Valorization of spent coffee grounds for biodiesel production: blending with higher alcohols, FT-IR, TGA, DSC, and NMR characterizations

Coffee is a global and popular drink with refreshing properties that is consumed in huge amounts daily. During the brewing process, a valuable dark brown organic waste known as spent coffee grounds (SCG) is generated in bulk. SCG has been classified as a promising raw material for the production of various biofuels and added-value products through biorefineries. This paper aims to valorize SCG into biofuel. Firstly, the oil extracted from SCG (SCGO) has been processed into biodiesel fuel. The oil content of SCG has been found to be similar to 12% (by mass). However, SCGO has an extremely high acid value of similar to 24 mg KOH/g oil. Therefore, biodiesel production was conducted through two steps of acid-catalyzed process followed by alkaline-catalyzed transesterification processes along with methanol and heating at 60 degrees C. It has been found that the properties of spent coffee grounds oil methyl ester (SCGOME) fulfilled ASTM D 6751 biodiesel standards with cetane number of 54.23, kinematic viscosity of 3.73 mm(2)/s (at 40 degrees C), flash point of 137.5 degrees C, density of 891.9 kg/m(3)(at 15 degrees C), oxidation stability of 5.53 h and higher heating value of 39.37 MJ/kg. This is attributed to its excellent degree of unsaturation of 141.54 and long-chain saturated factor of 6.94. Secondly, the qualities of SCGOME and its binary and ternary blends with Euro diesel and three long-chain alcohols of butanol, pentanol, and octanol were considered in this work. This strategy has resulted in a remarkable improvement in both density and cold flow properties and found very close to Euro diesel. Finally, fast, cheap, and reliable characteristics of DSC, FT-IR, TGA, and NMR were examined for the first time in this work to assess the quality of all blends. Such characteristics proved their quality and reliability. In conclusion, this study supports the ongoing research in valorizing SCG to biodiesel through integrated biorefineries towards sustainable circular bioeconomy. It is recommended to conduct detailed engine, emissions, and combustion tests of the blends in the future studies.