New scientific research shows how plant residues can contribute to sustainable energy and raw materials
On April 3, 2025, the scientific journal Scientific Reports a groundbreaking study on agricultural waste, conducted by researchers Mihai Brebu, Daniela Ioniță and Elena Stoleru. The article, entitled “Thermal behavior and conversion of agricultural biomass residues by torrefaction and pyrolysis”, investigates how residual flows from agriculture can be used to extract energy and raw materials.
Agricultural waste streams are the remains of plants after harvesting. Think of stems, peels, shells and pits that are often considered waste. Instead of simply composting or burning this waste, these residual products can be converted into valuable products, such as biofuels or chemicals, with the right processing.
Two processing methods: torrefaction and pyrolysis
The researchers investigated two processing methods: torrefaction and pyrolysis.
- Torrefaction is a process in which biomass is heated to approximately 250 degrees Celsius in an oxygen-poor environment. This causes the material to dry out and contain less moisture, increasing the energy content per kilo. This process is ideal for producing solid fuels that contain a lot of energy.
- pyrolysis is a more intensive process in which biomass is heated to 550 degrees Celsius without oxygen. This breaks down the material into solid residues (biochar), liquid oils and gases. The biochar can be used as fuel, while the oils can be used in the chemical industry.
Which residual flows are most suitable?
The research shows that not all agricultural residual flows have the same properties. For example, peels appear to be very homogeneous, which means that they have a constant composition and therefore exhibit predictable behaviour when heated. Stems, on the other hand, are much more variable, which means that the processing results are less constant.
In addition, shells often contain thermally sensitive substances that decompose faster, while kernels are rich in oils. Because of these differences, it is important to determine in advance which residual flow is suitable for which processing technique.
What do the processes yield?
- Torrefaction: At a temperature of 250 degrees Celsius, almost all the energy is retained in the solid, which means that there is hardly any energy loss. This makes torrefaction interesting for making efficient biofuels.
- pyrolysis: At 550 degrees Celsius, biochar, oil and gas are produced. The oil from the peels contains many phenolic compounds, which are useful in the production of glues and resins. The shells yield aromatic compounds, which can be used in perfumes or as chemical building blocks. Stems produce compounds such as furans and ketones, while kernels yield oils rich in fatty acids.
This research shows that agricultural waste does not have to be a worthless residual product. Through smart processing, these residues can contribute to sustainable energy solutions and the production of valuable chemical substances.
By knowing the specific properties of each type of waste, farmers and industries can handle agricultural waste streams more efficiently. In this way, we contribute to a circular economy and reduce waste.
More information about the research can be found at nature.com.
