Abstract
The large variations found in literature for the activation energy values of main biomass compounds (cellulose, hemicellulose and lignin) in pyrolysis TGA raise concerns regarding the reliability of both the experimental and the modelling side of the performed works. In this work, an international round robin has been conducted by 7 partners who performed TGA pyrolysis experiments of pure cellulose and beech wood at several heating rates. Deviations of around 20 – 30 kJ/mol were obtained in the activation energies of cellulose, hemicellulose and conversions up to 0.9 with beech wood when considering all experiments. The following method was employed to derive reliable kinetics: to first ensure that pure cellulose pyrolysis experiments from literature can be accurately reproduced, and then to conduct experiments at different heating rates and evaluate them with isoconversional methods to detect experiments that are outliers and to validate the reliability of the derived kinetics and employed reaction models with a fitting routine. The deviations in the activation energy values for the cases that followed this method, after disregarding other cases, were of 10 kJ/mol or lower, except for lignin and very high conversions. This method is therefore proposed in order to improve the consistency of data acquisition and kinetic analysis of TGA for biomass pyrolysis in literature, reducing the reported variability.
Highlights
Biomass is currently the main renewable energy source and it is expected to play a key role to reach the target formulated in the special IPCC report to limit global warming to 1.5 °C [1,2]
The determination of mass loss kinetics for biomass pyrolysis is still an unresolved topic, due to the broad range of values reported in literature
An international round robin of thermogravimetric analysis (TGA) pyrolysis experiments with pure cellulose and beech wood has been conducted by 7 partners
Summary
Biomass is currently the main renewable energy source and it is expected to play a key role to reach the target formulated in the special IPCC report to limit global warming to 1.5 °C [1,2]. Pyrolysis itself is a promising conversion process that can be used to produce liquid bio-oil [3,4] and biochar [5], and is a main intrinsic sub-process in other thermo-chemical conversion processes such as gasification or combustion. TGA experiments with small samples and low heating rates can be conducted in a pure kinetic regime, i.e. without heat and mass transport limitations. For cellulose pyrolysis, it was concluded by Antal et al [6] that mass loss at low heating rates can be described with a single first order reaction with a high activation energy (191–253 kJ/mol). Gronli et al [7] conducted a round robin at 8 European labs with commercial cellulose Avicel PH-105, showing some limited scattering in the results, with a temperature of peak conversion at 327 ± 5 °C and activation energy of 244 ± 10 kJ/mol at 5 °C/min
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