Defossilization of Refineries and Petrochemical Industries: Towards a Framework for Early-Stage Screening of Defossilization Pathways

Licentiate thesis, 2026

Defossilization of refineries and petrochemical industries requires replacing virgin fossil carbon feedstock with alternative carbon sources to produce carbon products that are hard to substitute, such as plastic building blocks (e.g., olefins) and transport fuels for hard-to-electrify applications (e.g., sustainable aviation fuel (SAF)). However, alternative carbon feedstock, such as waste and biomass, is heterogeneous and contains high levels of oxygenates, contaminants and unsaturated compounds, increasing process complexity, hydrogen demand and uncertainty in production pathway selection.
This thesis contributes to the development of an early-stage screening framework for defossilization technologies for refineries and petrochemical industries using thermodynamic analysis under technical, feedstock, and regulatory constraints. The framework evaluates feedstock carbon recovery potential, energy and exergy efficiency, and implications of European Union (EU) regulatory frameworks. The analysis includes two case studies focused on (i) SAF production through methanol as an intermediate fuel, focusing on production of renewable fuels of non-biological origin (RFNBO), and (ii) production of olefins and BTX for plastic through thermochemical recycling of waste using a fluidized bed steam cracking technology (FBSC) with Fischer-Tropsch synthesis for carbon recovery.
The results show that a high level of carbon recovery in FBSC systems is necessary to reduce on-site CO₂ emissions and improve resource efficiency. Increasing carbon conversion to plastic building blocks from 52% (without carbon recovery) to 90% (with full carbon recovery) is feasible while maintaining the overall energy efficiency between 60–70%. This corresponds to 30 percentage points higher energy efficiency than process pathways based on combustion in waste-to-energy plants with carbon capture and utilization. In contrast, current RFNBO requirements favor SAF production based on energy-depleted carbon sources (CO₂), resulting in an exergy efficiency of 58%, 10–26 percentage points lower than pathways based on energy-containing carbon feedstock.
The thesis highlights the importance of flexible technologies that can convert heterogeneous carbon feedstocks into essential carbon products. The proposed framework supports comparison of alternative production pathways to help decision makers identify key limitations related to carbon efficiency, energy efficiency, exergy losses and costs during early-stage technology screening.