(739d) A General Evaluation Framework for Direct Nonoxidative Conversion Strategies of Methane to Aromatics

Natural gas is a versatile chemical feedstock, and natural gas conversion to commodity chemicals has recently attracted significant attention because of the shale gas boom in the United States and the low natural gas prices. In addition, direct nonoxidative methane coupling to form aromatics in the absence of O₂ has received significant attention. Yet, high coke yields and catalyst deactivation due to coke formation have presented a significant barrier to develop a commercial methane dehydroaromatization (DHA) process.

In this work, we study nonoxidative natural gas conversion technologies that directly convert methane to aromatics. We first develop an integrated strategy, employing a nonoxidative catalytic system, as well as downstream separation sections for product recovery and purification as well as recovery and recycle of unreacted methane. We then develop a flexible framework that allows us to systematically evaluate numerous technology alternatives. Specially, we develop an equilibrium reactor model based on Gibbs free energy minimization to capture the impact of conversion temperature, pressure, hydrogen extraction ratio, and coke formation ratio on the products yields. We also design a mixed refrigeration system for cryogenic separation of hydrogen, unreacted methane, and C2+ light components. Based on the rigorous process models, we then develop surrogate unit models and a database that allows us to easily calculate key variables from experimental results. Using these tools, we solve effectively 100,000 optimizations to evaluate the impact of various technology parameters, and ultimately identify the key technology gaps that must be overcome in order to develop commercially attractive processes. In addition, we study the impact of plant scale in terms of natural gas feed rate on process economics.

References

Huang, K.; Miller, J.B.; Huber, G.W.; Dumesic, J.A.; Maravelias, C.T.; 2018. A General Framework for Evaluation of Direct Nonoxidative Methane Conversion Strategies. Joule 2, 349-365.

Karakaya, C., and Kee, R.J.; 2016. Progress in the direct catalytic conversion of methane to fuels and chemicals. Prog. Energy Combust. Sci. 55, 60–97.

Morejudo, S.H.; Zanón, R.; Escolástico, S.; Yuste-Tirados, I.; Malerød-Fjeld, H.; Vestre, P.K.; Coors, W.G.; Martínez, A.; Norby, T.; Serra, J.M.; Kjølseth; C.; 2016. Direct conversion of methane to aromatics in a catalytic co-ionic membrane reactor. Science 353, 563-566.