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PCDDs, PCDFs and PCNs in products of microwave-assisted pyrolysis of woody biomass: Distribution among solid, liquid and gaseous phases and effects of material composition
Umeå University, Faculty of Science and Technology, Department of Chemistry.
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2016 (English)In: Chemosphere, ISSN 0045-6535, E-ISSN 1879-1298, Vol. 145, 193-199 p.Article in journal (Refereed) PublishedText
Abstract [en]

Microwave-assisted pyrolysis (MAP) of lignocellulosic biomass is a technique that could potentially be used to produce and upgrade renewable energy carriers. However, there is no available information about the formation of dioxins and other organic pollutants in MAP treatment of woody biomass. In this study, MAP experiments were conducted in lab-scale using virgin softwood, bark, and impregnated wood as feedstocks. The non-condensable gas, liquid (fractionated into aqueous and oil phases), and char fractions generated during pyrolysis were collected and analysed for polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and naphthalenes (PCNs). The concentrations of PCDDs, PCDFs and PCNs in the pyrolysis products ranged from 0.52 to 43.7 ng kg(-1). All investigated compound groups were most abundant in the oil fraction, accounting for up to 68% (w/w) of the total concentrations. The highest PCDD, PCDF and PCN concentrations were found from the pyrolysis of bark, which has relatively high contents of chlorine and mineral matter, followed by impregnated wood, which contains organic and metal-based preservatives. The homologue profiles of all three compound groups were dominated by the less chlorinated homologues. The homologue abundance decreased as the degree of chlorination increased. This trend was observed for all three feedstocks.

Place, publisher, year, edition, pages
2016. Vol. 145, 193-199 p.
Keyword [en]
Polychlorinated dibenzo-p-dioxins, Polychlorinated dibenzofurans, Polychlorinated naphthalenes, Persistent organic pollutants, Thermochemical conversion, Lignocellulosic biomass
National Category
Organic Chemistry
URN: urn:nbn:se:umu:diva-117388DOI: 10.1016/j.chemosphere.2015.11.110ISI: 000369196300025PubMedID: 26688256OAI: diva2:915123
Available from: 2016-03-29 Created: 2016-02-29 Last updated: 2016-04-06Bibliographically approved
In thesis
1. Dioxins and dioxin-like compounds in thermochemical conversion of biomass: formation, distribution and fingerprints
Open this publication in new window or tab >>Dioxins and dioxin-like compounds in thermochemical conversion of biomass: formation, distribution and fingerprints
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the transition to a sustainable energy supply there is an increasing need to use biomass for replacement of fossil fuel. A key challenge is to utilize biomass conversion technologies in an environmentally sound manner. Important aspects are to minimize potential formation of persistent organic pollutants (POPs) such as dioxins and dioxin-like compounds.

This thesis involves studies of formation characteristics of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and naphthalenes (PCNs) in microwave-assisted pyrolysis (MAP) and torrefaction using biomass as feedstock. The research focuses are on their levels, distributions, fingerprints (homologue profiles and isomer patterns) and the underlying formation pathways. The study also included efforts to optimize methods for extracting chlorinated aromatic compounds from thermally treated biomass. The overall objective was to contribute better understanding on the formation of dioxins and dioxin-like compounds in low temperature thermal processes.

The main findings include the following:

  • Pressurized liquid extraction (PLE) is applicable for simultaneous extraction of PCDDs, PCDFs, PCNs, polychlorinated phenols and benzenes from thermally treated wood. The choice of solvent for PLE is critical, and the extraction efficiency depends on the degrees of biomass carbonization.
  • In MAP experiments PCDDs, PCDFs and PCNs were predominantly found in pyrolysis oils, while in torrefaction experiments they were mainly retained in solid chars with minor fractions in volatiles. In both cases, highly chlorinated congeners with low volatility tended to retain on particles whereas the less chlorinated congeners tended to volatize into the gas phase.
  • Isomer patterns of PCDDs, PCDFs and PCNs generated in MAP were more selective than those reported in combustion processes. The presence of isomers with low thermodynamic stability suggests that the pathway of POPs formation in MAP may be governed not only by thermodynamic stabilities but also by kinetic factors.
  • Formation of PCDDs, PCDFs and PCNs depends not only on the chlorine contents in biomass but also the presence of metal catalysts and organic/metal-based preservatives.

Overall, the results provide information on the formation characteristics of PCDDs, PCDFs and PCNs in MAP and torrefaction. The obtained knowledge is useful regarding management and utilization of thermally treated biomass with minimum environmental impact.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2016. 72 p.
Polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, polychlorinated naphthalenes, PCDD, PCDF, PCN, persistent organic pollutants, torrefaction, pyrolysis
National Category
Organic Chemistry
urn:nbn:se:umu:diva-118861 (URN)978-91-7601-451-6 (ISBN)
Public defence
2016-04-29, KBC-huset, KB3A9, Umeå universitet, Umeå, 10:00 (English)
Available from: 2016-04-08 Created: 2016-04-05 Last updated: 2016-04-20Bibliographically approved

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