Pyrolysis kinetics, thermodynamics of PTA sludge and product characterization of cyclic in-situ catalytic pyrolysis by using recycled char as a catalyst

Pyrolysis is an effective way for the sludge harmless, reduction treatment and resource utilization. In this study, the pyrolysis kinetics and thermodynamics of PTA sludge was evaluated. Afterword, a cyclic in-situ catalytic pyrolysis of PTA sludge by using recycled char as a catalyst was conducted. The product characterization, e.g. pyrolysis syngas as well as the catalytic effect of pyrolysis char, were analyzed. The results demonstrated that the Kissinger-Akahira-Sunose (KAS), Ozawa-Flynn-Wall (OFW), and Starink model-free methods have good agreement on kinetic parameters, the average activation energy was calculated at 295.18, 286.62, and 290.55 kJ/mol, respectively. Meanwhile, thermodynamic parameters, e.g. the variations in enthalpy (ΔH), entropy (ΔS), and Gibbs free energy (ΔG), were evaluated based on the deduced kinetic results, whereby the suitable pyrolysis temperature was determined at 973 K. The results of cyclic in-situ catalytic pyrolysis showed that the pyrolysis char could promote tar cracking, which greatly increased the yield of pyrolysis syngas. After five rounds of in-situ catalytic pyrolysis, the yield of pyrolysis syngas increased from 0.089 L/g to 0.176 L/g and the carbon conversion increased from 24.8% to 36.5%, respectively. •A cyclic in-situ catalytic pyrolysis with recycled char as a catalyst was proposed.•The pyrolysis kinetics and thermodynamics of PTA sludge were evaluated.•The carbon conversion was increased to 36.5% by five rounds of in-situ pyrolysis.•The char has effects on improving the yield of syngas by promoting cracking of tar.