Study of an energy-integrated biodiesel production process using supercritical methanol and a low-cost feedstock

• A new supercritical biodiesel process is proposed, having low energy consumption.
• Process conditions are optimized by computer simulation to maximize heat recovery.
• The process has an energy duty of 262 W per kg/h of biodiesel product.
• Adiabatic flash drums and a low methanol/oil ratio are key for the energy efficiency.
• Highly acid chicken oil was converted into an ASTM technically compliant biodiesel.

The supercritical biodiesel production process has some disadvantages such as: high reaction temperature, large molar methanol-to-oil ratios (R) and large energy consumption. To mitigate these problems, an energy integrated process in which biodiesel is obtained in a continuous tubular reactor operating at a reaction temperature of 280 °C, R = 20, a residence time of 1 h and a pressure of 110 bar, is proposed. A low-cost lipid feedstock (chicken oil) was used as raw material for testing the process. The enthalpy content of the stream exiting the supercritical reactor was used to eliminate the unreacted methanol in an adiabatic flash drum. The operating conditions of the adiabatic flash were optimized to meet the specification of water and methanol content in the biodiesel phase and minimize the ester and acid content in the vapor phase. These conditions were: P = 0.1 bar and T = 178 °C. For these conditions the methanol content is 88–90% in the vapor phase and lower than 0.2% in the biodiesel phase. A scheme was developed for an energy integrated process maximizing the heat recovery. Composition, temperature and pressure of the streams were determined and also the amount of heat exchanged in each unit. In order to fulfill the quality restrictions the final content of FFA in the biodiesel product had to be further adjusted by adsorption over bleaching silica.