# Comparative Analysis of Marine Alternative Fuels for Offshore Supply Vessels
## 2 Methodology
### Environmental Impacts (Step 4)
#### 2.4.1 Environmental Data Collection
This makes it an attractive alternative for decarbonising the maritime sector, although several challenges need to be addressed to facilitate its adoption [24]. The environmental impact of hydrogen depends heavily on the production method. Steam Methane Reforming (SMR), a common production method, is cost-effective but emits high levels of carbon--around 11 kg of CO2 per kg of hydrogen produced [25]. electrolysis offers lower emissions--about 2.02 kg CO2 per kg--when powered by renewable energy. However, using grid electricity increases emissions to 17.2 kg CO2 per kg [25]. Biomass gasification is another alternative that can lower greenhouse gas emissions but is associated with significant aquatic ecotoxicity and human toxicity impacts [26]. In addition to environmental concerns, there are technological and economic barriers. Many advanced production methods, like thermochemical processes, require further development to enhance efficiency. Additionally, high capital and operational costs hinder the competitiveness of hydrogen compared to traditional fuels [27]. Despite these challenges, hydrogen remains a key component in the shift towards cleaner marine fuel systems. Continued research into production efficiency, cost reduction, and sustainability is crucial for hydrogen to fulfil its potential as a viable solution for maritime decarbonisation. Biodiesel  
Biodiesel, derived from renewable sources such as vegetable oil, animal fat, and recycled cooking oil, offers a cleaner alternative to conventional marine fuels. It significantly reduces emissions of sulphur oxides (SOx), nitrogen oxides (NOx), and particulate matter, contributing to improved air quality and environmental sustainability. The production process, primarily through transesterification, allows for the conversion of waste oils into biodiesel, which can displace fossil fuels and mitigate greenhouse gas emissions by up to 86% compared to petroleum diesel [28]. The environmental impact of biofuels largely depends on the feedstock and production methods used. Second-generation biofuels, derived from lignocellulosic materials like agricultural residues, can reduce greenhouse gas (GHG) emissions by 70-90% compared to heavy fuel oil (HFO). Advanced methods, such as biological pretreatment, significantly improve the yields of these biofuels [29; 30]. In contrast, first-generation biofuels produced from food crops like soybean and palm oil often result in indirect land use changes that negate GHG savings. When these changes are taken into account, GHG emissions from these biofuels can be similar to those from fossil fuels [31; 32]. This highlights the promise of second-generation biofuels for sustainability, while underscoring the need for better feedstock selection and production practices to ensure environmental benefits in biofuel development. Methanol  
Methanol can be combined with marine gas oil to create a low-emission fuel with virtually no sulphur content, making it well suited for maritime engines that have lower energy demands compared to traditional fuels [33]. Renewable production methods, such as carbon dioxide capture powered by renewable energy, enhance the sustainability of methanol [34]. However, conventional methods using fossil fuels like coal and natural gas are carbon-intensive and detrimental to the environment [35; 36]. In contrast, methanol produced from biomass has the potential to be carbon-neutral or even carbon-negative, representing a more sustainable pathway for the energy transition. LNG  
Liquefied natural gas (LNG), primarily composed of methane, has a lower carbon content compared to conventional marine fuels. Utilising LNG in marine engines can result in a reduction in CO2 emissions by approximately 20-25% [37]. Additionally, LNG provides significant environmental benefits by emitting considerably lower levels of sulphur oxides (SOx), nitrogen oxides (NOx), and particulate matter compared to traditional marine fuels [38].