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The aim of this study is to explain the consequences of the occurrence of enthalpy–entropy compensation (EEC) and isoequilibrium relationship during slow pyrolysis of cigarette butt filters (CBFs), consisting cellulose acetate (AC) as the main component. By using model-free and model-based kinetic methods and thermodynamic calculations, the complete reaction mechanism and extrathermodynamic issues about investigated process are completely resolved. It was established that compensation phenomenon where isoequilibrium temperature occurs is a consequence of formation of low-entropy molecular structure (cellulose II) and breaking of hydrogen bonds. Consequently, it was concluded that mechanisms which include a formation of low-entropy molecular structure and H-bonds breakage enter the changes in both enthalpy and entropy, which compensate each other. For the cellulose II generation, it was necessary to invest energy which represents use up energy. This "wasted" energy turns into work for creation of cellulose II molecular structures, whereby additional energy was provided from "local" decomposition reactions (which were identified in the established process mechanism) that arise from pyrolysis of starting material. Therefore, it was concluded that for "local reactions", a negative ΔS° value was identified, but for the global process, the entropy change retained a positive value. Considering thermodynamic effects manifested through compensation temperature found below glass transition temperature (Tg) in the undercooling conditions, it was concluded that small amounts of plasticizers affect reduction of free volume in the glassy state. Obtained results indicated a decrease in β-relaxation mode of cellulose acetate by an abatement of the polymer free volume. [ABSTRACT FROM AUTHOR]

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 α-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. [ABSTRACT FROM AUTHOR]