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

Abstract

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 correlationÀnuclear magnetic resonance (HSQCÀNMR) 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 HSQCÀNMR spectral data provides chemical-shift assignment of 27 different types of CÀH bonds presented in the pyrolysis oils. The HSQCÀNMR 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 CÀH and aliphatic CÀH 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 CÀH and aliphatic CÀH bonds in the pine wood pyrolysis oils were produced from the lignin component. The results demonstrate the capability of HSQCÀNMR to provide in-depth analysis of pyrolysis oils.

Thermal stability of low and high Mw fractions of bio-oil derived from lignin conversion in subcritical water

“…This is in agreement with the results obtained by Ben and Ragauskas [26], who reported that the bond energy of the C-O bond (CH 3 -O) in the methoxyl groups is lower than the O-H bond in the hydroxyl groups, which shows that the methoxyl groups decompose more easily than the hydroxyl groups.…”

“…5. These were performed based on the 1 H- 13 C NMR assignments of the model lignin-derived compounds in DMSO-d 6 and some references [26,[36][37][38][39][40][41][42]. These crosspeaks are related to the main types of aromatic products confirmed by GC-MS measurement.…”

“…However, since only minor changes were detected in samples aged for 1 h and 1 day compared to the fresh sample in the 1 H- 13 C HSQC NMR analysis, only the 1 week spectrum of aLO_ES_80_1w was interpreted in detail. Although the use of HSQC spectra is not ideal for quantification, it is possible to observe changes in the signal intensity since all samples were prepared at the same concentration, using the same solvent, and analysed at the same time [10,19,26]. The aliphatic and aromatic regions in the 1 H- 13 C HSQC NMR spectra of the LO and aged LO_DEE solubles for 1 week (aLO_ES_80_1w) are shown in Fig.…”

The use of combination of zeolites to pursue integrated refined pyrolysis oil from kraft lignin

“…After the use of Y zeolite, the heavy oils contained 76.4% less methoxyl groups than the blank pyrolysis oil, which indicates a very efficient decomposition of methoxyl groups and this result could explain the increasing contents of catechol type and p-hydroxyphenyl type hydroxyl groups detected by 31 P NMR. The two types of methyl aromatic bonds (methyl-Ar groups with and without a hydroxyl or ether group in the ortho position) in the heavy oils are reported to be the rearrangement products of methoxyl groups [24]. After the use of Y or M zeolites, the heavy oils contained relatively large amount of methyl aromatic bonds, which is the evidence for the enhanced cleavage of methoxyl groups.…”

“…However, the limitations of 13 C NMR can be addressed using modern 2D NMR (such as HSQC-NMR) techniques, which has been developed to semi-quantitatively analyze over 30 different C-H bonds in the pyrolysis oils [24][25][26][27]. We have previously shown that HSQC-NMR was uniquely well suited to analyze various C-H bonds present in the pyrolysis oils.…”