Comparative assessment of different intensified distillation schemes for the downstream separation in the oxidative coupling of methane (OCM) process

Downstream separation in the oxidative coupling of methane (OCM) is a major technical challenge limiting the industrial implementation of ethylene production from natural gas. This work focuses on the assessment of different thermally coupled cryogenic distillation schemes for the separation of OCM effluent gases. The composition of the feed gas was defined according to an experimentally validated OCM effluent stream, previously treated for H2O and CO2 removal, and containing N-2, H-2, CO, methane, ethane, and ethylene. The different separation schemes corresponded to conventional distillation trains using direct or indirect sequences at different pressures, configurations with side rectifier or side stripper, a dividing wall column (DWC), and a Kaibel column. All assessed alternatives incorporated the required propylene-ethylene-methane refrigeration cycle. Process simulations using validated models for physicochemical properties and phase equilibria calculations were implemented in Aspen Plus (R). Optimization of the different distillation schemes was done using the total annual cost (TAC) as an objective function, employing different algorithms coded in Python (R) and directly linked into Aspen. Results indicate that the side rectifier scheme is the preferred configuration enabling >10% savings concerning the best conventional configuration. DWC and Kaibel schemes have major drawbacks that make them unsuitable for the studied process.