Multi-criteria Analysis of Sustainable Aviation Fuel Technologies

Integrating Environmental, Economic, Social, and Technical Criteria along with Stakeholder Perspectives to Compare Fast Pyrolysis, Hydrothermal Liquefaction, and HEFA Pathways

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The aviation sector, responsible for approximately 2% of global anthropogenic greenhouse gas emissions, is projected to grow 4-6 times by 2050, conflicting with the European Union’s Green Deal target of achieving net-zero emissions by the same year. While aircraft electrification offers a promising solution, its application is largely limited to short-haul flights due to range and weight limitations. Sustainable Aviation Fuel (SAF) emerges as a compelling alternative for long-haul operations, as it is compatible with both existing infrastructure and can be blended with fossil fuels. Currently, Hydroprocessed Esters and Fatty Acids (HEFA) is the predominant pathway for producing SAF. There remains a significant supply gap for SAF, emphasising the need to scale up production and explore alternative technologies. This thesis evaluates the potential of hydrothermal liquefaction (HTL) and fast pyrolysis (FP) to address this supply gap.

The research objective is to compare HTL and FP with HEFA. A literature review identified three main knowledge gaps: (1) a lack of studies on the social impacts of HTL and FP, (2) the absence of stakeholder involvement in evaluating these technologies, and (3) the need for updated data integration to effectively compare HTL and FP with established SAF technologies like HEFA. This study addresses these gaps using a multi-criteria analysis (MCA) to provide a holistic evaluation across a multi-temporal timescale while considering diverse stakeholder perspectives.

The study employed a four-phase methodology. The first phase began with the identification of stakeholders through desk research. The second phase involved establishing the criteria for the MCA via a literature review focusing on four main dimensions: environmental (Global Warming Potential and use of by-products), economic (capital expenditure, operating expenditure, and feedstock price), technical (technology readiness level and efficiency), and social (safety and social impacts related to feedstock use). The stakeholders assigned the weightings of each criterion relative to the others during structured interviews using the Best-Worst Method (BWM). In the third phase, each technology was assessed against the established criteria through detailed analysis using specific methods. Based on the findings of the analysis, SAF experts assigned performance scores to each technology per criterion. Finally, in the fourth phase, the criteria and their weightings, along with the performance scores, were integrated to calculate a final weighted MCA score for each technology. This resulted in a final ranking of the technologies based on their overall MCA scores for each stakeholder.

HTL and FP are potential alternatives to the HEFA pathway to produce SAF, each with different advantages and disadvantages. Technically and economically, HEFA currently outperforms due to its maturity and lower costs. At the same time, HTL and FP offer potential environmental and social benefits, particularly in terms of the kind of feedstocks used and the possibilities of by-product valorisation. The preference for each technology varies between stakeholders, indicating the need for a balanced approach that integrates multiple perspectives in SAF implementation decision-making. This research provides actionable insights for advancing SAF technologies and supports the broader goal of achieving sustainable aviation.