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

Research highlight

  The current work therefore provides the first detailed quantitative data of the phenols and methoxy-benzenes produced from the hydrothermal conversion of alkali lignin in subcritical water and water−ethanol media.

Significance and impact

  An optimal conversion of alkali lignin to liquid effluent was achieved at 310 °C, 30 min, and at an ethanol concentration of 50%. The yields of the phenolic and methoxy-benzene compounds were higher in 25% ethanol than that of pure water. It was found that the reaction time had a positive impact on the generation of phenols, while further extension of the reaction time did not significantly increase phenol yield. Higher reaction temperatures or lower contents of ethanol appeared to improve the byproduct yields.

  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 °C, 25% ethanol): phenol (4.25 mg/g), 4-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 °C over 60 min in neat water.

http://dx.doi.org/10.1021/ie5011178 | Ind. Eng. Chem. Res. 2014, 53, 10328−10334