Hydroprocessing of Petroleum - Spent Hydroprocessing Catalysts - page 48

the ebullated bed reactors depends on the level of deactivation, particularly on the amount of
deposited metals such as V and Ni.

3.4.3 Comparison of Hydroprocessing Reactors

Fixed bed reactors have always been chosen for hydroprocessing distillate feeds. There is a
wide range of modifications to fixed bed reactors to suit different feeds, available
commercially. If properly designed and loaded with a suitable catalyst, any fixed bed reactor
can be used for hydroprocessing light feeds. Moreover, an optimal selection of conditions such
as temperature, H 2 pressure, feed rate, etc. can ensure an efficient and steady operation of fixed
bed reactors. Morel et al. [120] estimated ranges of the yields and of the properties of the
products from hydroprocessing of the Safania VR in different types of reactors. The properties
of the VR are shown in Table 3.5 , whereas those of the products together with their yields in
Table 3.6 [120] . With respect to the content of contaminants (e.g., sulfur, nitrogen and CCR) in
products, fixed/moving bed reactors were the most efficient followed by ebullated bed reactor.
Because of the higher temperature employed, the latter reactor gave the larger yields of
naphtha and gas oil. In the slurry bed reactors employing throw-away solids, the conversion to
liquid products have exceeded 80%. This resulted from the temperatures which were higher
than those typically used during conventional hydroprocessing. The residence time was
usually longer as well.

The quality of products ( Table 3.6 ) [120] from different reactors reflects the difference in
operating conditions. The lower quality for ebullated bed reactor compared with fixed/moving
bed reactor is attributed to a higher temperature used in the former. This may be offset by a
lower yield of VR in the products from ebullated bed reactor. The lowest quality products are
obtained in slurry bed reactors, most likely, because of the highest temperature used compared
with the other reactors. This suggests that a significant hydroprocessing of the liquid products
from the slurry bed reactors would be required to achieve specifications of the commercial
fuels. Moreover, feasibility of the slurry bed reactors may be affected by availability of the
catalytically active solids. Thus, the plant processing 10,000 tons per day of heavy feed,
requiring about 0.5 wt.% of catalyst to achieve acceptable conversion, would consume about

Table 3.5: Properties of Safania vacuum residue [From ref. 120 . Reprinted with permission].

Specific gravity (kg/L) 1 . 035

Sulfur (wt.%) 5 . 28

Nitrogen (ppm) 4600

CCR (wt.%) 23 . 0

Asphaltenes (heptane) 11 . 5

V + Ni (ppm) 203

CCR: Conradson carbon residue.