THE SHARP INTERFACE MODEL - ZERO-ORDER REACTION WITH VOLUME CHANGE

The sharp interface model is examined for isothermal gas-solid reactio ns following zero-order kinetics with respect to the gas phase and fir st-order kinetics with respect to the solid phase for spherical partic les either shrinking or growing during reaction. It is shown that depe nding on the relative magnitudes of the governing parameters which inc lude the volume expansion factor, Damkohler number, and mass Biot numb er, it is possible to have up to three successive transitions from one controlling regime (external mass transfer, product layer diffusion, or chemical kinetics) to another as the reaction evolves with time. Th is behavior gives rise to various gas concentration and solid conversi on profiles. A classification of all the possible situations is made.