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

Studies on the kinetics of carbothermic chlorination of zirconium dioxide in gaseous chlorine were carried out with petroleum coke fines in powder form. The amounts of ZrO sub 2 chlorinated were found to be directly proportional to the time of chlorination in the temperature range studied (973-1273K). The activation energy values for chlorination of ZrO sub 2 , in mixture with petroleum coke, was found to be 18.3 kJ/mole. the influence of particle size of petroleum coke on the chlorination of ZrO sub 2 (-38+25 mu m) was studied, and it was found that the rate of chlorination increased up to the size range of -75 to +53 mu m, and the size finer than this produced negligible increase. The amount of petroleum coke in the mixture > 17.41% in excess of the stoichiometry resulted in very little increase in the rate. The effect of the partial pressure of chlorine (pCl sub 2 ) on the rate of chlorination was found to obey the following relationship, derived from the Langmuir adsorption isotherm: v= sub 1+KpCl2 exp kKpCl2 where v is the amount of ZrO sub 2 (g/min) reacted, k is the rate constant, and K is the equilibrium constant for adsorption of two chlorine atoms (obtained from the dissociation of a molecule of Cl sub 2 at the carbon surface) on the surface of ZrO sub 2 . By plotting 1/v vs. 1/pCl sub 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...ZrO sub 2 ...Cl to ZrCl sub 2 and O sub 2 is suggested to be the rate-controlling step. Subsequently, the less stable ZrCl sub 2 combines with Cl sub 2 to form ZrCl sub 4 and the oxygen combines with C to form CO and CO sub 2 .