Pyrolytic kinetics, reaction mechanisms and products of waste tea via TG-FTIR and Py-GC/MS

The present study experimentally quantified the pyrolysis behaviors of waste tea (WT) as a function of four heating rates using thermogravimetric-Fourier transform infrared spectrometry and pyrolysis-gas chromatography-mass spectrometry analyses. The maximum weight loss of WT (66.79%) occurred at the main stage of devolatilization between 187.0 and 536.5 degrees C. The average activation energy estimates of three sub-stages of devolatilization were slightly higher (161.81, 193.19 and 224.99 kJ/mol, respectively) by the Flynn-Wall-Ozawa than Kissinger-Akahira-Sunose method. Kinetic reaction mechanisms predicted using the master-plots were f (alpha) = (3/2)(1 - alpha)(2/3)[1 - (1 - alpha)(1/3)](-1), f (alpha) = (1 - alpha)(2), and f (alpha) = (1 - alpha)(2.5) for the three sub-stages, respectively. The prominent volatiles of the WT pyrolysis were CO2 > C=O > phenol > CH4 > CO > NH3 > H2O > CO. A total of 33 organic compounds were identified including alkene, acid, benzene, furan, ketone, phenol, nitride, alcohol, aldehyde, alkyl, and ester. This study provides a theoretical and practical guideline to meeting the engineering challenges of introducing WT residues in the bioenergy sector.