Conclusion and Outlook
The work described here demonstrates that, relative to traditional
random packing, the separation efficiency of oxygen from air in an MCD
column can be greatly enhanced by using a custom AMPH internal
structure. This enhanced efficiency results from the porous liquid
wicking structures present in the AMPH column itself, not to anything
unique to air separation. Accordingly, this approach can reasonably be
expected to improve efficiency in other types of distillation systems as
well. This enhanced efficiency is an enabling technology for small scale
air separations including the collection of xenon from the atmosphere.
AM allows internal structures to be constructed that are not available
via traditional manufacturing techniques. Future work in distillation
could continue to explore other structural changes to improve mass
transfer. Further, the improvement observed here suggests that AM could
be applied to other processes for similar improvement. For example, it
is possible that the efficiency and/or selectivity of an adsorption
process could be improved by controlling the microstructure of the
adsorbent via AM. Similarly, AM could be used to create heat exchangers
with internal flow structures that optimize heat transfer in ways not
heretofore possible.
The principles that allow the AMPH MCD column to improve separation
efficiency should scale up to larger distillation systems, but current
direct metal laser sintering equipment constrains the maximum part size
that can be fabricated. For example, the i3DMFGTM EOS®
M400.4 platform used in this work is a 40x40x40 cm cube, so the part
must fit within those dimensions. Also, in a distillation column the
fluid entering the column must be properly distributed across its entire
width. In columns with small widths—such as those tested in this
work—this is straightforward and requires no special design, but with
a larger device this would likely require a specialized header to
distribute uniform liquid flow to the wicking structures.