Cost-effective reactive dyeing using spent cooking oil for minimal discharge of dyes and salts

Abstract

A reactive dyeing system is designed based on controllable chemical potential difference between the external and internal phases for minimal discharge of pollutants. Conventional aqueous reactive dyeing is widely used for cotton, generating large quantities of wastewater containing high concentrations of hydrolyzed dyes and salts. Although new reactive dyeing technologies have been developed to reduce pollutant discharge, they all failed due to release of toxic organic solvents or high costs. In the newly developed dual-liquid-phase system, spent cooking oil is served as external phase to disperse reactive dyes, while water is served as internal phase to swell cotton and fix dyes with alkali. 100% of reactive dyes move into the internal phase without the help of salts due to high chemical potential of dyes in the external phase. Compared to conventional aqueous system, the dual-liquid-phase system improves dye fixation by 33% and reduces discharge of dyes by 82% when the initial input of dyes is 3% owf. Discharge of salts is reduced by 100%. The external phase is reusable and biodegradable. Cotton fabrics were dyed with the dual-liquid-phase system on a pilot scale and achieved the same dyeing quality as those from conventional aqueous system. The dual-liquid-phase system also consumes less materials and energy than conventional aqueous system, indicating economic feasibility. The dual-liquid-phase system could be applied to current dyeing equipment, enabling quick implementation of lab results into real production. Clean large-scale reactive dyeing could be achieved with the dual-phase-liquid system.