Understanding thermal properties of plant biomass will give insight to its industrial application, such as converting biomass efficiently into fuels or valuable chemicals. Biomass possesses three main building components; they are hemicelluloses, cellulose, and lignin with different chemical reactivity. Identifying the kinetic properties of pyrolysis has been a challenge, previous work suggested the possibility of using thermal analysis techniques, such as thermogravimetric analysis.
A collaborative research between scientists at Aston University in the UK and Stellenbosch University in South Africa allowed Marion Carrier and colleagues to propose using the classical differential isoconversional analysis also called Friedman’s method to evaluate the activation energy dependency as a function of the conversion degree without any previous knowledge of the reaction model. The research paper is now published in peer-reviewed journal, Energy & Fuel.
They implemented a robust experimental guideline and MATLAB program to determine reliable apparent activation energy, a kinetic parameter that assesses the global reactivity of the chemically isolated biopolymers α-cellulose, holocellulose and lignin. A rigorous preparation method to conduct thermogravimetric experiments was used by the research team to minimize or correct systematic error in the temperature measurement that may affect determination of kinetic parameters.
The research team observed that the activation energy, Eα, dependencies obtained for the slow pyrolysis of the extractive-free Eucalyptus grandis, isolated α-cellulose and holocellulose remained constant for 0.05 < α < 0.80 and equal to 173 ± 10, 208 ± 11, and 197 ± 11 kJ/mol. According to the team, this confirmed the single-step nature of pyrolysis. They also found out large and significant variations in Eα for the Klason lignin from 174 ± 10 to 322 ± 11 kJ/mol in the conversion region of 0.05 and 0.79 and reported this trend for the first time. The team pointed out that non-monotonic nature of weight loss at low and high conversions had a direct consequence on the confidence levels of activation energy, Eα. The authors confirmed the Eα values obtained for α-cellulose and holocellulose in their work agree with values reported in the literature while Eα values for technical lignin pyrolysis were different which could be explained by different methods used in extraction as well as the occurrence of different lignin chemical structures. The model presented in this study is an important step forward to provide more accurate and reliable kinetic parameters of biomass pyrolysis.
Marion Carrier1, Lidia Auret2, Anthony Bridgwater1, and Johannes H. Knoetze2, Using Apparent Activation Energy as a Reactivity Criterion for Biomass Pyrolysis, Energy Fuels 2016, 30, 7834 −7841.Show Affiliations
- Bioenergy Research Group, European Bioenergy Research Institute (EBRI), Aston University, Birmingham B4 7ET, UnitedKingdom
- Process Engineering, Stellenbosch University, Private Bag X1, Matieland, 7602 Stellenbosch, South Africa
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