Slow pyrolysis of mixed textile waste: towards sustainable recycled coal and added value chemicals

In Europe, 12.6 million tons of textile waste are generated annually (European Commission − Press release, Circular economy for textiles, 2023), and most of them are incinerated or landfilled. The sustainable recycling of textile residues is a key challenge worldwide and thermochemical processes are promising solutions to transform textiles into added-value products. This study examines slow pyrolysis at pilot scale, by processing two textile waste samples with high (TXN) and low (TX) nitrogen content, to evaluate the impact of nitrogen on pyrolysis process and reaction products. The tests showed that textile waste can be turned into a coal-like product, with a mass yield from 24.7 to 29.1 % wt db. Both the chars had a high C content (TX: 85.66 % wt db; TXN: 80.62 % wt db.) and calorific value (TX: 32.74 MJ/kg db; 31.55 MJ/kg db), comparable with anthracite. The char from TX showed a high surface area (319 m²/g), not found in that from TXN (12 m²/g). The oil fraction obtained from TX showed a high concentration of benzoic acid (227 g/l), while a lower concentration was found in the oil fraction from TXN (55 g/l). Both fractions contained furans, acetic acids, ketones, and aromatic compounds. Results suggested that the nitrogen content of textile waste does not affect the energy and mass balance of the process, while it has an impact on the composition of the char and on the oil. Regardless the N-content, study shows that slow pyrolysis can turn textile waste into a high value coal-like material, and into an oil fraction suitable for chemicals extraction.