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Phase transitions involving Ca - The most abundant ash forming element - In thermal treatment of lignocellulosic biomass
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
Umeå University, Faculty of Science and Technology, Department of Applied Physics and Electronics.
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2021 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 285, article id 119054Article in journal (Refereed) Published
Abstract [en]

Torrefaction, pyrolysis and gasification are of interest to convert lignocellulosic biomass into fuels and chemicals. These techniques involve thermal treatment at low partial pressures of oxygen. However, little is known about the transformation of ash elements during these processes. The phase transition of the major ash element calcium (Ca) was therefore studied with powder from pine as biomass model treated at temperatures 300-800 degrees C under atmospheres of 100% N-2, 3% O-2 and 6% O-2 and thermodynamic equilibrium modelling. For evaluation, Xray powder diffraction and synchrotron Ca K-edge X-ray absorption near edge structure (XANES) spectroscopy in combination with linear combination fitting and reference compounds was used. The results indicated that the most abundant Ca-containing species in the untreated material was thermally unstable Ca oxalate (CaC2O4) primarily decomposing into Ca phases dominated by carbonates at temperatures up to 600 degrees C. Double carbonates of calcium and potassium were observed in the form of fairchildiite/butscheliite (K2Ca(CO3)(2)), and these phases were stable over the low temperature range studied. Hydroxyapatite (Ca-5(PO4)(3)OH) was expected to be present and thermally stable over the entire temperature interval and was found in untreated material. At temperatures above 600 degrees C calcium oxide (CaO) was formed. The amount of oxygen had little effect on the phase transitions. The results of thermodynamic modeling were in agreement with XANES showing that this is a versatile technique that can be applied to systems as complex as Ca phase transitions in thermally treated lignocellulosic biomass at low partial pressures of oxygen.

Place, publisher, year, edition, pages
Elsevier, 2021. Vol. 285, article id 119054
Keywords [en]
Pyrolysis, Calcium phases, Equilibrium modelling, XANES, XRD
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-179061DOI: 10.1016/j.fuel.2020.119054ISI: 000588132400026Scopus ID: 2-s2.0-85090129992OAI: oai:DiVA.org:umu-179061DiVA, id: diva2:1523740
Available from: 2021-01-29 Created: 2021-01-29 Last updated: 2023-03-23Bibliographically approved

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Backman, RainerBoström, Dan

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