Biofuel Aircraft Fuel from Tomato Waste

How waste from tomato processing could power aircraft in the future has been researched by a team led by TU Graz in the EU project ToFuel. A new biorefinery concept transforms tomato residues into sustainable aviation fuel, as well as fertilizer, animal feed, and cooking oil.

Tomatoes are the second most consumed vegetable worldwide after potatoes. Around 17 megatons are harvested in the EU alone. However, large amounts of residual biomass are generated during tomato production—plant material such as flowers, leaves and stems, skins, seeds, and tomatoes of insufficient quality. Most of this waste is burned as agricultural waste or disposed of at high cost.

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At the same time, the goal of European climate neutrality and the associated reduction of CO₂ emissions in the aviation sector largely depends on the production of sustainable and competitive aviation fuels (Sustainable Aviation Fuels; SAF) from renewable raw materials. "From the EU-wide amount of so-called tomato pomace, the residues from tomato processing, it is estimated that around three percent of the Sustainable Aviation Fuels needed in Europe by 2030 could be covered," explains project leader Marlene Kienberger from the Institute of Chemical Process Engineering and Environmental Technology at TU Graz.

From plant to oil to jet fuel

To transform tomato residues into high-quality fuel, the biomass must first be treated so that microorganisms can efficiently process it. ToFuel is investigating two modern fractionation technologies for this purpose. In extrusion, the biomass is treated with heat and pressure and then broken down into its cellular components through an abrupt pressure drop. This results in optimally processed biomass for the subsequent fermentation, during which microorganisms produce lipids that are later converted into aviation fuel. In the second fractionation technology, hydrothermal liquefaction, the biomass is converted into bio-oil and biochar under high pressure and high temperatures.

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Before the obtained bio-oil can be refined into aviation fuel, it must be purified of predominantly nitrogen-containing interfering ions. These undesirable ions would otherwise negatively affect the subsequent conversion into sustainable aviation fuel. The corresponding fractionation, biotechnological, and purification processes are being developed in close collaboration by the Laboratório Nacional de Energia e Geologia (LNEG) in Lisbon, TU Graz, and the University of Zagreb.

Our clear goal is to produce sustainable aviation fuel based on tomato residues at a competitive selling price.

Marlene Kienberger

Subsequently, the lipids and bio-oil are converted into a fuel at the Montanuniversität Leoben through the HEFA process, which meets international quality standards for sustainable aviation fuel. HEFA stands for "Hydroprocessed Esters and Fatty Acids" and is a process for producing sustainable aviation fuel from plant-based, animal, or recycled fats and oils.

The processes developed in the project are being gradually scaled up to a pre-industrial level and comprehensively tested. Consortium leader Marlene Kienberger emphasizes: "Our clear goal is to produce sustainable aviation fuel based on tomato residues at a competitive sale price. In the end, sustainable aviation fuels must also make economic sense." Additionally, the project team is analyzing the environmental, economic, and social impacts of the technologies. Furthermore, the use of tomato residues creates new revenue streams for food processing.