The invention relates to a counter-current extraction process with which the starting material to be extracted is conveyed in an extruder through zones of high and low pressure. The zones of high and low pressure can, for example, be formed by different screw elements of opposing pitch. Extractant is fed in in the high pressure zones which are located upstream of the screw elements of opposing pitch. The extractant then flows in counter-current to a discharge opening which is located in or close to the low pressure zone, downstream of a screw element of opposing pitch. With the extraction method according to the present invention a stable counter-current extraction process can be obtained over a very short extraction length and a high extraction yield can be achieved within a short time by intensive mixing of the starting material with the extractant. Furthermore, high pressures can be used in the extraction apparatus according to the present invention since the discharge openings are located close to the low pressure zones. As a result the extraction yield is further increased and extraction fluids in supercritical state can be used.
|Publication status||Published - 3 Jun 1999|