Scientists have developed a relatively simple method for recovering oil from used coffee grounds while preserving the remaining material for producing other renewable fuels and bio-based products.
Researchers at Universitat Rovira i Virgili (URV) studied how spent coffee grounds could be processed more efficiently as a raw material for biorefineries. Their findings were published in Biomass and Bioenergy.
Around 10 million metric tons of coffee beans are produced each year globally, while much of the solid material left after brewing is discarded. Spent coffee grounds contain roughly 15% lipids, making their oil potentially suitable for biodiesel production.
Researchers Recover Around 90% of Available Oil
The researchers examined how temperature, extraction time, and the amount of solvent affected oil recovery. They used n-hexane, a solvent commonly used for extracting fats.
The team identified optimal conditions of 45°C for 60 minutes using 35 milliliters of hexane for every gram of dry coffee residue. Under these conditions, the process recovered around 90% of the oil obtainable through Soxhlet extraction, a conventional laboratory technique that requires more time and energy.
The resulting oil was also significantly cleaner. It contained only 0.3% impurities, compared with 3.9% using Soxhlet extraction.
Its fatty acid composition remained stable across the conditions tested, with linoleic and palmitic acids making up the main components. Researchers said this profile supports the oil’s potential for biodiesel production.
The Rest of the Coffee Grounds Remains Useful
The researchers deliberately avoided damaging the lignocellulosic material left after oil extraction.
This residue contains cellulose, hemicellulose and lignin that could later be used to produce bioethanol, lactic acid, polyhydroxyalkanoate bioplastics, phenolic compounds and precursors for sustainable aviation fuel. Removing the oil may also make subsequent processing easier by giving solvents, enzymes and catalysts better access to the remaining biomass.
The researchers also compared conventional batch extraction with ultrasound- and microwave-assisted techniques. Although those methods accelerated the initial release of oil, they offered no clear overall advantage when energy use, purity, efficiency and large-scale implementation were considered.
The team therefore identified moderate-temperature batch extraction with n-hexane as a practical option for biorefineries seeking to turn spent coffee grounds into several useful fuels, chemicals and materials instead of treating them simply as waste.
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