Jaume Cot

Supercritical CO2 extraction as a clean degreasing process in the leather industry

Abstract The content of natural fat in sheepskins is variable and depends on the animal origin. In woolskins from Australia and New Zealand, this content can account for up to 50% of dry skin weight. The production of a high-quality leather article requires the skins to be degreased to some extent. Degreasing of sheepskins is conventionally carried out with organic solvents, resulting in the emission of volatile organic compounds. Alternative aqueous systems, based on the use of non-ionic surfactants, give rise to large volumes of effluents with high COD values. Supercritical fluids have been employed to extract a number of substances. Supercritical CO 2 is the most widely used fluid in the extraction processes given the easy accessibility of its critical properties. This study deals with the feasibility of the supercritical CO 2 extraction technology in degreasing sheepskins. The degreasing efficiency achieved by this technology was determined as a function of the following variables: moisture content of the sample, CO 2 density, CO 2 flow rate and extraction time. The grease content was determined before and after CO 2 extraction using a Soxhlet apparatus. Degreasing efficiency levels up to 94% were obtained when sheepskins with an original natural fat content of approximately 6% were extracted. The degreasing efficiency decreased with the moisture content in the skin and increased with the CO 2 density, flow rate and extraction time.

Application of the supercritical CO2 extraction technology on the recovery of natural fat from the sheepskin degreasing process

Abstract The content of natural fat in sheepskins can amount up to 50% on the dry skin weight. In order to have skins in good conditions to be adequately processed afterwards, it is necessary to degrease them to a some extent. One of the degreasing methods is carried out with non ionic surfactants in aqueous medium. At the end of this degreasing process a highly pollutant emulsion consisting of natural fat and surfactant in water is obtained. In order to reduce the high contamination load of this emulsion, this is heated to 90°C, at which temperature the emulsion breaks. In this way, water with a reduced contamination load and a fatty phase made up of water, salt, natural fat and non ionic surfactant are obtained separately. Given the nature of this fatty phase, no suitable use has been found up to now. This study deals with the feasibility of the supercritical CO2 extraction technology to separate the fatty phase obtained from the residual bath of sheepskin aqueous degreasing into its components, natural fat and non ionic surfactant. On the other hand, the natural fat of sheepskins consists of different components: lanoline, waxes, triglycerides, fatty acids, cholesterol, mono- and diglycerides. The fractionation of the different components of the natural fat as a function of the CO2 pressure and temperature has also been studied. Supercritical fluid extraction technology allows the recovery of natural fat present in the fatty waste obtained from the residual bath of sheepskin degreasing. An increase in the CO2 density leads to the extraction of a larger number of components of natural fat. All the components of natural fat are extracted at an extraction temperature of 45°C and at CO2 density of 0.70–0.75 g/ml. The non ionic surfactant is not extracted under these conditions.