Old Christmas trees could be recycled into renewable fuels and other useful products

The past research indicated that the chemical structure of pine needles could be broken down into a liquid product (bio-oil), which could be used in the production of sweeteners, paint, adhesives and vinegar and a solid by-product (bio-char), which could be used in other industrial chemical processes.

“One of the things that we do when reacting carbon dioxide to capture CO₂is to use a metal to promote the reaction. This can be inefficient and expensive, so we went back to some of the work we’ve done previously with pine needles, because we realized that we could potentially use these to promote turning the carbon dioxide into formic acid,” said Dr McGregor, Senior Lecturer in the Department of Chemical and Biological Engineering at the University of Sheffield.

Generating formic acid

María Andérez-Fernández, a University of Valladolid PhD student and the lead of the new study, added that instead of the metal and the carbon dioxide reacting, the researchers could get carbon dioxide to react with pine needles and water at high temperatures and a fraction of the pine needles would turn into the same product as the CO₂. 

“Carbon dioxide is introduced as sodium bicarbonate, commonly known as baking soda or bicarbonate of soda. This co-conversion with captured carbon dioxide, that we didn’t have before in the previous pine needles research, has found that the two things enhance the conversion of each other, making it more efficient and in this case, making more of the end product - formic acid,” she explained.

This resulting formic acid has many useful applications. It can be most notably used in fuel cells to store and transport hydrogen, which can then be used as a clean power source.

Other use cases include pine needles transformed as preservative for foods and an antibacterial agent in livestock feed. Additionally, they could be used to manufacture leather and rubber.

“With these results, this study sets a new strategy for CO2 and residual biomass valorisation (the process of reusing waste materials and converting them into more useful products) to produce renewable fuels and value-added chemicals, using only water as a solvent and producing a simultaneous reaction that simplifies the process and makes it more efficient,” Andérez-Fernández concluded.