Production of esters from soybean oil deodorizer distillate in pressurized ethanol

• Increasing the temperature and pressure in the reactor enhanced the FFA conversion.
• 275 °C, 20 MPa, ethanol to FFA molar ratio of 7:1 and 30 min were identified as the optimal conditions.
• Reaction rate is fast and the thermodynamic equilibrium is rapidly reached.
• At high temperatures the conversion decreased with increasing residence time.

The aim of this study was to obtain esters from soybean oil deodorizer distillate (SODD) in pressurized ethanol without the use of a catalyst. Experiments were carried out to evaluate the effects of the operating variables (pressure, temperature, residence time and ethanol to free fatty acids molar ratio) using a minimum factorial experimental design. The results indicate that increasing the temperature, pressure and residence time in the reactor enhanced the conversion of free fatty acids (FFA) while increasing the ethanol to FFA molar ratio decreased the conversion. The experiment carried out under optimum conditions (20 MPa, 275 °C, 20 min and ethanol to FFA molar ratio of 7:1) reached ~ 87% of FFA conversion. The reaction kinetics was investigated at different temperatures and the results obtained reveal that a high rate of FFA consumption and conversions close to the thermodynamic equilibrium were quickly reached. At high temperatures (325 and 350 °C) the conversion decreased with increasing residence time, indicating that the reverse reaction occurred. The reaction in two steps increased the FFA conversion, indicating that the conversions obtained were close to the thermodynamic equilibrium and the removal of water between the steps shifted the equilibrium, making it possible to achieve higher FFA conversion and ester yields.