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Characterization of free radicals by electron spin resonance spectroscopy in biochars from pyrolysis at high heating rates and at high temperatures
Department of Chemical and Biochemical Engineering, Technical University of Denmark, Søltofts Plads Bygning 229, Kgs. Lyngby 2800, Denmark.ORCID iD: 0000-0002-6571-3277
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2016 (English)In: Biomass and Bioenergy, ISSN 0961-9534, E-ISSN 1873-2909, Vol. 94, 117-129 p.Article in journal (Refereed) Published
Abstract [en]

The concentration and type of free radicals from the decay (termination stage) of pyrolysis at slow and fast heating rates and at high temperatures (above 1000 degrees C) in biomass char have been studied. A room temperature electron spin resonance spectroscopy study was conducted on original wood, herbaceous biomass, holocelluloses, lignin and their chars, prepared at high temperatures in a wire mesh reactor, an entrained flow reactor, and a tubular reactor. The radical concentrations in the chars from the decay stage range up between 7.10(16) and 1.5.10(18) spins g(-1). The results indicated that the biomass major constituents (cellulose, hemicellulose, lignin) had a minor effect on remaining radical concentrations compared to potassium and silica contents. The higher radical concentrations in the wheat straw chars from the decay stage of pyrolysis in the entrained flow reactor compared to the wood chars were related to the decreased mobility of potassium in the char matrix, leading to the less efficient catalytic effects of potassium on the bond-breaking and radical re-attachments. The high Si levels in the rice husk caused an increase in the char radical concentration compared to the wheat straw because the free radicals were trapped in a char consisting of a molten amorphous silica at heating rates of 10(3)-10(4) K s(-1). The experimental electron spin resonance spectroscopy spectra were analyzed by fitting to simulated data in order to identify radical types, based on g-values and line widths. The results show that at high temperatures, mostly aliphatic radicals (g = 2.0026-2.0028) and PAH radicals (g = 2.0027-2.0031) were formed.

Place, publisher, year, edition, pages
2016. Vol. 94, 117-129 p.
Keyword [en]
Electron spin resonance spectroscopy, Biomass, Char, Fast pyrolysis, Alkali
National Category
Chemical Process Engineering
Identifiers
URN: urn:nbn:se:umu:diva-134554DOI: 10.1016/j.biombioe.2016.08.020ISI: 000385330600014OAI: oai:DiVA.org:umu-134554DiVA: diva2:1093981
Funder
The Kempe Foundations
Available from: 2017-05-08 Created: 2017-05-08 Last updated: 2017-08-08Bibliographically approved

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