Structural Analysis of Pyrolytic Lignins Isolated from Switchgrass Fast-Pyrolysis Oil

Abstract

Structural characterization of lignin extracted from the bio-oil produced by fast pyrolysis of switchgrass (Panicum virgatum) is reported. This is important for understanding the utility of lignin as a chemical feedstock in a pyrolysis-based biorefinery scheme. Pyrolysis induces a variety of structural changes to lignin in addition to reduction in molecular weight. The guaiacol structural units remain largely intact, and some hemicellulose stays covalently linked to the lignin. However, twodimensional 1 H− 13 C HSQC NMR analysis shows an absence of γ-methylene hydrogens from β-O-4 linkages, implying that rearrangements in the propyl linking chains have occurred. Ferulate and hydroxyl phenol esters are still present in the pyrolyzed lignin, but at lower concentrations than in unpyrolyzed switchgrass lignin.

Analytical Strategies Involved in the Detailed Componential Characterization of Biooil Produced from Lignocellulosic Biomass

“…In the structural characterization of lignin extracted from the biooil produced by fast pyrolysis of switchgrass (Panicum virgatum) , the results of 2D 1 H- 13 C HSQC-NMR analysis showed the absence of γ -methylene hydrogens from β -O-4 linkages, implying rearrangements in the propyl linking chains. Ferulate and hydroxyl phenol esters are still present with lower concentrations in pyrolyzed lignin compared to unpyrolyzed switchgrass lignin [ 56 ]. The 1 H- 13 C heteronuclear multiple-bond correlation (HMBC-NMR) spectrum showed that β -O-4 linkages, ferulate esters, and guaiacyl ether linkages remained together, indicating significant difference from the pyrolyzed material [ 56 ].…”

“…Ferulate and hydroxyl phenol esters are still present with lower concentrations in pyrolyzed lignin compared to unpyrolyzed switchgrass lignin [ 56 ]. The 1 H- 13 C heteronuclear multiple-bond correlation (HMBC-NMR) spectrum showed that β -O-4 linkages, ferulate esters, and guaiacyl ether linkages remained together, indicating significant difference from the pyrolyzed material [ 56 ].…”

“…After preseparation of moieties in biooil [ 21 , 33 , 49 ], such as liquid-liquid extraction (LLE), distillation, and column chromatography, both spectroscopic and chromatographic methods are applied to the qualitative analysis and quantitative analysis of the species in biooil [ 17 , 44 , 50 – 53 ]. For spectroscopic methods, Fourier transform infrared (FTIR) spectroscopy [ 29 , 54 – 56 ] and nuclear magnetic resonance (NMR) spectroscopy [ 56 – 59 ] are mostly used, which can provide information on the functional groups of species in biooil. However, such information is integral information, and not for a specific compound.…”

Characterization of Pyrolytic Sugars in Bio-Oil Produced from Biomass Fast Pyrolysis

“…In addition, the water-insoluble faction mainly consists of aromatic C−H bonds (i.e., guaiacyl structures), methoxyl groups, and aliphatic C−H bonds. Therefore, the sugar structures in the water-insoluble fraction appear to be linked with lignin oligomer structures (mainly guaiacyl 30 ). Moreover, no significant difference can be found between the 2D 1 H− 13 C HSQC spectra acquired from the water-insoluble CH 2 Cl 2 -soluble and the water-insoluble CH 2 Cl 2 -insoluble fractions.…”

Pilot-Scaled Fast-Pyrolysis Conversion of Eucalyptus Wood Fines into Products: Discussion Toward Possible Applications in Biofuels, Materials, and Precursors

“…Further interesting applications of levoglucosan-rich aqueous extract is the conversion of these pyrolytic sugars into ethanol by fermentation or lipids [47] as well as to manufacture surfactants, food additives, biodegradable polymers and pharmaceuticals [48]. The sugars present in the bio-oil are probably derived from higher molecular weight holocellulose fragments, which remained attached to the lignin chain after pyrolysis [49]. They may be used for the production of ethanol as well as anydrosugars [50,51].…”