5
sulfur compounds decreased in the order: 4,6- DMDBT > 4-MDBT > C1DBT >
DBT > C2-C3DBT in their study. Stanislaus et al. [3] described in detail the deep
HDS chemistry and kinetics in their comprehensive review of the recent advances
in the science and technology of ultralow sulfur diesel (ULSD) production.
3 Process Description
The process flow diagram of a typical diesel hydrotreater unit is shown in Fig. 2.
The fresh diesel feedstock (usually a mixture of straight-run diesel and cracked gas
oils) is initially heated in a feed-effluent exchanger and mixed with hydrogen gas
streams (make up and recycle hydrogen). The combined feed is heated in a charge
heater to the reactor inlet temperature. The furnace outlet stream is then sent to the
top of the reactor. The reactor usually has multiple catalyst beds with different types
and quantity of catalysts. In most of the cases, multiple reactors (usually two) are
used along with a number of catalyst beds. Cold recycle hydrogen is used as a
quench gas to control the exothermic temperature increase in the reactors. The
amount of interbed quench gas depends on the type of diesel feedstock processed in
the unit. Diesel hydrotreater units processing higher volumes of cracked stocks such
as FCC light cycle oil (LCO) and light coker gas oil (LCGO) require more quench
gas due to the highly exothermic nature of olefin and aromatic saturation reactions.
The reactor effluent after exchanging heat with the incoming feed is sent to a highpressure separator to separate the gas and liquid stream. The hydrogen-rich gas
stream is separated and recycled to the reactor after removal of acid gases in the
amine scrubber unit. Wash water is added upstream of the air cooler to dissolve
DDS
D D S
HYD
H Y D
H Y D
DDS
ISO
I S O
S
I S O
S
S
S
S
S
S
Fig. 1 HDS reaction of 4,6-DMDBT over NiMo/MY catalysts [1] (Reprinted from Applied
Catalysis B: Environmental, 238, Wenwu Zhou, Qiang Wei, Yasong Zhou, Meifang Liu, Sijia
Ding, Qi Yang, Hydrodesulfurization of 4,6-dimethyldibenzothiophene over NiMo sulfide catalysts supported on meso- microporous Y zeolite with different mesopore sizes, 212–224, 2018,
with permission from Elsevier)
Recent Advances in Hydrotreating/Hydrodesulfurization Catalysts: Part I: Nature…
sulfur compounds decreased in the order: 4,6- DMDBT > 4-MDBT > C1DBT >
DBT > C2-C3DBT in their study. Stanislaus et al. [3] described in detail the deep
HDS chemistry and kinetics in their comprehensive review of the recent advances
in the science and technology of ultralow sulfur diesel (ULSD) production.
3 Process Description
The process flow diagram of a typical diesel hydrotreater unit is shown in Fig. 2.
The fresh diesel feedstock (usually a mixture of straight-run diesel and cracked gas
oils) is initially heated in a feed-effluent exchanger and mixed with hydrogen gas
streams (make up and recycle hydrogen). The combined feed is heated in a charge
heater to the reactor inlet temperature. The furnace outlet stream is then sent to the
top of the reactor. The reactor usually has multiple catalyst beds with different types
and quantity of catalysts. In most of the cases, multiple reactors (usually two) are
used along with a number of catalyst beds. Cold recycle hydrogen is used as a
quench gas to control the exothermic temperature increase in the reactors. The
amount of interbed quench gas depends on the type of diesel feedstock processed in
the unit. Diesel hydrotreater units processing higher volumes of cracked stocks such
as FCC light cycle oil (LCO) and light coker gas oil (LCGO) require more quench
gas due to the highly exothermic nature of olefin and aromatic saturation reactions.
The reactor effluent after exchanging heat with the incoming feed is sent to a highpressure separator to separate the gas and liquid stream. The hydrogen-rich gas
stream is separated and recycled to the reactor after removal of acid gases in the
amine scrubber unit. Wash water is added upstream of the air cooler to dissolve
DDS
D D S
HYD
H Y D
H Y D
DDS
ISO
I S O
S
I S O
S
S
S
S
S
S
Fig. 1 HDS reaction of 4,6-DMDBT over NiMo/MY catalysts [1] (Reprinted from Applied
Catalysis B: Environmental, 238, Wenwu Zhou, Qiang Wei, Yasong Zhou, Meifang Liu, Sijia
Ding, Qi Yang, Hydrodesulfurization of 4,6-dimethyldibenzothiophene over NiMo sulfide catalysts supported on meso- microporous Y zeolite with different mesopore sizes, 212–224, 2018,
with permission from Elsevier)
Recent Advances in Hydrotreating/Hydrodesulfurization Catalysts: Part I: Nature…