## 3 Results and Findings from the Existing Literature
### Techno-Economic Analysis (TEA)
The LCOM analysis found that the DAC process costs more than the prevailing market price of methane, suggesting the need for technical improvements or economic incentives to increase the competitiveness of this power-to-gas technology [52]. The study presents a promising yet currently expensive option, highlighting the need for technical advancements and economic incentives. A recent TEA and LCA study for carbon conversion, hydrogen conversion, and power-to-liquids (PtL) efficiency conducted by [PERSON], [PERSON] [51] in the UK estimated a minimum jet fuel selling price (MFSP) of 5.16 GBP/kg, which is approximately6.53 USD/kg (GBP 1 = USD 1.26992, 5 July 2024). In the study, the system integrated a DAC unit, an offshore wind farm, an alkaline electrolyser, and a refinery plant. These were used to produce PtL SAF. It was found that the SAF price is highly sensitive to electricity and DAC costs. The carbon hydrogen conversions were recorded at 88% and 39.16%, respectively, and the PtL efficiency stood at 25.6% [53]. Although this obtained MJSP is prohibitively expensive, given that the weekly averaged commercial jet fuel price ending the week of 5 July 2024 was 805.82 USD/t, which converts at 0.81 USD/kg, the LCA of the system showed that the global warming potential (GWP) of the SAF produced through this PtL pathway is lower than that of fossil jet fuel, and it can meet existing aviation emissions reduction targets, such as the UK SAF mandate [53]. The GWP is, however, sensitive to the carbon footprint of the electricity, indicating its dependence on the energy source. This again suggests the need for technical improvements or economic incentives. Another TEA study by [PERSON] and [PERSON] [52] employed the methanol-to-olefin/methanol-to-gasoline and diesel (MTO-MOGD) process, electrolysis, and DAC. Synthetic hydrocarbon was produced using CO\({}_{2}\) and green hydrogen. The economic implications of the study were primarily focused on the potential for decarbonising road transport. The MFSP for e-gasoline was determined to be 3.24 USD/litre, and for e-diesel, it was 2.89 USD/litre when powered by solar energy. The levelised cost of electricity (LCOe) ranged from 379 to 564 USD/MWh, indicating that e-fuels can emerge as a carbon-neutral option, especially with the implementation of fossil CO\({}_{2}\) taxation. In the study aimed at the technical and economic feasibility of turning bio-oil to naptha, kerosene, glycerol, and diesel, [PERSON], [PERSON] [53] used different methods including hydrogenation, electrolysis, and aqueous-phase reforming (APR) in the assessment using feedstocks such as palm oil and H\({}_{2}\). APR led to an increase of 6.6% in the fixed capital investment. However, it resulted in a 22% decrease in direct manufacturing costs. The calculated MFSP based on this study was 1.84 USD/kg per [PERSON], [PERSON] [53]. It should be noted that the use of waste oils as feedstock can be challenging as they might contain higher fatty acids and lower triglycerides. The economic feasibility and environmental impact study conducted by [PERSON] and [PERSON] [54] focused on technical process evaluation, mass and energy balances, production cost estimation, and sensitivity analysis related to European SAF production potential. Utilising methods like Fischer-Tropsch and electrolysis with the Aspen plus(V10) computer software, the study found that only Norway and Sweden were suitable as PtL production sites in 2020 based on their grid mix. In the study, MFSP was found equal to 1.84 USD/kg, which is 17% lower than the one derived from conventional configurations of 2.20 USD/kg by [PERSON] and [PERSON] [54]. In a distinct TEA study on e-fuels production from CO\({}_{2}\) and low-carbon H\({}_{2}\) conducted by [PERSON] and [PERSON] [55], the process involved high-temperature electrolysis, reactants compression, RWGS reaction, Fischer-Tropsch process, utilities, carbon conversion and energy efficiency, hydrocracking, and other processes.