Synthetic methane (compressed gas or liquid)

Technology

What is it?

Carbon dioxide (from waste or from direct air capture) is reacted with clean or renewable hydrogen to produce methane, which is then liquefied for transport (note that this should not include hydrogen sourced from methane, as this would involve unnecessary conversions). Given the synthetic production routes (i.e. thermal catalysis, electrocatalysis or photocatalysis), methane produced may sometimes be referred to as synthetic natural gas (as opposed to fossil natural gas). Hydrogen can then be extracted from the synthetic methane at the point of use via cracking or steam reforming combined with CCUS. If CO₂ is sourced from direct air capture, methane combustion becomes carbon-neutral.

Why is it important?

Synthetic methane presents an opportunity to make use of carbon dioxide (from direct air capture or waste streams) with hydrogen to produce methane, which can be used as either a fuel, hydrogen transport carrier or fed into existing gas pipelines.

Characteristics

• Volumetric hydrogen density: Liquid state = ~100kg H₂/m³. At standard temperature and pressure = 0.7946g/100L
• Gravimetric hydrogen density: ~25% H₂ by weight
• Storage conditions: 90 to 120 bar

Benefits

• Can be mixed with traditional LNG – existing infrastructure can be leveraged
• Existing methane market for which synthetic methane could be supplied
• Carbon dioxide can be sourced from carbon emitting processes, enabling reductions in life cycle emissions
• It can accommodate emerging direct CO₂ air capture technologies to utilise CO₂
• Volumetric energy density approximately 3 times that of hydrogen
• Can be synthesised at lower pressures than conventional methanol synthesis
• Existing HSE practices and standards
• Reaction is exothermic, presenting an opportunity for heat released to be used for other chemical process or plant energy integration

Limitations

• Source of hydrogen cannot be steam methane reforming, in order to avoid unnecessary chemical conversions
• Heat management required, given the highly exothermic nature of the reaction

RD&D priorities

• Improve catalyst and reactor technologies for both thermocatalytic and electrocatalytic processes to reduce costs of synthetic methane production chain
• Develop carbon capture from the atmosphere,  to be integrated as a reactant
• Energy integration to use the “exothermicity” of the reaction to drive other aspects of the chemical process (energy integration/management)
• Integrate renewable H₂ production
• Integrate renewable energy sources to drive the process where required
• Develop mechanisms/technologies to cope with the intermittent nature of renewable energy which may drive such processes

Known active organisations

• CSIRO
• The Future Fuels Cooperative Research Centre
• The University of Adelaide
• The University of Melbourne
• The University of Newcastle
• The University of Technology Sydney
• The University of Western Australia