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The decarbonization of maritime transport requires scalable fuel pathways that achieve both economic viability and low life cycle emissions. This study presents a prospective life cycle assessment (LCA) of Power-to-Liquid (PtL) e-diesel production within the FLEET 4.0 framework, targeting maritime applications in Saudi Arabia. The work integrates detailed process simulation with system-level environmental assessment to quantify cradle-to-gate and well-to-wake impacts across multiple energy and feedstock scenarios.

An Aspen Plus-based model was developed to simulate the full e-diesel production chain, including hydrogen production via electrolysis, reverse water-gas shift (RWGS), Fischer–Tropsch (FT) synthesis, and product separation. Both pilot-scale (~100 t/year) and commercial-scale (~100 t/day) systems were evaluated. Four scenarios were defined based on hydrogen and CO₂ sourcing: (S1) renewable H₂ with point-source CO₂, (S2) grid-based H₂ with point-source CO₂, (S3) renewable H₂ with low-cost industrial CO₂, and (S4) renewable H₂ with direct air capture (DAC) CO₂ .

The LCA was implemented in Brightway 2.5 using the Activity Browser, enabling the construction of foreground systems and their integration with background inventories. A prospective framework was applied to capture evolving electricity carbon intensities in Saudi Arabia. Environmental impacts were assessed using GWP100, with sensitivity analyses on electricity mix, hydrogen production, and CO₂ sourcing.

Results demonstrate that electricity carbon intensity is the dominant driver of life cycle emissions across all scenarios, exceeding the influence of process configuration or CO₂ sourcing. Scenario S3 achieves the lowest carbon intensity due to the combined benefits of renewable electricity and low-burden CO₂ supply, highlighting the role of industrial symbiosis. In contrast, S2 results in the highest emissions, with grid-based hydrogen production offsetting any carbon utilization benefits and potentially exceeding fossil diesel benchmarks. While S4 enables near-complete carbon circularity, its high energy demand introduces a significant upstream burden, limiting its near-term environmental advantage.

Overall, switching to low-carbon electricity yields greater emission reductions than changes in CO₂ sourcing strategy, underscoring the critical importance of electricity decarbonization for PtL systems. At commercial scale, the best-performing configurations demonstrate strong potential to meet future maritime decarbonization targets.

This study highlights the need for integrated process–LCA frameworks to support decision-making and shows that system-level factors, particularly electricity supply, ultimately determine the environmental viability of e-fuels. The methodology is transferable and provides a robust basis for scaling PtL technologies under Saudi Vision 2030 and global net-zero pathways.