence of this parameter will be examined by changing it to 0.05. Fig 2a . presents the optimal control pattern for the column functioning with double decreased hold-up on all trays. Same as for the previous case, the optimal trajectory starts with the initial bang arc but is followed by two consecutive singular arcs, concatenated to the second bang arc. It is noticed, that both previously mentioned bang arcs are from extremely short duration, and that described part takes 12.5% of the total batch time. One can perceive that the control pattern has been changed: there are no more chattering arcs, but in the place of the second succession of the chattering arcs, after the zero arc, there exists a succession of "quazi-bang" arcs. The latter are from very short durations and reach not the allowable maximum but 55.55% to 90.90% of it, hereby, there are 14 switchings between different types of control. The rest of the optimal control trajectory follows the same pattern as in the previous case since it is composed of bang and zero arcs only, whereas there are eight bang/zero arcs, resp., with time they both are likely to last longer with time. Unfortunately, the influence of the double decrease of tray hold-up also affects the recovery rate, as it brings 88.02%, ie. less than 10% compared to the previous case, for the same total batch time (3.2