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 ~ 12% (by mass). However, SCGO has an extremely high acid value of ~ 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 °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 mm²/s (at 40 °C), flash point of 137.5 °C, density of 891.9 kg/m³ (at 15 °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.

Graphical abstract

咖啡是一种全球性且流行的饮料，具有令人耳目一新的特性，每天都会大量饮用。在酿造过程中，会大量散发出有价值的深棕色有机废物，称为废咖啡渣（SCG）。SCG已被归类为通过生物精炼厂生产各种生物燃料和增值产品的有前途的原材料。本文旨在将SCG转化为生物燃料。首先，从SCG（SCGO）提取的油已被加工成生物柴油燃料。已经发现SCG的油含量为〜12％（质量）。但是，SCGO的酸值极高，约为24 mg KOH / g油。因此，生物柴油的生产通过酸催化过程，碱催化酯交换过程以及甲醇和加热到60°C的两个步骤进行。² / s（在40°C下），闪点137.5°C，密度891.9 kg / m ³（在15°C下），氧化稳定性为5.53小时，较高的热值为39.37 MJ / kg。这归因于其出色的不饱和度141.54和长链饱和因子6.94。其次，在这项工作中考虑了SCGOME及其与Euro柴油以及丁醇，戊醇和辛醇的三种长链醇的二元和三元混合物的质量。此策略已导致密度和冷流特性的显着改善，并且非常接近Euro柴油。最后，在这项工作中首次检查了DSC，FT-IR，TGA和NMR的快速，便宜和可靠的特性，以评估所有混合物的质量。这些特性证明了它们的质量和可靠性。结论，这项研究支持正在进行的研究，即通过综合性生物精炼厂将SCG转化为生物柴油，以实现可持续的循环生物经济。建议在以后的研究中对混合物进行详细的发动机，排放和燃烧测试。

图形概要