Perspective Review on Ammonia and Methanol: The Next-Generation Marine Fuel for the Shipping Industry
The shipping industry is one of the leading contributors to greenhouse gas (GHG) emissions. The International Maritime Organization (IMO) has set ambitious targets under its 2023 GHG strategy, including reducing the carbon intensity by 40% by 2030 and achieving net-zero emissions by 2050. This review examines the adaptability of ammonia and methanol as alternative marine fuels toward achieving net-zero carbon emissions in the shipping sector. The analysis focuses on key assessment criteria covering well-to-wake emissions, production pathways, thermophysical properties, infrastructure scalability, safety, economic feasibility, and technological readiness. Ammonia is considered a promising long-term solution owing to its carbon-free composition; however, it faces significant challenges, including higher production costs (particularly for green ammonia), NOx emissions associated with combustion inefficiencies, acute toxicity, and regulatory barriers related to safety. In contrast, methanol is represented as a pragmatic short-term option because of its compatibility with existing infrastructure, bunkering, and storage systems with minimal modification. Moreover, the use of renewable methanol (biomethanol and e-methanol) significantly reduces carbon emissions and enhances sustainability. However, it requires larger storage volumes because of its lower energy density, in addition to concerns regarding its toxicity. The analysis reveals that a dual-fuel strategy is a viable pathway for methanol adoption in the short and medium term to meet net-zero carbon targets. However, the wider adoption of ammonia still requires further research and development to ensure compliance with safety regulations and to address long-term toxicity concerns associated with its handling to achieve a sustainable future.