Researchers at Lancaster University in the UK have developed a new faster single-step process to convert coffee grounds into biodiesel.
Around 2 billion cups of coffee are consumed annually in the UK giving rise to considerable volumes of spent coffee grounds. These have a high calorific value and potentially offer a good low-cost waste derived biofuel feedstock. However, most used coffee grounds, over nine million tonnes in 2014, end up in a landfill.
Although a small number of businesses are using spent coffee grounds to make solid biomass fuels such as briquettes or pellets or liquid biofuels, a team of researchers at Lancaster University have found a way to significantly improve the efficiency of the latter process– vastly increasing biofuel from coffee’s commercial competitiveness.
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.
Faster single-step process
The chemical engineers Dr Vesna Najdanovic-Visak, Florence Yee-Lam Lee, Marcia Tavares and Alona Armstrong have consolidated the existing multi-stage process into one step known as in-situ transesterification, which combines extraction of the oils from the spent coffee grounds and the conversion of it into coffee biodiesel.
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 are then added to make biodiesel and a glycerol by-product – which also needs separating.
Lancaster University researchers, led by Dr Vesna Najdanovic-Visak, 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.
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. 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.,” said Dr Najdanovic-Visak, Lecturer in Lancaster University’s Engineering Department.
The process has the potential to enable 720 000 tonnes of biodiesel to be produced each year in the UK from spent coffee grounds.