Results and Discussion
Before discussing the performance of the three devices, a few
observations are of note. First, previous PNNL MCD microwick
devices15, 16 had been operated in the horizontal
direction, with liquid flow manipulated via siphons. Balancing all
process parameters to achieve steady‑state operation with these devices
had required significant effort. Operating the PTL column vertically in
this work proved to be more straightforward, with no additional
equipment required to promote fluid flow. While this is an important
improvement, it does come at one cost: the flow rate at low flows cannot
be controlled as precisely as with the horizontal device. Where very low
flows are important, future work with AMPH columns could include both
horizontal structures to aid in separation efficiency and vertical
features to aid in operation, a sort of hybrid between gravity-driven
flow and capillary flow from wicking.
Second, the use of a vacuum can and a cryocooler—rather than a cold
box with liquid nitrogen—led to a significant reduction in both heat
losses and temperature fluctuations. This made the system more robust
and easier to operate than previous systems.
Separation efficiency
tests
Figure 6 shows a sample of the experimental results during separation
efficiency tests for the AMPH column. Note that the pressure values show
the partial pressures measured in the residual gas analyzer that
operates at vacuum conditions. These partial pressure measurements
provide information about the relative amount of each species exiting
the reboiler.