Coffee Grounds as Biofuel

Lenae Joe
December 11, 2023

Submitted as coursework for PH240, Stanford University, Fall 2023

Introduction

Fig. 1: The Coffee Bean Belt (Source: Wikimedia Commons)

Global coffee consumption has been rapidly increasing throughout the years. Most of the coffee is produced in the coffee bean belt, regions near the globe's equator shown in Fig. 1. Beyond its popularity as a morning staple drink, coffee may play a role in the shift towards cleaner energy. In addition to being a great source of caffeine, coffee grounds contain oil and have a high caloric value of over 24 MJ/kg, making them a potential energy source and an affordable alternative to fossil fuels. [1]

Converting Coffee Grounds into Biodiesel

10.7 million tonnes of coffee are produced globally per year. [2] Meanwhile a majority of the spent coffee grounds are going to waste. Researchers have found a way to extract oil from the spent coffee grounds using a Soxhlet apparatus and to convert the oil into biodiesel through alkaline transesterification. [3]

Quantity Value
Coffee Produced 1.07 × 1010 kg y-1
Coffee Grounds Energy Content 2.40 × 107 J kg-1
Coffee Grounds Total Energy 2.57 × 1017 J y-1
Extractable Coffee Oil 1.61 × 109 kg y-1
Coffee Oil Energy Content 3.97 × 107 J kg-1
Potential Coffee Grounds Biodiesel Energy 6.37 × 1016 J y-1
Table 1: Extractable biodiesel from waste coffee grounds. [1-3]

The total energy content of coffee produced is 257 PJ (257 × 1015 J) per year, and the energy of biodiesel produced from spent coffee grounds is 63.7 PJ per year. Thus, 25% of the total energy content of the coffee produced can be extracted as biofuel. To put this into perspective, the energy budget of civilization is 600 EJ (600 × 1018 J). [4]

Conclusion

The biodiesel produced from coffee grounds can be used as an environmentally-friendly substitute for petroleum diesel in diesel engines. Coffee's high caloric content, low cost, and high availability contributes to its favorability as a source of biofuel and a greener alternative to fossil fuels.

© Lenae Joe. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

References

[1] E. Sermyagina et al., "Spent Coffee Grounds and Tea Leaf Residues: Characterization, Evaluation of Thermal Reactivity and Recovery of High-Value Compounds," Biomass Bioenergy 150, 106141 (2021).

[2] S. Bermudez, V. Voora, and C. Larrea, "Coffee Prices and Sustainability," International Institute for Sustainable Development, September 2022.

[3] M. N. Uddin et al., "Waste Coffee Oil: A Promising Source for Biodiesel Production," Energy Procedia 160, 677 (2019).

[4] "Energy Statistics Pocketbook 2022," United Nations, 2022.