Diesel Quality-Current Global Scenario Maximum On-Road Diesel Sulfur - - PowerPoint PPT Presentation

Advances in ULSD catalyst systems

Alex C. Pulikottil Indian Oil Corporation Ltd, R&D Centre, Faridabad, India

16-17 April 2012 “Refining Challenges and Way Forward” New Delhi

Diesel Quality-Current Global Scenario

Maximum On-Road Diesel Sulfur Limit

Diesel Fuel Quality Changes

50 100 3 16 30

% NOx Conv. Efficiency

S (ppm)

0.05 0.1

3 16 30

PM (CDPF) g/bhp.h

S (ppm)

Sulfur (ppm) max 5-10 Aromatics (vol%) max 15 Polyaromatics (vol%) max 2 Density (kg/m3) max 820 Cetane number min 55 Distillation Point (T90) (o C) max 320

Major spec of diesel in WWFC category 4

Regulatory push major driver for innovation in HDS catalysis Tier Nox g/kW.h PM g/kW.h Euro-3 5.0 0.10 Euro-4 3.5 0.02 Euro-5 2.0 0.02

Major emission limits for diesel engine

Desulfurization Catalyst System

• Mo based catalyst system workhorse for HDS since 1940
• Ni and Co promote significant activity enhancement in the system
• Significant improvement in performance of these systems since last

decade

• Deeper insight on the active sites of the catalyst
• Understanding of the chemistry of desulfurization

To produce S free diesel conversion levels of more than 99.9% required Paradigm shift from a simple fuel processing to molecular chemical transformation

Desulfurization Catalyst System

• Dynamically evolving, flexible and versatile system
• Adapts itself in different reaction conditions

 Different feed stocks from light naphtha to Vacuum residue  Wide range of H2 partial pressures ( 5-200 bar) and H2S levels (0.5 to 10 vol%)  Temperature range of 260 – 430 oC

• Response to facilitate numerous reaction changes

 Exotic reactions like hydro dechlorination at low temperature and low H2 partial pressure  Diene saturation and isomerization at low temperature  SO2 hydrogenation at 1 bar and 300-400 C

MoOx NiO MoOxSx NiSx MoSx MoSx decorated with NiSx NiSx MoSx decorated with NiSx MoSx decorated with NiSx NiOxSx MoOxSx

Typical life cycle of HDS catalyst system

Evolution of active phase of HDS catalyst

Conversion to metal sulfides

• Finely dispersed oxides transformed

to sulfide

• Large oxide crystals do not get fully

sulfided

• Interaction of metal with support

changes

• Interaction of sulfides of Co(Ni) with

Mo to form edge decorated Co(Ni)S

• Formation of separate phases of

MoS2 and Co(Ni)S

• Migration and agglomeration of

sulfides during reaction cycle

Active phase of HDS catalyst

• Widely believed to be Co(Ni)MoS phase

 Exist as either Type-I and Type-II

• Type-II has high intrinsic activity compared to Type-I

 Type-II characterized by increased stacking and weaker support interaction  Type-I predominantly governed by stronger metal support interactions and single stack  Type-II formed at high temperature sulfiding

• Preparation methodology and sulfidation conditions

influences the nature of active sites

 Metal-support interaction  Metal loading approaches  Dispersion of active sites

Active CoMoS Phase Schematic of alumina supported catalyst (Topsoe et al)

Equilibrium morphologies in HDS condition

MoS2 phase CoMoS NiMoS

Mo Co Ni

Structure of active phase of HDS catalyst

MoS2 structure is hexagonal Mo sandwiched with hexagonal S Creates Mo edges Creates S edges CoMoS is an ensemble of MoS2 with Co (Ni) located at the edge Co(Ni) in the same plane of Mo Local coordination of Co(Ni) different depending on Mo or S edge Localized metallic states can be located at the cluster edge due to perturbation of electronic structure near edge High hydrogenation function

Chemistry of desulfurization

Two major pathways for HDS Direct desulfurization route (DDS)

Pre-Hydrogenation route (HYD)

Conversion of refractory S compounds proceeds by prehydrogenation route Presence of other compounds in feed changes relative role of HYD and DDS pathways

Nitrogen compounds mainly inhibit HYD pathway H2S mainly inhibits DDS pathway

HYD pathway favored at Mo edge (brim sites) and S edge for DDS pathway

Design of high active DHDS catalyst

• Enhance active site density

 Increase active metal loading

Surface loading in commercial catalysts in the range of <2-10 metal/nm2

 Increase active metal dispersion

Active phases with 7-8 Mo atoms corresponding to about 10 A theoretically feasible

• Prevent active site agglomeration/

deactivation

• Effective balance of hydrogenation

function for deep desulfurization

Influence of metal loading on accessible active site

DDS

• +

HYD ++ + I Type II Loading

Low High

10 20 30 40 50 60 70 80 90 100 TYPE-I (Low loading) TYPE-II (Low loading) TYPE-I (High loading) TYPE-II (High loading) DBT 4,6 DMDBT

Reactivities of different reactants are different Reactivities of reactants dependent on type of active site Increased metal loading in Type-I phase have less influence than in Type-II phase

Reactivity of DBT and 4, 6 DMDBT

Tailor the type of active phase based on feed characteristics/ operating conditions

Design of high active DHDS catalyst

INDICAT-Series of DHDS Catalyst

Active metals Ni & Mo Support

• alumina

Surface area (m2/g) > 200 Extrudate shape Trilobe Diameter (mm) 1.2 INDICAT-DH-IV Catalyst TEM of sulfided catalyst

5nm

 High dispersion of nano-crystallite active sites  Optimized distribution of high intrinsically active TYPE-II NiMoS phase

INDICAT-DH-IV Catalyst Performance: Case Studies

Case 1: SRGO feedstock and low pressure operation (49 bar) Case 2: Commercial operation at low pressure (55 bar) Case 3: Feed mix of SRGO and cracked stocks at 100 bar

Catalyst Performance

Catalyst Performance-Case-1

100 200 300 400 500 325 335 345

Relative Activity Indicat Base

Temperature, oC

Operating Conditions  Pressure 49 bar  LHSV 1.5 hr-1  H2/Oil 350 Nm3/m3

15

Catalyst performance- Case 1 (Contd…)

Feed Product Sulfur (ppm) 15000 30 Nitrogen (ppm) 185 5 Density (g/cc) 0.8466 0.8353 Aromatics (%) 27.9 18.2 Distillation(D-86)(Vol%/oC) 10 50 90 243 304 386 231 302 384

Operating Conditions  WABT 345oC  Pressure 49 bar  LHSV 1.5 hr-1  H2/Oil 350 Nm3/m3

200 400 600 50 100 150 200 Relative volume activity Days on stream

Sustained performance with deactivation rate of only <0.3 oC/month

Time-on-stream Studies

Catalyst performance- Case 1 (Contd…)

Catalyst Performance- Case 2

10 20 30 40 50 60 70 345 365 Product Sulphur, ppm Product Cetane

Temperature o C Pressure 55 bar LHSV 0.7 hr-1 H2/Oil 300-350

Feed Sulphur 1.7% Feed Cetane – 54.9

Catalyst performance- Case 2 (Contd…)

Diesel product sulfur with Time-on-stream

Sustained performance of catalyst (99% conversion) to produce low-sulfur diesel (<50 ppm) from a feed with 1.3-1.8% sulfur

40.0 45.0 50.0 55.0 60.0 65.0 70.0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 Cetane index Number of days

Product

Catalyst performance- Case 2 (Contd…)

Product cetane with time-on-stream

Feed

20

Catalyst performance- Case 2 (Contd…)

Percent desulfurization of VGO with time-on-stream

50 55 60 65 70 75 80 85 90 95 100 5 10 15 20 25 30 35 40 45 50 55

Days on Stream Percent Desulphurization Flexibility for VGO desulfurization

Catalyst Performance- Case 3

5 10 15 20 25 30 35 40 335 350 Product Sulphur, ppm Delta Cetane

Temperature, deg c Feed: SRGO/ CGO 75:25 Feed Sulphur 0.24% Feed Density 0.8857

Pressure 100 bar

Catalyst performance- Case 3

20 40 60 80 100 120 140 160 180 Sulphur Nitrogen Feed Product

1.1%

48 ppm

168 ppm

6 ppm

Feed- 85% SRGO and 15% LCO Pressure 100 bar WABT 363 deg c Cetane improvement by 6 units

Conclusions

 Considerable progress made to unravel the mystery of active phases in HDS catalyst systems  Insights on the active phases of the catalyst have led to design strategies for developing higher active catalysts.  Fundamental understanding of reaction pathways and inhibition effects have led to utilization of right catalyst systems or combinations to maximize the effectiveness  IOCL’s INDICAT series of DHDS catalysts enables upgrading diesel sulphur from 1.5-1.8% to 50/10 ppm.  Can handle wide range of gasoil feed stocks including cracked streams with high tolerance to deactivation  Commercially proven performance of the catalyst to meet BS(IV) diesel sulfur levels

