Conceptual Process Design and Economic Analysis of Oxidative Coupling of Methane

Abstract

Abstract Addressing the need for comprehensive analysis of the potentials and characteristics of ethylene production via Oxidative Coupling of Methane (OCM) process was the main motivation of performing the current study. In this context, technical, environmental and economic characteristics of alternative OCM process design structures including the integrated OCM and ethane dehydrogenation process for the industrial plants with the annual capacity of one million t ethylene production were analyzed and compared by predicting their performances using Aspen-Plus simulation and Aspen Economic Process Analyzer. The performance of the reactor section, carbon dioxide separation section and adsorption section in this simulation were mapped and validated using the observed performances of the OCM miniplant scale experimental facility constructed in TU Berlin. It was found that the operating cost in all cases is the main source of cost, so that even the one-year operating cost is estimated to be 3-4 times of the fixed cost. In the operating cost, the raw material cost stands for the major part of the cost to be around 750 million Euro annually. Most of the utility costs is needed for the energy-intense cryogenic distillation, which is avoided in the demethanizer section when adsorption unit is utilized. However, one percent loss of ethylene and significant increase on the fixed-cost are the main disadvantages of using adsorption technology. Yet, this process structure provides the fastest return of investments around 9 y based on the considered costs and the assumptions in this study. Using selective carbon dioxide membrane separation technology was also investigated and showed a marginal contribution specially by considering the expected 2% loss of ethylene in this case. If better membrane technologies for CO2 separation or preferably for ethylene separation becomes available, it can be beneficial in the whole economy of the process and in this case the best observed total energy consumed can be improved beyond current 40-50 GJ/t ethylene. Beside trying to reduce the total cost, the amount of the generated CO2 and the total energy consumed associated with production of one t of ethylene, potential of using bio-based materials for instance for producing the required adsorbents and also utilizing the whole OCM process for bio-based methane feedstocks were also taken into consideration. The technical challenges regarding the OCM catalyst and reactor operation should be addressed prior to any attempt for industrial scale operation of this process.