Direct Liquefaction of Alkali Lignin in Methanol and Water Mixture for the Production of Oligomeric Phenols and Aromatic Ethers

Alkali lignin was direct liquefied in methanol-water mixture, and the resulting converted lignin was dissolved in ethyl acetate to obtain low molecular weight phenols and aromatic ethers. Various temperatures (220 to 280 degrees C), residence times (30 to 120 min) and water and methanol ratio (0 to 3/7, wt) were evaluated. The maximum lignin conversion and oligomers yield of 85.4% and 66.1% respectively, were observed at 260 degrees C in methanol and water (9/1, w/w) for 120 min. Prolonged residence time and higher temperatures would lead further condensation. Furthermore, GPC results showed the degraded lignin had 5 C9 units and the oligomers had only 3 C9 units on average. H-NMR and FT-IR analysis indicated these oligomers were consisting of phenolic and aromatic ether compounds. A possible mechanism of water-methanol system was the water can inhibit the condensation between free radical and phenolic groups, which allows more C-O or C-C bonds cleavage at elevated temperatures.