Dye Extraction from Waste Textile Using Supercritical Carbon dioxide (ScCO₂) Technology

Sammanfattning

This thesis investigates the extraction of disperse dyes from dyed polyester waste fabrics using supercritical carbon dioxide (ScCO₂) as a sustainable and resource-efficient approach. The study aims to elucidate the underlying mechanisms and evaluate the influence of key parameters (temperature, pressure, time) on extraction efficiency from a fundamental perspective. By understanding these parameters, the thesis seeks to establish a green alternative to conventional resource-intensive dye extraction methods while con-tributing to the advancement of supercritical carbon dioxide technology. Dyed polyester fabrics using commercially available disperse dyes were subjected to color extraction in a laboratory-scale ScCO₂ system. The influence of temperature, pressure, extraction time, and bath ratio were explored under the synergistic effect of ScCO₂ and a dye absorber (pristine polyester fabric). Dye migration and process efficacy were quantitatively analyzed using color strength (K/S) values. The equilibrium constant (K) for dye partitioning be-tween the polyester substrate and the ScCO₂ phase (referring to the dyes on the absorber fabric) was calculated and modeled using the Peng–Robinson Equation of State (PR-EOS), enabling predictions of dye phase behavior under ScCO₂ conditions. Results showed that dye extraction efficiency from Polyester was strongly dependent on temperature, pressure, treatment time, and fabric ratio. In-creasing treatment time from 10 to 60 minutes significantly enhanced dye extraction, which then plateaued. A similar trend was observed with pressure (up to 25 MPa) and temperature (up to 120°C), while increasing the amount of absorber fabric led to a linear improvement. Under optimized conditions, up to 85% extraction efficiency was achieved. The thermodynamic model showed qualitative agreement with experimental K values, with an AARD of 27–32%, though limited by the absence of critical dye data. Additionally, the study examined the influence of co-solvents (methanol, benzyl alcohol) and a concept for color modulation through mixing pre-dyed fabrics. Both solvents enhanced dye extraction using paper absorber (up to 87%), and color redistribution demonstrated a proof-of-concept for forming new, uniform shades on waste textile fabrics. These findings sup-port the development of closed-loop recycling systems and contribute to reducing environmental burdens in textile processing.