Potentiometry of the Reaction of Residual Lignin of Lignocellulose Powder Material with Chlorine Dioxide

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The consumption rate of chlorine dioxide in the reaction with the residual lignin was studied using measurements of the potential of a redox couple ClO₂/ClO₂⁻ in an aqueous suspension of lignocellulose powder material. The methodology was developed for the study of reaction kinetics of chlorine dioxide with the residual lignin using the first order reaction model with the initial lignin concentration in the reaction medium varying in the range of (1–17) × 10^–4 М at the initial chlorine dioxide concentration of 4.48 × 10^–4 М. The monochronic rate constant of the second order reaction of chlorine dioxide with the residual lignin was calculated by the dependence k_eff(I) = k_eff(II)[L]₀ under the lignin excess conditions, it was 1462 ± 108 М^–1 s^–1. Considering the initial concentrations of reagents, it was found that, with increasing the degree of lignin conversion Θ from ≈0.27 to 0.54, its reactivity in the interaction with the chlorine dioxide is reduced, and the value of k_eff(II) decreased from ≈1280 to 900 М^–1 s^–1, which according to the theory of polychronic kinetics was a manifestation of the kinetic nonequivalence of the various ensembles of macromolecules of the residual lignin. Thus, it was experimentally shown for the first time that residual lignin of lignocellulose powder material had a kinetic nonequivalence in the interaction with chlorine dioxide.