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.