4.7 Article

Upcycling of the Used Cigarette Butt Filters through Pyrolysis Process: Detailed Kinetic Mechanism with Bio-Char Characterization

Journal

POLYMERS
Volume 15, Issue 14, Pages -

Publisher

MDPI
DOI: 10.3390/polym15143054

Keywords

devolatilization; kinetics modeling; autocatalysis; cellulose triacetate; carbonization; mesoporous charred carbon

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This study successfully valorized and upcycled cigarette butt (CB) filters through thermo-chemical conversion. The decomposition mechanism of the precursor material, cellulose acetate filter (r-CAcF), was analyzed using micro-scale experiments and detailed kinetic study. The results revealed complex mechanisms involved in the decomposition, including cellulose polymorphic transformation and hydrolytic decomposition of cellulose. Macro-scale experiments showed the effects of operating temperature and heating rate on the surface characteristics of the manufactured carbon.
Thermo-chemical conversion via the pyrolysis of cigarette butt (CB) filters was successfully valorized and upcycled in the pre-carbonization and carbonization stages. The pre-carbonization stage (devolatilization) of the precursor material (cellulose acetate filter, r-CAcF) was analyzed by micro-scale experiments under non-isothermal conditions using TG-DTG-DTA and DSC techniques. The results of a detailed kinetic study showed that the decomposition of r-CAcF takes place via complex mechanisms, including consecutive reaction steps and two single-step reactions. Consecutive stages include the alpha-transition referred to as a cellulose polymorphic transformation (cellulose I -> II) through crystallization mechanism changes, where a more thermodynamically ordered system was obtained. It was found that the transformation rate of cellulose I -> II ('cellulose regeneration') is strongly affected by the presence of alkali metals and the deacetylation process. Two single-step reactions showed significant overlapping behavior, which involves a nucleation-controlled scission mechanism (producing levoglucosan, gaseous products, and abundant radicals) and hydrolytic decomposition of cellulose by catalytic cleavage of glycosidic bonds with the presence of an acidic catalyst. A macro-scale experiment showed that the operating temperature and heating rate had the most notable effects on the total surface area of the manufactured carbon. A substantial degree of mesoporosity with a median pore radius of 3.1695 nm was identified. The presence of macroporosity on the carbon surface and acidic surface functional groups was observed.

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