1. Impacts of acidic or basic sites on poplar sawdust on pyrolytic products and pyrolysis kinetics.
- Author
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Jiang, Yuchen, Li, Chao, Zhang, Lijun, Zhang, Shu, Wang, Dong, Leng, Chuanjun, Tang, Yonggui, Cui, Zhenhua, and Hu, Xun
- Subjects
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PYROLYSIS kinetics , *WOOD waste , *ACTIVATION energy , *POPLARS , *BIOCHAR - Abstract
Pyrolysis of biomass typically involves intensive dehydration, cracking, secondary condensation, etc. It is known that these reactions could be accelerated or suppressed with externally added acidic/basic sites presenting on surface of a biomass feedstock, which is expected to impact evolution of pyrolytic products and pyrolysis kinetics. This was investigated herein by pyrolysis of the poplar sawdust loaded with H 2 SO 4 or NaOH at 600 °C. The results indicated that H 2 SO 4 presence enhanced charring of the volatiles including sugars, sugar-derivatives and some lignin-derivatives via dehydration, polymerization, etc. This enhanced biochar production while diminished bio-oil formation and abundance of most of the organics in bio-oil including carboxylic acids, heavy tar (i.e. π-conjugated aromatics), etc. Nevertheless, H 2 SO 4 did not lead to substantial removal of hydrogen and oxygen in the biochar, but increased the activation energy (Ea) of the pyrolysis from 162.6 kJ/mol in pyrolysis of unloaded sawdust to 194.7 kJ/mol. In converse, NaOH promoted cracking/gasification of biochar and the volatiles including heavy tar, forming dominantly gases. NaOH presence also made structures of the semi-char (biochar precursor) more fragmented, reducing the Ea for pyrolysis to 135.7 kJ/mol. The in-situ IR characterization of the pyrolysis process showed that H 2 SO 4 promoted removal of -OH via dehydration or transformation to C O and the further condensation of C O, but not dehydrogenation of -C-H. NaOH promoted mainly deoxygenation and cracking of the sugary structures but not dehydration of -OH to carbonyls. [Display omitted] • H 2 SO 4 enhances charring to form more biochar, while NaOH promotes cracking to gas. • Both H 2 SO 4 and NaOH diminish tar formation via condensation to solids or cracking. • Charring-H 2 SO 4 reserves H and O in biochar, while cracking-NaOH enhances aromatization. • Activation energy in pyrolysis is enhanced with H 2 SO 4 , while decreased with NaOH. • DRIFTS shows H 2 SO 4 does not promote dehydrogenation, while NaOH suppresses dehydration. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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