Pyrolysis of polyester and viscose fiber over ZSM-5: synergistic effect and distribution of products

Large amounts of textile wastes are discarded annually, not only polluting the environment but also causing a significant waste of resources. Here, we investigate a pyrolysis treatment that can be used for recycling polyester (PET) and viscose fibers (VFs) that are widely used in textiles to obtain valuable chemicals. Thermogravimetry analysis showed that free radicals generated by VF decomposition caused PET to fracture and depolymerize in the co-pyrolysis (CP) process, resulting in a decrease in the initial temperature (T-i). Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) investigation uncovered the fact that the addition of a co-feed influenced the product distribution, that the peak area% values of the products changed significantly in the CP process of PET and VFs, and that the presence of PET significantly decreased the relative content of oxygen-containing products. The experimental peak area% values of phenols and alcohols, acids and esters, aldehydes and ketones, and furans were lower during noncatalytic CP than the values calculated based on the individual pyrolysis of PET or VFs, indicating that cross-reactions occurred between PET and VFs, leading to net deoxygenation. Furthermore, it was revealed that the generation of polycyclic aromatic hydrocarbons in catalytic co-pyrolysis was reduced from 67.11 to 25.71% when ZSM-5 was present, while the production of monocyclic aromatic hydrocarbons (MAHs) increased from 32.87 to 74.27%. These results show that ZSM-5 was beneficial for achieving improved MAHs selectivity.

Automated summary

Large amounts of textile wastes are discarded annually, causing pollution and resource waste. A pyrolysis treatment has been investigated to recycle polyester and viscose fibers, obtaining valuable chemicals. The addition of a co-feed influences the product distribution, and PET decreases the relative content of oxygen-containing products. The presence of ZSM-5 reduces the generation of polycyclic aromatic hydrocarbons and increases the production of monocyclic aromatic hydrocarbons, improving selectivity.