Evolutionary algorithms, derived by observing the process of biological evolution in nature, have proven to be a powerful and robust optimizing technique in many cases. This paper describes the use of evolutionary algorithms for simultaneous structural and parameter optimization in process synthesis in a modular program environment. The commercial simulator ASPEN; PLUS(TM) was integrated for the determination of the target function value. The ModelManager(TM) was utilized for a comfortable graphical problem definition. The simulations and the cost calculations exploit the complete process modeling accuracy without the necessity of simplifications due to restrictions imposed by the optimization method. The user can be sure that the best solution does not get lost by the application of crude models. In this paper the optimization method will be demonstrated by the synthesis of separation sequences and the overall process synthesis with limited degrees of freedom.