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The overall degradation scheme of biomass ‘fast’ pyrolysis can be seen as a combination of parallel and competing reactions through non-ionic and ionic mechanisms, whose occurrence depends on the physical states of pyrolysis products, gaseous and condensed phases. The presence and dominance of these phases obey the thermodynamic laws of transport (mode) and transfer (limitations), mainly controlled by the design of reactor. As a result, the pyrolysis regime must be controlled to allow the description of biomass degradation patterns in real-world reactors and under ‘fast’ conditions. An on-going discussion on the importance and dominance of the ionic and/or non-ionic character of pyrolysis reactions provides clues that could be used to rationalize the degradation mechanisms. If radical mechanisms are assumed and are dominant in coal pyrolysis, experimental evidence[2,3] and theoretical calculations[4,5] for biomass fast pyrolysis (FP) until recently invoked the presence of radical/concerted mechanisms during the primary ‘fast’ pyrolysis stage.
By combining the use of analytical pyrolysis (Py-GC/MS) and carbon-13 enriched materials, this study reveals important information on degradation pathways and the type of chemical reactions occurring during the primary stage of ‘fast’ pyrolysis of extracted biopolymers (i.e., cellulose and technical lignin). The inspection of good prediction of mass spectrometric fragmentation patterns (Fig.1) for key pyrolysis organic compounds confirmed the absence of scrambling during the primary pyrolysis stage; thus indicating the dominance of unimolecular mechanisms such as internal molecular rearrangements and H-abstraction as only bimolecular reaction.