Kinetics, thermodynamics and mechanisms for hydroprocessing of renewable oils

• Hydroprocessing of triglycerides are not diffusion–limited over Ni-W/SiO2-Al2O3.
• Propane removal reaction was most exothermic, 85% of the total energy (1.34 MJ/kg).
• Highest exothermicity in top 1/5 (15–18%) of the catalyst bed due to depropanation.

Intrinsic kinetics, diffusivity, energy calculations and reaction mechanism studies for the conversion of plant-oil triglycerides over Ni-W/SiO2-Al2O3 hydrocracking catalyst is reported. Specific insights into reaction mechanisms, are established using kinetic modeling and validated with experimental results. Diffusion studies and effectiveness factor calculations established diffusion–free intrinsic kinetics, with an activation energy of 115 kJ/mole required for triglycerides conversion. Thermodynamic calculations further established that the heat released during propane removal step (1.15 MJ/kg) was 8-times higher than that for hydrodeoxygenation step (0.14 MJ/kg) and lowest for hydrocracking reactions (0.08 MJ/kg). Such high exothermicity resulted in high temperature gradient across the catalyst bed (370 °C above the reaction temperature).

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