Upgrading of esterified bio-oil from waste coffee grounds over MgNiMo/activated charcoal in supercritical ethanol

In this work, the effect of reaction parameters such as temperature (250–375 °C), holding time (0–4 h), and bio-oil concentration (0–100 wt%) was investigated on upgrading of esterified CG-BO (CG-EBO) over MgNiMo/AC in supercritical ethanol. The esterification of CG-BO was conducted as a pretreatment to minimize the esterification reaction during the catalytic upgrading in supercritical ethanol. The MgNiMo/AC catalyst was found to play two crucial roles in the supercritical upgrading of CG-EBO; firstly, it facilitated hydrogen production through the dissociation of ethanol. Secondly, it enables the hydrodeoxygenation (HDO) reactions of CG-EBO by utilizing the hydrogen generated in situ. The biofuel products obtained by the supercritical upgrading were characterized by GC–MS, FT-IR, TAN, and elemental analyses. The catalyst characterization was accomplished by SEM-EDX, XRD, BET, N2-physiosorption Isotherms, H2-TPR, and TG analyses. Optimized conditions at 375 °C, 2 h holding time, and 20 wt% CG-EBO concentration were suggested for supercritical ethanol upgrading of CG-EBO over MgNiMo catalyst. A biofuel product with 48.6 wt% yield, 44.2 mg KOH/g TAN, and 4.0 wt% oxygen content (0.07 O/C) was obtained under the conditions. Simplified reaction pathways are suggested for supercritical ethanol upgrading of CG-EBO based on the products identified.