Upcycling Wool Textile Waste by Slow Pyrolysis to Recover Nitrogen-Rich Bio-Oil and Bio-Char and CO-Rich Gas Using...

The valorisation of textile wool waste through sustainable conversion technologies such as pyrolysis has gained increasing attention as an effective strategy to reduce textile waste, recover valuable resources, and support the transition toward a circular economy. Herein, we investigated the pyrolysis of processed wool textile waste in CO₂ and N₂ atmospheres to recover valuable products and reduce the environmental impact. Key factors such as the temperature, carrier gas type, feed size, condensation set-up, and reactor configuration were evaluated for their influence on product distribution and quality. Pyrolysis at 900 °C in the presence of CO₂ led to greater gas formation (79 wt%), enhanced the stability and BET surface area of the char (10-12 wt%), and increased byproducts including phenol and indole in the bio-oil (13 wt%) product. CO made up over 65% of the gas at 900 °C due to the prevalence of the reverse (endothermic) Boudouard reaction, with the remnant gas made of CO₂ (21%) and small amounts of NH₃ (2%), HCN (0.8%) and SO₂ (0.3%). This CO-rich gas could have industrial applications such as Fischer-Tropsch after conditioning and N/S removal. Moreover, the higher carbon content (82.5% at 900 °C) increased the stability of char produced with CO₂ (compared to N₂), making it suitable for soil enhancement (~10% N at 900 °C) or pollutant removal and allowing it to be categorised and marketed as biochar. Despite low-temperature pyrolysis (350 °C) not being efficient in decomposing the whole wool waste, a staged pyrolysis with an initial low-temperature stage was shown to be effective in separately removing bromine-rich compounds. In summary, this study provides insights into the thermal decomposition behaviour of wool and the influence of the reaction conditions and reactor type on product distribution.