(555d) Natural Gas Pyrolysis: Advantaged Production of Low-Emissions Hydrogen and Carbon Materials

David Dankworth, Jayashree Kalyanaraman, Anjaneya Sarma Kovvali, Sophie Liu,
Ying Liu, Steven Pyl, Sumathy Raman, Ramon Strauss, Joshua Willis

ExxonMobil Research and Engineering Company (EMRE), Annandale, NJ

Hydrogen produced with low or zero associated GHG emissions is considered an important energy carrier for more sustainable future energy systems; with a broad range of existing and potential applications in transportation, heating, and power generation and storage.

Commonly considered technologies for the production of low-emissions hydrogen include natural gas reforming combined with CO₂ capture and storage (CCS), and water electrolysis powered by renewable electricity. Natural gas pyrolysis has recently emerged as a promising alternative. Pyrolysis (or thermal decomposition) converts the methane in natural gas into hydrogen and solid carbon (CH₄ → C + 2H₂). Unlike reforming, the pyrolysis chemistry does not inherently generate CO₂. Pyrolysis could therefore enable the use of natural gas for hydrogen production in places where CCS is not feasible for geological or policy reasons. While handling and storing solid carbon (e.g. via landfill or abandoned coal mines) instead of CO₂ can be considered an advantage over reforming; pyrolysis only produces about half as much hydrogen per unit of natural gas. The economics of pyrolysis technologies may become much stronger if the carbon product is a valuable, marketable material (e.g. carbon black, graphene or carbon nanotubes).

In recent work, the potential of natural gas pyrolysis in a fluidized bed reactor as well as in a molten-salt bubble column reactor¹ has been explored. Both of these pyrolysis technologies produce predominantly amorphous solid carbon, but reactor design and operating conditions can be adjusted to tailor the nature and structure of the carbon product. The use of a plasma reactor was investigated for the production of hydrogen and carbon black². The value of the latter, as an additive in rubbers, could significantly help offset the hydrogen production cost.

While several natural gas pyrolysis technologies hold considerable promise, they are currently only practiced at relatively small scales. Significant scale-up challenges remain to turn pyrolysis into a viable option for large-scale production of low-emissions hydrogen and carbon materials. Continued R&D is required to address these challenges, including improvement of methane conversion efficiency, and development of scalable means of providing the required process heat without negating the potential GHG advantages.

References

[1] Brett Parkinson, Clemens F. Patzschke, Dimitrios Nikolis, Sumathy Raman, Klaus Hellgardt, Molten salt bubble columns for low-carbon hydrogen from CH4 pyrolysis: Mass transfer and carbon formation mechanisms, Chemical Engineering Journal, 417, 2021,127407

[2] Alan Mašláni, Milan Hrabovský, Petr Křenek, Michal Hlína, Sumathy Raman, Vineet Singh Sikarwar, Michal Jeremiáš, Pyrolysis of methane via thermal steam plasma for the production of hydrogen and carbon black, International Journal of Hydrogen Energy, 46 (2), 2021, 1605-1614