568
The Chemistry and Technology of Petroleum
hydrotreated product to, for example, a fluid catalytic cracking unit. However, there is also the
potential for hydrotreating to change the stability of the asphaltene constituents in the oil (Bartholdy
and Andersen, 2000).
In such cases, it is even more important that particular attention must be given to hydrogen management and promoting hydrodesulfurization and hydrodenitrogenation (even fragmentation) of
asphaltene and resin constituents thereby producing a product that may be suitable as a feedstock
for catalytic cracking with reduced catalyst destruction. The presence of a material with good
solvating power to assist in the hydrotreating process is preferred. In this respect it is worth noting
the reappearance of donor solvent processing of heavy feedstocks (Vernon et al., 1984; Bakshi and
Lutz, 1987) that has its roots in the older hydrogen donor diluent visbreaking process (Bland and
Davidson, 1967).
However, it must be forgotten that product distribution and quality vary considerably depending
on the nature of the feedstock constituents as well as on the process. In modern refineries, hydrocracking is one of several process options that can be applied to the production of liquid fuels from
the heavier feedstocks (Chapter 22). A most important aspect of the modern refinery operation is
the desired product slate, which dictates the matching of a process with any particular feedstock to
overcome differences in feedstock composition.
Hydrogen consumption is also a parameter that varies with feedstock composition (Tables 16.2
and 16.3), thereby indicating the need for a thorough understanding of the feedstock constituents
if the process is to be employed to maximum efficiency. A convenient means of understanding
the influence of feedstock on the hydrotreating process is through a study of the hydrogen content
(H/C atomic ratio) and molecular weight (carbon number) of the various feedstocks or products. It
is also possible to use data for hydrogen usage in residuum processing where the relative amount
of hydrogen consumed in the process can be shown to be dependent on the sulfur content of the
feedstock.
Hydrotreating processes differ depending on the feedstock available and catalysts used.
Hydrotreating can be used to improve the burning characteristics of distillates such as kerosene.
Hydrotreatment of a kerosene fraction can convert aromatics into naphthenes, which are cleanerburning compounds.
Lube-oil hydrotreating uses catalytic treatment of the oil with hydrogen to improve product
quality. The objectives in mild lube hydrotreating include saturation of olefins and improvements in
color, odor, and acid nature of the oil. Mild lube hydrotreating also may be used following solvent
processing. Operating temperatures are usually below 315°C (600°F) and operating pressures below
800 psi. Severe lube hydrotreating, at temperatures in the 315°C–400°C (600°F–750°F) range and
hydrogen pressures up to 3000 psi, is capable of saturating aromatic rings, along with sulfur and
nitrogen removal, to impart specific properties not achieved at mild conditions.
Hydrotreating (Brunet et al., 2005) also can be employed to improve the quality of pyrolysis naphtha-gasoline, a by-product from the manufacture of ethylene. Traditionally, the outlet for
pyrolysis-produced naphtha-gasoline has been motor gasoline blending, a suitable route in view
of its high octane number. However, only small portions can be blended untreated owing to the
unacceptable odor, color, and gum-forming tendencies of this material. The quality of pyrolysis
gasoline, which is high in olefin content, can be satisfactorily improved by hydrotreating, whereby
conversion of olefins into mono-olefins provides an acceptable product for motor gas blending
(Brunet et al., 2005).
21.2 PROCESS PARAMETERS AND REACTORS
All hydrodesulfurization processes react a feedstock with hydrogen to produce hydrogen sulfide
and a desulfurized hydrocarbon product (Figure 21.5). The feedstock is preheated and mixed with
hot recycle gas containing hydrogen and the mixture is passed over the catalyst in the reactor
The Chemistry and Technology of Petroleum
hydrotreated product to, for example, a fluid catalytic cracking unit. However, there is also the
potential for hydrotreating to change the stability of the asphaltene constituents in the oil (Bartholdy
and Andersen, 2000).
In such cases, it is even more important that particular attention must be given to hydrogen management and promoting hydrodesulfurization and hydrodenitrogenation (even fragmentation) of
asphaltene and resin constituents thereby producing a product that may be suitable as a feedstock
for catalytic cracking with reduced catalyst destruction. The presence of a material with good
solvating power to assist in the hydrotreating process is preferred. In this respect it is worth noting
the reappearance of donor solvent processing of heavy feedstocks (Vernon et al., 1984; Bakshi and
Lutz, 1987) that has its roots in the older hydrogen donor diluent visbreaking process (Bland and
Davidson, 1967).
However, it must be forgotten that product distribution and quality vary considerably depending
on the nature of the feedstock constituents as well as on the process. In modern refineries, hydrocracking is one of several process options that can be applied to the production of liquid fuels from
the heavier feedstocks (Chapter 22). A most important aspect of the modern refinery operation is
the desired product slate, which dictates the matching of a process with any particular feedstock to
overcome differences in feedstock composition.
Hydrogen consumption is also a parameter that varies with feedstock composition (Tables 16.2
and 16.3), thereby indicating the need for a thorough understanding of the feedstock constituents
if the process is to be employed to maximum efficiency. A convenient means of understanding
the influence of feedstock on the hydrotreating process is through a study of the hydrogen content
(H/C atomic ratio) and molecular weight (carbon number) of the various feedstocks or products. It
is also possible to use data for hydrogen usage in residuum processing where the relative amount
of hydrogen consumed in the process can be shown to be dependent on the sulfur content of the
feedstock.
Hydrotreating processes differ depending on the feedstock available and catalysts used.
Hydrotreating can be used to improve the burning characteristics of distillates such as kerosene.
Hydrotreatment of a kerosene fraction can convert aromatics into naphthenes, which are cleanerburning compounds.
Lube-oil hydrotreating uses catalytic treatment of the oil with hydrogen to improve product
quality. The objectives in mild lube hydrotreating include saturation of olefins and improvements in
color, odor, and acid nature of the oil. Mild lube hydrotreating also may be used following solvent
processing. Operating temperatures are usually below 315°C (600°F) and operating pressures below
800 psi. Severe lube hydrotreating, at temperatures in the 315°C–400°C (600°F–750°F) range and
hydrogen pressures up to 3000 psi, is capable of saturating aromatic rings, along with sulfur and
nitrogen removal, to impart specific properties not achieved at mild conditions.
Hydrotreating (Brunet et al., 2005) also can be employed to improve the quality of pyrolysis naphtha-gasoline, a by-product from the manufacture of ethylene. Traditionally, the outlet for
pyrolysis-produced naphtha-gasoline has been motor gasoline blending, a suitable route in view
of its high octane number. However, only small portions can be blended untreated owing to the
unacceptable odor, color, and gum-forming tendencies of this material. The quality of pyrolysis
gasoline, which is high in olefin content, can be satisfactorily improved by hydrotreating, whereby
conversion of olefins into mono-olefins provides an acceptable product for motor gas blending
(Brunet et al., 2005).
21.2 PROCESS PARAMETERS AND REACTORS
All hydrodesulfurization processes react a feedstock with hydrogen to produce hydrogen sulfide
and a desulfurized hydrocarbon product (Figure 21.5). The feedstock is preheated and mixed with
hot recycle gas containing hydrogen and the mixture is passed over the catalyst in the reactor