New trial by MHI, partners aims to cut methane slip from LNG-powered vessels

Japan’s Mitsubishi Heavy Industries Marine Machinery & Equipment (MHI-MME), an arm of Mitsubishi Heavy Industries (MHI), recently commenced demonstration testing for a methane oxidation catalyst system for vessels fueled by liquefied natural gas (LNG).

As disclosed, the system was created in collaboration with compatriot mechanical/industrial engineering company Daihatsu Infinearth Mfg, whose engine optimization technology was used.

According to MHI, the demonstration test began in May this year and is planned to be done continuously for one year. It is being conducted in collaboration with KEYS Bunkering West Japan (KEYS), a joint venture established by Kyushu Electric Power, NYK Line, Itochu Enex, and Saibu Gas, as the partner in this project.

As explained, the effort entailed fitting the equipment on the KEYS Azalea, an 82.4-meter-long dual-fuel LNG bunkering vessel owned by KEYS and constructed by Mitsubishi Shipbuilding. The unit, which was launched in July 2023 and completed its first bunkering operation in April last year, is described as the “first ship of its kind in Japan.”

Methane oxidation is a chemical reaction in which methane (CH4) reacts with oxygen and is converted into carbon dioxide (CO2) and water vapor. While it is a natural part of the methane cycle, it contributes to environmental concerns as it increases the concentration of CO2 (a greenhouse gas) in the atmosphere. It also affects ozone formation.

Representatives from MHI have explained that the methane oxidation catalyst system oxidizes unburnt (or slip) methane contained in the exhaust gas of marine engines, suppressing the emission of carbon dioxide and, thus, allowing a ship to operate in a more eco-friendly manner.

Per the results of the experiments on KEYS Azalea, Mitsubishi Heavy Industries has reportedly been able to see a methane oxidation rate of 70% or higher in the initial performance, contributing ‘tremendously’ to reductions in greenhouse gas emissions. This is said to be the reason why the company decided to conduct the trials for the next year.

Methane slip remains the primary source of methane emissions from ships, but emissions throughout the LNG supply chain—from loading to engine delivery—pose a significant concern.

These fugitive emissions, though often unintended and short-lived, need to be accurately identified, measured and mitigated to support the maritime industry’s broader decarbonization objectives.

Solutions across the board have emerged over the past years as industry players sought ways to address this ‘critical’ piece of the net zero puzzle. In August 2024, industry coalition SEA-LNG highlighted the progress made in reducing the methane slip, believing that it could be eliminated for all engine technologies by the end of the decade as long as maritime stakeholders keep working together.

Moreover, SEA-LNG has shared that two-stroke diesel cycle engines, which account for approximately 75% of the LNG-fueled vessel order book, have effectively eliminated slip already.

Finland-headquartered technology major Wärtsilä has been keeping pace with these developments. The company has set a target of minimizing the slip by at least 75% via a solution introduced for the Wärtsilä 50DF dual-fuel engine.

Namely, in April 2025, it was unveiled that this new technology could allow for a more optimized combustion process, boosted efficiency, and lower methane emissions. As divulged, the system was engineered in collaboration with Chevron Shipping Company.