Using Apparent Activation Energy as a Reactivity Criterion for Biomass Pyrolysis

• Published in: Energy & fuels Vol. 30; no. 10; pp. 7834 - 7841
• Main Authors: Carrier, Marion, Auret, Lidia, Bridgwater, Anthony, Knoetze, Johannes H
• Format: Journal Article
• Language: English
• Published: American Chemical Society 20-10-2016
• Subjects: Chemical and Process Engineering; Engineering Sciences
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/acs.energyfuels.6b00794

The reactivity of chemically isolated lignocellulosic blocks, namely, α-cellulose, holocellulose, and lignin, has been rationalized on the basis of the dependence of the effective activation energy (E α) upon conversion (α) determined via the popular isoconversional kinetic analysis, Friedman’s method. First of all, a detailed procedure for the thermogravimetric data preparation, kinetic calculation, and uncertainty estimation was implemented. Resulting E α 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 ± 118 kJ/mol, thus confirming the single-step nature of pyrolysis. On the other hand, large and significant variations in E α with α from 174 ± 10 to 322 ± 11 kJ/mol in the region of 0.05 and 0.79 were obtained for the Klason lignin and reported for the first time. The non-monotonic nature of weight loss at low and high conversions had a direct consequence on the confidence levels of E α. The new experimental and calculation guidelines applied led to more accurate estimates of E α values than those reported earlier. The increasing E α dependency trend confirms that lignin is converted into a thermally more stable carbonaceous material.