Environmental impacts of biodiesel production from waste spent coffee grounds and its implementation in a compression ignition engine

Abstract

This study explores the environmental, economic, and technical feasibility of using spent coffee grounds as parent feedstock for biodiesel production. Biodiesel is produced from the spent coffee grounds, and four blends are prepared—B5, B10, B15, and B20. The effects of two extraction solvents (hexane and petroleum ether) on oil yields of the spent coffee grounds are investigated, employing the Soxhlet extraction technique. The properties of any intermediate yield throughout the production process are characterised and adjusted by post processes to ensure the conformity of the final biodiesel product with the standards (ASTM D6751 and ISO EN14214). The major part of the study investigates the effects of blends on tailpipe emissions and performance of a naturally aspirated single-cylinder compression ignition engine. A wide range of engine speeds (1600–3600rpm at 200-rpm increments) has been considered at three engine loads (100, 75, and 50%). The standard diesel fuel is set as a basis for comparison. Results show that the post processes on the extracted oil yielded water content of 0.038%, free fatty acid fraction of 0.41%, and acid number of <2mg KOH/g. The highest oil extraction (14.12%) was obtained over a 45-min extraction time using a hexane solvent. Biodiesel blends produced lower levels of CO2, CO, and HC. Blend B5 showed average reductions of 0.34, 12.5, and 4.23% at full load for the three aforementioned emissions, respectively; B10 reductions were 3.12, 29.85, and 19.14%, respectively. Higher levels of NOx emissions were detected from all blends. At full load, the average NOx increments of B5, B10, B15, and B20 were 0.35, 1.28, 1.8, and 2.3%, respectively. The outstanding environmental and ecological benefits of using the spent coffee grounds as a potential feedstock for biodiesel production are apparent.