THERMOCHEMICAL CONVERSION OF DIOXANLIGNIN OF WHEAT STRAW IN SUB/SUPERCRITICAL DIMETHYL CARBONATE MEDIUM

Abstract

The aim of this work was to study the conversion processes of dioxanlignin of wheat straw in sub/supercritical dimethyl carbonate medium. The experiment was performed in autoclave in a temperature range from 200 to 350 °С. The low-molecular-weight products were extracted from liquid fraction using hexane. GC-MS was used to analyze their composition. The solid products were analyzed by IR-spectroscopy method. The low-molecular-weight products consist of esters, aldehydes, ketones and alkyl aromatic compounds. Thirty-four compounds were identified by GC-MS, including 12 compounds С6–С3, i.e. structures which relates to acknowledged phenylpropane structure of lignin. The composition of low-molecular-weight products fraction predominantly comprised of methyl esters of aromatic and fatty acids. More than 95% of identified low-molecular-weight products are veratrous-type compounds. New data on the conversion processes of dioxanlignin of wheat straw in sub/supercritical dimethyl carbonate medium were obtained. It is shown that high solubility of dioxanlignin under subcritical conditions can be caused by cleavage of intramolecular interaction, including hydrogen bonds between macromolecules of dioxanlignin, as a result of thermal exposure and methylation reactions. Fragmentation of molecules under supercritical conditions includes the processes of a radical cleavage of alkyl aryl ester bonds as well as the reactions of dealkylation, dehydration, methylation, re-esterification and demetoxylation.