NMR Characterization of Pyrolysis Oils from Kraft Lignin

The pyrolysis of softwood (SW) kraft lignin was examined at 400, 500, 600, and 700 degrees C. The yields of pyrolysis oil, char, and gas were determined to be 35-44%, 57-38% and 8-18%, respectively. The pyrolysis oil has a comparable heating value with ethanol and coal. The elevated temperature of 700 degrees C was found as the point of primary decomposition of lignin and the secondary decomposition of pyrolysis oil. Gel permeation chromatography (GPC) and quantitative C-13 and P-31 NMR were used to characterize the pyrolysis oil. A C-13 NMR database was created to provide a more accurate chemical shift assignment database for analysis of pyrolysis oils. On the basis of the results of C-13 and P-31 NMR for the pyrolysis oil, aliphatic hydroxyl, carboxyl, and methoxyl groups are eliminated during pyrolysis. Cleavage of ether bonds in lignin was also shown to be a primary decomposition reaction occurring during thermal treatment. The results of GPC analysis indicated that lower pyrolysis temperatures yielded a bio-oil that had a lower molecular weight and lower polydispersity value.