Generally, spent or used coffee grounds are just dumped. However, they have a high calorific value, and offer a good low-cost alternative feedstock. Now, researchers at Lancaster University have found a way to significantly improve the efficiency of biofuel production using coffee grounds. The chemical engineers have consolidated the conventional multi-stage process into one step (known as in-situ transesterification), which combines extraction of the oils from the spent coffee grounds and its conversion into coffee biodiesel.
A conventional process exists for producing fuel from coffee grounds. In this process, manufacturers mix spent coffee grounds with hexane and cook the mixture at 60°C for 1-2 hours. The hexane is then evaporated to leave behind the oils. Methanol and a catalyst are added to make biodiesel, and a glycerol by-product. Steps are additionally required to separate the glycerol.
In the new method, the Lancaster researchers combined 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. This led to a significant reduction in time and also the associated energy costs. The process has the potential to enable 720,000 tonnes of biodiesel to be produced each year from spent coffee grounds.