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In the frame of circular economy, wastes are perceived as sources not only for the recovery of high added-value compounds but also for energy production. Coffee is one of the most popular beverages with the consumption continuously increasing and generating huge amounts of solid residues in return. This solid waste after the extraction of the coffee beverage is known as Waste or Spent Coffee Grounds (WCG). Among others, the valorization has the potential to be directed as a bioresource for sustainable energy and particularly for the production of alternative liquid fuels for internal combustion engines. The aim of the current study is to formulate alternative fuel from WCG and to examine the fundamental properties per relevant specifications and requirements. Parameters related to stability, cold flow properties, lubricating characteristics and ignition quality are studied in comparison with other types of biodiesel fuel.

The lubricating efficiency is an important property of diesel fuel since several diesel engine parts, such as pumps and injectors, are lubricated by the fuel itself only. The evolution of oxidation products during oxidative deterioration may as well affect the lubricating properties of the biodiesel fuel blends and thus the proper functioning of a diesel engine. In this study Fatty Acid Methyl Esters were produced from various types of feedstock that significantly differentiate in their fatty acid profile. Each methyl ester was blended with an Ultra Low Sulphur Automotive Diesel (ULSD) at a concentration of 7% v/v which is currently the maximum acceptable FAME content according to the European Standard EN590. The B7 biodiesel blends were evaluated regarding fundamental physicochemical properties as well as their lubricating efficiency. Oxidation stability was examined on a Rancimat apparatus according to EN 15751 standard.

This study investigates the effectiveness of seven phenolic compounds, including pyrogallol (PY), butylated hydroxytoluene (BHT), 2,5-di-tert-butylhydroquinone (DTBHQ), 4-tert-Butylcatechol (TBC), 2,5-bis(dimethylaminomethyl) hydroquinone, 2,5-bis(piperidinomethyl) hydroquinone and 2,5-bis(morpholinomethyl) hydroquinone on the oxidation stability of sunflower and soybean oil methyl esters. The seven phenolic compounds were dissolved in the base fuels at the same concentration levels, i.e., 200, 600, 800, 1000 and 1200 ppm. The oxidation stability measurements were carried out by employing a Rancimat accelerated oxidation unit according to EN 14214. Additionally, the antioxidant activity of the above mentioned compounds was also determined in a RSSOT apparatus (Rapid Small Scale Oxidation Test) according to ASTM D7545.