Modelling of the isothermal oxidative stabilization of mesophase pitch fibre

Isothermal experiments were conducted to elucidate the rate process of stabilization for mesophase petroleum pitch fibre. The rate of oxygen consumption in the fibres was quantified by measuring the time course of the oxygen concentration in the effluent gas from the reactor. A mathematical model of the stabilization, in which the mass transfer of molecular oxygen and the autoxidation reaction with the active sites in the fibre were taken into account, was also constructed and a numerical simulation of the model equations was conducted. Physical parameters such as the effective diffusivity of molecular oxygen in the fibre, the reaction rate constant and the gas—solid equilibrium coefficient of molecular oxygen, which are included in the mathematical model, were determined by comparing the experimental values of oxygen concentration in the exit gas with theoretical values. Physicochemical processes of the stabilization were also discussed on the basis of the theoretical results. It was concluded that the stabilization is complete even when the reaction does not proceed deeply into the fibre.