## 3 Results and Findings from the Existing Literature
### Life Cycle Analysis (LCA)  
Life cycle analysis (LCA) plays a pivotal role in understanding the environmental implications of e-fuels by evaluating their entire life cycle, from raw material extraction to end-of-life disposal. This section systematically reviews the LCA studies focused on e-fuels, providing insights into their greenhouse gas emissions, energy consumption, and overall sustainability. By examining various production pathways, including electrolysis, direct air capture (DAC), and Fischer-Tropsch synthesis, this review highlights the potential environmental benefits and challenges associated with e-fuels, thereby informing future research and policy decisions aimed at reducing the carbon footprint of the energy sector. The study by [PERSON] and [PERSON] [67] revolved around a life cycle assessment (LCA) with a primary focus on energy consumption and GHG emissions, along with a sensitivity and uncertainty analysis. Utilising methods like direct fermentation and gasification plus fermentation, as modelled in Aspen Plus V11, ethanol-to-jet fuel (ETJ) was produced from feedstocks such as corn, cassava, and corn cob. A salient feature of this study was the revelation that there are only a few life cycle assessments of ETJs available in the context of China. The research, thus, plays a pivotal role in assisting policymakers in deciding the direction of China's sustainable aviation fuel (SAF) evolution. A noteworthy result from the LCA showed the process had the least energy and GHG emission, registering at 370.05 KJ/MJ for jet fuel and 31.66 gCO\({}_{2}\)eq/MJ for jet fuel. Additionally, the study revealed the potential to reduce GHG emissions by up to 21.55% when cleaner sources of electricity and heat are employed. The study encapsulated the process design and provided a holistic life cycle analysis on energy consumption and GHG emissions pertinent to jet fuel production from bioethanol. A comprehensive life cycle assessment (LCA) was carried out alongside a techno-economic study by [51]. The LCA revealed a global warming potential (GWP) of 21.43 gCO\({}_{2}\)eq/MJ synthetic aviation fuel (SAF) when dependent on offshore wind electricity. This GWP is significantly below the UK's mandate, which demands a 50% emission reduction in comparison to fossil jet fuel. Additionally, the water-to-water adjusted (WtWa) water footprint was computed to be 0.480 1/MJSAF, showcasing the environmental impact of the process from a broader perspective. The environmental feasibility of the process was evaluated, particularly focusing on the carbon footprint, by [PERSON], [PERSON] [53]. The advanced scenario showed a carbon footprint of 12 g CO\({}_{2}\)/MJSAF, which is 54% lower than conventional methods, indicating a significant improvement in environmental impact. A life cycle analysis (LCA) study was carried out by [PERSON], [PERSON] [54] to assess the environmental impact of the methods. Based on the results, 25 Mt a\({}^{-1}\) fuel output is achievable using direct renewable electricity sources while consuming 33% forest residue. This has the potential to help the EU achieve its goal of 32% of total aviation fuel demand by SAF in 2040. An LCA study focused on the WTW GHG emissions of FT fuels originating from electrolytic H\({}_{2}\) pathways and CO\({}_{2}\) sources, conducted by [PERSON], [PERSON] [68]. By considering various process designs and system boundaries, the results showed that FT fuels have 57-65% lower WTW GHG emissions when integrated with corn ethanol production. Moreover, 45% of carbon in CO\({}_{2}\) was fixed in FT fuel, with an energy efficiency of 58%. Utilising sources like nuclear/solar/wind electricity, the WTW GHG emissions were reduced by a staggering 90-108% as compared to petroleum fuels. [PERSON], [PERSON] [55] presented a study incorporating an LCA using the GREET model. The study examined the environmental impact of electrofuels produced from CO\({}_{2}\) and low-carbon H\({}_{2}\).