Friday, June 9, 2023

Discarded Christmas trees could be turned into renewable fuels

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Researchers at the University of Sheffield and the University of Valladolid have found that pine needles from discarded Christmas trees or other sources could be used to produce renewable fuels and value-added chemicals, such as preservatives used in agriculture, using only water as a solvent.

In the U.K. alone, an estimated seven million Christmas trees end up in landfill each year at the end of the festive period. In addition to being expensive, once in a landfill, each tree will release 16 kg of greenhouse gases as they decompose, producing methane gas, which is 25 times more potent than carbon dioxide (CO2).

Now, new research is showcasing that these discarded Christmas trees could be turned into renewable fuels and new products, potentially reducing their carbon footprint. It is based on previous University research from 2018 that found that useful products could be made from the chemicals extracted from pine needles when processed. The earlier research estimated 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 CO2 is to use 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.

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,” said María Andérez-Fernández, who led the research. “This co-conversion with captured carbon dioxide, which 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 the end product – formic acid.”

The resulting formic acid has many applications. It can be used in fuel cells to store and transport hydrogen, which can then be used as a power source, offering a clean alternative to fossil fuels. It is also widely used as a preservative for foods and an antibacterial agent in livestock feed, as well as in the manufacture of leather and rubber.

“With these results, this study sets a new strategy for CO2 and residual biomass valorization (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,” Maria added.

Journal reference:

  1. María Andérez-Fernández, Eduardo Pérez, Ángel Martín, James McGregor, and María Dolores Bermejo. Synergistic Hydrothermal Conversion of Aqueous Solutions of CO2 and Biomass Waste Liquefaction into Formate. ACS Sustainable Chemistry & Engineering journal, 2022; DOI: 10.1021/acssuschemeng.2c06218
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