Modeling Framework for Joint Product and Process Synthesis with Material Recovery Opportunities

The circular economy paradigm requires process synthesis to be expanded beyond the consideration of production activities aimed at market needs and to integrate valorization processes upcycling waste from different sources (industrial and urban). With this aim, this contribution presents a modeling approach for the joint synthesis of production processes and products from a waste-to-resource perspective. The system is modeled through a superstructure with features from state-task network (i.e. the activation/deactivation of units) and state-equipment network (i.e. multiple tasks in a unit) representations. The problem is formulated using a Generalized Disjunctive Programming approach (GDP). The proposed approach is tested with a case study addressing the synthesis problem of polyethylene pyrolysis, as a central step required to address the need to close the associated material loops. Decisions are made on the separation and reuse of the pure or mixed light gases from the reactor outlet (material reuse vs. energy valorization). Results demonstrate the ability of the proposed approach to represent alternatives that cannot be considered if only STN or SEN models were used.