Alkaline degradation of ALCELL® lignin

ALCELL® lignin has been depolymerized by alkaline hydrolysis using a magnetically stirred batch autoclave. The effects of reaction temperature and time, combined into a single parameter (the reaction ordinate), were quantified in terms of the yields of unreacted lignin and identifiable liquid degradation products. At a high treatment severity, about 40% of the unreacted lignin is recovered as an alkaline-insoluble reactor residue, whilst at low to medium severities, this lignin is essentially all recovered by acid precipitation from the product mixture. The predominant identifiable liquid phenolic products ranged from guaiacol and syringol at low severities to catechol and its derivatives at high severities. Increasing concentrations of sodium hydroxide from 0 to 4% increased the conversion of lignin to liquid products from 7 to 30%. Based on the initial lignin, a maximum concentration of 4.4% identifiable phenols (mostly syringol = 2.4%), was found when using 0.5% NaOH, with a subsequent decrease with increasing alkali concentration. When a 50% ethanol-water mixture was used as the solvent, conversion remained essentially the same, but the methylene chloride solubles increased from 5 to 19%.