Supercritical CO 2 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.