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THE ACTION OF NITRIC ACID ON LIGNIN IN A WATER–DIMETHYL SULFOXIDE MIXTURE

V. Veshnyakov, M. Yokubjanov, Y. Khabaro
Wednesday 19 December 2018 by Libadmin2018

ABSTRACT

Lignin as a by-product of chemical or biochemical processing of wood is usually burned to generate energy. However, its use as a source of chemicals and materials is considered more promising. Treatment of lignin with nitric acid is used in practice for its depolymerization. In our study, we investigated the treatment of Klason lignin with mixtures of concentrated nitric acid with dimethyl sulfoxide of various compositions. The effect of such treatments was evaluated by UV-Visible spectrophotometry of alkaline solutions of the formed products. Klason lignin was completely dissolved in alkaline medium after its treatment at 100°C for 10 min with mixtures of nitric acid with dimethyl sulfoxide of various compositions. Absorbance at 280 nm of the products in solutions decreased with an increase in the content of nitric acid in the initial reagent mixture that confirms a stronger degradation of lignin macromolecules. When the reaction mixture was diluted with distilled water there remained a residue, which was soluble only in the alkaline medium. The amount of the precipitate decreased with an increase in the content of nitric acid in the initial reagent mixture that may also be due to a stronger degradation of lignin macromolecules. The isolated precipitates were characterized by IR spectroscopy. IR spectra of the products have characteristic absorption bands of NO2 and C=O groups that confirms the processes of nitration and oxidation of lignin. The obtained effect of transforming the insoluble Klason lignin into a water-soluble form can be used to develop ways of hydrolysis lignin utilization.

Keywords: lignin, nitration, dimethyl sulfoxide, depolymerization


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