Spray dried SiO2 WO3/TiO2 and SiO2 vanadium pyrophosphate core-shell catalysts

Abstract

Commercial catalytic gas-solid fluidized reactors operate best with a wide particle size distribution (PSD) centered around 70μm. Spray drying micro-sized powders with binders—colloidal silica, for example—provides the attrition resistance required to withstand the mechanical stresses inherent in these reactors. Commercial dryers 8m in diameter treat slurries at a rate of 1000kgh−1 and particle residence times are greater than 1min. Residence times in laboratory scale spray dryers are an order of magnitude lower. Droplets forming at the nozzle must be smaller in laboratory units so that they dry, consequently the average particle size is smaller. Here, we spray dried WO3/TiO2 and vanadium pyrophosphate catalysts with a combination of colloidal silica, polyvinyl alcohol and H3PO4 at 180° C and 245° C. The colloidal silica formed a 2μm shell at the outer surface of the particle regardless of the spray drying temperature. However, the lower temperature was insufficient to dry all the droplets formed at the nozzle and so particles agglomerated. Particle diameters are higher with high slurry concentrations and low atomization pressures, but the nozzle blocks when the slurry concentration is greater than 25%. Increasing the nozzle pressure to maintain the nozzle clear produces smaller droplets.