(570e) Techno-Economic Analysis of Direct Non-Oxidative Conversion of Shale Gas Via Non-Thermal Microwave (MW) Plasma Catalysis

Commercially, shale gas (mainly methane) is typically converted to higher value added chemicals like aromatics and olefins using a multi-step process. Syngas is first produced using reforming or autothermal reforming process followed by syngas conversion processes like methanol-to-olefins/aromatics, oxidative coupling of methane, or Fischer-Tropsch process. This multi-step route has a low carbon utilization efficiency since substantial quantity of carbon gets removed from the process in the form of carbon monoxide/dioxide during the aromatics/olefins synthesis steps. Moreover, the syngas synthesis step is very capital- and energy-intensive so a synthesis route that can avoid or reduce the number of steps is highly desired.

While it may be desired to convert shale gas to aromatics/olefins directly, direct conversion of methane, the main component of shale gas, is challenging because it is a very stable molecule and it cannot be easily activated. Methane has a strong C-H bond with a first bond dissociation energy of 439.3 kJ/mol [1], which indicates that high amount of energy would be needed in order to break the bond. Moreover, the C-H bond of methane is stronger than higher hydrocarbon products and as a result these products are more reactive than methane [2]. Existing approaches for direct conversion of methane to higher hydrocarbons are thermal and catalytic pyrolysis, oxidative coupling and non-oxidative conversion of methane [3]. However, all these synthesis routes suffer from low methane conversion, high reaction temperatures (>800°C) and pressure, low product selectivity, high coke formation and catalyst deactivation [3]. Contrary to these conversion routes, non-thermal microwave plasma catalysis will enable direct non-oxidative conversion of shale gas at atmospheric pressure and under mild reactor conditions (>400°C) with high product yield. To the best of our knowledge, there are no studies in the open literature that has developed a model for this process. In this work, first a detailed first-principles model of the MW plasma reactor for aromatics/olefins production is developed. A plant-wide model is then developed to generate the products at desired specifications. Finally a techno-economic analysis of this novel process is undertaken. A number of sensitivity studies are done evaluating the impact of operational variables and investment parameters on key economic measures.

References

[1] Schwach P, Pan X, Bao X. Direct Conversion of Methane to Value-Added Chemicals over Heterogeneous Catalysts: Challenges and Prospects. Chem Rev 2017;117:8497–520.

[2] Holmen A. Direct conversion of methane to fuels and chemicals. Catal Today 2009;142:2–8.

[3] Alvarez-Galvan MC, Mota N, Ojeda S, Rojas S, Navarro RM, Fierro JLG. Direct methane conversion routes to chemicals and fuels. Catal Today 2011;171:15–23.