NMR Characterization of Pyrolysis Oils from Kraft Lignin

Abstract

The pyrolysis of softwood (SW) kraft lignin was examined at 400, 500, 600, and 700 °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 °C was found as the point of primary decomposition of lignin and the secondary decomposition of pyrolysis oil. Gel permeation chromatography (GPC) and quantitative 13C and 31P NMR were used to characterize the pyrolysis oil. A 13C 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 13C and 31P 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.