Hydroprocessing catalysts, deactivation

J. Wood, L. F. Gladden 2003, (Effect of coke deposition upon pore structure and self-diffusion in deactivated industrial hydroprocessing catalysts), Appl.Cat. A General, 249, 241. 

However, residuum hydrotreating catalysts themselves are susceptible to irreversible deactivation caused by the accumulation of sulfided metal impurities. The gradual buildup of these impurities in the pores of a hydroprocessing catalyst causes plugging and deactivation. 

Fig. 40. Typical deactivation curve for residuum hydroprocessing catalyst. Arabian Heavy atmospheric residuum desulfurized to 1.10 wt. % product sulfur with a iV-in. extrudate catalyst (Tamm ei al., 1981).

In a recent study of deactivated resid hydroprocessing catalysts [14] it was concluded that resid catalysts in some situations deactivate under coke control. In this study it was shown that predominantly coke deactivated catalysts had residual activities that were in line with what was expected from the data in Fig. 8, e.g, 12.4% C ( 18.3% on a fresh catalyst basis) reduces the HDS activity to 35%, and 17,5% C (25% C on a fresh catalyst basis) gave a reduction of HDS activity to 22% of fresh catalyst activity. 

Catalysts currently employed in process development units for coal liquefaction are hydroprocessing catalysts developed for petroleum refining (5l6). They are composed of combinations of Mo or W with Co, Ni or other promoters dispersed on alumina or silica-alumina supports. When used in liquefaction, these catalysts deactivate rapidly f6-9i causing decreases in product yield and quality and problems with process operability. Thus the... 

Generally, an amount of coke on the catalyst increases from the entrance to the exit of the fixed bed reactors in residue hydroprocessing (1, 6, 7). Tamm et al. showed the highest remained catalyst activity at the outlet of the bench-scale fixed-bed reactor after a constant desulfurization operation (1), while Myers et al. found the highest catalyst deactivation rate in the last stage of three-stage pilot-scale expanded-bed reactors after a 60 - 70% vacuum residue conversion operation (7). These results from two typical reactor operations support that the catalyst deactivation in a lower... 

Effect of Process Conditions and Catalyst Properties on Catalyst Deactivation in Residue Hydroprocessing... 

In many studies it has been shown that V and Ni deactivate resid hydroprocessing catalysts [7, 9, 11, 13], The deactivation is caused by poisoning/foultng of the active sites and by restriction of the access of reacting species to the catalyst pore system. 

The hydroprocessing of heavy oils is associated with extensive catalyst deactivation mainly as a result of the deposition of coke and of metal sulphides. Deactivation is fast when the catalyst is first brought on line subsequent loss of activity is much slower. The importance of various effects occurring during deactivation has been re-assessed. 

Various industrial processes have been developed to convert heavy crude oils into transport fuels [3,4], Most of those in use are based on residual cracking or on hydroprocessing over cobalt-molybdenum, nickel-molybdenum or nickel-tungsten based catalysts [3], Given the nature of the feed and the severity of the processing, it is not surprising that catalyst deactivation is a major problem. 

There is little doubt that the rapid initial deactivation is associated with heavy deposition of coke and the resulting loss of catalyst surface area (figure 3) [18,19,20]. About 50% of the surface area of a typical hydroprocessing catalyst can be lost [19,21], largely as a result of blockage of pores of small diameter [19, 21]. Macroporous volume is not greatly affected 2-5 nm radius pore volume is greatly reduced [22]. 

In this paper we discuss the effect of the mode of operation on catalyst deactivation and product properties in residue hydroprocessing. Other mentioned issues have been addressed in other publications [1-2]. 

---