Producing Biodiesel from Used Coffee Grounds by Transesterification

by Ben Laurie-Machin

The manufacturing of transportation fuels such as petrol produces around 20% of all greenhouse gases. Therefore, it is essential to find alternative, greener fuels. One such alternative fuel is biodiesel produced from waste products and resources. My group’s project was to turn used coffee grounds, taken from one of Bath University’s cafes, and turn them into biodiesel.

Extraction

First of all, we had to extract the coffee oil from the grounds. We did this by mixing the grounds with a solvent, hexane, and then filtering the mixture. We then took the mixture and heated it under reflux while stirring it. After that, we filtered out the solvent-oil solution.

Evaporation

Once the solvent-oil solution had been obtained, we had to evaporate the mixture. Evaporation is an important step as it allowed us to concentrate the solution by removing the hexane. We did this by heating the solvent in a rotary evaporation unit.

Coffee Biodiesel Synthesis

The final step was to turn the coffee oil into biodiesel. We did this through a process called transesterification. Transesterification is the process of exchanging the organic group on an ester with the organic group on an alcohol.

In our experiment, we used an alcoholic catalyst (ethanol) to turn the oil (triglycerides) into biodiesel.

fig 1

Analysis

Throughout the transesterification stage, which happened over 24 hours, we took samples from the solution and tested them to see how much biodiesel had been made throughout the experiment. To be able to test the samples, we put them in an NMR (nuclear magnetic resonance) machine. The NMR machine can detect the magnetic field around each proton within the sample. From this, we can determine what sort of bonds are near each proton and quantify the amount of biodiesel in the sample.

In the end, our experiment turned out to have a 0.170% efficiency. This is mainly due to the transesterification stage in which we heated the solution for 24 hours. A lot of energy was wasted here. If biodiesel was going to be produced on an industrial scale from coffee grounds, a more efficient process will need to be found.

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