Navigating Cost-Efficient Circular Integration of Plastic Waste-to-X Pathways into Oil Refinery Using the Graph-Theoretic Approach

Plastic waste conversion has been widely recognized as a promising strategy to address growing waste management challenges. However, the feasibility of its integration into existing industrial systems remains uncertain. This paper explores a plastic waste-to-X strategy aimed at reintegrating plastic waste into its original supply chain, in alignment with circular economy principles. A graph-theoretic optimization model is developed using P-graph to identify the optimal and near-optimal pathway configurations under multiple scenarios. Under a cost minimization scenario, the optimal solution achieves a 0.013–0.19% lower cost compared with alternative pathways; however, related to the higher opportunity cost of up to 24,364 USD/y from forgone utility savings and carbon tax reductions. Incorporating carbon credits shifts the focus toward balancing cost efficiency and emission reduction. Under budget constraints, the benefit-cost analysis reveals that emission reduction does not increase linearly with budget expansion. These findings guide decision-makers in setting realistic emission reduction targets and allocating budget efficiently, while helping policymakers to develop a financial scheme that promotes greater emission reductions without excessive expenditure.