Kinetics of chlorination of zirconia in mixture with petroleum coke by chlorine gas

Studies on the kinetics of carbothermic chlorination of zirconium dioxide i n gaseous chlorine were carried out with petroleum coke fines in powder for m. The amounts of ZrO2 chlorinated were found to be directly proportional t o the time of chlorination in the temperature range studied (973 to 1273 K) . The activation energy values for chlorination of ZrO2, in mixture with pe troleum coke, was found to be 18.3 kJ/mole. The influence of particle size of petroleum coke on the chlorination of ZrO2 (-38 + 25 mu m) was studied, and it was found that the rate of chlorination increased up to the size ran ge of -75 to +53 mu m, and the size finer than this produced negligible inc rease. The amount of petroleum coke in the mixture above 17.41 pet in exces s of the stoichiometry resulted in very little increase in the rate. The ef fect of the partial pressure of chlorine (pCl(2)) on the rate of chlorinati on was found to obey the following relationship, derived from the Langmuir adsorption isotherm: v=k . K . pCl(2)/1+K . pCl(2) where v is the amount of ZrO2 (g/min) reacted, k is the rate constant, and K is the equilibrium constant for adsorption of two chlorine atoms (obtaine d from the dissociation of a molecule of Cl-2 at the carbon surface) on the surface of ZrO2. By plotting 1/v vs 1/pCl(2), a straight-line relationship with an intercept in x-axis is obtained, further supporting the preceding equation. The dissociation of the adsorbed complex, Cl... ZrO2... Cl to ZrC l2 and O-2 is suggested to be the rate-controlling step. Subsequently, the less stable ZrCl2 combines with Cl-2 to form ZrCl4 and the oxygen combines with C to form CO and CO2.