Hydrolytic degradation of alkaline lignin in hot-compressed water and ethanol.
Alkaline lignin of a very high molecular weight was successfully degraded into oligomers in a hot-compressed water-ethanol medium with NaOH as the catalyst and phenol as the capping agent at 220-300 degrees C. Under the optimal reaction conditions, i.e., 260 degrees C, 1 h, with the lignin/phenol ratio of 1:1 (w/w), almost complete degradation was achieved, producing <1% solid residue and negligible gas products. The obtained degraded lignin had a number-average molecular weight M(n) and weight-average molecular weight M(w) of 450 and 1000 g/mol respectively, significantly lower than the M(n) and M(w) of 10,000 and 60,000 g/mol of the original lignin. A higher temperature and a longer reaction time favoured phenol combination, but increased the formation of solid residue due to the condensation reactions of the degradation intermediates/products. The degraded lignin products were soluble in organic solvents (such as THF), and were characterized by HPLC/GPC, IR and NMR. A possible mechanism for lignin hydrolytic degradation was also proposed in this study.
Yuan
Zhongshun
Z
Department of Chemical Engineering, Lakehead University, Thunder Bay, ON, Canada P7B 5E1.
Cheng
Shuna
S
Leitch
Mathew
M
Xu
Chunbao Charles
CC
D000468:Alkalies / Q000737:chemistry*; D002850:Chromatography, Gel; D000431:Ethanol / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry; D006358:Hot Temperature; D006868:Hydrolysis; D008031:Lignin / Q000737:chemistry*; D019800:Phenol / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013997:Time Factors; D014867:Water / Q000737:chemistry*
D000468:Alkalies; D012997:Solvents; D014867:Water; D019800:Phenol; D000431:Ethanol; D008031:Lignin