higher hydrogen consumption. Large amounts of unsaturated hydrocarbons can also
cause a heat balance problem if the unit has not been designed to process that type
of feed.
Boiling Range
The typical charge stock to a hydrocracker for distillate production is a
700
F+ (370
C+) boiling range vacuum gas oil or other feedstocks with similar
boiling ranges such as heavy coker gas oil from a delayed coming unit. Increasing
the boiling range usually makes the feed more difficult to process which can lead
to higher catalyst temperatures and shorter catalyst life. This is especially true
if the feed quality is allowed to decrease significantly due to entrainment of
catalyst poisons in the feed. Higher endpoint feeds also usually have higher
sulfur and nitrogen contents, which again make a feedstock more difficult to
process.
Cracked Feed Components
Cracked feedstocks derived from catalytic cracking or thermal cracking can also be
processed in a hydrocracker. These cracked components tend to have higher
contaminants such as sulfur, nitrogen, and particulates. They are also more refractory, with high aromatics content and PNA precursors. These compounds make
cracked stocks harder to process and harder to produce quality products.
Permanent Catalyst Poisons
Organometallic compounds contained in the feed will be decomposed, and the
metals will be retained on the catalyst, thus decreasing its activity. Since metals are
normally not removable by oxidative regeneration, once metals have poisoned a
catalyst, its activity cannot be restored. Therefore, metal content of the feedstock is
a critical variable that must be carefully controlled. The particular metals which
usually exist in vacuum gas oil-type feeds are naturally occurring nickel, vanadium,
and arsenic as well as some metals which are introduced by upstream processing or
contamination such as lead, sodium, silicon, and phosphorous. Iron naphthenates
are soluble in oil and will be a poison for the catalyst. Iron sulfide as corrosion
product is normally not considered a poison for the catalyst and is usually omitted
when referring to total metals.
The tolerance of the catalyst to metals is difficult to quantify and is somewhat
dependent upon the type of catalyst being employed and the severity of the
operation, i.e., the higher the severity, the lower will be the metals’ tolerance
since any impairment of activity will affect the ability to make the desired
352
M. Bricker et al.
cause a heat balance problem if the unit has not been designed to process that type
of feed.
Boiling Range
The typical charge stock to a hydrocracker for distillate production is a
700
F+ (370
C+) boiling range vacuum gas oil or other feedstocks with similar
boiling ranges such as heavy coker gas oil from a delayed coming unit. Increasing
the boiling range usually makes the feed more difficult to process which can lead
to higher catalyst temperatures and shorter catalyst life. This is especially true
if the feed quality is allowed to decrease significantly due to entrainment of
catalyst poisons in the feed. Higher endpoint feeds also usually have higher
sulfur and nitrogen contents, which again make a feedstock more difficult to
process.
Cracked Feed Components
Cracked feedstocks derived from catalytic cracking or thermal cracking can also be
processed in a hydrocracker. These cracked components tend to have higher
contaminants such as sulfur, nitrogen, and particulates. They are also more refractory, with high aromatics content and PNA precursors. These compounds make
cracked stocks harder to process and harder to produce quality products.
Permanent Catalyst Poisons
Organometallic compounds contained in the feed will be decomposed, and the
metals will be retained on the catalyst, thus decreasing its activity. Since metals are
normally not removable by oxidative regeneration, once metals have poisoned a
catalyst, its activity cannot be restored. Therefore, metal content of the feedstock is
a critical variable that must be carefully controlled. The particular metals which
usually exist in vacuum gas oil-type feeds are naturally occurring nickel, vanadium,
and arsenic as well as some metals which are introduced by upstream processing or
contamination such as lead, sodium, silicon, and phosphorous. Iron naphthenates
are soluble in oil and will be a poison for the catalyst. Iron sulfide as corrosion
product is normally not considered a poison for the catalyst and is usually omitted
when referring to total metals.
The tolerance of the catalyst to metals is difficult to quantify and is somewhat
dependent upon the type of catalyst being employed and the severity of the
operation, i.e., the higher the severity, the lower will be the metals’ tolerance
since any impairment of activity will affect the ability to make the desired
352
M. Bricker et al.