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.