Near-critical solvent extraction of wool with modified carbon dioxide — experimental results

The extraction of a natural wax from raw wool was carried out with modified near-critical solvent in order to develop a cleaner, less polluting extraction process compared with the conventional soap-and-water washing process. As shown previously, natural wax is soluble in near supercritical carbon dioxide but only at very high pressures. Thus, carbon dioxide would be a very interesting non-aqueous solvent provided that lower pressures could be used. It has been found that the addition of a modifier increases the solvent polarity, hence increasing the solvating power of the mixture. In the present study, solutions of carbon dioxide and ethanol were employed, either in subcritical or supercritical conditions at moderate pressure (<200 bar). The experiments were done on a Separex 200 bench-scale unit. An experimental study was conducted to see the effects of pressure (70–200 bar), temperature (30–80°C) and wool packing densities ranging from 106 to 318 kg/m3. Specific solvent flowrates ranged from 10 to 25 kg/h per l of extractor. Also, the approximate lanolin solubilities were measured in separate experiments in order to interpret extraction rates and yields. Under the conditions of the study it is possible to extract 90% of the lanolin from raw wool.