Subsequently, TS1 increases, followed by TD. At t = 42 min, the product draws are activated. In ). Time of feed introduction highlighted as dashed grey line; time of product draw activation highlighted as dotted grey line. If the feed is introduced before the reboiler is at boiling temperature for scenarios IIa and IIb (Fig. and Fig. ), the initial overshoot of TS1 and TS2 during the beginning of the start-up, before the side streams stabilize at their respective steady state values, is greatly reduced in relation to scenario I. The change in the side stream purities from the first to the second sampling is also reduced in relation to scenario I. For scenario IIa (Fig. ), TB increases slightly in the time between t = 25 to 65 min. This could be an indication that the amount of feed that is added before the vapor stream establishes is contaminating the reboiler mixture in the first case and this amount of light boiler is removed from the bottom in the mentioned period. The product purities of streams D, S1, and S2 change very slowly during the start-up process and obtain constant values after a time of approximately 210 to 220 min. For scenario IIb, TB is constant after around 20 min (Fig. ). The feed is introduced 4 min earlier than in scenario I and as a result, the pronounced kink in the evolution of TS2 disappears in this scenario, without leading to an increase in TB during this time like in scenario IIa. This means that the feed reaches the bottom of the column roughly at the same time as the vapor stream establishes, without causing a contamination of the reboiler. Despite a larger difference in the product purities of the side streams between the first and second sampling than in scenario IIa, the purities obtain constant values already after approximately 130 min in scenario IIb.