Twin-screw extruder for oil processing of sunflower seeds: Thermo-mechanical pressing and solvent extraction in a single step

A new application of twin-screw extruder as a machine to conduct a thermo-mechanical pressing and a solvent extraction of sunflower oil in a single step and in a continuous mode was studied. Experiments were conducted using a CLEXTRAL BC 45 co-rotating twin-screw extruder and whole sunflower seeds with fatty acid methyl esters as a solvent. The influences of screw rotation speed (SS), feed rate (QS) and solvent-to-solid (S/S) ratio were examined to define the best performance of the oil extraction yield, the oil quality and the specific mechanical energy.Generally, the screw rotation speed, feed rate and solvent-to-solid ratio affected oil extraction yield. An increase of oil extraction yield was observed as screw rotation speed and feed rate were decreased, and solvent-to-solid ratio was increased. In addition, oil extraction yield increased as screw rotation speed and feed rate were simultaneously increased to QS/SS ratio of 0.2. Highest oil extraction yield (98%) with best cake meal quality (residual oil content lower than 3%) was obtained under screw rotation speed of 185 rpm, feed rate of 30 kg/h, and solvent-to-solid ratio of 0.55. Furthermore, the operating parameters and solvent-to-solid ratio influenced energy input. A decrease of screw rotation speed and feed rate followed by an increase of solvent-to-solid ratio increased energy input, particularly specific mechanical energy input.