Oxidation of a coal particle in flow of a supercritical aqueous fluid

A study was made of the conversion of single spherical coal particles of diameter 1–5 mm in a supercritical H$_2$O/O$_2$ fluid with an oxygen mass fraction of 0–6.6% in a semibatch reactor at a pressure of 30 MPa and a temperature of 673–1023 K. A decrease in the particle mass was observed in two parallel processes: gasification of coal with water and oxidation of coal with oxygen. An activation energy 19 $\pm$ 7 kJ/mole and a pre-exponential factor 10$^{-2\pm0.4}$ sec$^{-1}$ were obtained under the assumption of zero order for the concentration H$_2$O and an Arrhenius dependence for the rate of gasification with water. The oxidation with oxygen at a temperature above 780 K was found to be limited by the rate of O$_2$ diffusion to the coal organic matter. Below 780 K, the rate of heterogeneous oxidation with oxygen is described by a first-order reaction for the concentration of O$_2$ and a zero-order reaction for the concentration of H$_2$O with an activation energy of 150 $\pm$ 27 kJ/mole and a pre-exponential factor of 10$^{7.6\pm1.9}$ cm$^3$/(g $\cdot$ sec).