Low waste and low-energy consumption automation renovation of anhydrous dyeing system using anhydrous washing

Supercritical carbon dioxide, ethanol, and dimethyl sulfoxide mixed medium enable cotton fabric anhydrous dyeing, reducing energy consumption, simplifying color matching, improving levelness and color depth, and enabling an expanded range of available reactive dyes. However, residual alkalis, ammonium carbamate, and unfixed reactive dyes remain on cotton fabric, necessitating further treatment to satisfy the requirements for ecological textiles. This study used and recycled ethanol and dimethyl sulfoxide to effectively eliminate residual alkalis, ammonium carbamate, and unfixed reactive dyes from dyed cotton fabric and achieved the automation renovation of the corresponding anhydrous dyeing system to minimize waste discharge. The results show that residual alkalis and ammonium carbamate could be eliminated by washing with an ethanol solution containing citric acid, and the unfixed reactive dyes could be eliminated by washing with dimethyl sulfoxide. After being washed with ethanol and dimethyl sulfoxide, the dyed cotton fabric exhibits a grade 4 washing and rubbing fastness or higher and a pH value of 7, satisfying requirements for ecological textiles. The renovated automatic anhydrous dyeing system could achieve an E factor of 0.037, while its theoretical energy consumption of solvent recycling was 0, according to the Green Chemistry Principles 1 (prevention) and 6 (design for energy efficiency). It indicates that the automatic anhydrous dyeing system aligns more closely with the requirements outlined in the United Nations Sustainable Development Goal 12 (responsible production and consumption) than previously published dyeing systems.