e-methane

The main feedstocks for producing e-methane are low-emissions electricity, water, and renewably sourced CO₂, i.e. biogenic CO₂ or CO₂ removal solutions such as direct air capture (DAC) or direct ocean capture (DOC). Carbon from renewably sourced CO₂ is combined with hydrogen (separated from water using electrolysis powered by low-emissions electricity) to produce e-methane.

Mature low-emissions electricity generation technologies like solar, wind, and hydro are commercially available, but large-scale build-out is needed to support e-methane production. The potential use of nuclear power for e-methane production remains uncertain and an area for further exploration. Scaling up low-emissions electricity generation is one of the main feedstock challenges for e-methane production.

While water is globally plentiful, accessible fresh water makes up just less than 1% of the planet’s water. The remaining almost 99% is seawater that can be purified by desalination – but the briny discharge requires sustainable disposal.

Renewable CO₂ can be waste CO₂ released by combustion or decomposition of biomass and its derivatives. Point sources of renewable CO₂ are too limited to provide for full maritime decarbonization, but global volumes should be sufficient in the near term to supply e-fuels for a small fraction of the world fleet. However, access to this CO₂ is challenged by competition from other uses, such as permanent sequestration. Carbon removal solutions such as DAC and DOC are very costly due to low efficiencies of selecting ppm-level concentrations of CO₂ in air and dilute concentrations in the ocean, respectively.

Key feedstock challenges in the production of e-methane remain the availability of renewably sourced CO₂ and low-emissions electricity at the required scale.

E-methane is produced by combining carbon from renewably sourced CO2 with hydrogen that has been separated from water using electrolysis powered by low-emissions electricity. The use of low-emissions electricity to produce the hydrogen needed for the synthesis of e-methane is relatively new, largely due to the recent adoption of electrolysis.

The electrolyzer stack is the core technology needed to split water into oxygen and hydrogen. Global electrolyzer production today is challenged by a scarcity of raw materials, the low stack manufacturing technology maturity and capacity, and the need to produce replacement stacks (current stacks have an average lifespan of 3-12 years).

Additionally, substantial infrastructure for dedicated low-emissions electricity is required to generate hydrogen via electrolysis at an industrial scale. However, the build-out of low-emissions electricity is constrained by issues like the expansion of electricity grids, availability of raw materials such as copper, and competition from other sectors.

An efficient e-methane synthesis plant requires large quantities of renewable CO2 (see also feedstock availability tile for e-methane) at a centralized location. Such CO2 sources typically come from industrial waste streams like flue gas. The industrial plants that produce these waste streams are often located where it is not possible to build adjacent CO2 capture and e-methane production infrastructure. As a result, transportation of CO2 feedstock from its source to a methane production facility presents logistical challenges, which can increase the well-to-wake environmental impact of the resulting fuel.

Therefore, the primary challenges to the advancement of e-methane synthesis lie in expanding low-emissions electricity infrastructure, centralized access to renewably sourced CO2, and increasing the manufacturing capacity of electrolyzer stacks.

Fuel supply logistics and bunkering are well established for liquefied natural gas (LNG). Given that methane is the main constituent of LNG, e-methane does not represent any fundamentally new challenges in fuel storage, logistics, and bunkering. Relevant safety and operating procedures are already in place to deal with e.g., explosion risk.

A remaining challenge at terminals and during bunkering is methane’s low boiling point, which creates a latent risk of boil-off. Finally, well-to-wake emissions accounting will require strict control of methane venting and release across the entire supply chain.

Liquid storage of methane requires advanced cryogenic storage systems at -163°C. Technologies for storing and converting methane on board vessels are already commercially available. Methane-fueled internal combustion engines are currently used by the existing liquefied natural gas (LNG) fleet. Different engine technologies (including dual-fuel high-pressure and low-pressure two-stroke and four-stroke) are currently used with varying cost, efficiency, and emissions. Furthermore, methane-fueled fuel cells are entering the market, with multiple small-scale demonstrations ongoing.

Hundreds of vessels primarily fueled by methane in the form of liquefied natural gas (LNG) are currently in commercial operation. If regulations and safety management practices are followed, no significant barriers exist regarding safety and onboard operations for methane as a maritime fuel (see also regulation and certification tile for e-methane).

When assessing the overall environmental impact of e-methane as a marine fuel, it is crucial to consider both tank-to-wake and well-to-wake emissions. E-methane combustion releases CO₂ tank-to-wake. However, e-methane produced using renewably sourced CO₂, through processes that capture and store CO₂, can achieve close to net-zero well-to-wake emissions (see also tiles for feedstock availability and fuel production of e-methane). In addition, emissions of NO_x, SO_x, and particulate matter (PM) can be effectively reduced or controlled through existing technologies, further enhancing the sustainability of e-methane as a marine fuel.

As methane is a potent greenhouse gas, onboard emissions of uncombusted methane (methane slip) are a concern for this fuel pathway. It is crucial to address the potential negative impacts associated with methane slip, as unregulated emissions can undermine the environmental advantages of e-methane. High-pressure two-stroke engines have very low methane slip (~0.2%). Other engine types, such as low-pressure two-stroke and four-stroke engines, have higher methane slip (1.7% and 3.1%). Methane slip should be reduced through regulations that incorporate methane emissions into a CO₂-equivalent methodology, combined with further development of onboard emissions reduction technologies like catalysts.

To fully realize the sustainability of e-methane, comprehensive regulation and continued development of technology are essential. These efforts will ensure that the net-zero emissions potential of e-methane is realized, while addressing both upstream and downstream environmental impacts.

Methane as a fuel is fully covered by mandatory regulatory text from the International Maritime Organization (IMO), notably the International Code of Safety for Ships Using Gases or Other Low-flashpoint Fuels (IGF Code). The industry has implemented bunkering guidelines and procedures for this fuel, making it scalable from a safety point of view.

Nevertheless, further regulatory development and clarification specifically for e-methane are essential. It will be critical to address environmental aspects and establish clear life-cycle accounting of emissions for e-methane. This includes defining how e-methane produced from renewable sources, particularly through processes such as electrolysis and carbon capture, will be certified and integrated into existing regulatory frameworks. Addressing these gaps will ensure that e-methane can be recognized and utilized effectively in maritime applications, promoting its role in achieving decarbonization goals within the shipping sector.

The IMO is advancing its development of well-to-wake-based regulations to promote the use of sustainable fuels, including e-methane. Regulating the climate impact of fuel use from a life-cycle (well-to-wake) perspective offers the industry the opportunity to establish sustainable fuel production and consumption patterns. Such regulation can help mitigate the risk of shifting climate impact from the downstream (tank-to-wake) segment of the value chain to the upstream (well-to-tank). This is a crucial consideration for alternative marine fuels, as a significant portion of their climate impact is associated with upstream activities (see also tiles for feedstock availability and fuel production). However, many elements of these regulations remain to be discussed and finalized, particularly certification, sustainability criteria, rules for electricity production, and implementation in the IMO mid-term measures. The European Union (EU) has made progress with the introduction of the EU Emissions Trading Scheme (ETS) and the FuelEU Maritime regulation, which may promote the uptake of e-methane. With that said, some aspects relating to the certification of e-methane remain to be resolved. One point of concern is how fugitive methane emissions will be handled during the certification of e-methane under the EU Renewable Energy Directive (RED), which is yet to be developed.

More broadly, it is important for regulation to support the control of methane emissions from this fuel pathway. Therefore, e-methane requires strong regulatory focus, including monitoring and control of fugitive methane emissions upstream as well as slips during onboard combustion. Regulation can also help to incentivize continued technological development and adoption of solutions that reduce methane emissions.