Hydrogen burns with a blue colour. This attribute has nothing to do with the appellation ‘Blue Hydrogen,’ which is the name for Hydrogen produced by reacting methane gas with steam with the waste Carbon Dioxide captured and sequestered. This process is called steam methane reforming (SMR). More than 90% of Hydrogen in the world is produced by reforming methane or fossil fuels by reacting with steam. When the waste CO2 is not sequestered, the process gives ‘grey’ hydrogen. This process produces about 10 kg of CO2 per kg of Hydrogen and contributes to 800 million tonnes of CO2 emissions annually (1). The competing alternative is to produce Hydrogen through electrolysis where an electrical current passed through water breaks it down to Hydrogen and Oxygen. This is called ‘green’ Hydrogen. This production method demands huge quantities of electricity and expensive and scarce materials such as platinum as catalysts in the reaction. The cost of green Hydrogen can range from ~$4 to $6/kg-H2. The EU Hydrogen Strategy plans to install at least 80 GW of electrolysers energised by renewable electricity by 2030 (1). Turquoise hydrogen produced by pyrolysing methane — also known as methane cracking — is an alternative low-Carbon Hydrogen production pathway (2). The process is based on direct methane decomposition (DMD), proposed in 2006 by Muradov et.al (3). Methane pyrolysis is an endothermic process, requiring external heat energy to propel the reaction. Electricity, rather than combustion of fossil fuels can supply the heat. The waste carbon produced in the process is in solid form rather than CO2. When renewable electricity is used to drive pyrolysis, the process is zero-carbon. With bio-methane rather than natural gas as the feedstock, the process is Carbon negative. Turquoise hydrogen has significantly less energy demand than water electrolysis and SMR from a thermodynamic perspective and benefits from the existing infrastructure of natural gas. External heat can be supplied in various ways. One option is to burn hydrogen or natural gas in burners. Electrical plasma can also supply the heat. Renewable electricity can be the source of energy. Hydrogen is a potentially valuable aid for decarbonisation. The Hydrogen Council projects a significant growth of hydrogen demand by 2050, with the role of Hydrogen being distributed in large-scale power generation, transportation, industry energy use, and building heating. The economic viability of Hydrogen in these sectors, and how large would be its scope, depend substantially on its Carbon negativity economic competitiveness (1). Methane Pyrolysis is generating growing interest due to its lower energy cost and reduced carbon intensity (4). The chemical bonds holding Carbon and Hydrogen atoms together in methane are weaker than the Hydrogen — Oxygen bonds in water. Also, the carbon intensity of Hydrogen produced using this novel method is 90% lower than that of grey hydrogen. If renewable-natural gas is used, the Carbon intensity would be negative (reaching — 4.09 to — 10.40 kgCO2e/kgH2 at 100% renewable natural gas), the lowest compared to Hydrogen produced by all other processes. Experts claim that this would make turquoise hydrogen a “game-changer” (4) for the energy transition. Interest in Methane pyrolysis via thermal plasma has revived recently. Thermal plasma converts electrical energy to thermal energy in plasma torches, devices developed in the 1960s to simulate the shock-ionized air plasma generated during missile reentry into the atmosphere. Plasma temperatures can easily reach tens of thousands of reaching temperatures that cannot be achieved in traditional combustion processes. They are particularly interesting for endothermic processes for their tuneable enthalpy and the absence of direct CO2 emissions in the process itself. Pyrolysis is claimed to be more cost-effective than electrolysis at a commercial scale (1). However, pyrolysis has relatively higher operating expenses than electrolysis but considerably lower capital costs. Moreover, the by-product of pyrolysis is solid carbon (carbon black), which has a market. A significant question in the cost benefit evaluation of methane pyrolysis is the market for solid carbon. If the methane feedstock is renewable, produced using atmospheric CO2, the methane pyrolysis could be a net Carbon negative process and can supply sustainable solid carbon or graphite for industrial applications. The technology behind Turquoise hydrogen is an emergent one with new advances emerging globally. Research began in the 1960s, though production never scaled up to industrial levels for many decades. The Norwegian company Kvaerner patented a process of thermal plasma pyrolysis of natural gas to produce carbon black in the 1990s. After operating a pilot plant at 3 MW, the Karbomont plant with a thermal black production of 20,000 t annually was set up in Canada. The operations continued from 1997 to 2003; and were terminated due to the indifferent quality of the thermal black. Monolith Materials started developing its methane pyrolysis process based on the Kvaerner process and its modifications in 2012. The first plant at Olive Creek in Lincoln, Nebraska, was commissioned in 2020 and has a yearly production capacity of 14 000 Ton of carbon black and around 2500 Ton of Hydrogen (2). A second, larger plant has a projected capacity of 194000 t/y of carbon black and close to 40000 t/y of Hydrogen. In 2008, the universities in Tomsk, Siberia, in cooperation with the company TOMSK-GAZPROM, patented a process that combines a plasma torch with a catalyst stage (5). In the pyrolysis reactor, a metallic catalyst bed is heated by microwaves, and, micro-discharges occur between the catalyst particles, which support the decomposition of the natural gas. Further reaction occurs in a plasma torch kept at the exit of the catalyst bed. They claimed splitting natural gas in a plasma torch without employing catalysts in 2018. BASF has been conducting research on methane pyrolysis since 2010 (2). Under a project funded by the Federal Ministry of Education and Research (BMBF), a lab-prototype was built and operated at Ludwigshafen, Germany, for identifying key process parameters. This is followed up with a larger pilot plant that began in 2019. HiiROC, in Britain, has developed a plasma-mediated electrolysis process as a less expensive alternative to the SMR and water electrolysis options (6). HiiROC claims its technology converts natural or biomethane into clean Hydrogen at costs competitive to SMR but without the CO2 emissions. The energy demand will be one-fifth of that required by water electrolysis. The HiiROCplant can be set up where Hydrogen is in demand. This allows use of existing infrastructure and avoids storage and transport costs. German gas company Wintershall Dea Ag proposes setting up a 400kg/day pilot facility in partnership with Northern Gas Networks. Another Canadian company, PyroGenesis, has launched an alternative thermal plasma process for hydrogen production for which patents are pending (6). PyroGenesis estimates a capital cost similar to that of steam methane reforming. The cost of electricity is one-third of that of water electrolysis. References 1. https://fsr.eui.eu/between-green-and-blue-a-debate-on-turquoise-hydrogen/ 2. https://www.digitalrefining.com/article/1002720/turquoise-hydrogen-production-by-methane-pyrolysis#.YsZhmcFBxlY 3. Muradov, N.; Smith, F.; Huang, C.; T-Raissi, A. Autothermal catalytic pyrolysis of methane as a new route to hydrogen production with reduced CO2 emissions. Catal. Today 2006, 116, 281–288. 4. International Journal of Hydrogen Energy “Why turquoise hydrogen will Be a game changer for the energy transition” Available online 22 June 2022, Jad Diaba, Laurent Fulcheri, Volker Hessel, Vandad Rohani, Michael Frenklach 5. https://onlinelibrary.wiley.com/b0750944-ffac-4cbf-b34a-de70fc46eb15, Stefan Schneider, Siegfried Bajohr, Frank Graf, Thomas Kolb “State of the Art of Hydrogen Production via Pyrolysis of Natural Gas” 6. https://www.enlit.world/hydrogen/turquoise-hydrogen-an-emerging-variety-in-the-colour-spectrum/ Jonathan Spencer Jones: Turquoise hydrogen — an emerging variety in the colour spectrum
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