Influence of the extraction temperature on the properties and yield of ethanollignin from fir wood

The extraction of lignin from fir wood (Abies sibirica Ledeb) with aqueous solutions of ethanol was studied in the temperature range I80 220°C using an enlarged laboratory installation. The influence of the pulping temperature and the reactor discharge temperature, as well as the concentration of ethanol on the lignin yield was investigated. It was shown that the optimal cooking temperature of 200°C allows obtain high yields of lignin while maintaining its morphology. The pulping temperature significantly affects not only the yield of ethanol lignin, but also its physicochemical properties. Ethanol lignins isolated from fir wood at temperatures of 200 and 220°C were analyzed by the TG-DTA-DSC and GPC methods. It is shown that there is a change in the morphology, thermal properties, and molecular weight distribution of ethanol lignin at 220°C and higher. Ethanol lignin derived from wood at temperature of 200°C is more thermally stable compared to lignin derived at temperature of 220°C. Ethanol lignin obtained at temperature of 200 °C has an average molecular weight of 1,781 Da and a degree of polydispersity of 2.49. Ethanol lignin derived at a temperature of 220°C has an average molecular weight of 1,341 Da and a polydispersity degree of 2.22. The lignin yield substantially depends on the temperature at which the reactor is discharged and the extract is separated from the solid residue. When the unload temperature was 20°C the maximum lignin yield was 8.58 g per 100 g of completely dry wood. In the case when the unload temperature was 70°C the lignin yield achieved 10.34 g. The maximum yield of ethanol lignin for the cooking temperature of 200°C is 10.34 g (34.9 wt. % of the initial content of lignin in fir wood). An increase in temperature from 20 to 70°C allows us to significantly increase yields. Lignin obtained as the result of organosolvent extraction offir wood can be used as a raw material in the production ofpolymers or for the production of aromatic compounds.

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