Heteronuclear Single-Quantum Correlation–Nuclear Magnetic Resonance (HSQC–NMR) Fingerprint Analysis of Pyrolysis Oils

The pyrolysis of softwood kraft lignin, cellulose, and Loblolly pine wood was examined at 400, 500, and 600 °C. The analysis of the yields of pyrolysis products indicated that lignin yielded the largest amount of a heavy oil and char and only trace levels of a light oil. In contrast, cellulose produced minor amounts of a heavy oil and char and more light oil. All of the pyrolysis oils were analyzed by heteronuclear single-quantum correlation–nuclear magnetic resonance (HSQC–NMR) to analyze the structural components of the bio-oils, and three chemical-shift databases of compounds reported to be presented in pyrolysis oils produced from lignin, cellulose, and pine wood were employed for data analysis. On the basis of databases, analysis of the HSQC–NMR spectral data provides chemical-shift assignment of 27 different types of C–H bonds presented in the pyrolysis oils. The HSQC–NMR analysis of these pyrolysis oils indicated that there are two different types of methoxyl groups presented in the pyrolysis oils produced from lignin and pine wood, which indicated that the native methoxyl group in the lignin rearranges during the thermal treatment. The content of aromatic C–H and aliphatic C–H bonds in the pyrolysis oils produced from lignin and pine wood was increased with increasing pyrolysis temperatures. Levoglucosan was shown to be one of the major components in the pyrolysis oils produced from cellulose and pine wood, and furfurals and phenols were also found as the major components in the cellulose pyrolysis oils. Most aromatic C–H and aliphatic C–H bonds in the pine wood pyrolysis oils were produced from the lignin component. The results demonstrate the capability of HSQC–NMR to provide in-depth analysis of pyrolysis oils