Dynamic analysis of the oxidative coupling of methane (OCM) process to produce sustainable ethylene from biogas derived from organic fraction of municipal solid waste (OFMSW)

Abstract

This study investigates the Oxidative Coupling of Methane (OCM) process, a technology designed to convert methane into ethylene, a valuable chemical. Specifically, a dynamic analysis is conducted to evaluate the performance of a plug-flow reactor in the OCM process for producing sustainable ethylene from biogas derived from the anaerobic digestion of OFMSW (Organic Fraction of Municipal Solid Waste). The dynamic behavior of the system is assessed using Aspen HYSYS simulation software to ensure both process productivity and safety. A steady-state analysis of the reactor is conducted, using a kinetic model based on a Na₂WO₄/Mn/SiO₂ catalyst to operate with 417 Nm³/h of biogas. An inlet temperature of 610 °C to activate the reaction, and a pressure of 300 kPa to take advantage of low-pressure operation benefits. Based on trial and error method, the controllers are tuned and optimized to achieve the desired system response, with biogas flowrate variations (±10 % and ±20 %). Biogas flowrate upset (±5 %) tests are conducted to evaluate the system's response. Additionally, start-up tests are performed using biogas and nitrogen streams to determine an enhanced procedure for managing the process under dynamic conditions. The control system is fine-tuned, successfully limiting the reactor temperature to safe levels, below 800 °C. Flowrate variations are managed adjusting the key process parameters accordingly to maximize methane conversion, ethylene selectivity, and yield. Rapid start-up phases, allow to reach steady-state conditions approximately 13 min with biogas and 12 min with nitrogen.