Figure 7. (a) Cost of CO2 capture of 8
different cases studied (case M1-4) MIL-101(Cr), green circles, (Case
U1-U4) UiO-66, navy triangles as compared to CO2recovery of the PSA unit. Cases M5 and U5 were not included to make the
figure clear. (b) Cost of capture for the five MIL-101(Cr) cases, broken
down into capital and energy costs.
Considering sorbents on the whole for this sub-ambient PSA process, it
appears that the main room for improvement will come about by increasing
the purity of the CO2 product from the PSA without
sacrificing recovery and still showing productivities exceeding 0.015
mol kg-1 s-1. This goal may be
reached in a variety of ways, including sorbent design/selection or an
improved PSA cycle design. Increasing the selectivity of the sorbent
while not sacrificing too much of its capacity for CO2at sub-ambient conditions would drive the Pareto frontier in Figure 6 to
more desirable conditions. Sorbents which could reach the desired
purities, recoveries, and productivities shown for MIL-101(Cr) and
UiO-66, but not requiring as low a vacuum condition would also be able
to drive down the cost. The PSA cycle considered here did not consider
any pressure equalization between beds. The inclusion of this feature
and similar degrees of freedom for the PSA cycle design may result in
further improvements in PSA performance.