Carbon supports hydrotreating catalysts

Work by Prins, de Beer, and co-workers represents a great contribution to our knowledge of the structure of carbon-supported hydrotreating catalysts as well as of the kinetics and mechanisms of these reactions. These authors first reported that the activity of carbon-supported molybdenum and tungsten catalysts was higher than that of their counterparts supported on alumina or silica [80,81]. They... 

Data from tests at 250,275,300, and 325 C were used to calculate pseudo-first order rate constants for the formation of H2S. These data are expressed on a standard Arriienius plot (Fig. 2) for which the linear least squares coefficient of determination, r, is 0.98. The apparent activation energy calculated from the slope is 28.5 kcal/mol. This result is in excellent agreement with the recent work of Abotsi, who studied the performance of carbon-supported hydrodesulfurization catalysts (10). Using Ambersorb XE-348 carbon lo ed with sulfided ammonium molybdate (3% Mo loading) prepared by the same procedure reported here, Abotsi hydrotreated a coal-derived recycle solvent The apparent activation energy for... 

It is well-known that a new generation of hydrotreating catalysts prepared with a silica promoted alumina support has been developed and are in use in a number of commercial hydrotreating units. Improved and more flexible operation should be possible especially in thermally cracked feedstocks with these catalysts having a higher HDS activity and resistance to carbon deposition than conventional CoMo or NiMo catalysts. 

Transition metal sulfides of the 3" row show high activity in hydrotreating reactions and some of them are studied as potential promoters of conventional catalysts in order to improve their performance. Carbon supported Pt sulfide was highly active in hydrodesulfurization (HDS) of thiophene and hydrodenitrogenation (HDN) of quinoline and pyridine [1,2]. The Pt/silica-alumina sulfide catalyst has been investigated as the promising candidate for deep HDS [3]. 

Shu and Oyama have recently proposed a new type of hydrotreating catalytst transition metal phosphides supported on carbon [97], and compared their behavior in the deep HDS of 4,6-DMDBT with that of the silica-supported counterparts and a commercial alumina-supported Ni-Mo sulfide hydrotreating catalyst. The carbon-supported catalysts were prepared by temperature-programmed reduction of the corresponding phosphates, and the activity was studied under simulated industrial conditions of 613 K and 3.1 MPa with a model liquid feed coutaiu-ing 500-ppm sulfur as 4,6-DMDBT, 3000-ppm sulfur as dimethyl disulfide, aud 200-ppm nitrogen as quinoline. The Ni2P/C catalyst showed an excellent performance in HDS and HDN, and it was also the best for sulfur removal from... 

It is probable that a combination of a lower temperatures (450 C) and higher pressures to those employed in this initial study will represent the optimum conditions for maintaining catalyst surface area. In order to prevent possible reduction of the promoter to the corresponding metal (Ni/Co), hydropyrolysis should be carried out in the presence of a small amount of hydrogen sulphide to help maintain the catalyst to remain in a reasonably fiilly sulfided form. Hydropyrolysis for the virtual complete carbon removal would need to be carried out off-line since the combination of temperature, pressure and flow rate required cannot be achieved in hydrotreating units. In terms of potential applications, carbon-supported catalysts may represent the major area since these cannot be regenerated oxidatively. 

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