This study presents a structured decision-making framework for identifying high-value ethylene-based investment opportunities under feedstock and geopolitical constraints, using the Arya Sasol Polymer Company (ASPC) as a case study. Starting from a universe of 233 ethylene derivatives, a multi-phase screening process covering technological obsolescence, intermediate/by-product elimination, and economic scale filtering narrowed the field to 45 viable products. These candidates were then evaluated using a hybrid Analytic Hierarchy Process (AHP)–Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) approach, incorporating eleven techno-economic and strategic criteria with dual weighting from industry experts and executive stakeholders. Scenario-based constraints reflecting CAPEX, land, and utility limitations were subsequently applied. The resulting prioritization provides a robust, data-driven investment roadmap for ethylene downstream integration in emerging petrochemical economies facing market uncertainty and sanction-driven supply disruptions. Although the empirical analysis is based on Arya Sasol Polymer Company (ASPC) in Iran, the proposed framework is intended for petrochemical investors and decision-makers operating in ethylene-based value chains, particularly in emerging and resource-constrained petrochemical economies. The framework can be adapted to different geographical contexts, including other producers in Iran, the Middle East and West Asia, and other ethylene-producing regions, provided that the candidate products, market conditions, feedstock configuration, investment costs, technology accessibility, infrastructure constraints, and criterion weights are recalibrated for the target investment environment.