CO2-driven suppression of toxic aromatic formation during pyrolysis of acrylic fabric waste

Abstract

Given the non-biodegradable nature of synthetic textiles, their thermal treatment (incineration) presents a promising route to mitigate environmental issues associated with microfiber generation. However, this approach is hindered by the formation of toxic aromatic compounds, especially characterized when heteroatoms are present in the polymer backbones. To address this challenge, this study proposes a pyrolytic valorization of acrylic fabric waste (AFW) while using carbon dioxide (CO2) as a detoxifying agent to suppress the toxic aromatic byproducts. Compositional analysis of AFW revealed the presence of 85 wt% polyacrylonitrile (PAN) and 15 wt% polyvinyl acetate (PVA). Pyrolysis of AFW yielded a complex mixture of volatile products, predominantly AN-derived oligomers and their aromatic derivatives; however, direct interactions between these intermediates and CO2 were limited. To activate the reactivity of CO2, an ex-situ catalytic system using a nickel (Ni)-based catalyst was integrated to the conventional pyrolysis. The Ni catalyst facilitated the cyclization and aromatization of AN-derived oligomers, while the formed aromatics were partially oxidized by CO2 into carbon monoxide (CO), suppressing the aromatic analogues. Increasing the catalyst-bed temperature from 500 to 700 ˚C enhanced CO2 activation and promoted the conversion of aromatics to CO. At catalyst-bed temperature of 700 ˚C, catalytic pyrolysis under CO2 exhibited a 35.9 % reduction in toxic aromatic formation compared to pyrolysis under nitrogen environment. Overall, this work demonstrates a sustainable strategy for AFW disposal with elucidating the mechanistic role of CO2 in transforming toxic aromatic species into detoxified gaseous products, primarily CO.