CHARACTERIZATION OF SPENT FLUID CATALYTIC CRACKING CATALYSTS BY NUCLEAR MICROPROBE TECHNIQUES

The nuclear microbeam analysis techniques of proton-induced X-ray emis sion (PIXE) and nuclear reaction analysis (NRA) have been used to prob e the distribution of carbon and other elements in used fluid catalyti c cracking catalyst particles. The catalyst was sampled from the strip per standpipe in one of Shell's commercial riser FCC units processing feedstocks containing up to 4 wt% Conradson carbon residue (CCR), PIXE and NRA gave quantitative information on the metal and carbon distrib utions. Samples were embedded in waterglass (Na2O . SiO2) to overcome the problem of carbon contamination from conventional embedding materi als. Elemental line scans and images were obtained with a spatial reso lution of a few microns and sufficient sensitivity to allow quantifica tion of ah elements of interest. Correlations were found between the s patial distribution of Ti, V, and, to a lesser extent, Fe. Ni was foun d to be confined to the outermost 10 mu m or so of each particle. The degree of correlation appeared to reduce with particle age. Despite th e high CCR content of the feedstock, it was found that carbon was unif ormly distributed through the particles, indicating that even the bulk ier molecules present in the feed are cracked on the external surface of the FCC particle. (C) 1998 Academic Press.