Elucidation of cellulose-lignin interaction during pyrolysis: A Py-GC-MS study

Abstract: Interaction between the three main components (cellulose, hemicelluloses,

and lignin) of biomass is notably observed under pyrolysis condition 1-15. Method (both experimental and analytical) for estimating the extent of interactions is required in order to gain the better understanding of the mechanism of pyrolysis of whole biomass system. In this work, two kinds of mixture (direct mixture and table mixture) for cellulose-lignin and levoglucosan-lignin were pyrolyzed in Pyroprobe 5250 coupled with GC-MS under temperature range 500-700 ?. While there is a slight difference between calculated and experimental volatile and char yield, the significant interactions on the product distribution were observed: the presence of lignin promoted the formation of light-molecular weight compounds from cellulose (such as acetone, glycolaldehyde, acetone alcohol, and butanedial) but inhibited the formation of anhydrosugars, levoglucosan and oligosaccharides. While most of lignin-derived products showed stability under co-pyrolysis with cellulose, excluding some certain
compounds (p-cyresol, 2,3-dihydrobenzofuran, guaiacol and 4-vinylguaiacol). A statistical method by correlation r and p-value was adopted to evaluate the interaction strength on product distribution from two mixtures of cellulose-lignin pyrolysis, finding that interactions of table mixture were stronger than direct mixture (Figure
1A). Moreover, interaction strength of direct mixture was decreased with increasing temperature, while table mixture achieved the strongest interaction at 600 ?. For levoglucosan-lignin direct mixture, co-pyrolysis enhanced the levoglucosan-derived products while inhibited the lignin-derived products, revealing that hydrogen transfer and activated intermediates from cellulose and lignin maybe the dominant interaction mechanism (Figure 1B)16-18.. It is believed that the difference of interaction strength for direct and table mixture is caused by the difference of interaction phase. For table mixture, gas phase, liquid phase and even liquid-soild phase interactions are existed. But for direct mixture, only gas phase and limited liquid phase interaction is though to

be existed (Figure lC and lD).

Key words: Cellulose; Lignin; Interaction; Pyrolysis; Mechanism

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Figure. 1 Interaction on product distribution for the direct and table mixture of cellulose and lignin: (A): Comparison of pyrolysis products yields between calculated data and experiment

results (direct and table) at 600 ?, (The values for the absolute peak area are preceeded

with logarithm manipulation). (B): Proposed interaction mechanism in the intermediate pool. (C) and (D): Different interaction phases for the direct and table mixture.