Modeling of kraft lignin pyrolysis based on bond dissociation and fragments coupling

•The pyrolysis of kraft lignin can be divided to “dissociation” and “coupling” step.•The pyrolysis can be simulated by Boltzmann–Monte Carlo method.•The different secondary assumptions can be introduced to obtain different result.•The basic assumption is necessary but not sufficient by analyzing simulation result.•The assumption defining the formation of unsaturated bonds is crucial.

It is generally recognized that pyrolysis of biomass involves two steps: dissociation of covalent bonds to generate free radical fragments and coupling of the free radical fragments to form products. Experiments and simulations on biomass pyrolysis in the literature, however, ignored the role of each step and provided only the overall results of the two steps. Based on the two-step mechanism, this work simulates pyrolysis of a structural unit of kraft lignin. The first step is assumed to be governed by Boltzmann distribution of each bond in the unit at a given temperature and time, while the second step is assumed to follow Monte-Carlo algorithm. The Boltzmann–Monte Carlo pyrolysis model built is analyzed with the aid of basic and secondary assumptions. The mode is further validated by simulating pyrolysis of kraft lignin and comparing the results with experimental data in the literature. It is found that the model simulates the pyrolysis behavior reasonably well, in terms of changes in bonds’ population and amounts of radicals formed versus temperature and time.

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