In OSMAHRD, one-stage membrane separation unit is added in the upstream of the original amine absorption process (Fig. 2).Design variables need to be optimized to minimize EAOC (Eq. (1)).In this case, the only decision variable is membrane area. Design and operating conditions in the original process act as constraints because they should not experience major variation in the retrofit design; i.e., the absorber inlet stream pressure and temperature remain the same, and its mole fraction of acid components should not exceed 10% of the original value (due to corrosion problem). Objective function for optimization is: