Depolymerization of Condensed Lignins with Hydrogen Nitrate

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66.095.268+661.632.12+665.947.4

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Abstract

The aim of the work was studying depolymerizing action of hydrogen nitrate on condensed lignin in an aqueous-organosolvent medium. A comparative studies of technical hydrolytic lignin depolymerization in aqueous and aqueous-alcoholic medium with dilute hydrogen nitrate were carried out. It has been found that the reaction takes place about the same, full depolymerization of hydrolytic lignin is failed to reach even for 2 hours. In these conditions 50...60 % of hydrolytic lignin goes into solution. The fluid module 19...21 is optimal for performing the reaction in an aqueous-alcoholic medium. In aqueous medium hydrogen nitrate is stronger hydrolyze polysaccharides: 9,1 % cotton cellulose, 17,8 % bleached hardwood kraft pulp and 7,9 % bleached softwood kraft pulp. In aqueous-alcoholic medium these figures were 3,6, 9,4 and 8,0 %, respectively. We first have found that when using the aprotic solvents (dioxane, dimethylsulfoxide), full depolymerization of condensed lignins goes in just 15...30 min. Undissolved residues are different in physical properties and have different IR spectra. The absorption at 1506 and 1593 cm-1 due to the aromatic ring skeletal vibrations is strongly reduced. The absorption at 1720 cm-1  relating to the valent vibrations of the carbonyl and carboxyl groups is increased. First it has been found that hydrogen nitrate depolymerize rapidly and completely condensed lignins if the reaction is carried out in aqueous-dioxane or aqueous-dimethylsulfoxide medium.

Authors

U.G. Habarov, Doctor of Chemistry, Professor, D.E. Lakhmanov, Postgraduate Student Northern (Arctic) Federal University named after M.V. Lomonosov Naberezhnaya Severnoy Dviny, 17, Arkhangelsk, 163000, Russia, е-mail: dmi84339053@ya.ru

Affiliation

Northern (Arctic) Federal University named after M.V. Lomonosov

Keywords

Klason lignin, hydrolytic lignin, depolymerization, hydrogen nitrate, ethanol, dioxane, dimethylsulfoxide.

References

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