Process integration is a technique that allows to plan and design better systems by considering the whole chemical process rather than breaking it down into components. The synthesis of processes using these techniques starts with the reaction to generate the desired product. One of the techniques in reactor design is the attainable region (AR) theory. It involves determining the space of possible products yields from a reaction using geometric techniques. The development of AR approach addresses the limitation of optimization techniques used in chemical reactor design and process synthesis. However, the continuous feasible space of reaction yields lacks a framework for determining which points would be best given certain environmental and economic constraints. In this study, a P-graph approach is used to implement the AR technique to generate optimal and near-optimal reaction pathways. The approach involves determining the combinations of reacting species to produce one unit flow rate of a desired product based on material, energy, and work balance. Using the P-graph approach allows framing the AR technique as a mathematical programming tool by considering the flow rate limits and economic value of the reactants and side products. A case study involving methanol synthesis is used to illustrate the approach.