Figure 6. Sample measured data for the bottoms product of the AMPH column during steady state operation, with the partial pressure of each component shown as a function of time. The momentary drop in values at around 6 hours was the result of a temporary instrument failure.
In this plot the average partial pressures for oxygen and argon are 5.2⋅10‑4 and 1.3⋅10‑3 Pa, respectively, corresponding to mole fractions of 0.9975 and 0.0025. Apart from a momentary instrument failure shortly after the 6‑hour mark, the measurements showed little variation. For example, the standard deviation for the argon partial pressure over the final 4 hours is 1.3⋅10‑7 Pa. Adding one standard deviation in either direction of the mean gives an estimate of 0.0022 to 0.0027 for the argon mole fraction.
The plot also shows that the nitrogen partial pressure remained low throughout the process, indicating that virtually all the nitrogen in the feed was exiting in the overhead vapor. Values for other trace components in air (e.g., neon, krypton, and xenon) were measured as well, but their values all remained below those of nitrogen and are not shown here. To collect these trace components, the reboiler flow would need to be turned off to allow these noble gases to accumulate.
Comparable measurements for the PTL column showed an argon mole fraction of 0.0068 (± 0.0001), with just a small amount of nitrogen (0.0004 ± 10‑5). Measurements for the TRP column showed mole fractions of around 0.0090 for both argon and nitrogen.
Results for the three different simulation models are shown in Figure 7. These are sufficiently similar to allow a determination of the number of ideal stages equivalent for all three. Thus, the conclusions below are not dependent on a single simulator.