Kinetics of low-temperature chlorination of vanadium pentoxide by carbon tetrachloride vapor

Abstract

Low-temperature chlorination of vanadium pentoxide by carbon tetrachloride vapor in dilution with nitrogen has been carried out. The effect of time, particle size, partial pressure of CCl₄ vapor (0.1 to 0.6 atm), and temperature (553 to 788 K) on the extent of chlorination of V₂O₅ has been investigated. The extent of chlorination of the oxide is found to increase with a decrease in its particle size. In all cases, the reaction followed a topochemical reaction model, obeying the following relationship:

$$1 - (1 - \alpha )^{{1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-\nulldelimiterspace} 3}} = kt$$

where α is the fraction of V₂O₅ chlorinated in time t and k is the rate constant. The rate constant has been found to be directly proportional to the partial pressure of CCl₄ (PCCl₄). The activation energy values between 553 and 643 K and that between 683 and 788 K have been calculated and found to be 38.9 and 11.5 kJ/mole, respectively. Based on the kinetics results, mechanisms of reaction in the two temperature ranges have been suggested. It has been possible to chlorinate V₂O₅ at 753 K to about 87 pct in 30 minutes, using a very low partial pressure of CCl₄ of 0.15 atm.