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Dioxins and dioxin-like compounds in thermochemical conversion of biomass: formation, distribution and fingerprints
Umeå University, Faculty of Science and Technology, Department of Chemistry.
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.
Keyword [en]
Polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, polychlorinated naphthalenes, PCDD, PCDF, PCN, persistent organic pollutants, torrefaction, pyrolysis
National Category
Organic Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-118861ISBN: 978-91-7601-451-6 (print)OAI: oai:DiVA.org:umu-118861DiVA: diva2:917094
Public defence
2016-04-29, KBC-huset, KB3A9, Umeå universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2016-04-08 Created: 2016-04-05 Last updated: 2016-04-20Bibliographically approved
List of papers
1. Evaluation of solvent for pressurized liquid extraction of PCDD, PCDF, PCN, PCBz, PCPh and PAH in torrefied woody biomass
Open this publication in new window or tab >>Evaluation of solvent for pressurized liquid extraction of PCDD, PCDF, PCN, PCBz, PCPh and PAH in torrefied woody biomass
2015 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 154, 52-58 p.Article in journal (Refereed) Published
Abstract [en]

Biomass torrefaction for sustainable energy production has gained an increasing interest. However, there is a lack of information on the thermal formation of persistent organic pollutants such as dioxins in the torrefied solid product. In this paper, we investigated the applicability of pressurized liquid extraction (PLE) for simultaneous extraction of a number of polychlorinated planar aromatic compounds from torrefied wood. The targeted compounds included polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), naphthalenes (PCNs), benzenes (PCBz), phenols (PCPhs) and PAHs. PLE tests were conducted on torrefied and non-torrefied (i.e. raw) eucalyptus wood chips using 5 single solvents (n-hexane, toluene, dichloromethane, acetone and methanol) and a mixture of n-hexane/toluene (1:1, v/v). The performance of each solvent was evaluated in terms of recoveries of spiked internal standards and the amount of co-extracted sample matrix. High polarity solvents such as methanol and acetone resulted in poor recoveries from torrefied wood for most of the target compounds, probably due to the high co-extraction of thermally degraded lignocellulosic compounds. Raw wood was less solvent-dependent and comparable results were obtained for polar and non-polar solvents. Toluene showed the best performance of the investigated solvents, with average recoveries of 79 +/- 14% and 66 +/- 9% for raw and torrefied wood, respectively. The method was validated using pentachlorophenol-tainted spruce wood chips. The proposed PLE method was compared to the traditional Soxhlet method. Results show that PLE gave equivalent or better extraction for all target compounds.

Keyword
Persistent organic pollutants, PLE, Dioxin, Solvent effect, Torrefaction
National Category
Organic Chemistry
Identifiers
urn:nbn:se:umu:diva-103714 (URN)10.1016/j.fuel.2015.03.068 (DOI)000353893200007 ()
Funder
Bio4Energy
Available from: 2015-06-11 Created: 2015-05-28 Last updated: 2017-12-04Bibliographically approved
2. 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
Open this publication in new window or tab >>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
Show others...
2016 (English)In: Chemosphere, ISSN 0045-6535, E-ISSN 1879-1298, Vol. 145, 193-199 p.Article in journal (Refereed) Published
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.

Keyword
Polychlorinated dibenzo-p-dioxins, Polychlorinated dibenzofurans, Polychlorinated naphthalenes, Persistent organic pollutants, Thermochemical conversion, Lignocellulosic biomass
National Category
Organic Chemistry
Identifiers
urn:nbn:se:umu:diva-117388 (URN)10.1016/j.chemosphere.2015.11.110 (DOI)000369196300025 ()26688256 (PubMedID)
Available from: 2016-03-29 Created: 2016-02-29 Last updated: 2017-11-30Bibliographically approved
3. Mechanistic evaluation of polychlorinated dibenzo-p-dioxin, dibenzofuran and naphthalene isomer fingerprints in microwave pyrolysis of biomass
Open this publication in new window or tab >>Mechanistic evaluation of polychlorinated dibenzo-p-dioxin, dibenzofuran and naphthalene isomer fingerprints in microwave pyrolysis of biomass
Show others...
2016 (English)In: Chemosphere, ISSN 0045-6535, E-ISSN 1879-1298, Vol. 150, 168-175 p.Article in journal (Refereed) Published
Abstract [en]

Isomer distribution patterns of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and naphthalenes (PCNs) were investigated in microwave-assisted pyrolysis (MAP) products of woody biomass. The feedstocks included bark and impregnated wood. The results indicated that isomer distributions in MAP are more selective compared to those reported from wood burning and waste incineration. Favored formation of 4-MoCDF and highly selective chlorine substitution at the 2,4-position observed during MAP suggested a preferred formation pathway of PCDFs involving (chloro)phenol precursors followed by subsequent chlorination. The PCDD distribution was dominated by isomers typically formed from chlorophenol condensation at relatively low temperature. The PCN isomer distributions showed a tendency for sequential chlorination from non-substituted naphthalene at successive positions. The presence of isomers such as 1-MoCDD, 4-MoCDF, 1,2,3-TriCN with low thermodynamic stability indicates that kinetic factors may be important in the MAP process.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
PCDD, PCDF, Dioxin-like compounds, PCN, Persistent organic pollutants, Biomass thermochemical conversion
National Category
Organic Chemistry Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-118908 (URN)10.1016/j.chemosphere.2016.02.031 (DOI)000372765100022 ()26901473 (PubMedID)
Available from: 2016-04-06 Created: 2016-04-06 Last updated: 2017-11-30Bibliographically approved
4. Physical transformation and formation of PCDDs and PCDFs in torrefaction of biomass with different chemical composition
Open this publication in new window or tab >>Physical transformation and formation of PCDDs and PCDFs in torrefaction of biomass with different chemical composition
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Organic Chemistry
Identifiers
urn:nbn:se:umu:diva-118910 (URN)
Available from: 2016-04-06 Created: 2016-04-06 Last updated: 2016-04-06

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