Figure 1. Side-by-side
view of the three columns. (A) The traditional packed column with
Heli-Pack packing. (B) The plate-type layered (PTL) device alongside
sample layers of liquid wick and vapor shim. (C) The additively
manufactured porous honeycomb (AMPH) column.
All three columns were built with an active height of 25.4 cm and were
operated at 1 atm. Swagelok fittings and additional tubing were welded
to each column to provide a liquid inlet, an overhead vapor outlet, and
a bottoms liquid outlet. The oxygen-rich reboiler liquid was withdrawn,
and the composition determined using a residual gas analyzer. The
reboiler liquid level was maintained by monitoring the temperature at
different reboiler positions, and reboiler power was supplied via a 20 W
electrical heater attached to the outside or the reboiler.
Previous cryogenic experiments with PNNL MCD microwick devices were
conducted in an insulated cold box, with the required operating
temperatures maintained by periodically spraying liquid nitrogen inside
the box. This required significant quantities of liquid nitrogen; one
24‑hour experiment consumed multiple 180 L dewars. It also made
simultaneous control of both the cold box temperature and the condenser
duty difficult. To avoid these difficulties, in the present work each
distillation system was placed inside a vacuum can, which provides more
efficient insulation. A Stirling Cryocooler (SunPower CryoTel® GT) was
used as a cooling source, rather than liquid nitrogen.
Traditional Random Packing
(TRP)
The traditional packed column was a vertical cylinder with an inside
diameter of 1.09 cm. It was filled with stainless steel Heli‑Pak packing
distributed randomly. Liquid entered near the top of the column and
flowed downward through the packing. This TRP device is representative
of a typical small, packed column and served as a benchmark against
which to compare the other two columns.
Plate-Type Layering (PTL)
The PTL column was built in the shape of a rectangular prism, with inner
dimensions of 1.9 cm x 1.9 cm. It used an arrangement similar to that of
the previous PNNL microwick device; however, unlike previous PNNL
microwick experiments this device was operated in a vertical, as opposed
to horizontal, direction. Internally, it was configured with a specific
arrangement of three different types of materials: thicker vapor
channels (0.05 cm), thinner liquid wicks (0.01 cm), and fine screens
(~38 μm). The vapor channels and liquid wicks were
expanded metal screens, and the materials were layered as shown in
Figure 2, with each layer extending from the top to the bottom of the
column.