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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
0
50
100
3 16 30% N
Ox
Co
nv.
Eff
icie
ncy
S (ppm)
0
0.05
0.1
3 16 30
PM
(C
DP
F)
g/b
hp
.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
0
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
0
100
200
300
400
500
325 335 345
Re
lati
ve A
ctiv
ity
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
0
200
400
600
0 50 100 150 200
Rela
tive v
olu
me a
cti
vit
y
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
0
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
0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750
Ceta
ne i
nd
ex
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
0 5 10 15 20 25 30 35 40 45 50 55
Days on Stream
Pe
rce
nt
De
sulp
hu
riz
ati
on
Flexibility for VGO desulfurization
Catalyst Performance- Case 3
0
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
0
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
