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.