The mechanism and kinetics of the tungsten (vi)-oxide reduction in the vertical tube reactor

Abstract

Presented study shows the analysis of the process of reduction of WO 3 powder with hydrogen in the vertical tube reactor, representing a new approach in comparison to the conventional methods in the horizontal tube reactor. SEM analysis of the synthetisized tungsten powder shows the existence of particles, approximately 1,mu m in size, both individual ones and those within the porous agglomerates with a spongy structure. In order to study the mechanism and kinetics of the reduction process, the reduction degree and retention time of particles of WO3 powder in the reaction zone were calculated using a developed mathematical model, based on the application of Stokes' law. Kinetic parameters and activation energies were determined at the corresponding temperature intervals. Kinetic analysis showed that the process of WO3 reduction with hydrogen in the vertical tube reactor in the temperature interval from 700 to 900 degrees C occurs in the kinetic zone. Activation energy for the temperature interval from 700 to 800 degrees C is E-a1=7.5 +/- 0.1 kJ/mol, whereas for the temperature interval from 800 to 900 degrees C, activation energy is E-a2=14.6 +/- 0.1 kJ/mol. A model was proposed describing the mechanism of the reduction process in the vertical tube reactor according to which particles of tungsten powder I pm in size arise from the stretching and cracking of coarse particles in the reduction zone, as well as from the appropriate temperature shock outside this zone.