Kinetics of chlorination of niobium pentoxide by carbon tetrachloride

Abstract

Kinetics of the chlorination of Nb₂O₅ powder by CCl₄ vapor in mixture with N₂ in a static bed in the temperature range of 698 to 853 K were carried out at different partial pressures of CCl₄ (p_{CCl 4}) varying from 0.10 to 0.75 atm. The fraction of Nb₂O₅ chlorinated R at p _{CCl 4} of 0.6 atm in the temperature range of 698 to 773 K was found to be proportional to time t, and the activation energy E is calculated to be 112 kJ/mole. Results on the effect of p _{CCl 4} (0.4, 0.6, and 0.75 atm) at 723 K suggest that the rate v (R/min) is proportional to p_CCl4 ^1.5. However, at p_CCl4 of 0.2 atm, R is not linear with t, rather, R ^½ is linear with t. Based on these results, two mechanisms, one at low p_CCl4 (0.2 atm) and another at higher p_CCl4 values, in the temperature range of 698 to 773 K have been suggested. Similar studies in the higher temperature range (793 to 853 K), where p _CCl4 used to decompose to elemental chlorine and carbon, were also carried out. At all temperatures and p_CCl4 values, R is found to be directly proportional to t. At two higher p _CCl4 (0.4 and 0.6 atm), v is proportional to p _{CCl 4} ^1.5, whereas at two lower p_CCl4 (0.1 and 0.2 atm) it is proportional to p _{CCl 4} ^1.5. The E values obtained in the temperature range of 793 to 853 K at p _{CCl 4} of 0.6 and 0.2 atm are found to be 57 and 115 kJ/mole, respectively. In this higher temperature range, two different reaction mechanisms have been proposed.