The effects of the war in Ukraine on the oil market have increased focus on the EU's plans for its own production of fossil-free aviation fuel. However, EU regulations for synthetic aviation fuels risk steering development towards production routes that are both more expensive and more energy-intensive than necessary – and thus make it harder to reach climate goals. This is shown by a Chalmers study that has analysed different methods for producing synthetic methanol.

Last year, regulations were introduced requiring a blend of at least 2 per cent sustainable aviation fuel at EU airports. This blending requirement will increase progressively, to at least 70 per cent by 2050. Half of the sustainable aviation fuel must then consist of a category known as RFNBO: Renewable Fuel of Non-Biological Origin. It is synthetic fuels, also called electrofuels, which are produced from renewable hydrogen and captured carbon dioxide.

Researchers at Chalmers are now showing that the RFNBO rules favour a ”detour” in the production of synthetic fuels, which risks increasing both costs and energy consumption.

– The regulations not only affect industry investment in technology, but also what research and development is prioritised. Instead of driving innovation towards the most efficient solutions, we risk becoming locked into less resource-efficient production methods, says Henrik Thunman, professor of energy technology at Chalmers and co-author of the scientific article.

Thousands of new plants will be needed globally to meet the growing demand for sustainable aviation fuel in the coming decades. This involves very large investments in long-lasting facilities.

There's a big difference between different routes between the same raw material and final product.

Chalmers researchers have studied the production of synthetic methanol, which is an example of fuel molecules that can be converted into sustainable aviation fuel. It is a representative example for analysing how different production pathways affect resource consumption in the manufacturing of such fuel molecules.

These energy-rich molecules can be produced by combining carbon atoms and hydrogen gas in chemical processes. In studies Researchers compared three different production routes for methanol where the carbon atoms come from biomass – so-called biogenic carbon. Two of the methods are based on the combustion of biomass, where carbon dioxide is captured from the flue gases and then mixed with hydrogen produced separately using electricity. The third is based on gasification, where heated biomass is directly converted into synthesis gas, which contains both carbon and hydrogen.

All three production routes are technically feasible, and both the raw material and the final product can be the same. However, they differ distinctly in terms of energy usage, cost, and electricity requirements.

The direct production route may be omitted due to the design of the regulations.

– The gasification option proved to be the most resource-efficient in our analysis, with up to 46 percent lower production costs and 30 percent lower electricity demand than the two combustion-based options. The difference shows what significant energy losses can occur when biomass is first combusted to carbon dioxide, which is then rebuilt into fuel molecules using large amounts of electricity and hydrogen, says Johanna Beiron, researcher in physical resource theory at Chalmers and lead author of the article.

Despite this, combustion is significantly favoured over gasification by EU regulations. The RFNBO category – which is set to expand from almost zero today to a share of 35 percent of all aviation fuel in the EU by 2050 – covers all fuel from combustion alternatives, but excludes around half of the fuel from gasification.

The reason is that RFNBO cannot be produced using energy and carbon atoms that come directly from biomass, which is largely the case in gasification production. However, it is permitted to use carbon atoms from biomass during combustion, provided it is done by capturing the carbon dioxide formed when biomass is used for other energy purposes. An example of this is the combustion of residual material from the forestry industry in combined heat and power plants.

However, such residual material can therefore be used more resource-efficiently through gasification.

– One of the combustion-based alternatives we analysed was the process in combined heat and power plants, says Johanna Beiron. It has lower cost and energy efficiency than gasification, even when we account for the extra electricity needed to replace, for example, the district heating that the combustion process can contribute.

The steering risks counteracting its own goals

The purpose of the RFNBO classification includes driving increased production of renewable electricity, for the production of green hydrogen, and to reduce reliance on biomass, which is a limited resource.

But the carbon atoms for synthetic aviation fuel must come from somewhere. Biomass is expected to be the least costly fossil-free carbon source for RFNBO, and researchers estimate that current regulations will lead to a very high demand for carbon dioxide from biomass combustion. Instead of reducing the need for biomass, EU rules risk, on the contrary, driving a less energy-efficient use of the limited biomass resource.

The regulations do not sufficiently take into account how effectively different systems use energy and resources, says Henrik Thunman. The study thus highlights a structural issue in the EU's energy and industrial policy: governance risks counteracting its own goals when definitions of sustainable fuels are not aligned with fundamental energy principles and with the Union's overarching ambitions for resource efficiency.

Adjusted rules may be needed for effective transition

The researchers hope that their results will contribute to increased knowledge about the techniques and systems available.

– It is surprising that EU regulations do not steer more clearly towards the most efficient alternatives, says Johanna Beiron. Today's regulations risk leading to lock-in in combustion-based energy systems, even though technically mature processes already exist that would result in both lower energy use and cost – for example, gasification and electrification of district heating.

- Our study shows that certain parts of the regulatory framework will likely need to be adjusted for the EU to reach its long-term goals, says Henrik Thunman. Better coordination is needed between climate goals, resource efficiency, and industrial feasibility to address the current uncertainty. This makes it difficult to make rational investment decisions for the large-scale expansion of sustainable aviation fuel in the coming years.

More on: research

Studies Locked in on RFNBOs – Will EU mandates for drop-in synthetic aviation fuels lead to decreased energy- and cost-efficiency? is published in the journal Fuel. It has been carried out by Chalmers researchers Johanna Beiron, Simon Harvey and Henrik Thunman.

The research is part of the project FUTNERC, Transformative change towards net negative emissions in Swedish refinery and petrochemical industries. This is a five-year research project funded 50 percent by the Swedish Energy Agency and 25 percent each by the companies VaroPreem and Borealis. The project aims to accelerate the transition within the chemical industry to achieve net-negative greenhouse gas emissions from refineries and chemical industries by 2050 at the latest.

More on: the three methods for producing synthetic methanol

Researchers chose to investigate the production of methanol in particular because it serves as a clear example to demonstrate how the overall efficiency of fuel production is affected by whether carbon is used directly in the form of carbon-containing gas from biomass, or is first converted to carbon dioxide which is then rebuilt using hydrogen. The study compares three established, but not yet commercially used, production routes based on renewable hydrogen and biomass in the form of forestry industry residues.

1. Combustion with carbon dioxide capture

Biomass is incinerated and carbon dioxide is captured from the flue gases. Subsequently, hydrogen, which has been produced separately using water and electrical energy, is added. The carbon dioxide reacts with the hydrogen in a catalytic process to form methanol.

• High production cost (€1055 per tonne of methanol)
• High electricity consumption (1.8 megawatts of electricity per megawatt of methanol)
• Low energy efficiency (around 37 percent)

2. Combustion with carbon dioxide capture and simultaneous energy production
It resembles the first method, but combustion is also used to produce electricity or heat, for example for district heating systems. The study also includes the extra electricity required to replace this form of energy.

• Highest cost of the three options (€1495 per tonne of methanol)
• High electricity consumption (1.6 megawatts electricity per megawatt methanol)
• Similar low energy efficiency (around 37 percent)

3. Gasification of biomass
Biomass is converted through gasification into a synthesis gas, consisting of carbon monoxide and hydrogen, which is then used directly in methanol synthesis. During gasification, some carbon dioxide is also formed, which can also form methanol along with limited amounts of added hydrogen.

• Lowest cost of the three options (€820 per tonne of methanol)
• Lowest electricity consumption (1.2 megawatt electricity per megawatt methanol)
• Highest energy efficiency (approx. 46 percent)

More on: EU regulations

EU Regulation Refuel EU Aviation introducing binding requirements for a growing proportion of sustainable aviation fuels to be blended into aviation fuel sold at EU airports. The first requirements came into force in 2025 and will be progressively tightened to drive forward new production of sustainable fuels.

By 2050, at least half of all sustainable aviation fuel shall consist of RFNBOs (Renewable Fuels of Non-Biological Origin)). The second half is made up of four other categories of sustainable aviation fuel.