The Science Behind Co-Pyrolysis
Co-pyrolysis is a thermochemical process that involves heating organic materials, such as biomass, and fossil resources, like oil shale, in the absence of oxygen to produce liquid, solid, and gaseous products. The liquid products, primarily bio-oil, can be refined into transportation fuels like diesel, gasoline, or jet fuel, used directly in industrial furnaces and boilers, or serve as a feedstock for producing valuable chemicals such as phenols, acetone, and acetic acid. The solid product, char, can act as a high-energy fuel for power generation or industrial processes, and when derived from biomass, it serves as biochar for soil enhancement and carbon sequestration. The gaseous product, syngas, is an energy source for electricity generation, a precursor for producing chemicals like methanol and ammonia, and a source of hydrogen for industrial and fuel cell applications. 
In this study, Alejandro performed a thorough literature research, which led to designing and conducting a series of optimized experiments and a computational model, with the aim to analyse the co-pyrolytic behaviour at different scales as well as characterize the obtained products and their yields. The research included thermogravimetric analysis (TGA) to study the fundamental behaviour of each feedstock individually and in co-pyrolysis, as well as bench-scale co-pyrolysis and co-pyrolysis in a continuous feed reactor to produce oil and char. All products from the co-pyrolysis were put into advanced characterization—to evaluate how biomass and oil shale interact during the process and the potential benefits of the process.

Key Findings and Benefits
The study found that co-pyrolyzed oils exhibit superior qualities compared to oils derived from biomass or oil shale individual pyrolysis, which have had challenges due to bio-oil's high oxygen content and instability, and the environmental impact of shale oil production. Individually, biomass pyrolysis often produces bio-oil with a high oxygen content, resulting in poor thermal stability, low calorific value, and corrosiveness, making it unsuitable for direct use in engines or industrial applications without extensive upgrading. On the other hand, oil shale pyrolysis faces significant environmental concerns, including high greenhouse gas emissions, substantial energy consumption, and the production of toxic by-products such as sulphur compounds. 
Co-pyrolysis addressed these issues by blending the two feedstocks, which not only can improve the energy content and stability of the resulting oil but also mitigate the environmental and processing challenges associated with individual pyrolysis methods. This approach combines the properties of biomass and oil shale to produce cleaner, more efficient fuels while enhancing process efficiency and sustainability. The study resulted in liquid products with reduced oxygen content, increased calorific value, and enhanced thermal stability, making the fuel more efficient and cleaner to burn. Additionally, the process optimized the production of oil and minimized the formation of char and non-condensable gases, favouring oil production, which improves the overall efficiency and economic feasibility of the process.
By utilizing biomass—such as forestry residues—alongside oil shale, the co-pyrolysis method provides a practical way to integrate renewable and fossil resources. The physical blending and the similarity in the required thermal conditions to transform these feedstocks during pyrolysis, results in optimized resource use and a reduction in the dependency on fossil fuels. Contrary to other research, the detailed study of this research using different experimental equipment revealed that the interaction between biomass and oil shale during co-pyrolysis exhibits minimal synergy, meaning their combined reaction does not significantly enhance or inhibit chemical transformations or product yields. 
The studied process offers notable advantages that highlight its practical value. The additive behaviour in co-pyrolysis improves the quality of liquid fuels, making the resulting bio-oil more suitable for energy applications. Additionally, the process optimizes resource utilization by producing a higher yield of liquid fuels compared to single-feedstock pyrolysis. Furthermore, co-pyrolysis provides an effective means to integrate renewable biomass and fossil oil shale, demonstrating its potential to create cleaner, more efficient energy solutions while addressing both economic and environmental challenges.

A Strategic Opportunity for Estonia
Estonia’s energy sector has long been shaped by its reliance on oil shale, a resource with significant economic value but substantial environmental challenges. Co-pyrolysis, as demonstrated in this research, provides an opportunity to modernize the industry by incorporating biomass into the energy mix. This approach not only diversifies the country’s energy portfolio but also aligns with global efforts to reduce carbon emissions and transition towards more sustainable energy systems. The ability to produce cleaner, high-quality fuels locally could also have economic benefits, by adding value to forestry waste and leading Estonia to meet its European Union climate commitments by lowering greenhouse gas emissions from oil shale processing.
Alejandro´s research identifies the limitations of synergy between biomass and oil shale, it highlights the broader benefits of co-pyrolysis. The study shows that technological innovation can turn challenges into opportunities, making co-pyrolysis a viable tool for addressing both energy and environmental goals. As Estonia seeks to position itself as an example of sustainable energy innovation, research like this lead the way for a future where renewable and fossil resources are used together to create cleaner, more efficient energy systems.