Removing the Quantum Barrier to Sustainable LH2 Fuel in Aviation: A Mechanistic, Process, and Environmental Life Cycle Assessment of the Ortho-Para Conversion in Liquefaction

Liquid hydrogen (LH2) is a critical energy carrier for decarbonisation, yet its production is challenged by the high energy cost and boil-off losses associated with the exothermic ortho-to-para hydrogen conversion (OPC). A fundamental trade-off exists between the energy invested during liquefaction to achieve a high para-H2 content for storage stability and the practicality of producing lower-quality fuel for more immediate use. This Dissertation presents a comprehensive, multi-scale analysis of the OPC-integrated, H2 liquefaction process, linking fundamental reaction kinetics, process-level energy consumption, and life cycle environmental impact to establish a holistic framework for sustainable LH2 production. To quantify the techno-economic trade-offs, a large-scale hydrogen liquefaction process was modelled using Aspen Plus. This study systematically compared perfect, imperfect, and post-liquefaction OPC strategies. Results demonstrate that achieving high-purity (99.6%) para-H2 for long-term storage can increase the Specific Energy Consumption (SEC) by up to 57% compared to producing normal LH2, establishing a direct, quantifiable link between production energy and fuel storage quality. To understand the fundamental reaction mechanism, the cryogenic OPC kinetics were investigated experimentally over an IONEX® catalyst (27–77 K) using a differential reactor. A dual kinetic regime was identified, revealing a non-classical negative apparent activation energy below 35 K. This behaviour is explained by a modified Langmuir-Hinshelwood model where capillary condensation within the catalyst pores creates a dense reactive phase, dramatically accelerating the conversion rate and providing a new mechanistic basis for designing advanced cryogenic reactors. To assess the broader system implications, an environmental life cycle assessment (LCA) was conducted for LH2 use in aviation, uniquely incorporating the Global Warming Potential (GWP) of vented boil-off hydrogen. The findings reveal that the carbon intensity of the electricity source and boil-off management are the dominant factors determining the overall GWP. When produced with renewable electricity, LH2 can achieve GWP reductions of over 90% compared to jet fuel, a benefit that far outweighs the marginal environmental differences between OPC strategies. In summary, this dissertation demonstrates that optimising the LH2 supply chain requires a system-level approach that extends beyond maximising para-hydrogen content. By linking fundamental kinetics to process design and environmental impact, this work provides a new paradigm for LH2 production. The findings show that the most effective path to sustainable LH2 is not through perfect conversion alone, but through the integration of green energy sources and effective boil-off mitigation, opening new avenues for designing economically viable and environmentally sound H2 energy systems.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2026

Author dc:creator

• Mendoza Moreno, Paula Valentina

Advisor dc:contributor.advisor

• Onn, Tzia Ming

• Liquid hydrogen
• Hydrogen Storage
• Ortho-Para Hydrogen Conversion
• Isomeric Conversion
• Sustainable Aviation
• Sustainable Fuel
• Hydrogen Liquefaction
• Heterogeneous Catalysis
• Cryogenic Ortho-Para Kinetics

Licence

• https://www.repository.cam.ac.uk/bitstreams/494fea0b-70a9-4624-8462-a10b3d908d33/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.125200

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/395813