Abstract
Attrition of alumina catalyst carrier beads in reforming units causes operational problems and the loss of the catalyst particles due to the formation of fines and small fragments. This thesis addresses the characterisation and optimisation of the mechanical strength of these beads in collaboration with Institut Francais du Petrole (IFP) and Rhodia. A methodology was devised to test and improve the particle strength at various strain rates using both single particle and multiple particle tests by considering the mechanical stresses prevailing in industrial units. This methodology was tested with a commercial sample and then used to assess the strength of new samples for which the bead structure was modified by changing the filler concentration and type, the macroporosity, the drying regime and the surfactant concentration. A significant increase in the particle strength was achieved in comparison with the commercial samples. The mean crushing strength increased by a factor of about three and the extent of impact attrition was significantly decreased, e.g. by a factor of 30 for normal impacts at 20 m s-1. For single particle testing, a relationship between quasi-static and impact results was obtained when the impact breakage was compared with the percentage of weak particles obtained from the side crushing strength (SCS) test. This suggests that for this type of material the particle strength is not sensitive to the strain rate. Multiple particle tests confirmed the results obtained by single particle tests for two samples for which sufficient quantity of test material was available. In order to relate the extent of attrition in a particle assembly under compressive loading to the single particle properties, the BCS test was simulated by distinct element analysis using the TRUBAL code. Trends similar to the experimental work were obtained for the simulation of the attrition. However, the simulations tend to underestimate slightly the extent of attrition, which is highly dependent on the particle strength distribution and on the contact force distribution within the particle assembly. As a result of this work, the manufacture of the alumina catalyst carrier beads used in reforming units has been significantly improved.