CATALYTIC AND THERMAL EFFECTS DURING HYDROTREATING OF BITUMEN-DERIVEDHEAVY OILS

The relative magnitude of catalytic and thermal reactions during the h ydrotreating of PR Spring bitumen-derived heavy oil was evaluated in a fixed-bed reactor as a function of temperature, residence time and ca talyst selection. The relative effects of thermal and catalytic reacti ons were evaluated by hydrotreating the PR Spring bitumen-derived heav y oil over three catalysts: sulfided Ni/Mo/alumina HDN catalyst, Mo/al umina HDM catalyst and sodium-impregnated alumina. Catalytic and therm al effects for each of the catalysts were evaluated under a range of t emperature (625-685 K) and liquid hourly space velocity (0.14-0.81 h(- 1)). The reactor pressure, 13.7 MPa, and the hydrogen-to-oil ratio, 89 0 m(3) m(-3) (5000 scf H-2 per bbl), were fixed in all experiments. Th e catalysts' activities were ranked as follows: HDN catalyst > HDM cat alyst > sodium-impregnated alumina, based on their activities for nitr ogen, sulfur and nickel removal as well as for the conversion of Conra dson carbon residue (CCR) and residuum. The catalyst activities were s trongly dependent on the metal loading and were dependent, to a lesser extent, on the acidity of the alumina support. CCR and residuum conve rsion was closely linked relative to heteroatom and metal removal. Thi s is attributed to a significant overlap between moieties which are cl assified as CCR precursors and moieties which are classified as residu um. Catalyst selection significantly affected residuum conversion. Thi s is because the high catalyst densities employed in packed bed reacto rs accentuate catalytic reactions relative to thermal reactions. Altho ugh sulfur was generally more reactive than nitrogen, sulfur conversio ns in excess of 70% were difficult to achieve. It was presumed that 30 -40% of the sulfur was asphaltic in nature and exhibited low reactivit y. For this reason it was easy to achieve significant sulfur conversio n as low severities, but difficult to achieve deep desulfurization at high severities. The deactivation rates of HDN and HDM catalysts were 0.06 and 0.2 degrees API per day, respectively. (C) 1998 Elsevier Scie nce Ltd. All rights reserved.