(560dv) Mechanism of Oxidative Dehydrogenation of Ethane at High Temperatures

The large availability of low-cost shale gas reserves has generated interest for the production of high value-added chemicals. Although methane is the main component in shale gas (often more than 85%), ethane is also available. Olefin production has traditionally happened via steam cracking, a high energy and capital intensive process. It is crucial to develop on-purpose catalytic approaches that will not only help to reduce the carbon footprint of the chemical industry, but also enable the development of energy efficient processes. The short contact time reactor is a promising concept for autothermal conversion of light paraffins into their corresponding olefins in compact reactors at high temperatures. It has been experimentally shown that ethylene yields, approximately 60%, comparable to steam cracking can be obtained by partial oxidation of ethane at high temperatures with a contact time of ca. 1 ms using a platinum-tin catalyst.¹ Different mechanisms from purely heterogeneous to combination of both heterogeneous and homogeneous and purely homogeneous reaction mechanisms have been proposed in the literature. Fundamental understanding of the reaction mechanisms is required for the optimization of the reactor and hence commercialization of the process. In this work, we use detailed modeling which combines both catalytic and gas-phase reactions to understand the process. The latter includes more than 100 species and over 2,500 reactions.For the former, comprehensive reaction network of 311 reversible elementary reactions steps and 147 surface and 31 gas species was generated via a Reaction Network Generator (RING).² Simulations show that ethane oxidation occurs that produces water, CO, and CO₂. In later stages, ethylene is produced initially via dehydrogenation of ethane and consumed via steam reforming and hydrogenolysis reactions. Detailed analysis of the results reveals the substantial role of gas-phase chemistry. Overall, the interplay between catalytic and gas phase reactions is demonstrated and recommendations for improved yield are made.

1. Bodke, A. S., Olschki, D. A., Schmidt, L. D., & Ranzi, E. L. I. S. E. O. (1999). High selectivities to ethylene by partial oxidation of ethane. Science, 285(5428), 712-715.
2. Rangarajan, S., Bhan, A., & Daoutidis, P. (2012). Language-oriented rule-based reaction network generation and analysis: Description of RING. Computers & Chemical Engineering, 45, 114-123.