Enthalpy-entropy compensation and isoequilibrium relationship in thermo-chemical conversion of cigarette butt filters (CBFs) based on cellulose acetate (CA): causes and effects

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 Delta S degrees 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 beta-relaxation mode of cellulose acetate by an abatement of the polymer free volume.