Perspectives of transformation of dyed cotton-based used textiles into fuel products and valuable chemicals

In the “ Fast fashion ” business model, colourful cotton-based textiles quickly become waste that is difficult to dispose of. Synthetic additives, different types of dyes as well as auxiliary substances used in textile finishing processes, prevent the biodegradation of such materials in the natural environment. This work investigated the possibility of using dyed cotton (Co) yarns and cotton yarns doped with polyamide (CoPA) and polyester (CoPET) fibers as raw materials for the production of substrates for the cultivation of the yeast Saccharomyces cerevisiae . The morphology of the fibers and the degree of their coloration before and after acid hydrolysis were examined using microscopic, spectrophotometric, and spectroscopic techniques (FTIR and Raman). On the Co, CoPA and CoPET hydrolysates obtained by acid hydrolysis dyed yarns under mild conditions (T = 140 °C, C H3PO4 = 2 %) yeast strains S. cerevisiae (Tokay ŁOCK 0204, Ethanol Red) were cultivated, and it was determined that strain S. cerevisiae Ethanol Red is less sensitive to the presence of compounds released during hydrolysis from fiber colorants. Removal of non-sugar components resulting from the hydrolysis of colouring substances on an activated carbon bed results in more effective multiplication of yeast cells. Furthermore, ethanol fermentation of cotton hydrolysates was performed on a larger scale using strain S. cerevisiae Ethanol Red, and the resulting ethanol was subjected to catalytic coupling to form butanol and higher alcohols. The established route for the synthesis of butanol from cotton waste is promising but requires refinement at each of its stages in order to increase the yield of alcohols. • Acid hydrolysis of cotton in dyed textiles. • Potential use of dyed textile hydrolysates for yeast cultivation. • Ethanol fermentation of dyed textile hydrolysates containing cotton. • Catalytic coupling of ethanol to butanol and higher homologues. • Up-cycling of used textiles into green energy and chemicals.