Isolation of residual lignin from softwood kraft pulp. Advantages of the acetic acid acidolysis method.

Abstract Lignin in kraft pulp was extracted by enzymatic hydrolysis of the carbohydrates, acidolysis with dioxane–water–HCl (conventional method), and acidolysis with acetic acid–water–ZnCl 2 . The latter method was shown to extract lignin with a better yield than for conventional acidolysis and with a much lower content in impurities than for enzymatic hydrolysis. It was confirmed by 13 C NMR analysis of the lignin samples that conventional hydrolysis modified the lignin polymer, causing the cleavage of some aryl–ether linkages. The cleavage was also observed on a model compound submitted to the same extraction conditions. In that respect, the acetic acid–water–ZnCl 2 method was less damaging and consequently more suitable for analytical purposes. To cite this article: D. Lachenal et al., C. R. Biologies 327 (2004).