Effect of lanthanum content on physicochemical properties and thermal evolution of spent and beneficiated spent FCC catalysts

Two FCC spent catalysts with different amounts of La2O3 and similar Al2O3/SiO2 ratios and the corresponding residues of an optimized process of La-extraction are studied. The potential of the powders as feedstock for mullite refractories is established. The four powders have been fully characterized – chemical composition, crystalline phases, particle size, specific surface area, porosity, and morphology. Their thermal evolution up to 1500°C has been studied using dynamic techniques – hot stage microscopy, DTA-TG – and isothermal thermal treatments. The effect of powder characteristics on high temperature phase development, in particular, on mullite formation is discussed. Besides La, the La-extraction process also implies partial extraction of the matrix in which zeolites are dispersed, resulting in reduced impurities contents and Al2O3/SiO2 ratios.The powders present differences in the textural properties– porosity and specific surface area – that do not affect the high temperature behavior, which is determined by the impurities and the Al2O3/SiO2 ratio. The four powders can be proposed as precursors for mullite materials. The compositions of the spent catalysts can be envisaged for application up to 1200°C. The compositions of the residues of the La-extraction process can be proposed for higher temperatures once their composition is corrected by adding alumina to avoid extensive cristobalite formation together with mullite.