Old Christmas trees could be used to produce fuels

Each year, nearly eight million Christmas trees are sold in the United Kingdom, with an estimated seven million ending up in landfills after the holidays. Besides being costly, once in a landfill, each tree will release 16 kg of greenhouse gases as it decomposes, producing methane, which is 25 times more potent than carbon dioxide.

However, a new study led by the University of Sheffield and the University of Valladolid has found that pine needles from discarded Christmas trees could be turned into renewable fuels and other products that could be used as food preservatives or in agricultural and industrial manufacturing.

In previous studies, researchers have argued that pine needles could be processed with the aid of heat and solvents, breaking them down into a liquid product (bio-oil) – that could be used in the production of sweeteners, pain, adhesives and vinegar – and a solid by-product (bio-char), which could be used in other industrial processes.

Building upon this research, the new study showed that pine needles could also help producing formic acid, which could be used in hydrogen fuel cells, as well as a food preservative and a critical ingredient in agriculture and industry.

“One of the things that we do when reacting carbon dioxide to capture CO2 is 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,” explained study co-author James McGregor, a senior lecturer in Chemical Engineering at Sheffield.

“We found that instead of the metal and the carbon dioxide reacting, we could react carbon dioxide with pine needles and water at high temperatures and a fraction of the pine needles would turn into the same product as the CO2,” added lead author María Andérez-Fernández, a doctoral student at the University of Valladolid.

“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.”

According to the scientists, formic acid has many applications. For instance, it can be used in fuel cells to store and transport hydrogen, which can then be employed as renewable energy source. In addition, it can also play an important role as a food preservative or antibacterial agent in livestock feed, or can be used in the manufacture of leather and rubble.

If pine needles were collected and processed in this way, the chemicals obtained would replace less sustainable industrial chemicals, leading to a decrease in the UK’s carbon footprint and amount of biomass waste ending up in landfills, and potentially saving up to 100,000 tons of greenhouse gases that are currently released every year by landfilled Christmas trees.

The study is published in the journal ACS Sustainable Chemistry & Engineering.

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By Andrei Ionescu, Earth.com Staff Writer

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