Quantitative Analyses of Lignin Hydrothermolysates from Subcritical Water and Water-Ethanol Systems

The present research relates a universally practical and feasible approach toward chemically deconstructing the macromolecular architecture of lignin, specifically alkali lignin (AL), for the production of a number of valuable side-stream aromatic nuclei byproducts. The hydrothermolysates obtained at different subcritical conditions were tentatively qualitatively identified by gas chromatography mass spectrometry (GC-MS) and subsequently quantified by gas chromatography (GC). The influence of temperature (220-340 degrees C), residence time (0-60 min), and ethanol volume-% in a water ethanol cosolvent (0-100%) on the conversion of AL and the yield of the side-stream (liquid) products were explored. The results show that the yield and identity of the phenolic and methoxy-benzene compounds were strongly correlated to the conversion temperature and the ethanol volume-%, whereas residence time in the autoclave had only a minor influence. The following individual chemicals (mg liquid side-stream/g lignin) and associated yields were determined from the optimal hydrothermal conditions (30 min, 310 degrees C, 25% ethanol): phenol (4.25 mg/g), 1-methylguaiacol (2.93 mg/g), 3,5-dimethoxyacetophenone (0.78 mg/g), 1,2,4-trimethoxybenzene (2.47 mg/g), and 2,6-dihydroxy-4-methoxyacetophenone (2.47 mg/g). The highest yield of guaiacol (11.87 mg/g) and 2,6-dimethoxyphenol (12.17 mg/g) was obtained at a reaction temperature of 310 degrees C over 60 min in neat water.