This paper presents a new graphical approach for simultaneous process and molecular design (SPMD), in which elements from both areas can be considered at the same time and illustrative rules for designing the hybrid system can be derived. Traditionally, process design and molecular synthesis problems have been addressed separately, leading to sub-optimal results and a severe limitation of the degrees of freedom for the process design and for the molecule selection. In this work, a new, process-centered molecular design approach for material substitution through property-based integration and group contribution methods (GCMs) is introduced. The proposed methodology provides a consistent set of property-based visualization tools that are applicable for the process- and molecular-design tasks. These tools use the clustering concept to map the problem from the nonconserved property domain into the component-less cluster domain. In this regard, a common property-based domain is used to relate the two problems and a new reverse-problem formulation is developed to determine property constraints for the molecular design problem. Next, process characteristics and process integration opportunities were considered based on the cluster diagram of the required properties. GCMs are also used to estimate and represent the properties of pure organic compounds, based on their structural groups. This leads to transforming the process considerations to molecular design alternatives. In particular, the cluster diagram determines feasibility regions of candidate fresh material utilities (molecules) with target properties obtained by constraints characterizing the process. New candidate molecules are chosen by first being "screened and tested" and then by being "generated and tested", using the GCM molecular (functional) groups, to yield the maximum reuse of the process resources while satisfying all process constraints. Finally, a case study is investigated to illustrate the novelty and validity of the described approach.