Limitations to sustainable renewable jet fuels production attributed to cost than energy-water-food resource availability

Global biojet fuel sustainability index

The COVID-19 pandemic has irrevocably changed the global energy market, with the largest ever price swings between trough (March 2020) and peak (March 2022) in crude oil price within a two-year period being recorded at around -USD 37 and USD 130 per barrel, respectively10. While the former is due to logistic and petroleum storage issues, and the latter is a consequence of supply fears, the worldwide inflationary impacts of higher energy costs are expected to push crude oil prices eminently upwards.

We set the key scenario for the crude oil price of USD 135 per barrel, with biojet fuel production costs of OTJ, ETJ and GTJ at -USD 0.6378, USD 0.6334 and -USD 0.1824 per litre, respectively. In this scenario, Finland emerged as the top-ranked country with a sustainability index score (SIS) of 57.4 out of a possible 100 as shown in Fig. 2. See Supplementary Dataset 1 for the full ranking and index scores. This high SIS stemmed from a thriving RJF industry to rank first in the Energy domain, having robust governance to rank 4th, good food security with sufficient production to withstand shocks and being invulnerable to food shortage due to easy access to the food market. Overall, the country emerged in the top quartile for the energy, food and governance domains, while still having above-average water security.

Fig. 2: Global biojet fuel sustainability index ranking.
figure 2

The sustainability index scores for each country or territory is aggregated from the individual domains of energy, water, food and governance ranking. The colours in the choropleth map are categorically arranged in descending quartile order of green, orange, yellow and red.

Like Finland, most of the other countries in the top 10 have the distinction of being in the best quartile for 2-3 of the sustainability domains. There is no country or territory which is outstanding on all four domains as energy is heavily dependent on the availability of low-cost feedstocks, water security relies on having not already tapped into their water resources for other industries, food security is determined by either having easy access to food market or already producing surplus food, while good governance is required for policies to be passed through strong political will. This reinforces the idea that even country presently with the best sustainability rating will find it difficult to balance the utilitarian aims of using the finite EWF resources for sustainable aviation.

European countries dominate the sustainability ranking with 13 countries in the top 30, with the general characteristics of having secured food supplies and functioning governments, while being merely above average in water security but having low scores in energy security. The mostly South American countries in the Americas form the next largest group with nine being in a good position to push for RJF productions. Unlike the distinct characteristics of the European countries, the Americas countries (or territories) are a disparate group, each with their own strengths and weaknesses. Asia-Pacific countries with three apiece from Asia and Oceania round up the most sustainable countries for RJFs, with one coming from Africa. The African countries are generally ranked low for energy security due to issues in not having affordable feedstocks for RJF production and are still highly dependent on energy imports.

For individual domains, the energy security ranking favours countries with larger land area such as India, Brazil, USA and Indonesia as there are likelihood of more biomass resources that can potentially be collected for RJF productions, whether from crops, forest or agricultural wastes. Countries highly dependent on seed oil exports like Ukraine, Indonesia and Malaysia also tend to do well as there are abundant feedstock that can be converted to RJF using OTJ methods. Water security is tied to economic activities, so countries with additional allowances to divert water for RJF productions are also those with minor agricultural sector or minimal water-intensive industries, such as Somalia, Niger, Suriname, Mongolia and Gabon. Countries with high food security scores, in particular those in the top quartile, are usually wealthy countries with access to a well-regulated food market such as Switzerland, Belgium, Netherlands and Norway. Food security can be fragile even for highly ranked countries like Lebanon. The Russia-Ukraine conflict has severely jeopardised food security for Lebanon as it is reliant on imported food particularly sunflower oil from Ukraine15. The high-income countries as classified by the World Bank from Scandinavia, Western European and Australasia such as Norway, Sweden, Finland, Denmark, Netherlands, Switzerland, Luxembourg, New Zealand and Australia usually have high government effectiveness, leading to high placing in governance ranking.

Energy replaceability

Energy replaceability refers to the percentage blend that a country or territory has to displace existing conventional jet fuel usage. Presently, the ASTM-approved technological pathways for RJF only allows blending level up to 50% by volume. The limits were triggered by the lack of aromatics in RJF, which are required for high altitude usage, as all mixtures of RJF and conventional jet fuel must be undifferentiated once they are mixed, also referred as drop-in fuel. The RJF energy replaceability levels for each location when crude oil price is at USD 135 per barrel and there are provisions for partial subsidies to offset production costs, as shown in Fig. 3. It should be noted that the replaceability level worldwide is near identical even at USD 60 per barrel crude oil price, as the main deciding factor is the provision of financial support by governments. The support for this nascent industry is required until critical mass is reached and know-how in production technologies improves to drive down the production costs. Once the economies of scale are achieved, governmental subsidies can be removed.

Fig. 3: Replaceable jet fuel consumption level by renewable jet fuel (RJF).
figure 3

The total potential profitable RJF quantity that can replace present day petroleum-based jet fuel consumption at crude oil price of United States Dollar (USD) 135 per barrel with partial subsidies to defray production costs. The B1, B10 and B50 lines refer to 1%, 10% and 50% biojet fuel in the volumetric blend with fossil jet fuel, respectively. As most RJFs can only be mixed at 50% volumetric level to be classified as a drop-in fuel, countries above the diagonal red line have the potential to maximise the usage of RJF as a mixture component in a profitable manner. Insets are used to provide space for labelling. The abbreviation of the listed countries follows the ISO 3166-1 by the International Organization for Standardization (ISO), and is provided in the Supplementary Dataset 1.

As RJFs can be produced from a myriad of feedstocks, 74% of the 154 countries and territories analysed in this study can maximise the blending levels of RJF with conventional jet fuels in a profitable manner under favourable conditions, often with huge surpluses. Notably, few of the biggest jet fuel consumers, namely the USA, China, Russia, India and Brazil which collectively utilise 52.4% of global jet fuel, can exceed the maximum RJF blending levels of 50%. Japan, South Korea, Saudi Arabia, Netherlands and Belgium are among countries with high jet fuel consumption above 1 billion litres annually but are unable to achieve maximum blending levels (positioned below the red diagonal line) even under favourable economic conditions.

On the other hand, there are 13, 4 and 21 countries with the potential capacity to volumetrically displace only 10-50%, 1-10% and sub-1% of fossil jet fuels, respectively. Majority of the countries and territories with limited capacity to ramp up their RJF production are the countries with small land mass and limited agricultural output like Singapore, Malta and Luxembourg, or Middle East and North Africa (MENA) countries with generally lower land productivity such as Bahrain, Jordan, Kuwait, Oman, Qatar and United Arab Emirates, and are already managing food insecurity16.

Water footprint

Using a four-quadrant system in Fig. 4 to evaluate the balance between displacing conventional jet fuel with RJFs and water stress index (WSI), it is observed that every continent would have countries or territories that could develop their local RJF industries without overwhelming the water usage. If WSI above 0.4 is considered high and 100% blending ratio denotes total displacement of fossil fuel, then we have a water stress-blessed and low-high blending ratio matrix.

Fig. 4: Projected water stress index (WSI) against the potential blending ratio.
figure 4

Projected WSI on 100% replacement against the potential blending ratios as banded by continents. The four quadrants represent water stressed-blessed and high-low blending ratio dichotomies. A WSI value of 0.4 is classified as water stressed, while values above unity are only hypothetically plausible. Countries in the same continent are linked with lines. The abbreviation of the listed countries follows the ISO 3166-1 by the International Organization for Standardization (ISO), and is provided in the Supplementary Dataset 1.

Every continent has countries or territories with the potential to totally replace fossil-based fuels with the more sustainable alternative without incurring water stressed scenario (i.e. in Quadrant IV). The continents of Africa, Asia, Americas, Europe and Oceania have 32, 20, 18, 14 and 3 countries, respectively. In general, countries or territories in Oceania, Americas and Africa are less likely to have stress on water security. This is particularly crucial for countries or territories in Oceania as the predominant method to access these countries or territories for passengers is via airways, so there is an added incentive to improve energy security and be less susceptible to crude oil price volatility. Eighteen European countries will expect some degree of water stress (i.e. in Quadrants I and II) at 100% jet fuel replacement level.

Food and feedstock

Food supply chain stresses do not only stem from the lack of production, but also contributed by bottlenecks in the processing, transport and logistics, as well as major shifts in demands. The Organization for Economic Co-operation and Development (OECD) found that the COVID-19 pandemic has introduced unexpected stresses on the food supply chains, although also noted on the resilience of the supply chain actors to repivot themselves to resume the availability of food17. Policy makers were found to have avoided the same errors committed during the 2007-8 food price crisis. As such, it will be more strategic to look at land usage in addition to food stress, as the former is permanent while the latter is transient.

The total plantation area needed across all RJF pathways to tap into the full potential of the fuel amounts to 1.508 billion hectares. This number is the same as the global amount used in crop production, as the simulation model does not assume increased agricultural output, but instead divert oil, sugar, starch and utilise waste feedstocks for the RJF production. The production methods of OTJ, ETJ and GTJ are expected to co-utilise 24.6%, 23.6% and 51.8% of plantation land on top of normal agricultural practices, respectively. This remains positive as the release of captured and sequestered carbon within fossil-based jet fuel through aviation-sector combustion can be reduced without increase in precious arable land usage. As the increase in RJF feedstock and food availability are tied to agricultural land availability, there is little to be concerned on the food vs fuel debate, as there remains 2.7 billion hectares of land that can be brought under cultivation as estimated by the Food Agriculture and Organization of the United Nations18.

Profitability price point

The OTJ, ETJ and GTJ family of production methods have the largest distinction, with very different feedstock and biomass quality requirements. The OTJ method is best represented by the prevalent hydroprocessed esters and fatty acids (HEFA) which involves hydrotreatment, cracking and isomerisation of the feedstocks. It is also the most technologically advanced production method with a technology readiness level (TRL) among the ASTM-certified pathways at TRL 9. Despite the OTJ method allowing biojet fuel producers to turn in a profit at various crude oil price-production cost combinations as illustrated in Fig. 5, OTJ will eventually face feedstock availability limitations. There are only an estimated of 35.15 billion litres of feedstock that can be sustainably diverted from food sources for biojet fuels without impacting food supplies. Furthermore, some of the crude oil price-production cost permutations would require levels of governmental subsidies, pioneering incentives, and supportive policies to function.

Fig. 5: Profitability price point of biojet fuels by production technologies.
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Projected profitable biojet fuel volume for the oil-to-jet (OTJ), ethanol-to-jet (ETJ) and gas-to-jet (GTJ) production methods when crude oil price varies in the United State Dollars (USD) 0-400 per barrel range. The production method of OTJ, ETJ and GTJ is shown in shades of green, blue and red, respectively.

Ethanol-to-jet, which is part of the alcohol-to-jet methodology, involves the relatively mature dehydration, oligomerization and hydrogenation processes. It is unlikely to be financially viable under the present market price for crude oil. The industry for ETJ is also unlikely to receive governmental subsidies as the amount will be prohibitively exorbitant due to the already existing and thriving bioethanol industry globally. In the event if crude oil price increases above USD 165 per barrel, ETJ will be immediately viable and also have a higher ceiling for feedstock availability at 94.04 billion litres.

The syngas-based GTJ method has the greatest feedstock availability, which is an order of magnitude higher than that of OTJ and ETJ. This method has sufficient feedstock to produce 704.32 billion litres of RJF, as any organic biomass has the potential to be turned into GTJ feedstock. As agricultural wastes and other non-edible feedstocks are earmarked for valorisation as GTJ biojet fuels, the feedstock cost is a fraction of OTJ and ETJ feedstocks. This means that GTJ method is economically viable even at present crude oil price with zero to minimal governmental assistance. The only drawback is the low TRL, as the jet fuel range selectivity of the dominant GTJ method, namely the Fischer-Tropsch (FT) method remains low at larger scale productions.

Limiting factors

The delicate balance between the resources nexus requirements and economic climate of the aviation fuel industry requires limiting factors to be determined. This is to avoid the depletion of any individual resource and provide economics insights to policy-makers on the immediate dangers of scaling up their RJF industry. The limiting factors to produce profitable RJF for each country or territory at USD 60 per barrel and USD 135 per barrel with various subsidy scenarios are shown in Fig. 6. The subsidy amounts are benchmarked against the various US biofuel policies. The five limiting factors include energy diversity, water stress, food stress, feedstock availability and crude oil price.

Fig. 6: Limiting factors for the potential profitable renewable jet fuel (RJF) production.
figure 6

Limiting factors for each country and territory when crude oil price are in the range of United State Dollars (USD) 60-135/barrel under a binary subsidy scenarios. The colours represent the most critical limiting factor that countries and territories will face to produce profitable RJF.

The limiting factors are generally insensitive towards crude oil price in the USD 60-135/barrel range. Instead, they are almost exclusively influenced by the availability of the hypothetical governmental subsidies. In a ‘no subsidy’ scenario regardless of crude oil price, close to 90% of all countries and territories will be limited by the prohibitive economic factor to produce profitable RJF.

However, even if ‘partial subsidy’ is provided, then primarily EWF nexus-type limiting factors surface as profitability conditions become less of a concern. This might lead to RJF becoming a victim of their own success where a glut of RJF will enter the aviation sector for 80 countries and territories, leading to concerns about a lack of diversity in fuel sources. Such a risk is pertinent for localities which are over-reliant on a smaller subset of feedstocks, for example, Indonesia might have sufficient palm oil for RJF production, but the 2022 palm oil export ban in the country shed light on the dangers of using a dominant crop as a feedstock. Food stress and feedstock availability would affect 40 and 24 countries and territories, respectively. They either have socio-economic issues such as those in the northern African region, or have large swathe of barren land like Mongolia and Australia. There are still 10 countries that struggle to compete with petroleum-based jet fuel even with generous subsidies pumped in due to high feedstock costs. In all scenarios, water stress is unlikely to be the limiting factor as it is often caused by multiple sectors rather than primarily caused by biofuels.

Sustainability of RJF from SDG perspective

The relationship between the RJF production with the social and natural resource sustainability is mapped via the SDG as shown in Fig. 7. The production of sustainable and affordable RJF is directly linked to SDG 7, which serves as the foundation that leads to the spillover effects on the broader scale of sustainable development. The most direct impact of RJF production is energy diversity, water and food, which are closely linked to the SDG 8, 6 and 1, respectively. Development of the RJF industry will lead to job creation and economic growth, in which the spillover effects include the innovation in industry and infrastructure, paving the way for the development of a more sustainable city. From the resource perspective, responsible consumption of water and feedstock for RJF production is essential to safeguard the health and well-being of society. The utilisation of sustainable RJF on aircraft leads to reduction of GHG emissions, which is a positive contribution to climate change that will cascade to life on ground and water, so that the livelihood of society is protected. In the post-pandemic era, it is expected that RJF demand will soar in the pursuit of long-term carbon neutrality goal. The alignment of sustainable RJF with the environmental and social-economy aspects is pivotal to ensure long-term sustainability.

Fig. 7: Relevance of renewable jet fuel (RJF) production to the Sustainable Development Goals (SDG)42.
figure 7

Mapping of the cascading effect of RJF production on the well-being of society and environment by aligning with the SDG, taking into consideration the spill-over effects of energy diversity, water, food and greenhouse gas emissions.

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