Extraction of oil from jatropha seeds using a twin-screw extruder: Feasibility study

• Jatropha oil was extracted by mechanical pressing using a twin-screw extruder.
• Screw profile, pressing temperature and screw speed affected extraction efficiency.
• Highest oil yield was 71% with good press cake quality (7.7% oil content).
• Oil required less energy to be produced, compared to screw press of similar size.
• Its quality was satisfactory for biodiesel production (2.7% acidity).

The objective of this study was to evaluate the feasibility of mechanical pressing to extract oil from jatropha seeds using a twin-screw extruder. Experiments were conducted using a co-rotating (Clextral BC 21, France) twin-screw extruder. The influence of operating conditions on oil yield, specific mechanical energy and oil quality was examined. Operating conditions included screw configuration, pressing temperature and screw rotation speed.Generally, it was the screw configuration, or profile, that most affected oil extraction efficiency. The best oil yields, a minimum 57.5%, were obtained with a trituration zone composed of 10 monolobe and 10 bilobe paddles, and a pressing zone composed of 50 mm long, reverse pitch screws with a −33 mm pitch. In addition, oil extraction yield increased with decreasing temperature and screw rotation speed. Highest oil extraction yield (70.6%) with good press cake quality (residual oil content lower than 8%) was obtained under operating conditions of 153 rpm screw rotation speed, 5.16 kg/h inlet flow rate of jatropha seeds, and 80 °C pressing temperature. The corresponding expressed oil was inexpensive to produce (71 W h/kg seed processed or 314 W h/kg expressed oil for specific mechanical energy) compared with another continuous technique, i.e. the single expeller press, commonly used for mechanical extraction of jatropha oil. Its quality was also satisfactory for biodiesel production. The acid value, the density and the kinematic viscosity were 5.4 mg of KOH/g of oil, 915 kg/m3 and 36.7 × 10−6 m2/s, respectively.