Catalytic pyrolysis of vegetable oils to biofuels: Catalyst functionalities and the role of ketonization on the oxygenate paths

• Palm oil is fully converted by pyrolysis at 693 K both with and without catalysts.
• Thermal conversion produces big amounts of saponifiables as fatty acids.
• The basic catalyst MgO–Al2O3 kills saponifiables, but produces heavy ketones.
• Lewis acid catalysts as alumina produce more hydrocarbons.
• Brønsted acidic H-ZSM-5 zeolite kills olefins producing more paraffins and aromatics.

Thermal and catalytic conversions of palm oil were investigated at 693 K. The conversions of acetic acid and ethyl acetate in the gas phase were also investigated over the same catalysts as model reactions. The acido-basicity of the catalysts was assessed by IR spectroscopy of adsorbed pyridine. Oxide catalysts slightly decrease the liquid yield, but allow the strong reduction of the production of saponifiable compounds, including fatty acids, in the liquid. The basic catalyst calcined hydrotalcite is the most effective in reducing saponifiables, but produces big amounts of heavy ketones (stearone and palmitone) according to its high activity in acid and ester ketonization. The Lewis acid catalysts alumina (strong) and Na-faujasite (weak) favor decarboxylation reaction, producing hydrocarbon rich liquids with significant amounts of olefins. The Brønsted acid catalyst H-ZSM-5 zeolite produces liquids richest in paraffins with some aromatics. However, the volatility range of the produced liquids is quite broad.