Process Analysis of Waste Animal Fat Pyrolysis and Fractional Distillation in Semi-Batch Reactors: Influence of Temperature and Reaction Time

Waste animal fat (WAF) can be converted to distillate fractions similar to petroleum solvents and used as solvents via pyrolysis and fractional distillation. Pyrolysis oil from triglyceride materials presents adequate viscosity and volatility, compared to petroleum fuels, but shows acid values between 60–140 mg KOH/g, impeding its direct use as biofuels without considerable purification of its distillates. Fractional distillation can be applied for the purification of bio-oil, but only a few studies accurately describe the process. The purpose of this study was to evaluate the effect of temperature in the conversion of waste animal fat into fuel-like fractions by pyrolysis and fractional distillation in a semi-batch stirred bed reactor (2 L) according to reaction time. Waste animal fat was extracted (rendering) from disposed meat cuts obtained from butcher shops and pyrolyzed in a stainless-steel stirred bed reactor operating in semi-batch mode at 400–500 °C. The obtained liquid fraction was separated according to reaction time. The pyrolysis bio-oil at 400 °C was separated into four distinct fractions (gasoline, kerosene, diesel, and heavy phase) by fractional distillation with reflux. The bio-oil and distillate fractions were analyzed by density, kinematic viscosity, acid value, and chemical composition by gas chromatography coupled to mass spectra (GC-MS). The results show that, for semi-batch reactors with no inert gas flow, higher temperature is associated with low residence time, reducing the conversion of fatty acids to hydrocarbons. The distillate fractions were tested in a common application not sensible to the fatty acid concentration as a diluent in the preparation of diluted asphalt cutback for the priming of base pavements in road construction. Kerosene and diesel fractions can be successfully applied in the preparation of asphalt cutbacks, even with a high acid value.