Jose Luis Pinilla

Hydrotreatment of waste cooking oil (WCO) offers a cleaner route than transesterification for producing diesel-range transportation biofuels, primarily C15-C18 linear paraffins (green diesel). This work evaluates the H2-free hydrotreatment of WCO using methanol, isopropanol and formic acid as in-situ hydrogen donors over a Mo2C/CNF catalyst. This catalyst delivered an 86 % C15-C18 yield at 350 ºC with complete conversion using external H2. Reactions were performed in a continuous trickle-bed reactor at 350 ºC and 70 bar. Additionally, donor decomposition was also studied under N2 at 70 bar and 250-350 ºC to monitor H2 formation in the absence of WCO. Gas-phase analysis demonstrates that hydrogen was supplied exclusively via in-situ H2 formation, with no evidence supporting a dominant catalytic transfer hydrogenation pathway. The catalyst selectively converted WCO to diesel-range hydrocarbons without promoting significant cracking. Under an initial WCO/donor ratio of 70/30 v/v, hydroconversion was limited for all donors, but formic acid produced the highest C15-C18 fraction and the most hydrogenated product slate. Increasing formic acid to 45 vol.% raised diesel yield to ~60 mol %, approaching the performance obtained with external H2. Liquid products were characterised by GC-MS and GC-FID, and, to improve separation and semi-quantitative assessment of complex fractions, including compounds lacking chromophores or with poor UV absorption (saturated hydrocarbons, olefins), High-Performance Thin-Layer Chromatography (HPTLC) was incorporated as a complementary analytical technique, obtaining a repeatable and informative profiling of products. Beyond performance assessment, this study provides mechanistic insight into donor decomposition and hydrogen generation under continuous operation, constituting the first systematic comparison of multiple in-situ hydrogen sources for the continuous upgrading of a real waste-derived feedstock and demonstrating a practical pathway toward H2-free WCO hydrotreatment.