Oil extracted from spent coffee grounds for bio-hydrotreated diesel production

Abstract

Oil extracted from spent coffee grounds is utilized as a renewable source for bio-hydrotreated fuel production. In the present work, oil yield up to 13% can be obtained by Soxhlet extraction with hexane as a solvent. As the extracted oil contained high content of free fatty acids (6.14%), therefore one step alkali-catalyzed for ester based biodiesel production is impractical. Hydrotreating of extracted oil was performed over two catalysts i.e. NiMo/γ-Al2O3 and Pd/C with different operating parameters i.e. reaction time, operating temperature, and H2/oil. It was found that the reaction time of 2h and the reaction temperature of 400°C are favorable operating conditions. The liquid products mostly consisted of n-pentadecane and n-heptadecane, which contain one carbon atom shorter than the corresponding fatty acid (Cn−1) i.e. palmitic and stearic acid, respectively. Unfavorable cracking of diesel product is pronounced at high temperature and prolonged reaction time. In addition, although increased H2/oil promoted overall reaction and hydrodeoxygenation activity (Cn−1/Cn decreased) for both catalysts, hydrocracking is enhanced over Pd/C, leading to significant increase in gasoline yield. Moreover, Pd/C gave higher olefin content in liquid product (22.3wt%) than NiMo/γ-Al2O3 (4.8wt%). However, NiMo/γ-Al2O3 shows higher isomerization activity. The amount of isoparaffins catalyzed by NiMo/γ-Al2O3 and Pd/C were 10.8 and 1.7wt%, respectively. Physiochemical analysis of the diesel fraction exhibit satisfactory properties. The density and kinematic viscosity were consistent with the specification of commercial bio-hydrogenated diesel, NExBTL, while the cetane index was much higher than conventional diesel.