Comparative evaluation of methanol, isopropanol, and formic acid as hydrogen donors in the continuous H2-free hydrotreatment of waste cooking oil for green diesel production

Hydrotreatment of waste cooking oil (WCO) offers a cleaner route than transesterification for producing diesel-range biofuels, primarily C15-C18 linear paraffins (green diesel). This work evaluates the H 2 -free hydrotreatment of WCO using methanol, isopropanol and formic acid as in–situ hydrogen donors over a Mo 2 C/CNF catalyst. This catalyst delivered an 86 % green diesel yield with complete conversion using external H 2 . Reactions were performed in a continuous trickle–bed reactor at 350 °C and 70 bar. Catalytic performance was evaluated under steady-state conditions following a stabilization period, ensuring representative product distributions. Additionally, donor decomposition was studied under N 2 to monitor H 2 formation in the absence of WCO. Gas-phase analysis suggested substantial in-situ H 2 formation under reaction conditions; however, the possible contribution of catalytic transfer hydrogenation cannot be fully excluded. The Mo 2 C/CNF 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 H 2 . Liquid products were characterised by GC–MS, GC-FID and complementary HPTLC analysis to improve the profiling of complex product fractions. Beyond performance assessment, this study provides comparative evidence on donor decomposition and hydrogen availability, constituting the first systematic comparison of multiple in-situ hydrogen sources for the continuous upgrading of a real waste feedstock and demonstrating a promising pathway toward H 2 -free hydrotreatment of WCO.