Isoconversional determination of the apparent reaction models governing pyrolysis of wood, straw and sewage sludge, with an approach to rate modelling

Within the presented paper, different approaches to determine kinetic reaction models governing pyrolysis of three waste biomass types: waste wood (WW), waste straw (WS) and sewage sludge (SS) based on 5 dynamic heating runs (5, 10, 20, 30, 40 K/min) at TGA are presented and discussed. Fuel properties with lignocelluloses content of the investigated feedstock are presented and discussed. Ambiguous results of the generalized master-plot method draw the idea of determining actual reaction models using the isoconversional methodology. Friedman method provided apparent activation energies as a root for further calculations being the 48.1–294.3 kJ/mol for WS, 21.0–361.9 kJ/mol for WW and 58.1–484.3 kJ/mol for SS. Isoconversional pre-exponential factors were determined using linear compensation effect and were 7.2·106–1.8·1021 1/min, 1.6·104–1.2·1025 1/min, and 1.5·109–3.2·1030 1/min for WS, WW, and SS respectively. Based on isoconversional parameters, actual profiles of reaction models were estimated using the t-Students distribution for 95% confidence intervals and verified in the modelling of pyrolysis conversion profiles. Isoconversional pyrolysis models resulted in fitting to experimental profiles with non-linear coefficients of determination equal to 0.9912, 0.9876, and 0.9406 for WW, WS, and SS respectively.