Journal
PROCEEDINGS OF THE COMBUSTION INSTITUTE
Volume 38, Issue 3, Pages 3959-3967Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.proci.2020.06.287
Keywords
Phosphorus; Crosslinking; Char structure; Char reactivity; Biomass pyrolysis
Funding
- Australian Research Council
- Curtin International Postgraduate Research Scholarship (CIPRS) by Curtin University
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This study investigates the effect of phosphorus on the char structure and reactivity of biomass during fast pyrolysis. Experimental results show that the presence of phosphorus significantly increases char yield and C/H content, while decreasing O content. The form and content of phosphorus play an important role in the evolution of char structure and reactivity.
This paper investigates the effect of phosphorus (P) on char structure and reactivity of char prepared from the fast pyrolysis of purposely-prepared P-loaded biomass samples at 1000 degrees C in absence of other inorganic species. Biomass was first acid-washed then loaded with P of three different occurrence forms (one organic P i.e. phytic acid, and two inorganic P i.e. orthophosphoric acid and polyphosphoric acid) at the same P content of 0.8 wt%. Experimental results show that both organic and inorganic P substantially increase char yields during pyrolysis from 6.2% for the biomass sample without P to 23.0-26.0% for P-loaded samples due to the enhanced crosslinking by P-containing structures in char, leading to increases in the char C and H contents and decrease in O content. The presence of P in biochars from fast pyrolysis of various P-loaded biomass samples plays important role in the evolution of char structure and intrinsic reactivity measured during low-temperature oxidation at 500 degrees C in air under chemical-reaction-controlled regime. After pyrolysis and subsequent char oxidation, all P in biomass either as organic or inorganic P are found to be present in forms of acid-insoluble organic structures. For char prepared from acid-washed wood, char reactivity increases with char conversion due to the increasing pore surface area at higher conversion. Comparatively, for char prepared from acid-washed wood loaded with various P at char conversion below 60%, the presence of P increases char intrinsic reactivity due to the enhanced crosslinking of reactive carbon structures and reduced condensation of char structures. However, at conversions above 60%, P-containing species in char lead to a significant decrease in char reactivity, due to the formation of abundant C-O-P bonds, that is highly resistant to the oxidation in air, in the reacting chars. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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