Waste textile decolorization using supercritical carbon dioxide (ScCO₂) technology: Design and optimization

This report presents a dry and chemical free approach to waste textile decolorization using supercritical carbon dioxide (ScCO₂) technology. Dispersed dyed polyester (PET) fabrics was decolorized in a laboratory-scale ScCO₂ system with pristine PET serving as a dye absorbent guided by the principle of ScCO₂ dyeing. The influence of key process parameters such as time, temperature, pressure, and dyed-to-absorber fabric loading on extraction efficiency was analyzed through the equilibrium constant for dye partitioning. Results revealed that PET fabrics treated at 10:90 dyed-to-absorber loading under 120 °C, 25 MPa for 60 min exhibited the highest decolorization efficiency of (79 – 85) % for all dyes, reflected by the lowest color strength (K/S) values of 0.93 – 2.46. The equilibrium constant (Keq) increased with temperature, pressure, and absorber loading, reflecting improved dye partitioning efficiency. In an attempt to predict the thermodynamic behavior waste textile decolorization using ScCO₂, Peng-Robinson Equation of State (PR-EOS) was used to model the behavior and correlated with experimental values. Results showed modest qualitative agreement with experimental data with an AARD of 27-32%. In general, the experimental finding of the report demonstrates the promising potential of ScCO₂-mediated decolorization of waste textile fabric, offering a dry, energy-efficient strategy supporting textile recycling. • Dry and chemical free approach to waste textile decolorization using ScCO₂. • Dye decolorization reached 85% using ScCO₂ and absorber fabric synergy. • Time, temperature, and pressure influences decolorization until plateauing. • Dye removal increased linearly with fabric loading, driving dye migration. • Thermodynamic model shows partial qualitative agreement with experiments.