(359c) Amine-Functionalized MIL-101 Monoliths for CO2 Removal from Enclosed Environments

Lawson, S., Missouri University of Science and Technology
Griffin, C., Missouri University of Science and Technology
Rapp, K., Missouri University of Science and Technology
Rownaghi, A., University of Missouri S&T
Rezaei, F., Missouri University of Science and Technology

MIL-101 Monoliths for CO2 Removal from Enclosed Environments


Lawson, Connor Griffin, Kambria Rapp, Ali A. Rownaghi, Fateme Rezaei*

font-family:" times new roman> 

line-height:normal">Department of Chemical & Biochemical
Engineering, Missouri University of Science and Technology, Rolla, MO 65409-1230,
United States


line-height:107%;font-family:" times new roman>Abstract

line-height:107%;font-family:" times new roman>            I " times new roman>ncreasing CO2 concentrations from 400 to
2500 ppm decreases cognitive test scores from the 85th to the 25th
percentile. In high-risk environments, such as space craft or submarines, this diminished
cognitive functioning could have life-threatening ramifications. One way to
reduce these levels is by using an amine incorporated solid adsorbent.
Amino-solids are particularly effective sorbents for enclosed applications because
of their high CO2/N2 selectivity value at dilute
concentrations. Although these materials can reduce enclosed CO concentrations
to safe levels, amino-solid powders should be formed into structured contactors
to eliminate particulate scattering and equipment contamination. In our earlier
works, " times new roman>1–4 12.0pt;line-height:107%;font-family:" times new roman> we
demonstrated that 3D-printing is a facile approach to formulate structured
monolithic contactors for adsorption applications. Monoliths were produced with
a variety of supports, including aminosilica, zeolites, and metal-organic
frameworks (MOFs), and exhibited high CO2 adsorption capacities
under many conditions.  Using the techniques culminated previously, we have recently
formulated 3D-printed, amino-MIL-101 monoliths, for selective CO2
adsorption from enclosed environments. In this work, 5 a tailored
version of MIL-101 was impregnated with 85 wt. % Tetraethylenepentamine (TEPA)
and polyethyleneimine (PEI-800) to form the powder precursors. The powders were
then formed into pastes and printed into monoliths. Pristine MIL-101 monoliths
were also printed and secondarily impregnated for comparison. From CHN
measurements, the pre-impregnated TEPA and PEI monoliths contained 3.5 and 5.5
mmol N/g amine content, respectively. Over five adsorption/desorption cycles,
this corresponded to average adsorption capacities of 1.6 and 1.4 mmol/g,
respectively, at 3000 ppm CO2 concentration.  The post-impregnated
monoliths contained ~50 wt.% less amine content; leading to 0.3 and 0.6 mmol/g
CO2 adsorption capacities, for TEPA and PEI, respectively. The
adsorbent stabilities were also examined. PEI’s low volatility led to
exceptional stability throughout the five cycles for all materials while the
TEPA-impregnated powder and post-impregnated TEPA monolith leached heavily and
showed reduced CO2 uptakes by cycle two. These effects were not
observed in the pre-impregnated TEPA; which exhibited near zero capacity loss by
cycle five. The high stability was attributed to the covalent tethering of TEPA
to the MOFs chromium center during paste densification; where ultrasonic bath’s
heat forwarded the reaction mechanism. When examining the adsorption kinetics,
the post-impregnated monoliths showed the steepest kinetics; however, this was
partially attributed to their lower CO2 uptakes. The next-fastest
kinetics were observed in the impregnated powders; followed by the
pre-impregnated monoliths. Typically, structured contactors improve upon powder
kinetics; however, these effects were not observed here. Because the CO2
was dilute, the poor adsorption kinetics were attributed to a slow adsorbate diffusion
rate through the support walls. Whereas the powder was entirely accessible to
the CO2, the monolith required the gas to permeate the internal
structure; which acted as a rate limiting step. Improving this rate limiting
step will be a target of future works. Overall, though, this work provides a
novel approach to formulate structured amino-MOF contactors for CO2
removal from enclosed environments and could be highly promising with slight



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