New low-cost, one-step path to coffee biodiesel uncovered by UK research team

In the UK, researchers at Lancaster University led by Dr Vesna Najdanovic-Visak have developed a one-step system for making biodiesel from spent coffee grounds.  The team found they are able to combine the processes by using just methanol and a catalyst – removing the need for hexane altogether and saving on chemical waste. In addition, they also discovered that the optimal time for the process was 10 minutes to gain the same yield of oils from the spent coffee grounds – a significant reduction in time needed and associated energy costs. The process has the potential to enable 720,000 tonnes of biodiesel to be produced each year from spent coffee grounds.

In the traditional process, 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. Spent coffee grounds, which have a high calorific value, offer a good low-cost alternative feedstock for biodiesel. However, most used coffee grounds are currently just dumped. In 2014 more than nine million tonnes of spent coffee grounds were sent to landfill. The work, reported in the paper ‘Kinetics of extraction and in situ transesterification of oils from spent coffee grounds’ has been published by the Journal of Environmental Chemical Engineering.

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