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Stable Oligomer Formation from Lignin by Pyrolysis of Softwood in an Aprotic Solvent with a Hydrogen Donor

Von Wiley-VCH zur Verfügung gestellt

A thermally stable lignin oligomer is obtained from wood pyrolysis in an aprotic solvent with a H donor in 20 wt % (lignin basis) at 270 °C. The yield increases to 80 wt % when the temperature is raised above 300 °C, where cell wall cellulose and hemicellulose decompose.


Abstract

Pyrolysis of Japanese cedar wood in diphenoxybenzene (an aprotic solvent) with a hydrogen donor was investigated between 270–380 °C. Under these conditions, re-condensation via radical and quinone methide intermediates was efficiently suppressed and a thermally stable oligomer was obtained. The oligomer was stable even after the treatment time was extended. Yields of lignin-derived products at 270 °C were limited to approximately 20 wt %, but increased to >80 wt % (lignin basis) at the higher temperatures. The oligomer yield increased directly with the extent of the cellulose degradation at 350 °C. Based on the NMR analysis results, the ether bonds in lignin were largely cleaved, but condensed linkages such as β-aryl and β-β and 5-5’ types remained. The γ-hydroxypropyl group was identified as a typical side chain, formed by hydrogenation of the double bond of a coniferyl alcohol-type structure.

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