(61c) Intensified Plasma-Driven Methane Coupling to Ethylene through Tailor-Made Catalytic Monoliths

The increasing exploitation of shale gas reserves is rapidly changing the energy market, thus the abundant methane (CH₄) streams are gaining the spotlight for chemical valorization.¹ Ethylene (C₂H₄) is the most valuable product of methane upgrade being the most produced organic chemical worldwide due to its role of building block in several chemical processes.

Nonetheless, ethylene is mostly manufactured via steam cracking of naphtha at elevated temperature and with several downstream steps to purify the products mixture. Therefore, extensive research is focusing on alternative methods to exploit abundant methane resources to produce ethylene in a selective and sustainable fashion.²

In this context, non-thermal atmospheric plasma (NTAP) represents a promising method to activate stable CH₄ molecules via (renewable) electric energy locally generated next to extraction sites. The highly energetic plasma mixture contains electrons at temperature much higher than the surrounding gas, hence methane conversion beyond the thermodynamic limits can be attained.³ The most stable products of plasma-assisted methane activation are C₂ species with varying selectivity according to the plasma source.⁴

In this work, we employ a nanosecond pulsed discharge (NPD) plasma reactor to intensify the energy channeled into the system and we couple it with customized catalytic monoliths that drive hydrogenation of acetylene (C₂H₂) to ethylene. High energy efficiency can be attained by regulating the frequency of the nanosecond pulses and the applied voltage to reach single pass CH₄ conversion up to 40% and C₂H₂ selectivity of 80%.⁵ A structured electrode in the plate-to-plate configuration is covered with a catalytic layer to shift the selectivity of the C₂ species. The tailor-made, 3D printed monolith is designed upon CFD calculations and assessment of heat integration. Optimization of the (Pd based) catalyst loading and the thickness of the catalytic layer leads to complete conversion of acetylene. Thereby, the lab-scale results of this unique plasma reactor are promising for further development of the technology. The modular nature of the reactor allows numbering up to address large scale production, whilst long term operational stability must be assessed in the context of industrial implementation. This technology could suit decentralized methane valorization into value-added ethylene via an electrified process.

References

(1) Kim, S.; Oh, S. Impact of US Shale Gas on the Vertical and Horizontal Dynamics of Ethylene Price. Energies 2020, 13 (17). DOI: 10.3390/EN13174479.

(2) Dai, Y.; Gao, X.; Wang, Q.; Wan, X.; Zhou, C.; Yang, Y. Recent progress in heterogeneous metal and metal oxide catalysts for direct dehydrogenation of ethane and propane. Chemical Society Reviews 2021, 50 (9), 5590-5630. DOI: 10.1039/d0cs01260b.

(3) Scapinello, M.; Delikonstantis, E.; Stefanidis, G. D. The panorama of plasma-assisted non-oxidative methane reforming. Chemical Engineering and Processing: Process Intensification 2017, 117, 120-140. DOI: https://doi.org/10.1016/j.cep.2017.03.024.

(4) Heijkers, S.; Aghaei, M.; Bogaerts, A. Plasma-Based CH4 Conversion into Higher Hydrocarbons and H2: Modeling to Reveal the Reaction Mechanisms of Different Plasma Sources. The Journal of Physical Chemistry C 2020, 124(13), 7016-7030. DOI: 10.1021/acs.jpcc.0c00082.

(5) Delikonstantis, E.; Scapinello, M.; Van Geenhoven, O.; Stefanidis, G. D. Nanosecond pulsed discharge-driven non-oxidative methane coupling in a plate-to-plate electrode configuration plasma reactor. Chemical Engineering Journal 2020, 380, 122477-122477. DOI: https://doi.org/10.1016/j.cej.2019.122477.