For the major species, the reactions in this system are slow compared with the flows, so the reactions do not significantly affect their concentrations. Although the O 2 concentration is much smaller than some major species, its steady-state concentrations in each tray are majorly determined by the relatively fast flow, including O 2 evaporation, and are not significantly affected by reactions. : Temperature (a), major species concentrations in the bulk tray liquid (b) and tray overhead vapor (c), the residence time of the bulk tray liquid (d) and the tray overhead vapor (e), and oxygen concentration in the bulk tray liquid (f) and tray overhead vapor (g) at different locations in the debutanizer as computed using Aspen Plus. Tray 1 refers to the condenser, tray 40 refers to the reboiler, and tray 20 is the feed tray. The residence time of the liquid/overhead vapor is calculated as the liquid/vapor phase volume divided by the liquid/vapor outlet flowrate. The residence time of liquid in the reboiler is calculated using the inlet liquid flowrate, and the residence time of vapor in the condenser is calculated using the inlet vapor flowrate.