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Pyrolysis kinetic behaviour, TG-FTIR, and GC/MS analysis of cigarette butts and their components
Summary
Pyrolysis experiments on cigarette butts and their components showed thermochemical conversion can produce aromatic hydrocarbons, carbonyl compounds, and phenols from the cellulose acetate filter—a major source of microplastic pollution. With trillions of cigarette butts discarded annually as the world's most littered plastic, understanding their thermal decomposition is essential for developing recycling alternatives that prevent cellulose acetate from fragmenting into persistent microplastic fibers.
Cigarette butts (CBs) are emerging polluting toxic plastic and microplastic elements that present a major challenge to environmental issues and recycling technologies. This is due to their complex composition consisting of cellulose acetate, cigarette paper, tar particles, tobacco, and heavy metals, thus, making it difficult to mechanically recycle, landfill, or incinerate them. In order to maximize their economic performance, this research aims to convert CBs into valuable volatile and chemical products using thermochemical treatment. Pyrolysis experiments were performed on each CB component separately (paper, filter, and tobacco) and their mixture (MIX) to determine the most complex part in the reaction and their effect on the synthesized pyrolysis vapour (PV) products. The experiments were carried out using thermogravimetric analyser (TGA) at heating rates 5, 10, 15, 20, 25, and 30 °C/min. The PVs generated from each batch under the specified heating conditions were analysed using Fourier transform infrared spectroscopy (TG/FTIR) and gas chromatography–mass spectrometry (GC/MS). Meanwhile, the complexity of reaction of CB components was investigated using three isoconversional model-free methods (Friedman, KAS, and FWO) and two nonlinear isoconversional models (Vyazovkin and Cai). The FTIR results showed that the PV products were rich in aromatic hydrocarbons (paper), carbonyl C = O (filter), CO2 (tobacco), and CO2 and carbonyl C = O (MIX). Whereas, phenol (paper; 42%), acetic acid (filter; 94%), pyridine (tobacco; 45%), and acetic acid (MIX: 74%) were the major GC/MS compounds at lower heating rates, and phenol (paper; 50%), acetic acid (filter; 93%), pyridine (tobacco; 39%), and several compounds in MIX sample (propanal, acetic acid, propanone, limonene, and pyridine) were manifested at higher heating rates. Finally, the kinetic results showed that tobacco represents the most complex part in decomposition of CBs (348 kJ/mol) compared to paper (238 kJ/mol) and filter (269 kJ/mol). Meanwhile, mixing all these components together reduced the complexity up to 184 kJ/mol (MIX), which contributed to decrease in energy consumption during the treatment at industrial scale.