Thermal conversion behavior of cellulose and hemicellulose fractions isolated from tea leaf brewing waste: kinetic and thermodynamic evaluation

Abstract

This study aims at investigating the thermal decomposition process (pyrolysis) of tea leaf brewing waste (TLBW) and its main component (hemicellulose, cellulose) under non-isothermal conditions and these pyrolysis process kinetic/thermodynamic parameters. Hemicellulose (TLBW-H) and cellulose (TLBW-C) were isolated from the TLBW with delignification process. The isolation effectiveness was discussed and interpreted according to structural analysis (FTIR) results. The fuel analysis (proximate and ultimate), chemical analysis, and structural analysis (FTIR) of the tea leaf brewing waste and its main component were carried out. The thermal analysis (TGA and DTG) of TLBW, TLBW-H, and TLBW-C was investigated under a nitrogen gas atmosphere of 10 ml/min in the temperature range of 25-900 degrees C. Kinetic and thermodynamic parameters were calculated using Coast-Redfern (CR) model and main thermodynamic equations. A fourteen solid-phase theoretical degradation reaction model was then applied to evaluate the TGA results of the samples. Active pyrolysis started after 210 degrees C and ended at 527 degrees C for TLBW-H, 538 degrees C for TLBW-C, and 602 degrees C for the TLBW. For the total decomposition steps, the best model equation representing the degradation was found to be the chemical kinetic equation F(3) for all of the samples. Using the model equation that best represents the degradation, the activation energies and ln (A min-1) calculated from the thermal decomposition kinetics of raw tea brewing waste, hemicellulose and cellulose were determined as 46.71-14.42-23.84 kJ/mol and 7.67-13.41-11.92, respectively. As a result, it is predicted that the kinetic and thermodynamic parameters calculated in this study will be useful in terms of the pyrolysis process of TLBW and its main component and the design of pyrolysis reactors. Statement of novelty This is a research on the thermal decomposition behavior and kinetic analysis of tea leaf brewing waste and its main components (cellulose and hemicellulose). Activation energy was estimated for 14 different theoretical solid-phase decomposition model equations using the Coast-Redfern method. Important thermodynamic parameters for the pyrolysis process were calculated and compared. The findings will be useful for the thermal degradation process design of TLBW and its main components.