Effect of Fe3+ ions on transformation of hydrolysis lignin in water under sub- and supercritical conditionsстатья
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Дата последнего поиска статьи во внешних источниках: 15 февраля 2024 г.
Аннотация:The transformation of hydrolysis lignin in water under sub- and supercritical conditions(320—800 C, 10.0 MPa) in the presence of iron(III) ions was studied. At temperaturesabove 400 C, two processes are most signifi cant: deep depolymerization of lignin tophenolic monomers and condensation of aromatic moieties of lignin into carbonaceousdeposits. In the presence of Fe3+ ions, the content of monomeric phenols increases3—4-fold, which is indicative of the catalytic eff ect of iron in lignin depolymerization.When the reaction temperature increases from 400 to 660 C, the content of monomericproducts (mainly, phenol and guaiacol) increases from 1.8 to 7.5 wt.%. Under the sameconditions, considerable gasifi cation of lignin monomers and oligomers to a hydrogen-richmixture (up to 38 vol.%) takes place. The yield of carbon-containing gaseous products isindependent of the presence of Fe3+ ions, retaining a value of 27% in terms of carbon.Further temperature rise up to 800 C decreases the content of the monomeric productsof depolymerization and increases the contribution of gaseous products. In this case,the condensation of phenolic moieties to give carbonaceous deposits becomes the predominant reaction. The interaction of the Fe3+ ion with the β-O-4-dimer of coniferylalcohol was studied by quantum chemical calculations. According to the calculation results,in the presence of iron, the electron density of the highest occupied molecular orbital of thedimer partially shifts towards the iron ion, which facilitates cleavage of the C—O ether bond