As the reboiler is filled with the boiling feed mixture at the beginning of the start-up process, TB initially has a value of around 95 °C. Vapor is generated and the column gradually fills with ethanol, which can be discerned from the temperature of the whole column approaching the approximate boiling temperature of ethanol of 78 °C. As soon as the temperature profile inside the column is constant, the top product valve is opened at around 0.18 h and ethanol is withdrawn. As ethanol is removed from the top, n-propanol can move upwards. After around 4.3 h, an increase in the purity xS1 is noticeable. Simultaneously, the purity xD decreases. The first top product withdrawal is stopped at 4.6 h. Because the reboiler still contains ethanol, the remaining ethanol moves up in the column again and displaces the n-propanol at the upper side draw S1. xD returns to almost 100 mol%. TD, TS1, and TS2 stabilize at the approximate boiling temperature of ethanol of 77 °C. When the temperature profile inside the column is constant, the top product is withdrawn in three further analog steps. After the third product withdrawal, enough ethanol is removed from the column, that the n-propanol can reach the desired purity at S1. The lower part of the column fills with n-propanol and accordingly, TS1 and TS2 correspond to the approximate boiling temperature of n-propanol of 97 °C. When the temperature profile stabilizes, the n-propanol withdrawal at the upper side draw starts at 6.8 h. It follows the same principle as the ethanol withdrawal. In total, there are 10 steps of propanol withdrawal and after each step, more time is required to return to a constant temperature profile.