AN OVERVIEW OF NEW APPROACHES FOR REMOVING SULFUR FROM REFINERY SYSTEMS K.SHANTHI Department of...

AN OVERVIEW OF NEW APPROACHES FOR AN OVERVIEW OF NEW APPROACHES FOR REMOVING SULFUR FROM REFINERY SYSTEMSREMOVING SULFUR FROM REFINERY SYSTEMS

K.SHANTHIDepartment of Chemistry,

Anna University, Chennai-600025

INTRODUCTIONINTRODUCTION

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.

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 2006–2010 (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.

Contd…..Contd…..

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 Increasing awareness of the impact of environmental pollution by automobiles has shifted the responsibility of pollution by automobiles has shifted the responsibility of pollution control to the refiner’s side.pollution control to the refiner’s side.

REFININGREFINING

Hydrodesulfurisation(HDS)

Hydrodenitrogenation(HDN)

Hydrodeoxygenation(HDO) and (HDM)

PROCESS

Catalyticcracking

HydrocrackingCatalyticreforming

Hydrotreating

PROCESSES IN REFINERIESPROCESSES IN REFINERIES

Market share of main catalysts technology divisionsin percentage in terms of sales value

Hydrodenitrogenation (HDN) occurs simultaneously with Hydrodenitrogenation (HDN) occurs simultaneously with hydrodesulfurization HDS), hydrodeoxygenation (HDO), hydrodesulfurization HDS), hydrodeoxygenation (HDO), hydrogenation (HYD) and hydrodemetallization (HDM) hydrogenation (HYD) and hydrodemetallization (HDM) during hydroprocessing. Effects of these reactions upon during hydroprocessing. Effects of these reactions upon each other are rather complex. each other are rather complex.

The extent of the mutual effects depends on the origin of The extent of the mutual effects depends on the origin of feed, type of catalyst, and operating conditions.feed, type of catalyst, and operating conditions.

The HDN has been the focus of attention because The HDN has been the focus of attention because nitrogen removal is required to attain the level of sulfur nitrogen removal is required to attain the level of sulfur (S) required by fuel specifications. If not removed, (S) required by fuel specifications. If not removed, nitrogen (N)-compounds would inhibit HDS and other nitrogen (N)-compounds would inhibit HDS and other reactions because of their preferential adsorption on reactions because of their preferential adsorption on catalytic sites.catalytic sites.

HYDROTREATINGHYDROTREATING

HydrotreatingHydrotreating:: A process used in the oil industry to A process used in the oil industry to remove objectionable elements such as nitrogen remove objectionable elements such as nitrogen sulfur, oxygen and metals from petroleum distillates sulfur, oxygen and metals from petroleum distillates by reacting them with H2 over a catalyst.

Hydrodenitrogenation (HDN):Hydrodenitrogenation (HDN): is the removal of is the removal of nitrogen from nitrogen containing feeds in the form of NHnitrogen from nitrogen containing feeds in the form of NH33. . The resulting products are hydrogenated .The resulting products are hydrogenated .

Hydrodesulfurisation (HDS):Hydrodesulfurisation (HDS): is the removal of sulfur is the removal of sulfur from sulfur containing feeds in the form of Hfrom sulfur containing feeds in the form of H22S. The S. The resulting products are hydrogenated .resulting products are hydrogenated .

Hydrodeoxygenation (HDO) and hydrodemetalizationHydrodeoxygenation (HDO) and hydrodemetalization are the removal of oxygen and metals from the feed. are the removal of oxygen and metals from the feed.

Compound Sulfur in wt.%Nitrogen inppm level

Gas oil1.87 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.% -

Nitrogen And Sulfur Content Present in Different CrudeNitrogen And Sulfur Content Present in Different Crude

HDSHDS

Prevention of poisoning of the Prevention of poisoning of the metal catalysts by sulfurmetal catalysts by sulfur

Control of pollution by SOControl of pollution by SO22 produced in the combustion of produced in the combustion of gasolinegasoline

Removal of the unpleasant Removal of the unpleasant odour of lube oil caused by the odour of lube oil caused by the presence of sulfurpresence of sulfur

HDNHDN

Nitrogen containing compounds Nitrogen containing compounds severely reduce the activity of severely reduce the activity of cracking, hydrogenation, cracking, hydrogenation, isomerisation, reforming and isomerisation, reforming and HDS catalystsHDS catalysts

High nitrogen concentrations are High nitrogen concentrations are detrimental to product qualitydetrimental to product quality

To meet the NOTo meet the NOxx emission emission restrictions. restrictions.

If present, N-compounds affect If present, N-compounds affect the stability of fuels.the stability of fuels.

IMPORTANCEIMPORTANCE

COMPOUNDCOMPOUND STRUCUTRESTRUCUTRE

Six-membered

Pyridine

Piperidine

Quinoline

Tetrahydroquinoline

Acridine

Five-membered

Pyrrole

Indole

Indoline

Carbazole

Nonheterocyclic

Aniline

NH

N

NH

N

NH

NH

NH

NH

NH2

Typical Sulfur Compounds and their Hydrotreating pathwayTypical Sulfur Compounds and their Hydrotreating pathway

Reactivity of various organic sulfur compounds in HDSReactivity of various organic sulfur compounds in HDS

When organo sulfur compounds are decomposed, When organo sulfur compounds are decomposed, gaseous or solid sulfur products are formed and the gaseous or solid sulfur products are formed and the hydrocarbon part is recovered and remains in the hydrocarbon part is recovered and remains in the refinery streams. refinery streams. Conventional HDSConventional HDS

Sulfur compounds are separated from refinery stream Sulfur compounds are separated from refinery stream without decompositionwithout decomposition

Organo sulfur compounds are separated from the Organo sulfur compounds are separated from the streams and simultaneously decomposed in a single streams and simultaneously decomposed in a single reactor unit rather than in a series of reaction and reactor unit rather than in a series of reaction and separation vesselsseparation vessels

Classification of Desulphurization TechnologyClassification of Desulphurization Technology

Desulfurization technologies classified by nature of a key Desulfurization technologies classified by nature of a key process to remove sulfurprocess to remove sulfur

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.

CONVENTIONAL HDSCONVENTIONAL HDS

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

Hydrotreating catalystHydrotreating catalyst

Schematic picture of different phases present in a sulfided alumina-supported CoMo catalyst

Co is present in three

different 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 Schematic representation of the the CoMoS model under reaction conditionsreaction conditions

Co:Al2O3. 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.

Various Co compounds on Co-Mo catalystVarious Co compounds on Co-Mo catalyst

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.


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)


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.

ROLE OF THE PROMOTERROLE OF THE PROMOTER

Different models proposed for active phase Co-Mo-SDifferent models proposed for active phase Co-Mo-S

Surface structure models of a conventional HDS catalyst and the designed catalyst

HDS PROCESSHDS PROCESS

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

NEED FOR NEW AND EFFICIENT CATALYSTNEED FOR NEW AND EFFICIENT 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 one.

NEW GENERATION HDS CATALYSTSNEW GENERATION HDS CATALYSTS

What is deepWhat is deep desulphurization of the fuels ?

More and more of the least reactive sulfur compounds must be converted to H2S.

Why is deep desulphurization ?Why is deep desulphurization ?

DBT and/or DBT derivatives that are known to be the DBT and/or DBT derivatives that are known to be the most refractory S-containing compounds show most refractory S-containing compounds show reactivities 50-fold lower as compared to others. reactivities 50-fold lower as compared to others.

The concentration of the most refractory sulphur The concentration of the most refractory sulphur compounds in straight-run diesel oil and light cycle oil compounds in straight-run diesel oil and light cycle oil approaches 3000 and 5000 ppm, respectively. approaches 3000 and 5000 ppm, respectively.

DEEP DESULFURIZATIONDEEP DESULFURIZATION

How to approach deep desulfurization?How to approach deep desulfurization?

The modification of the physicochemical properties of The modification of the physicochemical properties of the supports is one of the still preferred modes of the supports is one of the still preferred modes of increasing catalytic activity. increasing catalytic activity.

The synthesis of mesoporous molecular sieves with The synthesis of mesoporous molecular sieves with high surface area and relatively ordered pore structure high surface area and relatively ordered pore structure offers new possibilities of using these materials as offers new possibilities of using these materials as modifiers of the porous support structure. 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.


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 The use of novel mesoporous supports for catalysts may help larger molecules to have access to the pores thereby enhancing the activity and molecules to have access to the pores thereby enhancing the activity and minimizing the S & N contentminimizing the S & N content


DESULPHURISATION ROUTE OF 4,6-DMDBTDESULPHURISATION ROUTE OF 4,6-DMDBT

Typical Reactivity pattern observed in HDS CatalysisTypical Reactivity pattern observed in HDS Catalysis

General classification of the catalystsGeneral classification of the catalysts

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.

Methods to improve DDS of 4,6-DMDBTMethods to improve DDS of 4,6-DMDBT

APPROACHES FOR DEVELOPING BETTER 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

ADVANCED HDS CATALYSTSADVANCED HDS CATALYSTS

Conventionally used industrial hydrotreating Conventionally used industrial hydrotreating catalyst Co (Ni)-Mo /catalyst Co (Ni)-Mo /γγ-Al-Al22OO33

Additives to Additives to γγ-Al-Al22OO33

Silica, CarbonSilica, Carbon Mixed OxidesMixed Oxides Clays, Zeolites like Y and USY Clays, Zeolites like Y and USY Mesoporous Material MCM-41, HMS, Mesoporous Material MCM-41, HMS,

mesoporous Alumina andmesoporous Alumina and SBA-15 large pores and bimodal structure SBA-15 large pores and bimodal structure

consisting of micro and mesoporesconsisting of micro and mesopores

CHOICE OF SUPPORTSCHOICE OF SUPPORTS

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 - GENERALFUNCTIONS OF SUPPORT - GENERAL

APPROACHES FOR DEVELOPING BETTER CATALYSTS

Effects of various additives on the properties of alumina-supported HDS catalysts

Comparison of first-order rate constants for theHDS of 4,6-DMDBT over alumina, HZSM-5 mixed alumina,

and HY mixed alumina-supported CoMo catalysts

Enhancement in flexibility of the partially hydrogenated 4,6-DMBT molecule for approaching

the active sites of the catalyst

The special features of SiMCM-41 The special features of SiMCM-41

(Conventional) (Conventional)

Mild acidityMild acidity

High surface areaHigh surface area

Medium uniform pore sizeMedium uniform pore size

MESOPOROUS MOLECULAR SEIVESMESOPOROUS MOLECULAR SEIVES

Spherical MCM-41 - well structured with Aluminium in Spherical MCM-41 - well structured with Aluminium in tetrahedral framework .tetrahedral framework .

No charge balancing cations other than ammonium and No charge balancing cations other than ammonium and proton.proton.

Possess active Bronsted acid sites.Possess active Bronsted acid sites.

Provides an easier access to their adsorption sites due Provides an easier access to their adsorption sites due to the presence of short channels of MCM-41(S)to the presence of short channels of MCM-41(S)

The special features of AlMCM-41 (spherical)The special features of AlMCM-41 (spherical)


As host material for catalytic active species offers As host material for catalytic active species offers approach for the synthesis of innovative catalyst due to approach for the synthesis of innovative catalyst due to textural advantages. textural advantages.

There will be more no of large pore mouths present on There will be more no of large pore mouths present on the MCM-41 (S) external surface.the MCM-41 (S) external surface.

The amount of isolated Si-OH groups and the The amount of isolated Si-OH groups and the topology of the diverse structures determine the types topology of the diverse structures determine the types of MoOof MoO33 species and prevent agglomeration. species and prevent agglomeration.

The presence of metals (Ti & Zr) on the surface of The presence of metals (Ti & Zr) on the surface of pores can modify the interaction of the active phases pores can modify the interaction of the active phases with the support changing their reduction properties with the support changing their reduction properties and their dispersion leading to catalysts more active for and their dispersion leading to catalysts more active for the HDS reaction.the HDS reaction.

AlMCM-41 (Spherical) as a supportAlMCM-41 (Spherical) as a support

Stabilize the metal oxide particles and does not allow Stabilize the metal oxide particles and does not allow metal oxide such as MoOmetal oxide such as MoO3 3 to grow to large size. Also to grow to large size. Also minimise stacking of active phases.minimise stacking of active phases.

The particle growth was limited because species The particle growth was limited because species movement to the external surface was hindered by movement to the external surface was hindered by the non interacting porous texture of MCM-41 the non interacting porous texture of MCM-41 material.material.

The wall structure of MCM-41 as an ordered meso The wall structure of MCM-41 as an ordered meso porous silica resembles amorphous silicaporous silica resembles amorphous silica


DBT and 4,6-DMDBT conversion for NiMo/P-MCM-41(R)catalysts with NiMo/Al2O3

HDS over sulfided Co-Mo/MCM-41 (50) and Co-Mo/Al2O3

SBA-15 possesses abnormal hydrothermal SBA-15 possesses abnormal hydrothermal stabilitystability

The large hexagonal pores (40-100AThe large hexagonal pores (40-100A˚̊) and ) and bimodal structure consisting of micro and bimodal structure consisting of micro and mesopores.mesopores.

The high surface area can be exploited for The high surface area can be exploited for achieving good dispersion of catalytically achieving good dispersion of catalytically active transition metal oxides. active transition metal oxides.

AlSBA-15AlSBA-15

The large pores of these materials may help larger The large pores of these materials may help larger molecules to have access to the pores thereby molecules to have access to the pores thereby enhancing the activity and minimizing the S & N content.enhancing the activity and minimizing the S & N content.

Diffusion of large molecules like 4,6-DMDBT will be slow Diffusion of large molecules like 4,6-DMDBT will be slow in Alumina supported catalyst and the reaction is in Alumina supported catalyst and the reaction is diffusion controlled. diffusion controlled.

With these new and novel supports like nano spherical With these new and novel supports like nano spherical MCM-41 and AlSBA-15 the process are made non MCM-41 and AlSBA-15 the process are made non diffusional. HDS takes place through two routes. One by diffusional. HDS takes place through two routes. One by HYDS and the other by DDS. HYDS and the other by DDS.

Sterically hindered compounds can be desulfurised by Sterically hindered compounds can be desulfurised by hydrogenation using new and novel supported catalysts.hydrogenation using new and novel supported catalysts.


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

NiMo/Al-SBA-15 for HDS of 4,6-DMDBT

SBA-15 - MODIFICATIONS BY POST ALUMINATIONSBA-15 - MODIFICATIONS BY POST ALUMINATION

Chemical grafting of aluminum(III) chloride on the Chemical grafting of aluminum(III) chloride on the surface of SBA-15 is a suitable synthetic method for the surface of SBA-15 is a suitable synthetic method for the preparation of mesoporous silicoaluminates of SBA-15 preparation of mesoporous silicoaluminates of SBA-15 type with weak Bro¨nsted acidity. This method resulted in type with weak Bro¨nsted acidity. This method resulted in the preparation of Al-SBA-15(X) materials without the preparation of Al-SBA-15(X) materials without significant changes in the original pore structure and the significant changes in the original pore structure and the long-range periodicity order of the parent SBA-15 long-range periodicity order of the parent SBA-15 sample.sample.

Mo/MCM-41 Mo/SBA Mo/AlMo/MCM-41 Mo/SBA Mo/Al22OO33

COMPARISION OF DDS OF VARIOUS SUPPORTS FOR MOCOMPARISION OF DDS OF VARIOUS SUPPORTS FOR MO

DDS HYD

Comparison of SBA-15 and Al-SBA-15 supported catalysts with -Al2O3 for HDS of thiophene

SBA-15 and Al-SBA-15 supported > -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.

SBA & Alumina supported Co-Mo CatalystsSBA & Alumina supported Co-Mo Catalysts

.

Proposed reaction network for the hydrodesulfurization of 4,6-DMDBT over NiMo/Al-SBA-15(X) catalysts.

3Ni12Mo/MWCNTs

Ni12Mo2.5P/MWCNTs

3Ni12Mo/Al2O3 (wb)

3Ni12Mo/Al2O3 (vb);

Multi-walled carbon nanotubes as efficient supportto NiMo hydrotreating catalyst for HDS

HDS of Thiophene over Pt/AlSBA-15HDS of Thiophene over Pt/AlSBA-15

Schematic representation of tungstenin the surface and wall of WO3-SBA-15:

(A) low tungsten content and (B) high tungsten content.

Impact of high-throughput techniques in the development and launching of a new product.

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.

CONCLUSIONCONCLUSION

AN OVERVIEW OF NEW APPROACHES FOR REMOVING SULFUR FROM REFINERY SYSTEMS K.SHANTHI Department of...

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