PNNL-13501 - Pacific Northwest National Laboratory

Here, we perform adsorption and desorption tests using a
standard zeolite 13X adsorbent (PQ Corporation, 180 to
212-µm sieve fraction) and a pure CO2 gas stream. To
evaluate performance, we compare measured working
capacities to those estimated from published CO2
isotherms. (a)
Feed
Gas
Feed Gas
Bypass
Feed
Gas
Adsorbent Bed
Cooling
Adsorbent Bed
Heating
Hot
Stream
Results and Accomplishments
Stripped
Gas
Cold
Stream
Concentrated
“Product” Gas
Figure 1. Schematic of the thermal swing adsorption process
during adsorption (upper) and desorption (lower) cycles
We designed a rapid thermal-swing microchannel
adsorber and successfully fabricated and tested a number
of these devices. The test devices incorporated only a
single adsorbent channel, although the design is suitable
for a multichannel unit that would be expected to have
comparable working capacity performance on a per mass
basis. The single adsorbent bed was integrated with heatexchange
channels to affect adsorption and desorption.
All-plastic (or all-metal) adsorbers incorporated plastic
(or stainless steel) in both the heat exchanger and the
adsorbent bed. The metal-plastic composite adsorber
(a) Isotherms provided by zeolite suppliers such as Zeochem ® .
incorporated a metal shim as a component of the heat
exchanger. The design of the all-metal heat exchangers
was somewhat different from those incorporating plastic
components, but the fluid channel thickness (0.010 inch)
was comparable. The plastic and metal shims used in the
adsorbers were fabricated using both conventional
machining and laser micromachining processes.
Channels in the relatively thick (0.05 to 0.06 inch)
adsorbent bed shims were machined using a CNC milling
machine. Except for the all-metal device, heat exchanger
shims were patterned using a Resonetics Maestro
Ultraviolet excimer laser machining station, which was
operated with a laser wavelength of 248 nm. Various
formulations of polyimide were used for all working
plastic components. Layers of the all-plastic and metalplastic
adsorbers were bonded together using a hightemperature
acrylic-laminating adhesive, and after
assembly, the units were compressed in a laboratory press
at ~5000 psi to seal all mating surfaces. Silicone (roomtemperature
vulcanizing rubber) was used to bond some
components of the all-metal adsorbers, while other
components were welded.
A test stand was assembled to control feed gas and heatexchange
fluid flow rates and to allow monitoring
adsorber and heat exchange fluid temperatures, pressure
drops, and evolved gas volumes. Type K surface mount
and immersion probe thermocouples were deployed in all
tests; in several tests, a type T hypodermic thermocouple
(Omega®) was embedded in the adsorbent bed to
measure the adsorbent temperature directly.
Temperatures were output and recorded each second to an
Omega data acquisition system on a personal computer.
The series of valves needed to switch between adsorption
and desorption cycles (Figure 1) were controlled
manually. (An upgrade to an electronically controlled
valve system is in progress.) Water, fed from separate
constant-temperature hot and cold reservoirs, was used as
the heat-exchange fluid. During desorption, gas was
evolved at essentially ambient pressure through a tube to
the head space of an inverted graduated cylinder which
was partially filled with water and whose opening was
submerged in a room-temperature water reservoir. The
water displaced from the cylinder provided the volume of
evolved gas. To monitor gas evolution as a function of
time, the water displacement from the cylinder was video
taped for subsequent evaluation. (Electronic mass flow
meters are available for incorporation in the next
generation system.) Ideal gas law assumptions were
applied to determine the equivalent mass of CO2 released
for comparison to the theoretical working capacity.
Micro/Nano Technology 343