Using Apparent Activation Energy as a Reactivity Criterion for Biomass Pyrolysis

Significance Statement

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.  

Using Apparent Activation Energy as a Reactivity Criterion for Biomass Pyrolysis - renewable energy global innovations

About The Author

Dr. Marion Carrier is a Marie Curie research fellow at the European Biomass Research Institute of Aston University, Birmingham (UK). She obtained degrees in Chemical engineering from CPE Lyon (MEng), in Analytical Science (MSc) and in Chemistry (PhD) from Claude Bernard University in Lyon (France). Trained as an interdisciplinary researcher, she has been applying her current skills and knowledge in the field of pyrolysis for the last 8 years at leading research organisations in France, South Africa, Chile and England.

Her research contributed to a wide range of research fields such as chemical mechanistic, pyrolysis chemical analysis, bioprocessing, thermochemical processing and soil sciences. Since October 2015, she joined Prof. Bridgwater’s team to pursue her research on molecular mapping of fast pyrolysis using fractionation and isotopic characterisation techniques along with molecular dynamics calculations.

About The Author

Dr. Lidia Auret is a senior lecturer at Stellenbosch University (South Africa). She obtained a BEng Chemical Engineering: Mineral Processing and a PhD in Extractive Metallurgical Engineering at Stellenbosch University.

Currently, she leads the research group of Process Monitoring which activities include the development of new process measurement systems (e.g. using image data to determine the efficiency of certain mineral processing units); research on novel methods with which to extract informative features from process data; and investigation into data-driven approaches for root cause analysis of abnormal behaviour on process plants.

About The Author

Prof. Anthony Bridgwater (BSc Tech, PhD, DSc., CEng. FIChemE, FIE) is a professor of chemical engineering and head of the European Bioenergy Research Institute (EBRI) at Aston University (UK). He has been working in bioenergy and biofuels since 1978, focussing on initially gasification for biofuels and later fast pyrolysis for direct production of liquids from biomass in high yields. He led the UK national centre of excellence in bioenergy and has participated in over 25 EC funded R&D projects.

About The Author

Prof. Hansie Knoetze (BEng, PhD) is the Dean Faculty of Engineering at Stellenbosch University since 2012. He has been teaching and researching in interconnected disciplines such as Engineering Propelling Science, thermochemistry and separation; then promoting Research in the field of energy and environmental engineering with the emphasis on the production of fuels and chemicals from renewable biomass, but also supporting progress in the understanding of the underlying thermodynamics and kinetics of the separation processes.

Reference

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
  1. Bioenergy Research Group, European Bioenergy Research Institute (EBRI), Aston University, Birmingham B4 7ET, UnitedKingdom
  2. Process Engineering, Stellenbosch University, Private Bag X1, Matieland, 7602 Stellenbosch, South Africa

 

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