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

Abstract

This study characterizes the pyrolytic sugars in three bio-oils (with a total sugar content range of 55.6−69.2 mg g −1 bio-oil) produced from biomass fast pyrolysis by high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) and two-dimensional 1 H− 13 C heteronuclear single-quantum correlation−nuclear magnetic resonance (HSQC-NMR). Depending on bio-oil sample, glucose (mainly derived from cellulose) contributes ∼67−79 wt % of total pyrolytic sugars in the bio-oil, and the rest of the sugars are derived from hemicellulose. The majority (>96%) of pyrolytic sugars are present in the water-soluble fraction of bio-oil, mainly in the form of cellulose-derived anhydrosugars such as levoglucosan and cellobiosan. A small portion of hemicellulose-derived sugar structures are also found in the water-soluble fraction of bio-oil. Unlike six-carbon sugars (glucose, galactose, and mannose) which are mainly present as anhydrosugars (i.e., ∼ 79−86% on a carbon basis for glucose), a large portion of five-carbon sugars (xylose and arabinose) in the water-soluble fraction of bio-oil are present as monomer sugars (i.e., ∼ 24−39% on a carbon basis for arabinose and ∼32−42% on a carbon basis for xylose). The results suggest that the formation of anhydrosugars from hemicellulose pyrolysis is difficult for five-carbon sugars and the hydrolysis of hemicellulose can be catalyzed by the organic acids produced during pyrolysis. A minor portion (<4%) of sugar structures also exists in the water-insoluble fraction of bio-oil, possibly formed via thermal ejection mechanism from hemicellulose components connected to lignin structures.

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

“…2D NMR and solid state 2D NMR have been proven versatile techniques for the structural analysis of lignin and biomass [ 176 , 177 ]. Heteronuclear single-quantum correlation-nuclear magnetic resonance (HSQC-NMR) was used to characterize the types of C-H bonds and their presence in different moieties of compounds in biooils [ 32 , 57 , 75 , 164 ]. 2D 1 H- 13 C HSQC-NMR was successfully used in the characterization of pyrolytic sugars in fractions of biooil by providing different C-H types in aliphatic, guaiacol, and ferulate structures [ 32 ] (see Figure 8 ).…”

“… Typical assignments of biooil and various sugar standards in 2D 1 H- 13 C HSQC spectra. Gray: biooil; red: sugar monomers including glucose, galactose, mannose, xylose, and arabinose; green: anhydrosugars including levoglucosan, cellobiosan, and cellotriosan [ 32 ]. …”

Production of Glucose from the Acid Hydrolysis of Anhydrosugars

“…Each sample was analysed in duplicate and the average was used to report the concentration of each compound. During HPLC analysis, the typical relative standard error was ±0.00026 for multiple injections from the same sample.Results and discussionAcid hydrolysis of cellobioseCellobiose is not commonly identified as a component of pyrolysis oil, however it was selected as it can be formed as intermediate during the acid hydrolysis of cellobiosan; the latter is a common compound present in the bio-oil composition together with levoglucosan[24,32,33]. During the hydrolysis of cellobiosan, two molecules of glucose can be formed via two different routes as shown inFigure 2[24,34].…”

Catalytic Hydrotreatment of the Pyrolytic Sugar and Pyrolytic Lignin Fractions of Fast Pyrolysis Liquids Using Nickel Based Catalysts

“…To gain a better understanding regarding the chemistry occurring during the catalytic hydrotreatment of PS and PL, the product oils obtained from reactions using a Ni-Mo catalyst were analyzed by 1 H-13 C-HSQC, and GC × GC-FID and the results were compared with the feeds. The assignments of different functional groups in HSQC were made based on either spiking of pure compounds or available literature [41][42][43][44]. The NMR data for PS show the presence of anhydrosugars (e.g., levoglucosan) and carbonyl compounds, as well as some aromatic structures.…”