RECOVERY OF MOLYBDENUM FROM AN HYDRODESULFURATION EXHAUSTED CATALYST: MODELING OF THE CARBOCHLORINATION REACTION

摘要

The recovery of molybdenum from an HDS exhausted catalyst was performed by means of chlorination, using two chlorinating agents (Cl_2-CO and Cl_4C). Three recovery procedures were developed obtaining close to 100% extractions in all cases. In order to obtain kinetic data applicable to a scale change and considering that the studied exhausted catalysts contain an important amount of carbon, the effect of several variables on the chlorination of MoO_3 in the presence of carbon were studied. The results showed that carbochlorination starts at 543 K, significantly increasing with temperature and reaction time, and slightly affected by chlorine molar fraction and flow rate, while direct chlorination starts at 803 K. The following global reaction was obtained by identification of the reaction products: 2 MoO_(3(s)) + 2 Cl_(2(g)) + C_((s))→ 2 MoO_2Cl_(2(g))+ CO_(2(g)). On the basis of the analysis of experimental data, thermodynamic results and observations by other authors, three basic stages are distinguished: 1) Formation of the chlorinating agent; 2) Chlorination of molybdenum trioxide; 3) Carbon oxidation. The kinetic treatment of the experimental data permits to propose a model of the "nucleation and growth" type as the most probable one. The characterization of reagents and products by scanning electronic microscopy corroborated the model validity.