Gas—liquid chromatography—mass spectrometry studies on pine kraft black liquors : III. The liberation of carboxylic acids in the initial phase of pulping

Abstract

Pine-wood chips were treated with sodium hydroxide at a rather low temperature (40°C) and the products obtained in solution were analysed by capillary gas—liquid chromatography—mass spectrometry. In addition to fatty and resin acids, which were the main products, 22 hydroxy monocarboxylic, 18 dicarboxylic and 6 aromatic carboxylic acids were identified as their trimethylsilyl derivatives. Hydroxy monocarboxylic acids (0.09–0.16% of wood) were primarily carbohydrate degradation products, whereas the dicarboxylic acid fraction (0.07–0.10% of wood) was mainly composed of oxalic and C 5–C 10 alkanedioic acids, which were obviously autoxidation products of fatty acids. Aromatic acids included benzoic acid and five lignin-related compounds, of which guaiacylglycolic and guaiacylglyceric acids had not been identified earlier after alkali treatment of softwood.