Cellulose–Hemicellulose and Cellulose–Lignin Interactions during Fast Pyrolysis

Abstract

Previously, the primary product distribution resulting from fast pyrolysis of cellulose, hemicellulose, and lignin was quantified. This study extends the analysis to the examinations of interactions between cellulose-hemicellulose and cellulose-lignin, which were determined by comparing the pyrolysis products from their native mixture, physical mixture, and superposition of individual components. Negligible interactions were found for both binary physical mixtures. For the native cellulose-hemicellulose mixture, no significant interaction was identified either. In the case of the native cellulose-lignin mixture, herbaceous biomass exhibited an apparent interaction, represented by diminished yield of levoglucosan and enhanced yield of low molecular weight compounds and furans. However, such an interaction was not found for woody biomass. It is speculated that these results are due to different amounts of covalent linkages in these biomass samples. This study provides insight into the chemistry involved during the pyrolysis of multicomponent biomass, which can facilitate building a model for bio-oil composition prediction.

Relationships between Biomass Composition and Liquid Products Formed via Pyrolysis

“…The observation that these constituents often represent minor components in raw biooil (Table 1) highlights the importance of catalytic degradation (Model 2) and possibly indirect effects (Model 3) on pyrolysis products. The latter model is only recently receiving attention as knowledge of cell wall structures and analytical repertoires blossom (Mante et al, 2014;Zhang et al, 2015). Detailed examination of the relationships between components and products is still sparse, with the biological literature providing detailed characterization of cell wall components, while the engineering literature analyzes the chemical components, or often just total yields, of different pyrolysis fractions.…”

“…Interactions between polysaccharides and lignin have been shown to alter pyrolysis products (Du et al, 2014;Zhang et al, 2015). The cellulose-lignin interaction can lead to a decrease in levoglucosan yield and an increase in light (C1-C3) compounds, especially glycolaldehyde and furans.…”

“…The cellulose-lignin interaction can lead to a decrease in levoglucosan yield and an increase in light (C1-C3) compounds, especially glycolaldehyde and furans. Based on the nature of the small products, Zhang et al (2015) hypothesized that the cellulose-lignin interaction occupies the C6 position, disfavoring glycosidic bond cleavage that is required for the formation of levoglucosan and favoring light compound and furan formation through ring scission, rearrangement, and dehydration reactions. The strength of this effect on pyrolysis products is most pronounced in grasses, followed by softwood and then hardwood, possibly due to the increased prevalence of covalent bonds between cellulose and lignin in grass cell walls (Jin et al, 2006;Zhou et al, 2010).…”

Cellulose, xylan and lignin interactions during pyrolysis of lignocellulosic biomass

“…Some researchers have predicted lignocellulosic biomass pyrolysis profiles based on the lignocellulosic composition with some degree of accuracy in thermogravimetric analyser (TGA), concluding that no detectable interactions between the three components took place during pyrolysis [8][9][10]. By contrast, some other reports claimed that the pyrolysis behaviour of lignocellulosic biomass cannot be explained by the simple superposition of three components due to their significant interactions [11][12][13][14][15], different for example from the additive behaviour found in coal macerals [16]. In terms of product distribution, the interaction between intermediate products from pyrolysis of cellulose powder and lignin extracted from Japanese cedar accelerated tar production, while reducing char and water formation [12].…”

“…The interaction among cellulose, xylan and lignin may have suppressed the evolution of levoglucosan and significantly increased the evolution rate of 5-methylfurfural [19]. Compared with a binary physical mixture of cellulose-hemicellulose, the levoglucosan deficit phenomenon is more obvious for a native mixture of cellulosehemicellulose [13]. Moreover, the product yields from the pyrolysis of lignocellulosic biomass are also closely linked to the detailed sample morphology [11].…”