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Due to depleting supplies of quality petroleum crudes,
refineries world-wide are increasingly being forced to use
inferior quality heavy oils (HO) for producing clean
Unfortunately, the low grades HO are considerably more
difficult to process and can significantly reduce the efficiency
of clean fuels production.
From the viewpoint of continual efficient supply of clean
fuels, it is therefore critical to improve key HO processes
such as sulphur and nitrogen removal.
Overall, new and more effective approaches and
continuing catalysis and processing research are needed
for producing affordable ultra-clean (ultra-low-sulfur and
low-aromatics) transportation fuels.
The society at large is stepping on the road to zero sulfur
fuel, so researchers should begin with the end in mind
and try to develop long term solutions.
Hydrodenitrogenation (HDN) occurs simultaneously with
hydrodesulfurization HDS), hydrodeoxygenation (HDO),
hydrogenation (HYD) and hydrodemetallization (HDM) during
hydroprocessing. Effects of these reactions upon each other
are rather complex.
The extent of the mutual effects depends on the origin of
feed, type of catalyst, and operating conditions.
The HDN has been the focus of attention because nitrogen
removal is required to attain the level of sulfur (S) required by
fuel specifications. If not removed, nitrogen (N)-compounds
would inhibit HDS and other reactions because of their
preferential adsorption on catalytic sites.
A process used in the oil
industry to remove
such as nitrogen sulfur,
oxygen and metals from
petroleum distillates by
reacting them with H2 over
(HDN): is the removal of
nitrogen from nitrogen
containing feeds in the form of
NH3. The resulting products
are hydrogenated .
(HDS): is the removal of
sulfur from sulfur
containing feeds in the
form of Hydrogen
Sulfide, H2S. The
resulting products are
(HDM) are the removal
of oxygen and metals
from the feed.
Compound Sulfur in wt.%
1.87 wt.% 1000 ppm
Medium cycle oil (MCO) 0.49 wt.% 695 ppm
Coal liquid 2.5 wt.% 5600 ppm
Vacuum gas oil (VGO) 1.7 wt.% 125 ppm
Desulfurized vacuum gas oil
Light cycle oil (LCO) 2.19 wt.% -
Nitrogen And Sulfur Content Present in Different Crude
• Prevention of poisoning of the metal
catalysts by sulfur
• Control of pollution by SO2 produced in
the combustion of gasoline
• Removal of the unpleasant odor of lube
oil caused by the presence of sulfur
• Nitrogen containing compounds
severely reduce the activity of cracking,
reforming and HDS catalysts
• High nitrogen concentrations are
undesirable to product quality
• To meet the NOx ,mono-nitrogen oxides
NO and NO2 (nitric oxide and nitrogen
• If present, N-compounds affect the
stability of fuels (fuel storage
degradation and contamination).
A fuel is considered unstable when it
undergoes chemical changes that
produce undesirable consequences
such as deposits, acidity
• When organo sulfur compounds are decomposed, gaseous or
solid sulfur products are formed and the hydrocarbon part is
recovered and remains in the refinery streams. Conventional
• Sulfur compounds are separated from refinery stream
• Organo sulfur compounds are separated from the streams
and simultaneously decomposed in a single reactor unit
rather than in a series of reaction and separation vessels
Classification of Desulphurization Technology
Desulfurization technologies classified by nature of a key
process to remove sulfur
Sulfided CoMo/Al2O3 and NiMo/Al2O3 catalysts
Their performance in terms of desulfurization level,
activity and selectivity depends on
The properties of the specific
(active species concentration,
Support properties, synthesis
The reaction conditions nature
and concentration of the sulfur
compounds present in the feed
stream, and reactor and
temperature, partial pressure of
hydrogen and H2S),
• Hydrotreating model catalyst systems are synthesized by
impregnating and spin-coating Mo and Co precursor
compounds onto flat discs with an oxidic layer as support, a
process much like real catalyst preparation.
• Subsequent sulfidation results in the formation of CoMoS or
Schematic picture of different phases present in a sulfided
alumina-supported CoMo catalyst
Co is present in three
(i) The active CoMoS
(ii) A thermodynamically stable
cobalt sulfide, Co9S8.
(iii) Co dissolved in the Al2O3 support.
Only the CoMoS particles are catalytically active
Schematic representation of the the CoMoS model under
Surface structure models of a
conventional HDS catalyst and the designed catalyst
Environmental restrictions on petroleum products to limit
the sulfur level in fuels to 50 ppm or lower necessitated
new generation hydrodesulfurization catalysts.
In addition, preparing hydrocarbon fuel feeds to the fuel
cell set up requires sulfur reduction to 0.1 ppm. Such a
demanding task requires catalysts that are several times
more active than the present catalysts used to achieve
500 ppm sulfur.
It is not only the high activity but they should also have
different activity profiles with respect to different
functionalities. In order to modify the activity to achieve
the above said objectives several approaches have been
pursued among which variation of support is an important
NEW GENERATION HDS CATALYSTS
• What is deep desulphurization of the fuels ?
More and more of the least reactive sulfur compounds must
be converted to H2S.
• Why is deep desulphurization ?
DBT and/or DBT derivatives that are known to be the most
refractory S-containing compounds show reactivities 50-fold
lower as compared to others.
The concentration of the most refractory sulphur compounds
in straight-run diesel oil and light cycle oil approaches 3000
and 5000 ppm, respectively.
• How to approach deep desulfurization?
The modification of the physicochemical properties of the
supports is one of the still preferred modes of increasing
The synthesis of mesoporous molecular sieves with high
surface area and relatively ordered pore structure offers new
possibilities of using these materials as modifiers of the porous
Deep desulfurization of refinery streams becomes possible
when the severity of the HDS process conditions is increased.
Instead of applying more severe conditions, perhaps HDS
catalysts with improved activity and selectivity can be
• Ideal hydrotreating catalysts should be able to remove sulfur,
nitrogen and, in specific cases, metal atoms from the refinery
streams. At the same time they must also improve other fuel
specifications, such as octane/cetane number or aromatics
content, which are essential for high fuel quality and meeting
environmental legislation standards.
• The use of novel mesoporous supports for catalysts may help
larger molecules to have access to the pores thereby enhancing
the activity and minimizing the S & N content
Typical Reactivity pattern observed in HDS Catalysis
Different approaches have resulted in new catalyst
formulations with improved performances
To improve catalyst performance, all steps in the catalyst
preparation-choice of a precursor of the active species,
support selection, synthesis procedure and
post-treatment of the synthesized catalysts-should be
taken into account
ADVANCED HDS CATALYSTS
• The strength of the interaction with the support controls the
dispersion, reducibility, acidity and catalytic activity.
• The support mesoporosity is important for better dispersion
of sulfide layer.
• Support design increase significantly the HDS, HYD and HDN
functionalities of hydrotreating catalysts.
• The nature of the support affects sulfidation of the active
species, leading to better-promoted active sites and
dispersion of the catalysts.
FUNCTIONS OF SUPPORT - GENERAL
APPROACHES FOR DEVELOPING BETTER CATALYSTS
Effects of various additives on the properties of
alumina-supported HDS catalysts
• Hydrotreating efficiency can also be increased by employing
advanced reactor design such as multiple bed systems within
one reactor, new internals in the catalytic reactor or new
types of catalysts and catalyst support (e.g. structured
• The best results are usually achieved by a combination of the
latter two approaches, namely, using an appropriate catalyst
with improved activity in a reactor of advanced design.