Studies on deposits of spent hydro-treating catalyst: A study by combined analytical techniques

Carbonaceous and non-carbonaceous deposits on a Ni-Mo catalyst, stemming from atmospheric residue upgrading in an ARDS unit were subjected to a combination of analytical techniques, i.e. SF extraction, TGA/DTA/MS, DRIFT, (13)C CP-MAS NMR, XRD and elemental analysis. Since the spectroscopic features of several components of the deposit interfere with each other a detailed deposit characterization was only achieved by stepwise removal of certain components by SFE deoiling and calcination. SF extraction stripped about 22 wt % of the carbonaceous deposit of the spent catalyst increasing the sp(2)/(sp(3) + sp(2)) ratio of the NMR-visible carbon from 0.63 to 0.67. TGA revealed three separate temperature ramps for stepwise driving off of deposited material- first ramp, 30 degrees C - 280 degrees C, loss of oil and sulfur from metal sulfides; second ramp, 280 degrees C - 450 degrees C, loss of carbonaceous material like coke; third ramp, 500 degrees C - 680 degrees C, loss of metal sulfates. Further calcination up to 1000 degrees C has no effect on the metal content of the deposition but transforms the framework gamma-Al(2)O(3) into alpha-Al(2)O(3). Entire burn-off of the precipitated oil and semi-volatile coke components increased the aromaticity of the carbonaceous deposit up to 0.95.