Title: AN OVERVIEW OF NEW APPROACHES FOR REMOVING SULFUR FROM REFINERY SYSTEMS
1AN OVERVIEW OF NEW APPROACHES FOR REMOVING
SULFUR FROM REFINERY SYSTEMS
2INTRODUCTION
- 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 transportation fuels. - 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.
3Contd..
- 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 and non-road fuels, because
meeting the new government sulfur regulations in
20062010 (15 ppm sulfur in highway diesel fuels
by 2006 and non-road diesel fuels by 2010 30 ppm
sulfur in gasoline by 2006) is only a milestone. - 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.
4REFINING
- Refining is the process, wherein, one complex
mixture of hydrocarbons is classified into a
number of other complex mixtures of hydrocarbons.
- or
- Petroleum refining is an important activity that
the product at the end of the process is a source
of transportation and involves heating of fuels
and petrochemicals. - Increasing awareness of the impact of
environmental pollution by automobiles has
shifted the responsibility of pollution control
to the refiners side.
5PROCESSES IN REFINERIES
6Market share of main catalysts technology
divisionsin percentage in terms of sales value
7HYDROTREATING
- 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.
8- Hydrotreating A process used in the oil industry
to remove objectionable elements such as nitrogen
sulfur, oxygen and metals from petroleum
distillates by reacting them with H2 over a
catalyst. - Hydrodenitrogenation (HDN) is the removal of
nitrogen from nitrogen containing feeds in the
form of NH3. The resulting products are
hydrogenated . - Hydrodesulfurisation (HDS) is the removal of
sulfur from sulfur containing feeds in the form
of H2S. The resulting products are hydrogenated . - Hydrodeoxygenation (HDO) and hydrodemetalization
are the removal of oxygen and metals from the
feed.
9Nitrogen And Sulfur Content Present in Different
Crude
Compound Sulfur in wt. Nitrogen in ppm level
Gas oil 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 (DS-VGO) 0.289 0.028
Light cycle oil (LCO) 2.19 wt. -
10IMPORTANCE
- HDN
- Nitrogen containing compounds severely reduce the
activity of cracking, hydrogenation,
isomerisation, reforming and HDS catalysts - High nitrogen concentrations are detrimental to
product quality - To meet the NOx emission restrictions.
- If present, N-compounds affect the stability of
fuels.
- HDS
- Prevention of poisoning of the metal catalysts by
sulfur - Control of pollution by SO2 produced in the
combustion of gasoline - Removal of the unpleasant odour of lube oil
caused by the presence of sulfur
11COMPOUND STRUCUTRE
Six-membered
Pyridine
Piperidine
Quinoline
Tetrahydroquinoline
Acridine
Five-membered
Pyrrole
Indole
Indoline
Carbazole
Nonheterocyclic
Aniline
12Typical Sulfur Compounds and their Hydrotreating
pathway
13Reactivity of various organic sulfur compounds in
HDS
14Classification of Desulphurization Technology
- 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 HDS - Sulfur compounds are separated from refinery
stream without decomposition - 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
15Contd..
16Desulfurization technologies classified by nature
of a key process to remove sulfur
17CONVENTIONAL HDS
- Sulfided CoMo/Al2O3 and NiMo/Al2O3 catalysts
- Their performance in terms of desulfurization
level, activity and selectivity depends on - 1. The properties of the specific catalyst
used (active species concentration, Support
properties, synthesis route), - 2. The reaction conditions (sulfiding
protocol, temperature, partial pressure of
hydrogen and H2S), nature and concentration of
the sulfur compounds present in the feed stream,
and reactor and process design.
18Hydrotreating catalyst
- 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 MoS2 particles
19Schematic picture of different phases present in
a sulfided alumina-supported CoMo catalyst
20Co is present in threedifferent phases. (i)
The active CoMoS nanoparticles. (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 reaction conditions
21Various Co compounds on Co-Mo catalyst
- CoAl2O3. Co atoms are dissolved in the alumina
support - Co9S8. The thermodynamically stable cobalt
sulfide - CoMoS. A bimetallic sulfide-compound of Co, Mo
and S. The compound has an MoS2-like texture,
into which Co atoms are incorporated. The phase
is non-stoichiometric with respect to the Co/Mo
ratio, and no unit cell can be defined in the
crystallographic sense. - Of the three phases, only the last CoMoS
structures are associated with an appreciable
catalytic activity, and is therefore the
structure of prime interest.
22Contd..
- CoMoS clusters are described as being essentially
MoS2-like, but with additional Co atoms embedded
into the MoS2 lattice at the perimeter of the
cluster. - It is proposed that Co atoms located at edge
positions create new and more active sites. - The promoting role of Co is, however, still
extensively discussed, and the exact location of
Co has not been identified. - A prerequisite for a thorough elucidation of this
seems to be a better understanding of the
morphology and atomic-scale structure of CoMoS
clusters.
23Contd..
- The ternary CoMoS phase is non-stoichiometric and
thus has no thermodynamically stable counterpart. - It has, however, been established both
experimentally and theoretically that the CoMoS
phase can be formed independently of any support,
and it should thus be possible to form CoMoS
clusters and study them independently. - In the literature it is suggested that the number
of sulfur vacancies is the main factor
controlling the catalytic activity. This is
mainly based on a number of studies dealing with
trends in the hydrodesulfurization of
transition-metal sulfides (TMS)
24ROLE OF THE PROMOTER
- The intercalation model
- The pseudo-intercalation or decoration model
- The remote control or contact synergy model
- The so-called CoMoS model, in which Co atoms
decorate the edges of MoS2-slabs. This model was
first proposed by Ratnasamy and Sivanskar.
25Different models proposed for active phase Co-Mo-S
26Surface structure models of a conventional HDS
catalyst and the designed catalyst
27Contd..
28HDS PROCESS
29NEED FOR NEW AND EFFICIENT CATALYST
- 1999 500ppm
- 2001 50 ppm
- 2003 10 ppm
- Keeping up with changes in the environmental
requirements later the final target has been
changed to develop catalysts which attain 10ppm S
or less by the end of 2003
30NEW GENERATION HDS CATALYSTS
- 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
one.
31DEEP DESULFURIZATION
- 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.
32Contd..
- How to approach deep desulfurization?
- The modification of the physicochemical
properties of the supports is one of the still
preferred modes of increasing catalytic activity.
- 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 support structure. - 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 synthesized.
33Contd..
- 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
34DESULPHURISATION ROUTE OF 4,6-DMDBT
35Typical Reactivity pattern observed in HDS
Catalysis
36General classification of the catalysts
37Methods to improve DDS of 4,6-DMDBT
- One way of reducing the steric hindrance of the
methyl groups is to shift these groups from 4,6
to 3,7 or to 2,8 positions through an
isomerization reaction - The complete removal of one or both methyl groups
through a dealkylation reaction offers another
possibility. - The scission of the single C-C bond in the
thiophenic ring (isomerization, dealkyalation,
and C-C bond scission reactions) as
non-hydrogenative routes for desulfurization. - This can take place by the following 2 ways.
- 1.The saturation of one of the phenyl rings
depends primarily on the hydrogenation - 2. By incorporating a suitable metal such as Ni,
W, Pt, Pd, Ru, etc., and/or by providing a
suitable support.
38APPROACHES FOR DEVELOPING BETTER CATALYSTS
39ADVANCED HDS CATALYSTS
- 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
40CHOICE OF SUPPORTS
- Conventionally used industrial hydrotreating
catalyst Co (Ni)-Mo /?-Al2O3 - Additives to ?-Al2O3
- Silica, Carbon
- Mixed Oxides
- Clays, Zeolites like Y and USY
- Mesoporous Material MCM-41, HMS, mesoporous
Alumina and - SBA-15 large pores and bimodal structure
consisting of micro and mesopores
41FUNCTIONS OF SUPPORT - GENERAL
- 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.
42Effects of various additives on the properties of
alumina-supported HDS catalysts
APPROACHES FOR DEVELOPING BETTER CATALYSTS
43Comparison of first-order rate constants for
theHDS of 4,6-DMDBT over alumina, HZSM-5 mixed
alumina,and HY mixed alumina-supported CoMo
catalysts
44Enhancement in flexibility of the partially
hydrogenated 4,6-DMBT molecule for approaching
the active sites of the catalyst
45MESOPOROUS MOLECULAR SEIVES
- The special features of SiMCM-41
- (Conventional)
- Mild acidity
- High surface area
- Medium uniform pore size
46Contd..
The special features of AlMCM-41 (spherical)
- Spherical MCM-41 - well structured with Aluminium
in tetrahedral framework . - No charge balancing cations other than ammonium
and proton. - Possess active Bronsted acid sites.
- Provides an easier access to their adsorption
sites due to the presence of short channels of
MCM-41(S)
47AlMCM-41 (Spherical) as a support
- As host material for catalytic active species
offers approach for the synthesis of innovative
catalyst due to textural advantages. - There will be more no of large pore mouths
present on the MCM-41 (S) external surface. - The amount of isolated Si-OH groups and the
topology of the diverse structures determine the
types of MoO3 species and prevent agglomeration. - The presence of metals (Ti Zr) on the surface
of pores can modify the interaction of the active
phases with the support changing their reduction
properties and their dispersion leading to
catalysts more active for the HDS reaction.
48Contd..
- Stabilize the metal oxide particles and does not
allow metal oxide such as MoO3 to grow to large
size. Also minimise stacking of active phases. - The particle growth was limited because species
movement to the external surface was hindered by
the non interacting porous texture of MCM-41
material. - The wall structure of MCM-41 as an ordered meso
porous silica resembles amorphous silica
49DBT and 4,6-DMDBT conversion for
NiMo/P-MCM-41(R)catalysts with NiMo/Al2O3
50HDS over sulfided Co-Mo/MCM-41 (50) and
Co-Mo/Al2O3
51AlSBA-15
- SBA-15 possesses abnormal hydrothermal stability
- The large hexagonal pores (40-100A) and bimodal
structure consisting of micro and mesopores. - The high surface area can be exploited for
achieving good dispersion of catalytically active
transition metal oxides.
52Contd..
- The large pores of these materials may help
larger molecules to have access to the pores
thereby enhancing the activity and minimizing the
S N content. - Diffusion of large molecules like 4,6-DMDBT will
be slow in Alumina supported catalyst and the
reaction is diffusion controlled. - With these new and novel supports like nano
spherical MCM-41 and AlSBA-15 the process are
made non diffusional. HDS takes place through two
routes. One by HYDS and the other by DDS. - Sterically hindered compounds can be desulfurised
by hydrogenation using new and novel supported
catalysts.
53 NiMo/Al-SBA-15 for HDS of 4,6-DMDBT
- The interaction of Ni and Mo species with the
support becomes stronger with Al loading into the
SBA-15. Both framework and extraframework Al3
species participate in the interaction with the
deposited Mo species acting as anchoring sites
for Mo. In line with this, the dispersion of
oxidic and sulfided Mo species increases leading
to an increase in the catalytic activity of NiMo
catalysts. - NiMo catalysts supported on Al-containing SBA-15
materials with Si/Al molar ratio between 30 and
10 show high activity in HDS of
4,6-dimethyldibenzothiophene. - This can be attributed to both good dispersion of
Ni and Mo active phases and to the bifunctional
character of these catalysts, namely, to the
participation of Bronsted acid sites of the
support in the catalytic transformations of
4,6-DMDBT prior to its desulfurization
54SBA-15 - MODIFICATIONS BY POST ALUMINATION
- Chemical grafting of aluminum(III) chloride on
the surface of SBA-15 is a suitable synthetic
method for the preparation of mesoporous
silicoaluminates of SBA-15 type with weak
Bronsted acidity. This method resulted in the
preparation of Al-SBA-15(X) materials without
significant changes in the original pore
structure and the long-range periodicity order of
the parent SBA-15 sample.
55COMPARISION OF DDS OF VARIOUS SUPPORTS FOR MO
DDS
HYD
56Comparison of SBA-15 and Al-SBA-15 supported
catalysts with g-Al2O3 for HDS of thiophene
57SBA Alumina supported Co-Mo Catalysts
- SBA-15 and Al-SBA-15 supported gt g-Al2O3
supported
co-Mo catalysts - SBA-15 Al-SBA-15 supported catalysts for HDS
- For Hydrogenation reaction Al-SBA-15 is a better
support for Mo, CoMo and NiMo than SBA-15. - It appears high molybdenum dispersion on isolated
Al sites in Al-SBA-15 and consequent increase of
anion vacancies at the edge sites of Mo as a
function ofSi/Al ratio appears to be responsible
for the outstanding activities of SBA-15 and
Al-SBA-15 supported catalysts.
58.
Proposed reaction network for the
hydrodesulfurization of 4,6-DMDBT over
NiMo/Al-SBA-15(X) catalysts.
59Multi-walled carbon nanotubes as efficient
support to NiMo hydrotreating catalyst for HDS
60HDS of Thiophene over Pt/AlSBA-15
61Schematic representation of tungstenin the
surface and wall of WO3-SBA-15(A) low tungsten
content and (B) high tungsten content.
62Impact of high-throughput techniques in the
development and launching of a new product.
63CONCLUSION
- 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 catalysts). - 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.
64Thank You