Researchers have found that oil extracted from used coffee grounds makes viable biodiesel, and currently could supply up to 350 million gallons of the fuel according to a report in the Journal of Agricultural and Food Chemistry.
As we attempt to ween ourselves off fossil fuels, biodiesel has become big business, and world production could hit the 3 billion gallon mark by 2010. Biodiesel can be made from many plant oils, such as soybean oil and palm oil, and even cooking oil recycled from restaurants – giving the exhaust a very distinctive smell!
However, with the world’s population rising, we must strike a balance between land used to grow food, and land set aside to grow crops to meet demand for biodiesel. This is why extracting oil from used coffee grounds is such an attractive prospect – it’s already a very successful crop, with more than 7 million tonnes produced worldwide, and much of the used grounds end up in the bin or in compost.
Mano Misra and colleagues at the University of Nevada observed that spent coffee grounds contain between 11 and 20% oil by weight, a similar amount to the more traditional biodiesel crops like rapeseed. They acquired spent grounds from a multinational chain of coffee shops, destined to be sold off for compost, and set about extracting the oil and converting it to biodiesel.
To extract the oils, they dried the grounds and then mixed them with solvents like ether and hexane. The oils dissolve in to the solvents, they then filter out the solids and allow the solvents to evaporate, leaving ‘crude’ oil. The solids then went on to compost and the solvents were reused for the next batch.
The next stage was to purify the oils and convert them into biodiesel using a process called transesterification – mixing the oil with methanol and a catalyst. They observe the process using high performance liquid chromatography, and keep it running until there was no trace of oil, showing it had all been converted to biodiesel. Interestingly, the fuel actually smells of coffee, which could make for far nice exhaust smells!
When testing the resulting fuel, they found it can be used industrially as an alternative to diesel, and is of a better quality and more cost effective than other waste sources of oil. So next time you go to a coffee shop to re-fuel yourself, the grounds from your coffee could be refuelling your car!