(392h) Dynamic Simulation and Control of an Ldpe-to-Ethylene Plant: Effects of Feedstock Variability and Turndown Capacity

Ethylene is an essential petrochemical, widely utilized in the production of plastics, polymers, and various chemical intermediates, playing a significant role in the global chemical industry. The increasing emphasis on sustainability and circular economy practices has intensified interest in the chemical recycling of plastics, particularly low-density polyethylene (LDPE), back into ethylene monomer. However, existing research predominantly addresses steady-state operational conditions, neglecting critical dynamic challenges such as fluctuations in feedstock quality, availability, and varying operational demands (turndown capacity). These dynamic factors significantly impact the practical scalability and economic viability of LDPE-to-ethylene recycling processes.

This study aims to (1) develop a dynamic simulation framework for an LDPE-to-ethylene chemical recycling plant and (2) propose advanced control strategies capable of mitigating process disturbances arising from variability in feedstock properties and operational turndown. The reactor is a packed bed that is heated via a microwave heating source and operates at a temperature of 400 ^oC and a pressure of 1 bar. The feed to the reactor is a stream of LDPE that is preheated so that it enters the reactor in liquid phase. The outlet of the reactor is cooled and sent to a demethanizer column, followed by a deethanizer column, and finally to an ethylene column, similar to the separation process used in conventional ethane steam reforming product separation. In addition, an extra column is designed to recover propylene.

Dynamic simulations conducted in Aspen Dynamics rigorously evaluate the system’s transient responses to feedstock disturbances, variations in feedstock composition, and flowrate fluctuations. To ensure robust and reliable plant operation, a hierarchical control strategy is developed: (1) a feed-forward controller rapidly adjusts reactor temperature and residence time in response to fluctuations in LDPE feedstock flow and quality, and (2) an advanced composition controller utilizing model predictive control (MPC) manages the downstream distillation and purification units, stabilizing ethylene purity despite disturbances.

This research advances LDPE-to-ethylene chemical recycling technology by clearly demonstrating how dynamic simulation combined with advanced process control can effectively manage variability and operational turndown. By integrating flexible control strategies into the dynamic operation and separation units, the study provides a robust template for industrial-scale, economically feasible chemical recycling of LDPE into high-purity ethylene, aligning closely with global sustainability goals and the advancement of circular economy principles.