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New process could produce 720,000 tonnes of biodiesel a year from coffee grounds

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A new breakthrough could allow 720,000 tonnes of biodiesel to be produced each year from spent coffee grounds.

Lancaster University researchers say that the high calorific value of coffee waste could be exploited with a more efficient technique than at present, producing a greener, commercially competitive biofuel.

As well as reducing our reliance on fossil fuels, the breakthrough could address the food versus fuel debate which makes purpose-grown feedstocks for biodiesels so controversial. In 2014, more than nine million tonnes of spent coffee grounds were dumped in landfill.

In the traditional process currently used by a small number of businesses; manufacturers mix spent coffee grounds with hexane and cook the mixture at 60°C for between 1-2 hours. The hexane is then evaporated to leave behind the oils. Methanol and a catalyst is then added to make biodiesel, and a glycerol by-product – which also needs separating.

The chemical engineers have consolidated the existing multi-stage process into a single step, known as in-situ transesterification. The new procedure combines the extraction of oil from the coffee grounds with its conversion into biodiesel.

Led by Vesna Najdanovic-Visak, the researchers have consolidated the process by using just methanol and a catalyst. This completely removes the need for hexane as well as saving on chemical waste. Najdanovic-Visak and colleagues’ method can extract the same amount of biodiesel as the old method in just ten minutes.

“Our method vastly reduces the time and cost needed to extract the oils for biofuel making spent coffee grounds a much more commercially competitive source of fuel,” said Najdanovic-Visak, Lecturer in Lancaster University’s Engineering Department. “A huge amount of spent coffee grounds, which are currently just being dumped in landfill, could now be used to bring significant environmental benefits over diesel from fossil fuel sources.”

Up to 720,000 tonnes of biodiesel could be extracted each year from the new process. The report detailing the study has been published in the Journal of Environmental Chemical Engineering.