A first step towards identification of tannin-derived black carbon: Conventional pyrolysis (Py–GC–MS) and thermally assisted hydrolysis and methylation (THM–GC–MS) of charred condensed tannins |
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| Institution: | 1. Instituto de Ciencias del Patrimonio (Incipit), Consejo Superior de Investigaciones Científicas (CSIC), San Roque 2, 15704 Santiago de Compostela, Spain;2. Department of Earth Sciences – Organic Geochemistry, Faculty of Geosciences, Utrecht University, P.O. Box 80021, 3508 TA Utrecht, The Netherlands;3. Southern Cross GeoScience, Southern Cross University, P.O. Box 157, Lismore, 2480 New South Wales, Australia;4. Pacific Forestry Centre, Natural Resources Canada, 506 West Burnside Rd., Victoria, BC, Canada V8Z 1M5;1. Dept. of Soil & Crop Sciences, Texas A&M University, College Station, TX 77843, United States;2. Dept. of Nutrition and Food Science, Texas A&M University, College Station, TX 77843, United States;1. Department of Chemical and Biological Engineering, University of Maine, USA;2. Unidad de Desarrollo Tecnológico, Concepción, Chile;3. Forest Bioproducts Research Institute, University of Maine, USA;1. Texas A&M University, Soil & Crop Sciences Department, 2474 TAMU, College Station, TX, 77843, USA;2. Texas A&M University, Nutrition & Food Science Department, College Station, TX, 77843, USA;1. Université Grenoble Alpes, CEA, Laboratoire de Préparation des Bioressources (LPB), F-38000, Grenoble, France;2. Université de Toulouse, INPT, UPS, Laboratoire de Génie Chimique, 4 Allée Emile Monso, F-31030, Toulouse, France;3. CNRS, Laboratoire de Génie Chimique, F-31030, Toulouse, France;4. VTTTechnical Research Centre of Finland Ltd, P.O. Box 1000, FI-02044, VTT, Finland;5. FCBA, InTechFibres Division, CS 90251, F-38044, Grenoble, France;6. RAGT Energie, zone Innoprod, Chemin de la Teulière, F-81000, Albi, France;7. IHE Delft Institute for Water Education, Department of Environmental Engineering and Water Technology, Delft, the Netherlands |
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| Abstract: | Tannins account for a significant proportion of plant biomass and are likely to contribute to the residues formed by incomplete biomass combustion (black carbon, BC). Nonetheless, the molecular properties of thermally modified tannins have not been investigated in laboratory charring experiments. We applied conventional analytical pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) and thermally assisted hydrolysis and methylation (THM–GC–MS) to investigate the effects of heat treatment with a muffle furnace on the properties of condensed tannins (CT) from Corsican pine (Pinus nigra) needles. Py–GC–MS showed a decrease in the relative abundance of the 1,2,3-trihydroxybenzenes (pyrogallols) at ?300 °C and of the dihydroxybenzenes (mainly catechols) at ?350 °C due to dehydroxylation of the CT B ring. Further dehydroxylation led to formation of monohydroxybenzenes (phenols), which showed a strong enrichment between 350 and 400 °C and, at higher temperatures, to a series of monocyclic and polycyclic aromatics benzene, alkyl benzenes and polycondensed aromatic hydrocarbons (PAHs)]. Degradation of the A ring could not be recognized via Py–GC–MS, probably because of the poor chromatographic behavior of 1,3,5-trihydroxybenzenes (phloroglucinols). The progressive dehydroxylation and eventual polycondensation of the CT B ring was corroborated using THM–GC–MS. In addition, with THM–GC–MS the thermal rearrangement of CT A rings at 300 °C and higher was inferred from the relative abundance of 1,3,5-trimethoxybenzenes (methylated phloroglucinol derivatives). These compounds were observed at moderate/high temperature (up to 450 °C) and can not be produced from THM of lignin, suggesting that they may be markers of CT in natural BC samples. |
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