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This paper discusses the research activities done at Politecnico di Milano in the field of the detailed kinetic modeling of pyrolysis and combustion of biomass and bio-oil formation. Different critical steps are involved in this multicomponent, multiphase and multiscale problem. The first complexity relies on biomass characterization with the selection of reference species: cellulose, hemicellulose, lignins, and extractives. Fast pyrolysis involves kinetic mechanisms, first in the solid phase for biomass pyrolysis, then in gas-phase for secondary reactions of released products. These mechanisms involve large number of species and reactions, which make computations expensive. They need to be simplified, while still maintaining their description capability. Lumping procedures are extensively applied to allow the development of the overall model. Multistep pyrolysis mechanisms of reference species are discussed in this Note, with several comparisons with experimental data. A peculiarity of the model is its ability to provide detailed compositions of pyrolysis products and solid residue. Catalytic effect of ash on pyrolysis products is also discussed. A companion paper will discuss the successive or secondary gas phase reactions of pyrolysis products, together with the heterogeneous reactions of residual char. Finally, the modeling of bio-oil formation requires a comprehensive description of the coupling of kinetic and transport processes, both at the particle and the reactor scale

The main goal of this paper is to extend an existing biomass characterization method, which, on the basis of the elemental carbon, hydrogen, and oxygen composition, derives the biochemical composition, in terms of cellulose, hemicellulose, and lignin. Because of their elemental composition, several biomasses cannot be characterized by a feasible mixture of these reference components. This limitation is removed by accounting for the presence of a couple of new lumped species, representing hydrophobic and hydrophilic extractives. This extended characterization method allows one to enlarge its range of validity significantly, thus covering most of the biomass samples. The accuracy of the extended method is validated by comparing experimental data on structural or biochemical composition with model predictions. The multistep kinetic scheme of biomass pyrolysis is then extended to the new reference species, on the basis of comparisons with TGA experiments on triglyceride and tannin pyrolysis. The new pyrolysis model is proved to be fully consistent with the previous one, already widely validated under\ud different conditions. Several comparisons of pyrolysis of biomass samples, outside the applicability range of the original method, validate the proposed extension. Moreover, the results show that this predictive model is not very sensitive to the different degrees of freedom of the new biomass characterization approach

This paper summarizes the research activities done at Politecnico di Milano in the field of the detailed kinetic modeling of fast pyrolysis of biomass to produce bio-oil. Note I of this work already discussed biomass characterization and the multistep pyrolysis mechanisms of reference species. The model is able to provide a detailed composition of pyrolysis products and char residue. Different critical steps are involved in this multicomponent, multiphase and multiscale problem. The first complexity relies in biomass characterization. Then, fast pyrolysis process involves detailed kinetic mechanisms, first in the solid phase for the biomass pyrolysis, then in the gas-phase for the secondary reactions of released products. The complexity of these kinetic mechanisms requires strong simplifications, thus chemical lumping procedures are extensively applied. Successive or secondary gas phase reactions of gas and tar components released during the pyrolysis process complement the kinetic model, together with the heterogeneous reactions of residual char. The modeling of fast pyrolysis process requires a comprehensive description of the coupled transport and kinetic processes, both at the particle and the reactor scale. A few examples and comparisons with experimental data validate the reliability of the overall model. Finally, the composition and physical properties of the pyrolysis bio-oil are also discussed, with emphasis on combustion and pollutant emissions.

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