The period is defined by a move toward integrated dynamic modeling of separation processes, combining component and energy balances with mass transfer and interfacial phenomena to directly predict multicomponent separations. Simultaneously, low-order representations through dynamic compartmental models emerged, offering practically tractable tools for design, simulation, and control. Membrane separations also rose to prominence as a core unit operation, with pervaporation studies of aqueous mixtures advancing mechanistic understanding and guiding subsequent membrane design. Historical Significance: These advances unified a dynamic, transport-centered paradigm for chemical separations that bridged rigorous process modeling with material-based separation technologies. The framework laid the groundwork for modern simulation-driven design, enabling scalable, integrated process development and supporting the maturation of membranes as standard separation units. The introduction of crosslinked polymer membranes and linked transport knowledge shaped subsequent diversification of separation technologies and system-scale integration.