Supercritical Carbon Dioxide Extraction of Wool Wax from Wool Scour Sludges

Abstract

Wool wax was extracted with supercritical carbon dioxide at 150°C and 50 MPa from a variety of sludges derived from wool scour effluent. The extraction rate from flotation sludges increased as the moisture content dropped below 70%, corresponding to bound water contents less than 1.3 g/g-DS. This was attributed to the combined effects of increased wax concentration per unit volume of sludge and decreased mass transfer resistance. The polyelectrolyte dose and pH used in flotation had no direct effect on wax extractability, but dosing of high concentrations 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 extraction of the free wool wax acids and alcohols in the initial stages of extraction was not observed and this was attributed to the interaction of these compounds with other particulate matter present in the sludges. Flotation and flocculation sludges were shown to be more amenable to wax recovery by supercritical carbon dioxide extraction than either centrifuge or anaerobic digester sludge. However, wax recovered from all sludge sources appeared to be of similar or lower quality to raw wool wax, and hence further refining would be required in order to achieve a saleable product.