Centinel Technology catalysts for distillate desulphurisation:
Science and Applications
T.J. Remans (*), W.H.J. Stork (*), J.A.R. van Veen (*),
A. Gabrielov (°), B.J. van der Linde (#),
J. Swain (+), D. di Camillo ( %) and R.S. Parthasarati ( !).
+
(*) Shell International Chemicals BV
(#) Shell Global Solutions International BV
Shell Research and Technology Center,
Amsterdam,
Badhuisweg 3, 1031 CM Amsterdam,
The Netherlands
(° ) Shell Chemicals LP
Westhollow Technology Center
3333 Highway 6 South, Houston, TX 77082,
USA
( ) Criterion Catalysts & Technologies
1650 Parkway, The Solent Business Park,
Whiteley, Fareham, Hampshire, PO15 7AH,
England
%
( ) Criterion Catalysts & Technologies
16825 Northchase Drive, Suite 1000
Houston, Texas 77060-6029, USA
!
( ) Criterion Catalysts & Technologies
298 Tiong Bahru Road
#07-03/04/05 Tiong Bahru Plaza
Singapore 168730
1. Introduction
Refineries convert a wide range of crude oils into products, such as transportation fuels
and feedstocks for petrochemical industries. Conversion processes, among which
hydroprocessing, play a key role in modern refineries, removing heteroatoms and
changing chemical structures. In the drive towards clean fuels, tightening product
specifications pose increasing challenges to the refiners. For improvement of the
hydroprocesses, in addition to the development of better catalysts, based on mechanistic
research, attention is being given to technology improvements as well.
In September 2000, CC&T introduced its new catalyst technology, Centinel, for refinery
hydroprocess applications. Both CoMo and NiMo type catalysts were launched
simultaneously in distillate HDS, First-Stage Hydrocracking (FSHC) (DN-3120, DN3100) and Cat feed Hydrotreating (CFH) (DC-2118, DN-3110). At present, more than
100 batches of Centinel catalysts have been sold, in a combined amount of over 20 MM
lbs, for applications in distillate HDS, First Stage Hydrocracking and Cat cracker Feed
Hydrotreating. Centinel technology catalysts generate much higher value in a world of
ever-tightening specifications, as the performance advantages of Centinel over
conventional catalysts, already important at deep desulphurisation levels, will increase
strongly upon Ultra Deep desulphurisation.
In the present paper the focus is on the novel catalyst technologies and on a better
understanding of the chemistry involved. In order to derive the maximum benefits out of
high performance catalysts, also the reactor designs and process conditions should be
optimized. It is essential to use an optimized combination of catalysis and reactor/process
technology to arrive at optimum results in demanding applications such as Ultra Deep
HDS. In the present paper, however, we will strongly focus on the catalysis aspects and
only briefly deal with optimized reactor design.
-1-
2. Future specifications
Ever tightening product specifications continue to pose increasing challenges to the
refiners. In the European Union, the sulphur specification for automotive gasoil has
steadily decreased from 3000 ppmw S in 1989 to 2000 ppmw in 1993, 500 ppmw in
1996 and 350 ppmw in 2000. Other diesel specifications, e.g. for ceta ne, density, T95
and Di+ aromatics have also tightened during these years. In the near future, the
specification for sulphur will continue to decrease to 50 ppmw S by 2005 (Auto Oil II
program) and sub 10 ppmw S by 2008-2011 (Clean Air For Europe or “CAFE”
initiative). The US mandates 15 ppmw S for diesel by the year 2006. Gasoline sulphur
specifications are not discussed here but in general follow the same trend. The paper
focuses on diesel application only. The complete overview of past and future
specifications for diesel as specified by the European Union is given in Table 1.
Table 1: Diesel specifications as specified by the European Union
1989
1993
1996
2000
2005
2008-2011
(AO-I)
(AO-II) (CAFE*)
3000
2000
500
350
50
"0" (< 10)
S, ppmw
860
860
860
845
845
845
d 15/4, kg/m3
49
49
49
51
51
51
Cetane No
370
370
370
360
360
360
T95, °C
11
11
11
Di+ Arom., wt%
*: Press release Dec 2001 states a compromise has been made on CAFE specs between
the 2008 and 2011 targets and the new data for total implementation would be 2009,
phased-in from 2005 onwards.
A strong drive for reducing sulphur in diesel even before the European Unions legislation
becomes effective comes from tax incentives set by specific states. A recent overview of
current and proposed tax incentives for low sulphur diesel is presented in reference 1.
3. Increased workload
For an average EU refinery feedstock containing 1.2 wt% S, the tightened S-specification
from 3000 to 10 ppmw S implies an increase in HDS conversion level from 75 % to
99.92 %. A graphical presentation of the S-specification and concomitant HDS
conversion level, see Figure 1, suggests that the largest steps were taken in the past and
future specifications seem to require only a marginal increase in conversion. A more
accurate way of illustrating the effect of the tightening S-specifications on the HDS
reaction is by calculating the workload on the catalyst, as given in Figure 2. The
workload quantifies the required additional catalyst volume to reach the tightened
specifications for a given existing HDS unit, the feed it processes and the catalyst loaded.
Now, it becomes clear that there is a continuous and steady increase in the workload of
the HDS catalyst over the years. On average, every new specification has increased the
workload by a factor of about 2. Or in other words, the catalyst activity had to increase
each time by a factor of about 2 to achieve the new specification. In total, a 20 times
increase in workload is required to go from the 1989 specification to the 2011
specification. It is clear that only catalyst improvements will not get us there.
-2-
100
HDS conversion
S-spec (ppmw S)
2500
95
2000
90
1500
85
1000
80
S-specification
500
0
1985
75
1990
1995
2000
2005
2010
HDS conversion (%)
3000
70
2015
Year
Figure 1: EU S-specification and associated HDS conversion level for a 1.2 wt%
S feed.
100
Workload on catalyst
(Log scale)
HDS conversion
95
90
10
85
80
Workload
1
1985
1990
1995
2000
2005
75
2010
HDS Conversion (%)
100
70
2015
Year
Figure 2:
HDS conversion level for a 1.2 wt% S feed to reach the imposed EU
specification in the given year and associated workload on the HDS
catalyst.
These large increases in workload ask for an optimum match between the use of high
performance catalysts as well as customer specific unit modifications. To bridge the gap
from one workload level to the next, one can apply higher activity catalysts, upgrade the
technology by e.g. installing Shell Global Solutions’ High Dispersion (HD) trays or
expanding in reactor volume. The first step –the drop-in solution of a more active
catalyst- was sufficient when going from 3000 to 2000 ppmw S. The step from 2000 to
500 ppmw S in 1996 required additional measures to reach the new workload level.
Improving the gas/liquid dispersion and catalyst wetting becomes more critical as the
specifications tighten. The installation of an HD tray can on average yield a 30 % higher
-3-
catalyst activity as well as a reduced deactivation rate. The combined effect of these two
effects results in a reduction of the workload by 50 %. More details on the technology
improvements can be found in paragraph 7. The remaining gap between effective
workload and required workload will have to be –and historically has been- bridged by
expanding reactor volume. Figure 3 shows to what extent each of these factors contribute
to reaching the increased workload levels. Taking into account the activity level of the
catalysts in the specific time frames, Figure 3 shows that the gap requiring reactor
extension has been reduced upon going from 1996 to 2000. Improvements in catalyst
activity outpaced the increase in required workload such that the step from 500 to 350
ppmw S could easily be met by a drop-in solution of a newer generation catalyst. From
Figure 3, it becomes also clear that this gap becomes much larger again when targeting
the 2005 specifications of 50 ppmw S with the current generation of highest performance
catalysts. Based on the integrated approach required here, CC&T’s Clean Fuels Team is
specialized to help out by creating customer-tailored solutions for achieving both the
2005 and 2011 specifications, considering both process and catalyst options.
Workload on catalyst
(Log scale)
100
Required Workload
Remaining Gap:
Capacity expansion
10
Workload after
Installation of HD tray
Workload after
Catalyst improvement
1
1985
Figure 3:
1990
1995
2000
Year
2005
2010
2015
Bridging the gap between required workload and existing by
applying more active catalysts and installing a HD tray.
-4-
4. Catalyst improvements
Recent advances in hydroprocessing catalyst development by CC&T have taken a high
flight in a field that is already decades old. The large log scale in Figure 3 masks this
somewhat, but when expressed on a natural scale, it becomes clear that we are on the
steep edge of a new S-curve in catalyst development for refinery applications, see Figure
4.
Relative activity of HDS catalysts
260
240
220
Centinel
200
180
160
Conventional
140
120
100
1985
1990
1995
Year
2000
2005
Figure 4: Recent advances in hydroprocessing catalyst development.
This has been achieved by the fast track development of a new way of producing
hydroprocessing catalysts, named CC&T’s Centinel Technology. The combination of this
new technology and the knowledge already built up on conventional type catalysts yielded
a remarkable series of catalysts with optimized pore structure, metals dispersion and
active phase selectivity. An example would be improved hydrogenation activity.
Without being in a position to offer catalyst preparation details, the Centinel technology
leads to catalysts that are very different to the conventional hydroprocessing catalysts.
This difference is schematically shown in figure 5, where a Centinel catalyst is compared
with a conventionally prepared one with the same composition. The following detailed
characterization studies should underpin these conclusions.
-5-
Centinel versus conventional on fundamental level
Centinel:
Highly dispersed
MoS2 Type II
Conventional:
Normal dispersed
MoS2 Type I
HO
HO
Al
O
Al
O
Al
HS
S
Mo
O
S
Mo
S
Mo
O
HS
O
S
S
S
SH
O
Mo
Mo
Al
Al
Al
Al
SH
S
Al
S
O
O
O
O
Al
O
Al
O
Al
Al
O
O
Al
Al
Al
Al
MoS2 bonded to alumina via O-bridges
à Not 100 % sulfided
à Conventional activity
MoS2 without O-bridges
à 100 % sulfided
à Higher HDA, HDS and HDN activity
Figure 5: schematic representation of Centinel catalysts
In the hydrotreating Co(or Ni)/Mo catalysts the active metals are largely present in
sulphided form, specifically as layers of MoS2 (MoS2 has a layered structure) promoted
with Co or Ni; these latter are considered to be the active sites (ref. 2). Electron
microscopic studies on CoMo catalysts show (figure 6) that, as indicated, the size of the
MoS2 layer in the DC 2118 Centinel catalyst is smaller than in the DC 130 conventional
one, while the number of layers tends to be larger.
Catalyst
DC-130 Reference
Average slab size (nm)
Average stacking
Base
Base
Base – 21 %
Base – 4 %
DC-2118
Figure 6: electron microscopic results of DC 2118 Centinel catalyst
This is due to the deliberately selected catalyst recipe, where the interaction between the
alumina support and the active metals during preparation is closely controlled. As a
consequence, the metals are more completely sulphided than in conventional catalysts
(see figure 5). Evidence for this is shown in figure 7, where X-ray photoelectron
spectroscopic measurements (XPS) were carried out on conventional and Centinel
catalysts after various sulphidation treatments, showing that clearly in the Centinel
catalyst the sulphidation proceeds faster, further than in the conventional catalyst. In
addition, Temperature Programmed Sulphidation (TPS) studies were carried out on
conventional and Centinel catalysts: results are given in figure 8, and show that in
Centinel catalysts, molybdenum is quickly converted to a MoS 3 intermediate species,
while in conventional catalysts it is directly, but less completely, converted to MoS 2.
-6-
85 % (68 %)
100 % (84 %)
68 % (46 %)
65 % (44 %)
68 % (62 %)
As is
57 % (41 %)
As is
Figure 7: Temperature Programmed Sulfidation of Centinel NiMo.
Percentage of sulfided phase indicated for both Centinel and
conventional catalysts (conventional value in brackets).
Inset: S-uptake and release for conventional catalysts
Applied T ramping
S-uptake and release for Centinel
Heat release upon activation (same as for conventional)
Figure 8: Temperature Programmed Sulfidation for Centinel versus conventional
in inset (same scale) demonstrating the typical Type II behaviour of
high S uptake by Mo VI to MoS3 prior to reduction to MoS2 .
-7-
Centinel
Conventional
Figure 9: NO-chemisorption on Centinel and conventional catalyst showing the
same types of sites and also the higher amount of Co at the MoS 2 edges
relative to the available sites.
As shown in figure 5, this means that the Centinel catalyst has a structure that brings about
a large fraction of so-called type II sites, but does not appear to involve any new or
unconventional type of sites. This is also the conclusion that is drawn from in-situ IR
studies, using NO as a probe gas. Figure 9 shows the spectra typical of NO adsorbed to
the Co on MoS2 and to vacant MoS2 sites, and do not indicate any novel type of site. The
magnitude of the peak at 1850 cm-1 underlines the high number of active sites relative to
the available sites at the MoS 2 edge.
In conclusion, taking all fundamental characterization results together, one arrives at
figure 5, showing very well dispersed metals, well sulphided, with a high proportion of
type II sites.
-8-
5. Chemistry of desulphurization
The chemistry of hydrodesulphurization has been studied in recent years extensively. With
the detailed analysis of sulphur compounds that is now possible by element selective
detection in a GC, or even better, using two-dimensional GC, (ref. 1), we can now
identify the most refractory compounds (figure 10a,b), the alkyl substituted
dibenzthiophenes.
2
5
C
F
2
0
1
5
1
0
n
B
e
d
A
T
n
M
t
C
e
1
k
0
0
1
.
3
6
2
0
0
0
2
5
6
1
2
5
2
0
1
5
1
0
3
* *
*
**
o
l
t
s
2
h
e
4
V
S
S
c
oc
no
cn
ec
ne
t
n
tr
ar
ta
it
ion
o
5
n
5
0
0
0
1
0
2
0
3
0
4
0
5
M
C
h
0
9
5
6
n
7
B
-
H
D
A
n
S
-
t
2
e
1
i
n
0
u
6
t
e
0
7
Boiling point
Boiling point
0
8
s
0
9
0
k
3
9
-
B
-
5
2
.
2
2
.
2
2
.
0
2
.
0
1
.
8
1
.
8
1
.
6
1
.
6
1
.
4
1
.
4
1
.
2
1
.
2
1
.
0
1
.
0
0
.
8
0
.
8
V
V
o
o
l
l
t
t
s
s
2
0
1
0
2
0
3
0
4
0
5
M
i
n
u
0
t
6
e
0
7
0
8
0
9
0
s
Figure10a: S-distribution of a European refinery gasoil.
Figure10b: S-distribution of liquid product after HDS down to 75 ppmw S.
Examples of identification:
*: 4,6-dimethyldibenzothiophene
**: 4-methyl, 6-ethyldibenzothiophene
There are strong indications that the mechanism for the refractory compounds is different
to that for the other compounds: “”easy sulphur”” reacts via direct desulphurization, the
substituted dibenzothiophenes react via prior hydrogenation of an aromatic ring (figure
11).
-9-
Alternative
HDS route
S
CH3
H3C
CH3
Usual
Indirect
HDS
Ring opening
S
CH3
CH3
H3C
CH3
CH3
CH3
CH3
CH3
HYD
Direct
HDS
S
CH3
Isomerization
H3C
CH3
Alternative
HDS route
H3C
S
CH3
CH3
Subst.
Alternative
HDS route
S
CH3
CH3
Figure 11: Overview of possible pathways for the HDS of highly refractive Scompounds.
Originally this was attributed to steric hindrance of the sulphur atom; at present it rather
seems caused by the electronic factors (ref. 3).
The overall conclusion remains, however, that deep desulphurization requires prior
hydrogenation, and is hence effectively done on CoMo catalysts with a high proportion of
type II sites. Indeed, at equal conversion different product distributions are obtained over
different catalysts, indicating different relative contributions of both reaction pathways
(table 3). As can be seen, Catalyst B is more effective in removing the most refractive Scompounds than Catalyst A such that the former catalyst is preferred for deeper
conversion levels as the last S-compounds are all highly refractive. The overall HDS
activity is the same for the applied catalyst formulations, but the selectivity is
significantly different. Alternatively, NiMo catalysts, preferably also with a high type II
site content, can be used.
-10-
Catalyst
CoMo A
CoMo B
Ratio of highly refractive DBT over less refractive DBT
10.8
7.4
Table 3:
Example of changed ratio of S-compounds at comparable
conversion level applying two CoMo based HDS catalysts
It has also become clear that in HDS the catalyst is easily poisoned. A detailed study in
our laboratory (ref. 4) showed that basic nitrogen compounds are really the main catalyst
poisons. In Figure 12 the catalyst activity for HDS of dibenzothiophene in a gasoil matrix
is shown as a function of the basic nitrogen content, and clearly the HDS activity suffers
substantially at basic nitrogen levels of 5-20 ppm.
1400
-dS/dt (ppmw S/min)
1300
1200
1100
CoMo
1000
NiMo
900
800
700
0
5
10
15
20
Nbasic content of feed (ppmw)
Figure12: DBT conversion activity as a function of basic nitrogen content.
As nowadays the nitrogen compounds can also be separated (as for sulphur), as shown in
figure 13; one may expect that detailed identification of the nitrogen compounds at various
stages in the process (conversion of more reactive species, intermediate hydrogenated
compounds) will add further to our understanding. References for detailed identification
of these N-compounds can be found in Reference 7.
One interesting point in this respect is the observation that at comparable HDN
conversion level, Centinel catalysts remove more of the most difficult N-compounds than
conventional catalysts do. This is shown in Figure 13 as the surface area under the curve
between the two vertical bars that demarcate the region of the highly refractive Ncompounds. For both Centinel catalysts, this area is significantly smaller than for the
conventional catalyst at the same N-slip. Therefore, Centinel catalysts are not only for
HDS but also for HDN more non-selective in the removal of the normal, refractive and
highly refractive S- and N-compounds yielding a higher conversion of the more difficult
S- and N-species at comparable conversion levels. This makes them especially attractive
for attacking those final highly refractive S- and N-compounds.
-11-
DN-3110
DC-2118
DC-130
Figure 13: Separation of N compounds in hydrotreated gasoil by N-specific
chromatography for Centinel NiMo (DN-3110), Centinel CoMo (DC2118) and conventional CoMo (DC-130) at about 20 ppmw N level in
liquid product.
Thin lines indicate drift in base line.
Vertical thick lines demarcate region of highly refractive Ncompounds.
Separately, a study showed that extraction of nitrogen compounds from a gasoil results in
a product that was clearly easier to desulphurize. (ref. 5).
In contrast with the effect of nitrogen compounds, the presence of polyaromatics is not
very harmful, as can be seen from figure 14 (ref. 4).
350
S content (ppmw)
300
250
200
150
100
50
0
Low S feed
+ PCAs
Figure14: Effect of poly cyclic aromatics on HDS activity
Basis the above results the differences between conventional CoMo and NiMo catalysts
in the gasoil HDS are easily explained: the CoMo catalysts are the more active for HDS,
but the NiMo catalysts, with their higher HDN activity, can be preferred at times: in a
stacked bed NiMo over CoMo, or with high N/cracked feeds at higher pressures.
-12-
Interestingly enough, data in ref. 4 suggests that at very deep HDS, possibly where the
hydrogenation reaction path prevails, NiMo catalysts are more active than CoMo
catalysts, even on (synthetic) feedstocks without any N compounds. The results reported
in ref. 4 were obtained on conventional catalysts; with the high proportion of type II sites
in the Centinel catalysts, one would expect the NiMo and CoMo catalysts to come a little
closer in performance (as reported in ref 1).
Next to the above poisoning effects, it has also been shown that at the production of Ultra
Low Sulphur Diesel (ULSD), effects of apparent thermodynamic constraint can easily
play a role. Under certain conditions, with increasing temperature the effective activation
energy decreases. A similar effect has been observed in denitrogenation over
NiMo/alumina catalysts, and has been attributed to the shifting between e.g. the
substituted acridines and their hydrogenated counterparts, well-known intermediates in
the denitrogenation reaction (ref. 6). In ultra deep HDS similar effects are observed:
under specific conditions (low pressure, cracked feedstocks, etc) the increase in reactor
temperature does no longer result in the rate increases expected basis the traditional
activation energy. A real example of the onset of thermodynamic limitation at low PP(H2)
in targeting sub 50 ppmw S (Ultra Deep-HDS) is presented in Figure 15. Here, 3
conditions on a typical European refinery feed after more than 2000 h on stream time are
highlighted out of a long lab experiment on DC-2118. Condition 1, the base condition,
yields a S-slip of 25 ppmw at low pressure and medium temperature. In condition 2, all
conditions remained the same except for the temperature that was significantly increased.
With a S-slip still as high as 21 ppmw in the new condition, it is clear that the
temperature response at low pressure in UD-HDS is lower than anticipated. The
normalized k-value indicates a 35 % lower response. Increasing the H2 partial pressure,
as done upon going from condition 2 to 3, shows that more than half of the lower response
has now been removed. After correcting the k-value for the temperature only, the k-value
now is higher than in condition 1 but upon including the pressure correction as well, it
still hasn’t reached the activity level of condition 1. A higher PP(H2) shifts the
thermodynamic limitation to lower concentrations (actually ratio’s of concentrations) such
that the pure kinetics become the major player again. The thermodynamic limitation on the
aromatics is reflected in the change in di+ aromatics, also in Figure 10. The first
condition was repeated at the end to ensure that deactivation could be ruled out as a
cause.
-13-
S-slip, ppmw
50
Low P,
Medium T
Low P,
High T
Medium P,
Low P,
High T
Medium T
24
S-slip
20
40
16
30
12
k-value
60
k at norm.
WABT
20
8
k at norm.
WABT and
PP(H2)
10
4
wt% di+
Aromatics
0
0
1
2
3
Condition No
1
Figure 15: Thermodynamic effects in deep HDS
The effect has severe consequences, in that a higher reaction temperature becomes a less
effective tool to reach ultra deep sulphur levels, making such levels unattainable in a
number of existing low-pressure units except by means such as severely reducing the
endpoint of the feedstock.
6. Performance of Centinel catalysts
In chapter 4 it was established that Centinel catalysts predominantly have type II active
sites, which are known to have higher selectivity to hydrogenation and
hydrodenitrogenation than type I sites (ref. 2). In chapter 5 the chemistry of deep
desulphurization was reviewed, highlighting the importance of an indirect
desulphurization route in deep HDS, and the poisonous effect of nitrogen compounds
under those conditions. In addition, it emerged that apparent thermodynamic effects can
limit the reaction rate at high reaction temperatures.
Figures 16, 17 and 18 show the performance of the Centinel CoMo 2118 catalyst in HDS
and HDN, and at various HDS levels. The catalyst has a higher selectivity to HDN than a
conventional CoMo catalyst (DC 130, also supplied by Criterion), and shows it largest
activity benefit at very deep HDS levels, where we have seen the effects of nitrogen
poisoning and of the hydrogenation step required in the indirect route. With the limited
response to temperature in mind, these catalyst activity gains are of course of paramount
importance in commercial units to achieve the required sulphur target at an acceptable
catalyst life.
-14-
280
260
240
220
RVA (%)
200
RVA HDS
RVA HDN
180
160
140
120
100
80
DC-130
DC-2118
DN-3110
Figure 16: RVA for HDS and HDN of Centinel CoMo (DC-2118 and Centinel
NiMo (DN-3110) versus conventional CoMo (DC-130)
SRGO Feed, medium PP(H 2 ), high LHSV, S-slip around 200 ppmw S.
200
180
RVA (%)
160
140
RVA HDS
120
100
80
DC-130
DC-2118
DN-3110
Figure 17: RVA for HDS of Centinel CoMo (DC-2118 and Centinel NiMo (DN3110) versus conventional (DC-130). N-slip around 0 for both
Centinel catalysts.
SRGO Feed, medium PP(H 2 ), low LHSV, S-slip around 10 ppmw S.
-15-
HDS improvement vs Conventional, °F
+ 27
+ 18
+9
Base
S-slip
Figure 18: HDS activity improvement of Centinel over conventional catalysts as a
function of S-slip.
The good performance of DC 2118 shown in laboratory testing is also confirmed by
commercial experience. Figure 19a shows the performance of DC2118 (in combination
with a conventional CoMo catalyst, DC 185) in ultra deep HDS, with a clear
performance gain over the previous conventional catalyst, giving products with sulphur
contents between 10 and 50 ppm. Figure 19b gives commercial results for a unit with DC
2118 and DN 3110 producing consistently sub-10 ppm S.
CENTINEL USER f: FSU
FEED & PRODUCT SULPHUR
1
250
225
Heat exchanger leak
Feed Sulphur (wt%)
0.8
200
0.7
175
0.6
150
0.5
125
0.4
100
0.3
75
0.2
50
0.1
25
16.0
0
10.0
13.0
10.0 10.0
0
50
Product Sulphur (ppmw)
0.9
100
150
200
250
0
300
Days on oil
Feed
Product
Figure 19a: Commercial performance of DC-2118 (with some DC-185) at 35
ppmw S.
-16-
CENTINEL USER D - EUROPE
400
Temperature (oC)
380
360
340
320
300
280
0
50
100
150
200
250
300
350
Days on Oil
WABT
NWABT HDS
Figure 19b:Commercial performance of DC-2118 (with some DN-3110) at 8
ppmw S.
D N -3 1 1 0
Centinel
D C -185
NiMo
D C - 2118
Centinel
CoMo
Medium
Low
H2 Partial Pressure
High
As was pointed out above, NiMo catalysts become more and more attractive when going
to lower Sulphur levels, to increasing amounts of cracked feedstocks, and to higher
hydrogen pressures. Figure 20 schematically shows at what conditions the Centinel NiMo
catalyst DN-3110 is better than its CoMo analogue.
D C -1 8 5
Ultra High SA
CoMo
Potentially
Thermodynamically Ltd
Technology Solution Required
10
50
Product Sulfur ppmw
Figure 20: Application area for full bed CoMo or NiMo as a function of S-level
and PP(H 2).
-17-
500
Upon targeting sub 15 ppmw S (US market) and sub 10 ppmw S (EU market), it will
become crucial to fully understand the kinetics of the various reaction pathways in
distillate HDS. In general, the discussion usually revolves around the direct and indirect
HDS reaction pathway, the indirect pathway being the one in which full hydrogenation of
the neighboring aromatic ring precedes the S-removal step. Figure 11 gives an overview
of all theoretically possible pathways to remove sulphur from a highly refractive Scompound in hydrodesulfurization. The normal HDS pathway for the non-refractive Scompounds is via direct HDS, this in clear contradiction to HDN where the indirect
pathway is always followed due to the stronger C-N bond in the aromatic ring structure.
For removal of the last refractive S-compounds, the indirect reaction pathways, with
aromatics hydrogenation as a first step, are crucial.
7. Technology improvements
CC&T and Shell Global Solutions have successfully demonstrated on numerous
occasions that the net reactor performance can be increased up to50% at a fraction of the
investment cost of a new vessel and with implementation within a matter of months
(typically during next planned shutdown). Consider the example in Figure 21 which
demonstrates that improved space utilization can either result in (1) construction of a 20%
smaller reactor if considering a grassroots design or ( 2) a 28% increase in catalyst
volume within an existing vessel.
Shell Design Increases
React or Volume utilizat ion:
drawn to scale
Typical Open Art
Vessel design:
100 m 3 vessel
67 m 3 catalyst
67% vol utilisation
Shell Design: Sam e
Catalyst Volum e
80 m 3 vessel
67 m 3 catalyst
84% vol utiliz ation
Shell Design:
Sam e Vessel Siz e
100 m 3 vessel
86 m 3 catalyst
86% vol utilisation
Figure 21: Improved reactor space utilization can decrease size of a reactor
design or increase available catalyst volume in an existing vessel.
Maximum catalyst utilization can only be achieved if the gas and liquid reactants are
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uniformly distributed both volumetrically and thermally before they are introduced into
the very top of each and every one of the catalyst beds. As mentioned previously, even
some designs as recent as the late 1990’s don’t use distribution trays that have high
dispersion. Shell High Dispersion (HD) and Ultra Flat Quench (UFQ) trays have been
developed to incorporate the use of the unique HD nozzles that attain near 100% catalyst
utilization for trickle phase reactors. The HD tray is of the latest proprietary Shell design,
creating an almost perfectly uniform liquid distribution as depicted in Figure 22. The
UFQ in turn additionally provides nearly perfect mixing of process liquid and gas, and
quench medium between the beds, while using minimum reactor volume. Compared with
many distribution trays being offered today, the Shell internals can boost the catalyst
utilization from 80 to nearly 100%, generating an equivalent improvement in activity of
25% RVA HDS or 7°C.
Conventional Tray
va pour
Bubble Cap Tray
va pour
Grading Material
Shel l HD Tray
vapo u
No Grading Materi al
Al l Cat al yst Bed
Cat al yst Bed
Figure 22: Visualization of distributor tray flow patterns
8. Conclusions
The paper focused on the need for optimally using existing distillate HDS units for
achieving the ever-tightening sulphur specifications. The huge increase in workload both
in the near past and future quantifies this need.
Recent catalyst development by CC&T has led to the commercialization of the Centinel
technology catalysts that maximize the HDS conversion level with balanced H 2
consumption. Currently, 36 distillate HDS units have been started-up with Centinel
Technology catalysts. In distillate, as well as in other catalytic processes as CFH and
FSHC, clear advantages over conventional catalyst systems have been demonstrated.
Centinel catalysts have been thoroughly characterized; given the fact that the Centinel
catalysts are rich in type II sites, their performance could be well understood.
In most cases, a drop-in catalyst option is not enough to reach the increased workload
levels, especially when targeting 50 or 10 ppmw S. Thermodynamics will start to play an
important role which can result in higher than expected start-of-run WABTs as well as in
a less efficient use of the available operating window.
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RVA (%)
Relative Catalyst Volume Activity (RVA) of commercially produced
catalysts for Hydrodesulfurisation (HDS) of diesel range gasoil
600
Explorative samples
500
Legislation
changes
400
300
200
Commercially produced
100
0
1980
1985
1990
1995
2000
2005
Year
Figure 23: Novel catalysts currently being developed.
In addition to the catalyst, the need for perfect gas/liquid dispersion as well as for
complete wetting of the catalyst bed becomes increasingly more important to reach the
required workload level. The use of HD trays was shown to bridge a major part of the
gap between available workload and required workload for the new specifications. It
should be clear that the combination of an optimum catalyst and prime technology know
how will be crucial for implementing the future sulphur specifications.
Of course catalyst research does not stop, and, using fundamental insights as presented
here, several new and improved catalysts are currently under development (figure 23).
These will help the refiner to manufacture the 10 and 50 ppmw S products in existing
units with their existing constraints.
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2010
9. References
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J. Swain, D. di Camillo and R.S. Parthasarati, Centinel Technology catalysts for
refinery hydroprocess applications: Recent advances in the HDS catalyst
portfolio of Criterion Catalysts & Technologies and the integrated approach
with optimum process conditions and reactor internals. European Catalyst and
Technology Conference (ECTC), February 26-27, 2002, Amsterdam, The
Netherlands (2002).
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and J.A. Moulijn, On the difference between gas- and liquid phase
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[5] M. Macaud, E. Schulz, M. Vrinat and M. Lemaire , A new material for selective
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[7] P. Wiwel, K. Knudsen, P. Zeuthen and D. Whitehurst, Assessing Compositional
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G.C. Laredo, S. Leyva, R. Alvarez, M. T. Mares, J. Castillo and J.L. Cano,
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