where α, β, γ, and δ are the coefficients of the surrogate functions. The underlying and surrogate functions are plotted in Figure Dynamic responses of electrochemical reactions are generally fast, e.g., water electrolysis , so the CO 2 separation unit is likely to limit the ramping speed of the sub-processes (T Ramp ). Possible technologies for CO 2 separation would differ in the ramping speed. For instance, membrane gas separation and PSA allow fast ramping while chemical absorption takes longer time to change the operation level. In order to investigate how much the maximal ramping speed affects the optimal operation as well as the cost savings, we assume different values of T Ramp (one to three hours).