Researc and development of a Fluidized bed catalyst for production of phthalic anhydride and commercialization thereof (part 2) deactivation and improvement of silica-supported V_2O_5-K_2O-SO_3 catalyst

摘要

Recently,a new spray-drying method was developed,using fine silica sols,whci can easily prepare micro-sperica catalysts with unifrom quality and good attrition.Use of the newly developed catlayst for fluidized-bed oxidation of napthahalene in a commerical plant achieved ideal operation with effective cataplyst performance at start-u,so the yield of phthalic anhydride was about 4% higher than when using the catalyst licensed by Badger Corp.However, a rapid decrease in activity and poor fluidization of te catalyst occurred during naphalene oxidation at lower temperature operation (320degC).The present sutdy tried toclarify the cause of deactivatio nand poor fluidization of this eutectic catalyst,byinvestigating the change in catalyst active components using SEM-EPMA techniques and the melting poit of eutectic mixtures.The changes in the catalsyt were a result of the migration of active components and the change inthe V_2O_5/K_2O/SO_3 molar ratio in the catalyst particles,caused by both the lower temperature operation and te load of naphthalene (W/F),forming a high melting point eutectic mixture at the catalyst surface.The volataity of SO_2 from the catalyst surface may be involved in the decreased activity and poor fluidization.Evaluation tests at a commercial plant,using a new eutectic mixtures catalyst with a lower melting point modified by the addition of Cs_2SO_4,revealed high catlayst perofrmance and stableoperation.There was a good correlation between V~(5+) in the catalst and the yield of phthalic anhydride at this plant,demonstrating tha tthe presence of V~(5+) catalyzes theproduct formation.