The question remains: How much stability improvement is necessary to offset the reduced working capacity of the modified PEI sorbents? The answer is useful not only for the 2-hydroxypropyl functionalized polyamine series but also any sorbent modification that improves stability at the expense of productivity. To answer the question for one case, we evaluated the DAC cost of PEI, 0.05HP-PEI, 0.10HP-PEI, and 0.15HP-PEI with various degradation rates, using the experimentally measured properties and piecewise exponential form (Fig. ). The observed experimental capacity loss in Fig. was used to define the deactivation in the first part of the piecewise form (Fig. , left panel). We then determined the degradation rate at which the modified samples yielded an equivalent DAC cost to unmodified PEI. The necessary capacity fade profile for each modified sorbent is depicted in Fig. (middle panel), and the resulting LCOC for each is in the right panel.