Hydrocracking catalyst activity

Figure 6. Effect of feed nitrogen content on strongly acidic hydrocracking catalyst activity (amorphous and crystalline components)...

A-CAT [Activity adjustment by ammonia adsorption] A method for pre-sulfiding and passivating hydrocracking catalysts. Developed by EUROCAT in 1989. 

Figure 16.5 Impact of pretreating severity on the activity of a hydrocracking catalyst temperature required for conversion of a feed hydrotreated to (a) 40 ppm nitrogen, (b) 10ppm nitrogen.

From the general inaccessibility of both the sodium and TMA ions, we postulate that most of the acidic sites generated by thermal treatment of the derived NH4+/TMA+ zeolite will also be inaccessible to reactant molecules. Likewise, catalytically active metals such as Pt and Pd introduced by ion exchange are expected to be located in or near these same inaccessible sites. This may explain the poor approach to equilibrium observed with the isomerization catalysts, and the poor hydrogenation activity of the hydrocracking catalyst indicated by excessive coking and catalyst decline, even in the presence of a massive 3.1 wt % palladium. 

V (Ni-Mo) and the lowest yields with catalysts III (Ni-W) and IV (Ni-W). The highest conversion, i.e., material converted to products boiling below 550°F, was attained with catalyst VI (Ni-Co-Mo). The lowest conversion was attained with catalyst IV (Ni-W), a hydrocracking catalyst. The highest yields of naphtha and light oil were attained with catalysts I (Co-Mo) and VI (Ni-Co-Mo). Because of its high sustained denitrification activity, catalyst V (Ni-Mo) was selected for use in the preparation of syncrude by hydrogenation of the in situ distillate fractions. 

The acid function of the catalyst is supplied by the support. Among the supports mentioned in the literature are silica-alumina, silica-zirconia, silica-magnesia, alumina-boria, silica-titania, acid-treated clays, acidic metal phosphates, alumina, and other such solid acids. The acidic properties of these amorphous catalysts can be further activated by the addition of small proportions of acidic halides such as HF, BF3, SiFit, and the like (3.). Zeolites such as the faujasites and mordenites are also important supports for hydrocracking catalysts (2). 

In order to obtain quantitative measurements of hydrogenation activity and acidity, various schemes are employed. For example, metal surface area has been related to hydrogenation activity and the adsorption of bases such as pyridine and ammonia have been correlated with acidity ((3). Some authors have used certain key reactions involving pure compounds as an indication of catalytic properties (16). Each of these methods is useful however, because of the complex interdependence of the catalytic functions of the hydrocracking catalysts and changes in these functions with catalyst aging, results from each method must be interpreted with caution. 

In the present context, the deposition of coke on a desulfurization catalyst will seriously affect catalyst activity with a marked decrease in the rate of desulfurization (Chapter 5). In fact, it has been noted that even with a deasphalted feedstock, i.e., a heavy feedstock from which the asphaltenes have previously been removed, the accumulation of carbonaceous deposits on the catalyst is still substantial. It has been suggested that this deposition of carbonaceous material is due to the condensation reactions that are an integral part of any thermal (even hydrocracking) process in which heavy feedstocks are involved. 

In a number of petrochemical processes, a gas (hydrogen) is present as reactant. In hydrodesulfurization (HDS), hydrocracking (HC), and hydrodenitrogenation (HDN), the reaction products H2S and ammonia, respectively, are known to decrease the catalyst activity, but are partly transferred to the gas phase. Therefore, also these processes profit from reactive stripping. 

The catalysts were hydrocracking catalysts, both fresh and deactivated up to periods of two years. Hydrogenation activity is shown to be related to sulfur content, while ESR studies indicate a correlation between activity and in the catalyst. 

The DHC-8 and HC-24 catalysts in Figure 4.12 are second-generation, state-of-the-art catalysts for maximum diesel and maximum naphtha, respectively. In 2000-2001, UOP introduced a third generation of hydrocracking catalysts that further improve the efficiency of the hydrocracking process (15). HC-110 is a third-generation maximum-diesel catalyst that provides up to 3 vol-% higher distillate yield than DHC-8 at the same activity. Another distillate catalyst, HC-... 

The analysis presented above uses empirical relations for the catalyst activity functions for the desulfurization and demetalization reactions. These activity functions assume that the major cause for the decline of the catalyst activity is the metal sulfide deposition. In reality, the activity decline would be caused by coke as well as metal deposition. The extent of activity decline due to coke deposition will depend on the extent of hydrocracking reactions. At high temperatures, hydrocracking reactions would be important. The studies of Oxenreiter et al.35 and Beuther and Schmid1 show that the coke deposition on an HDS catalyst can be very rapid initially, due to uncontrolled hydrocracking. This initial rapid coke deposition would, however, reach an equilibrium level. 

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