Introduction - Spent Hydroprocessing Catalysts - page 1

CHAPTER 1
Introduction
Several types of commercial processes for upgrading various petroleum feeds have been
developed. They involve either hydrogen addition to the feed or carbon rejection from the feed.
A number of carbon rejecting processes (e.g., visbreaking, delayed-, fluid-, and flexi-coking)
and asphaltenes and metals separation processes (e.g., deasphalting) have been used on a
commercial scale for several decades [1,2] . The hydrogen addition processes require the
presence of an active catalyst. For catalytic processes, it is more difficult to upgrade vacuum
residues (VR) than atmospheric residues (AR), whereas far fewer problems have been
experienced with catalytic upgrading of vacuum gas oil (VGO), heavy gas oil (HGO), and
deasphalted oil (DAO). Decades of refinery experience confirmed that the atmospheric
distillates can be upgraded without any difficulties. The difficulty and/or severity of upgrading
increases with increasing content of contaminants (e.g., metals, resins, asphaltenes, sulfur, and
nitrogen) in the feed. The increase in severity results in the increased consumption of
hydrogen and catalyst. Compared with thermal processes, hydroprocessing operations are
more flexible, giving higher yields of liquid fractions. However, the costs of high-pressure
equipment, catalyst inventory and H 2 required for hydroprocessing have to be offset by the
increased yields and quality of liquid products.
In an extreme case (e.g., extra heavy feeds), carbon rejection is the route of choice compared
with the hydrogen addition. In this regard, there is little information suggesting that petroleum
feeds containing more than 300 ppm of metals can be economically upgraded via catalytic
route on a commercial scale, in spite of the fact that some hydrogen addition processes have
been designed to handle heavy feeds containing as much as 700 ppm of the metals and more
than 20 wt.% of asphaltenes [3-6] .
The composition of distillate feeds obtained from conventional crude via distillation may differ
from that of a similar boiling range distillates produced using carbon rejecting processes. For
the latter, the constituents of primary interest (e.g., S- and N-containing compounds) are of a
more refractory nature. Therefore, more severe hydroprocessing conditions are required to
achieve a desirable level of hydrodesulfurization (HDS) and hydrodenitrogenation (HDN).
Also, these feeds have a higher content of Conradson carbon residue (CCR) forming
precursors. Therefore, a higher consumption of hydrogen and catalyst may be anticipated.
General trends in crude oil supply indicate on a growing volume of heavy crude. The
upgrading of the corresponding heavy feeds, such as atmospheric and/or vacuum residues via
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