Revolutionising sustainable hydrogen fuel as a green fuel for the aviation sector
By Associate Professor Bridgid Chin Lai Fui
Globalisation and rising energy needs are related to the increased demand for conventional fossil fuels. However, the economy based on fossil fuels and its constant usage as a source of energy has resulted in worrying issues that contribute to environmental pollution crises and greenhouse gas emissions (GHGs).
According to the International Energy Agency (IEA), the emission of carbon dioxide (CO2) had risen by over 2 billion tonnes in 2021, which was reportedly the highest-ever annual rise in absolute terms. This was linked to the rapid recovery of the global economy from the COVID-19 pandemic, which in turn led to significant power usage fuelled by coal.
This has prompted relevant stakeholders and policymakers to seek sustainable alternative energy options to reduce fossil fuel dependency. Among the results of these initiatives is a gradual increase in societal interest in using hydrogen generation from renewable energy in a move towards decarbonisation and meeting the needs of the energy sector.
Aviation is said to be an industry where emissions should be reduced significantly due to these efforts. Before the COVID-19 pandemic, it was reported that the yearly consumption of aviation fuel was 343 billion litres in which 0.015 billion litres were formulated from renewable sources.
From a commercial perspective, the emitted GHGs from the aviation sector was anticipated to rise by 5 per cent by 2050. To mitigate this, the International Air Transport Association (IATA) aims to reduce CO2 emissions by 50 per cent by 2050 by implementing sustainable aviation fuel, advancing aircraft technologies, improving the efficiency of operations and infrastructure, and advancing innovative zero-emission energy sources such as electric and hydrogen power.
According to Morgan et al. (2019), there are five production pathways that meet ASTM 7566 standards for the synthesis of biofuels, namely hydrogenated esters and fatty acids (HEFA) fuels derived from used vegetable and animal oils, Fischer-Tropsch from biomass, Fischer-Tropsch with aromatics using biomass, synthetic iso-paraffin from fermented hydro-processed sugar, and alcohol-to-jet fuels derived from isobutanol.
However, there are challenges in the production of sustainable aviation fuels derived from lignocellulosic biomass and residual wastes. They include the low energy density of feedstocks, heterogeneity of feedstock, expensive capital costs, and low carbon efficiency of the processes involved. Due to these difficulties, only minimal amounts of sustainable aviation fuel were manufactured.
Hydrogen is said to play a crucial role in meeting the world sustainable energy strategy for the future whereby it can lessen the climate change threat and potentially provide zero-emission fuel for transportation. According to Yusaf et al. (2023), airplanes powered by hydrogen have contributed to substantially reduced operating costs compared to those powered by kerosene.
However, the main drawback of airplanes powered by hydrogen is that they require quadruple fuel tank sizes compared to kerosene fuel tanks. In addition, hydrogen fuel tanks need to be placed within the airplane, thus occupying space in passenger cabins or goods compartments, compared to conventional fuel tanks which are normally built into the inside of the wings as illustrated in Figure 1.
Furthermore, the mere design of hydrogen tanks can influence the energy efficiency of the airplanes powered by hydrogen. It was reported by Yusaf et al. (2023) that an increment of energy usage of between 6 to 19 per cent can be expected due to the incremental fuel tank weight. However, it was concluded that long-range aircraft using hydrogen fuel are able to achieve an energy efficiency of 12 per cent, hence it can be summarised that the design of hydrogen storage tanks for airplanes require special attention.
Figure 1: Position of fuel tank in airplane powered by kerosene (a) and airplane powered by hydrogen (b-c) adapted by Yusaf et al. (2023) and Baroutaji et al. (2019).
On 9 May 2022, Premier of Sarawak Datuk Patinggi Abang Johari Tun Openg announced that the Sarawak government had initiated research on sustainable aviation fuel production to sustainably generate jet fuel that will aid in the reduction of carbon emissions during his keynote address at the World Hydrogen 2022 Summit and Exhibition in Rotterdam, the Netherlands.
The premier added that the exploration of sustainable aviation fuel to produce sustainable jet fuel will aid in the reduction of carbon emissions across its life cycle beyond 80 per cent in comparison with fossil fuels.
Recently, Sarawak successfully introduced its first industrial microalgae plant, the CHITOSE Carbon Capture Central Sarawak (C4 Sarawak), on 23 May 2023. It was a significant step in its pursuit of a sustainable green economy consistent with its Green Energy Agenda.
Renewable hydrogen can be produced through various processes using water and biomass. Water electrolysis, water thermolysis, photocatalytic water splitting, and thermochemical water splitting are the few examples of hydrogen production pathways utilising water. These methods can be achieved with the presence of wind, solar and nuclear energy.
Meanwhile, hydrogen production using biomass can be achieved via gasification, pyrolysis and microbial action. The commonly debated argument against hydrogen is its uneconomical cost rather on the safety aspects. Although ‘green hydrogen’ can be produced via the presence of water and renewable energy sources, the majority of the hydrogen produced is from ‘grey hydrogen’ which addresses the depleting sources of fossil fuels.
Therefore, it can be claimed that fossil fuels continue to be the main source of energy for the world’s transport and infrastructure despite their commercial hegemony. However, based on the carbon budget projected by the Paris Agreement, transport will be GHG-free in a few decades and will be expected to be climate neutral.
As a result, an immediate response is required and hydrogen fuel can contribute significantly to the supply of clean energy to satisfy the needs of the community and achieve the goals embedded in the United Nations Sustainable Development Goals (UN SDGs). Hence, the advancement of hydrogen technology in terms of hydrogen-powered airplanes, hydrogen production and storage, and hydrogen aero gas turbines will be critical to the aviation industry.
Associate Professor Bridgid Chin Lai Fui is the Student and Alumni Committee Chair of Curtin Malaysia’s Faculty of Engineering and Science and an associate professor in its Chemical and Energy Engineering Department where she is actively involved in teaching, research, supervising research students, and providing academic leadership and administrative support. Her research focuses on converting lignocellulosic waste and plastic waste into value-added bioproducts and biohydrogen using green technology. She has received a number of international and national research grants and has authored and co-authored numerous academic journal articles and conference papers on related topics. She previously led an international JASTIP-Net funded research project on the upgrading of bio-oil targeting sustainable jet fuel range and its implementation study in the ASEAN region, and is currently leading an international research project on sustainable production of value-added products and energies from oil palm residues and plastic waste mixtures in the ASEAN region. She is a Chartered Engineer (CPEng) of Engineers Australia (EA) and also a Fellow of the Higher Education Academy, UK. Associate Professor Chin welcomes opportunities for partnerships and collaboration from interested parties and can be contacted by email at bridgidchin@curtin.edu.my.
