Pyrolysis characteristics, kinetics, and evolved gas determination of chrome-tanned sludge by thermogravimetry–Fourier-transform infrared spectroscopy and pyrolysis gas chromatography-mass spectrometry

The pyrolysis characteristics, kinetics, and evolved gas analysis of chrome-tanned sludge were investigated by thermogravimetry (TG) with Fourier-transform infrared spectroscopy (TG–FTIR) and pyrolysis with gas chromatography and mass spectrometric detection (Py–GC/MS). Friedman, Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS) methods were used to calculate kinetic parameters in the kinetic study. The chrome-tanned sludge contained 7600 mg kg−1 Cr in the form of CrOOH and 41,400 mg kg−1 S in the form of S8. The activation energy derived by Friedman method increased from 139.83 to 590.72 kJ mol−1 as the temperature increased from 50 to 500 °C, much higher than those of lignocellulosic biomass and sewage sludge. The TG–FTIR results showed that the main component of the pyrolysis gases was organics that contained alkane groups, and this component reached a maximum at ∼500 °C. The Py–GC/MS results indicated that the diesel-range organics (C10–C28) accounted for more than 65% of the evolved gases; 20%–31% of the evolved gases were C16 and C18, and included mainly palmitic, stearic, and oleic acids. The evolved gases contained high contents of sulfur and nitrogen compounds, mainly in the forms of elemental sulfur (S6 and S8) and nitriles, respectively. Kinetics and evolved gases determining provide a better understanding of tanned sludge pyrolysis and references for pyrolysis reactor design and scale-up.