Kim, Seokyoung Chris; (2025) De-fossilising liquid hydrocarbons in a net-zero economy. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Carbon-based jet fuel and chemical feedstocks will be needed even in de-fossilised economies in 2050. These could be manufactured from biomass or electricity with captured CO2. Yet economic uncertainties and energy system challenges remain in enabling large-scale deployment, despite the established status of the Fischer-Tropsch (FT) and methanol synthesis pathways. This study investigates the costs and implications of these pathways. Process-level cost estimates vary substantially across the literature. A techno-economic analysis of these processes that systematically accounts for variations in assumptions shows that FT and methanol synthesis have narrow interquartile cost and performance ranges. This demonstrates the benefit of using diverse evidence bases rather than relying on individual studies. A comparative assessment of future levelised costs for jet fuel and chemical feedstocks finds methanol synthesis is best suited to chemicals production, while FT is more economical for jet fuel production. Bio-hydrocarbons may reach cost parity with fossil alternatives in the near future. Electricity-based routes remain dependent on long-term subsidies and low-carbon power systems and will likely be more expensive than offsetting fossil-derived hydrocarbons using carbon removal technologies. The UK TIMES energy system model was extended to represent all scalable hydrocarbon pathways and high-value chemical demands. In a net-zero pathway, bio-methanol underpins low-emission propylene and aromatics production, with the latter later supported by FT-naphtha co-produced with jet fuel. Electricity-based hydrocarbons lack system value in scenarios with high biomass availability and unrestricted CO₂ storage. Many models that omit these pathways will produce less optimal outcomes. The scenario analysis shows that electricity-based hydrocarbons become essential for eliminating residual fossil fuel use in aviation and petrochemicals if biomass and CO₂ storage are limited. Their deployment requires extensive upstream infrastructure and emerges only after widespread electrification elsewhere in the energy system. Yet they remain one of few scalable options for near-complete de-fossilisation.

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