Sorbent degradation, specifically how the capacity fades over time, is dictated by the degradation mechanism. In Fig. , three functional forms of sorbent degradation are illustrated: (1) linear, (2) exponential, and (3) piecewise exponential. Linear degradation is characterized by a constant rate of capacity decline over time. This form of degradation is typically expected in scenarios where sorbent material physically exits the bed, when pores become obstructed with contaminants (fouling), or in cases of structural collapse, where the degradation does not depend on the remaining adsorption sites. Exponential degradation, in contrast to the linear form, depends on the concentration of available sites. This type of degradation is frequently observed in instances of poisoning of chemical adsorbents, where the rate of deactivation is proportional to the remaining sites. Piecewise exponential degradation, sometimes referred to as "hockey stick kinetics," encompasses two or more exponential functions with distinct break points. The first exponential function exhibits a more rapid rate of degradation compared to later functions. This functional has been observed for amine-supported materials, where the initial rate of degradation is faster as primary amines are deactivated first, eventually leading to a seemingly stable or plateaued capacity. Volatilization of low molecular weight amines can cause faster degradation, which would result in a higher initial rate for polyamine sorbents with a molecular weight distribution.