The processes of reaction, mixing, and separation are crucial in any chemical process flowsheet. Process synthesis schemes have traditionally considered these processes sequentially in the flowsheet. In the last decade, the superior performance of reactive distillation and membrane reactor units has aroused considerable interest in the area of simultaneous synthesis of reaction, mixing, and separation along with the rest of the flowsheet. Recent incentives to develop new unit operations have resulted in synthesis schemes which focus on specialized cases of reactive distillation. In this paper we consider reaction, mixing, and separation by a mass separating agent. We integrate our reactor network synthesis algorithm, which is a mixed integer nonlinear programming formulation consistent with geometric attainable region concepts, with mass exchange network concepts. The streams in the process are characterized as rich and lean streams, and we develop a reaction-mixing-separation model which may be solved simultaneously with the rest of the process constraints in an attempt to mass integrate the process flowsheet.