THE EFFECT OF TIME AND TEMPERATURE ON THE HYDROGENATION OF ASPEN LIGNIN

Abstract

A study has been made of the hydrogenation of preextracted aspen sapwood meal under conditions whereby the lignin is degraded to identifiable products. By gas liquid chromatography, guaiacol, 4-methylguaiacol, 4-ethylguaiacol, 4-n-propylguaiacol, dihydroconiferyl alcohol, syringol, 4-methylsyringol, 4-ethylsyringol, 4-n-propylsyringol, and dihydrosinapyl alcohol were separated and identified.The relative abundance of these 10 compounds was determined in the chloroform-soluble product after hydrogenation using a dioxane–water (1:1) solvent medium, Raney nickel catalyst, an initial hydrogen pressure of 500 p.s.i. and temperatures of 150°, 165°, 185°, 195°, 210°, and 220° for a reaction time of 5 hours and a temperature of 195° for times of 0, 1.3, 5.0, and 24 hours. The best yield (52.2% of the Klason lignin) of such phenolic derivatives was obtained at a reaction temperature of 195° for 5 hours.The significance of the observed variation in the yields of these compounds with time and temperature and the relationship of these yields to the structure of lignin is discussed. Evidence is presented in support of both γ-alkyl ether and β-aryl ether linkages in the lignin substance.