Lignin pyrolysis, kinetic models

As shown in the preceding parts, kinetic parameters cannot be directly calculated when internal heat transfer limits pyrolysis. A model taking into account both kinetic scheme and heat- mass transfers becomes necessary, A one-dimension model has already been implemented and solved. It features a classical set of equations for heat and mass transfers in porous media, i.c. heat transfer through convection, conduction, radiation and mass transfer due to pressure gradient (Darcy s law) and binary diffusion. Different kinetic schemes from e literature arc and will be tested mass-loss as lumped first order reaction, formation of volatiles, tars and char from decomposition of cellulose, hcmicellulose and lignin [26], the Broido-Shafi2adeh model [30] and the one proposed by Di Blasi [31]. None of them can describe the composition of the volatiles and supplementary schemes have to be found. 

Such stochastic modelling was advanced by Klein and Virk Q) as a probabilistic, model compound-based prediction of lignin pyrolysis. Lignin structure was not considered explicitly. Their approach was extended by Petrocelli (4) to include Kraft lignins and catalysis. Squire and coworkers ( ) introduced the Monte Carlo computational technique as a means of following and predicting coal pyrolysis routes. Recently, McDermott ( used model compound reaction pathways and kinetics to determine Markov Chain states and transition probabilities, respectively, in a rigorous, kinetics-oriented Monte Carlo simulation of the reactions of a linear polymer. Herein we extend the Monte Carlo... 

Miller, R. S. and Bellan, J. (1997) A generalized biomass pyrolysis model based on superimposed cellulose, hemicellulose and lignin kinetics. Comb. Sci. and Techn., 126, 97-137. 

The chemical reactions that accompany the extraction of volatiles (1) from hydrocarbon resources are frequently obscured by the complexities of the reaction system. In contrast, the comparative simplicity of model compound structures and product spectra permit resolution of reaction fundamentals 2) and subsequent inference of the factors that control real reacting systems. Herein is described the use of model compounds to probe the kinetics of pyrolysis and solvolysis reactions that likely occur during the extraction of volatiles from coals and lignins. 

Miller R.S, and Bellan J. (1997) A Generalized Biomass Pyrolysis Model Based on Surinqjosed Cellulose, Hemicellulose and Lignin Kinetic. Combust. Sci. Tech.,m, 97-112. 

Judging from the success of the analytical model in Section 7.4.3.1 to reproduce substituent effects on a//3-selectivities, we will soon be able to model the pyrolysis of lignin model compounds including a complete set of relevant reactions. In a future vision, the combination of hundreds of computational studies of model compounds in the kinetic simulation of biomass conversion will enable us to bridge the gap between molecular understanding and industrially applicable processing techniques. 

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