The objective of this paper is to propose a method for synthesizing the optimal mass
exchange network (MEN). In order to synthesize optimal MEN, it is necessary to determine the network
structure and its operating conditions. The material and operating unit nodes that are essential to use
the Process graph theory (Friedler et al., 1992) are defined. The maximal structure of MEN synthesis
problem can be easily obtained using the P-graph theory. Furthermore, only feasible structures can be
extracted from the maximal structure, the size of the search space is extremely reduced. The feasible
structures are formulated as nonlinear programming problems (NLP) and their operating conditions are
determined by optimization of NLP.