Experimental study of the oxidation and pyrolysis of dibenzofuran at very low concentration

International audience“Dioxins” (or PCDD/F) are persistent organic pollutants (POP) which are emitted in the atmosphere by several combustion and thermal processes. Many studies concern the formation of dioxins, but very few thermal destruction. The present study concerns the oxidation and the pyrolysis of dibenzofuran which is chosen as a model molecule of “PCDF” (polychrorodibenzofurans). The reaction is studied at very low concentration of dibenzofuran (i.e. near 2 ppm) in a continuous perfectly stirred reactor, at atmospheric pressure. The residence time is varying between 3 s and 5 s, whereas the temperature is ranging from 500 to 950 °C. Dibenzofuran is a solid compound in standard conditions, so a difficulty of this study is to realize a continuous gas flow of this species.During dibenzofuran decomposition, the conversion can be close to 100% and several intermediary species are formed. These species are identified by GC/MS and then quantified by GC/FID. The main byproducts are derivatives of benzofuran, polyaromatic hydrocarbons and other volatile organic compounds. These experimental data are used to improve a kinetic mechanism and previously validated with experimental data obtained with higher ranges of DBF concentration

Chemical Characterization of Non-Saccharidic and Saccharidic Components of Rapeseed Hulls and Sunflower Shells

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Homolytic and heterolytic cleavage of beta-ether linkages in hardwood lignin by Steam Explosion

International audienceSteam explosion lignin (SEL) was extracted with ethanol from steam exploded hardwood (okoumé, Aucoumea klaineana Pierre) pretreated at various severities after neutral or acidic impregnation. The SELs were subjected to a structural characterization by 2D HSQC NMR, 31P NMR, SEC and compared to Milled Wood Lignin (MWL). A strong decrease in the -O-4 content is observed with increasing steam explosion severity accompanied with a gradual increase in molecular mass. C-oxydized S units (S’, Hibbert’s ketones) were quantified by NMR and used as a marker of the hydrolytic mechanism as well as naphthol used as a carbonium ion scavenger. It has been observed that mixed reactions of hydrolysis and homolysis are involved but the SEL is mainly cleaved homolytically, favouring recondensation through radical coupling even at low reaction severity. However, acidic pre-impregnation of wood prior to steam explosion enhanced the carbonium ion pathway

Microwave-assisted extraction of high-molecular-weight hemicelluloses from spruce wood

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Extraction and Characterization of Fibers from Palm Tree

The characterization of fibers extracted from leaflet, the empty fruit bunches, leaf sheath, and spath of palm tree was performed. The fibers were extracted using three different procedures through chemical and / or enzymatic methods. The raw fibers studied have xylose contents between 13-22% and glucose content between 30% and 45%. The microfibrillar angle (MFA) values are in the order: bunch > spath > leaf sheath >> leaflet. Spath and leaf sheath, which naturally occur in a woven form present poor mechanical strength but could be readily used to produce cheap composites. Leaflet fibers extracted from date palm tree exhibiting a low MFA (16 degrees), a high cellulose content, and cellulose crystallinity present the highest ultimate tensile strengths (approximate to 1250 N.mm(-2))

Steam explosion process for the selective extraction of hemicelluloses polymers from spruce sawdust

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High voltage electric discharges treatment for high molecular weight hemicelluloses extraction from spruce

International audienc