This paper describes how an interface between the dynamic simulator SpeedUp and the Shell Multivariable Optimising Controller has been developed and applied to the design of a new PP-splitter. This interface is used for the integration of the process design with the design of the process control system. It allows for a direct evaluation of disturbance behaviour of the controlled process with respect to possible design alternatives. Issues addressed are the choice of the control method, the location of quality measurement instruments and equipment sizing.