SUPERCRITICAL CARBON-DIOXIDE EXTRACTION OF WOOL WAX FROM WOOL SCOUR SLUDGES

Wool wax was extracted with supercritical carbon dioxide at 150 degree s C and 50 MPa from a variety of sludges derived from wool scour efflu ent. The extraction rate from flotation sludges increased as the moist ure content dropped below 70%, corresponding to bound water contents l ess than 1.3 g/g-DS. This was attributed to the combined effects of in creased wax concentration per unit volume of sludge and decreased mass transfer resistance. The polyelectrolyte dose and pH used in flotatio n had no direct effect on wax extractability, but dosing of high conce ntrations of polyelectrolyte at pH 4.3 was able to reduce the moisture content into the region of 70%. Drying of the sludge was required to decrease the moisture content below 70%. The expected preferential ext raction of the free wool wax acids and alcohols in the initial stages of extraction was not observed and this was attributed to the interact ion of these compounds with other particulate matter present in the sl udges. Flotation and flocculation sludges were shown to be more amenab le to wax recovery by supercritical carbon dioxide extraction than eit her centrifuge or anaerobic digester sludge. However, wax recovered fr om all sludge sources appeared to be of similar or lower quality to ra w wool wax, and hence further refining would be required in order to a chieve a saleable product.