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 Major spec of diesel in WWFC category 4 % NOx Conv. Efficiency 100 max 5-10 Sulfur (ppm) Aromatics (vol%) max 15 50 Polyaromatics (vol%) max 2 Density (kg/m 3 ) max 820 0 Cetane number min 55 3 16 30 Distillation Point (T90) max 320 S (ppm) ( o C) PM (CDPF) g/bhp.h 0.1 Major emission limits for diesel engine Tier No x PM g/kW.h g/kW.h 0.05 Euro-3 5.0 0.10 0 Euro-4 3.5 0.02 3 16 30 Euro-5 2.0 0.02 S (ppm) Regulatory push major driver for innovation in HDS catalysis
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 H 2 partial pressures ( 5-200 bar) and H 2 S levels (0.5 to 10 vol%) Temperature range of 260 – 430 o C Response to facilitate numerous reaction changes Exotic reactions like hydro dechlorination at low temperature and low H 2 partial pressure Diene saturation and isomerization at low temperature SO 2 hydrogenation at 1 bar and 300-400 C
Evolution of active phase of HDS catalyst Typical life cycle of HDS catalyst system MoO x S x MoO x Conversion to metal sulfides Finely dispersed oxides transformed MoS x to sulfide MoO x S x NiS x NiO Large oxide crystals do not get fully NiO x S x sulfided MoS x decorated with NiS x Interaction of metal with support NiS x changes MoS x decorated with NiS x MoS x decorated with NiS x Interaction of sulfides of Co(Ni) with Mo to form edge decorated Co(Ni)S Formation of separate phases of MoS 2 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
Structure of active phase of HDS catalyst MoS 2 structure is hexagonal Mo sandwiched with hexagonal S Creates Mo edges Creates S edges Active CoMoS Phase Schematic of alumina supported catalyst (Topsoe et al) CoMoS is an ensemble of MoS 2 with Co (Ni) located at the edge Co Ni Co(Ni) in the same plane of Mo Local coordination of Co(Ni) different depending on Mo or S edge Mo Localized metallic states can be located at the cluster edge due to perturbation of electronic MoS2 phase CoMoS NiMoS structure near edge Equilibrium morphologies in HDS condition 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/nm 2 Increase active metal dispersion Active phases with 7-8 Mo atoms corresponding to about 10 A theoretically feasible Prevent active site agglomeration/ deactivation Influence of metal loading on accessible active site Effective balance of hydrogenation function for deep desulfurization
Design of high active DHDS catalyst High DDS HYD 100 ++ - 90 DBT 80 4,6 DMDBT 70 Loading 60 50 40 30 + 20 + 10 Low 0 TYPE-I TYPE-II TYPE-I TYPE-II (Low (Low (High (High I Type II loading) loading) loading) loading) Reactivity of DBT and 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 Tailor the type of active phase based on feed characteristics/ operating conditions
INDICAT-Series of DHDS Catalyst INDICAT-DH-IV Catalyst Active metals Ni & Mo Support -alumina Surface area (m 2 /g) > 200 Extrudate shape Trilobe Diameter (mm) 1.2 TEM of sulfided catalyst High dispersion of nano-crystallite active sites Optimized distribution of high intrinsically 5nm active TYPE-II NiMoS phase
Catalyst Performance 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-Case-1 500 400 Relative Activity 300 Indicat 200 Base 100 0 325 335 345 Temperature, o C Operating Conditions Pressure 49 bar LHSV 1.5 hr-1 H2/Oil 350 Nm3/m3
Catalyst performance- Case 1 (Contd …) Feed Product Sulfur (ppm) 15000 30 Nitrogen (ppm) 185 5 Operating Conditions Density (g/cc) 0.8466 0.8353 WABT 345 o C Aromatics (%) 27.9 18.2 Pressure 49 bar LHSV 1.5 hr-1 Distillation(D-86)(Vol%/ o C) H2/Oil 350 Nm3/m3 10 243 231 50 304 302 90 386 384 15
Catalyst performance- Case 1 (Contd …) Time-on-stream Studies Relative volume activity 600 400 200 0 0 50 100 150 200 Days on stream Sustained performance with deactivation rate of only <0.3 o C/month
Catalyst Performance- Case 2 70 Pressure 55 bar 60 LHSV 0.7 hr-1 H2/Oil 300-350 50 40 Product Sulphur, ppm Product Cetane 30 20 Feed Sulphur 1.7% 10 Feed Cetane – 54.9 Temperature o C 0 345 365
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
Catalyst performance- Case 2 (Contd …) Product cetane with time-on-stream 70.0 Product 65.0 60.0 Cetane index 55.0 Feed 50.0 45.0 40.0 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 Number of days
Catalyst performance- Case 2 (Contd …) Percent desulfurization of VGO with time-on-stream 100 95 Percent Desulphurization 90 85 80 75 70 65 60 55 50 0 5 10 15 20 25 30 35 40 45 50 55 Days on Stream Flexibility for VGO desulfurization 20
Catalyst Performance- Case 3 40 Feed: SRGO/ CGO 75:25 Feed Sulphur 0.24% 35 Feed Density 0.8857 Pressure 100 bar 30 25 Product Sulphur, ppm 20 Delta Cetane 15 10 5 0 Temperature, deg c 335 350
Catalyst performance- Case 3 Pressure 100 bar Feed- 85% SRGO and 15% LCO WABT 363 deg c 180 1.1% 160 168 ppm 140 120 100 Feed 80 Product 60 48 ppm 40 6 ppm 20 0 Sulphur Nitrogen 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
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