“CoMo/NiMo Catalyst Relay” System for Clean Diesel Production
Yasuhito Goto and Katsuaki Ishida
Petroleum Refining Research & Technology Center, Japan Energy Corporation
3-17-35 Niizo-Minami, Toda, Saitama 335-8502, Japan
Abstract
“CoMo/NiMo Catalyst Relay” system is able to achieve ultra low-sulfur diesel
production (S = 50ppm or less) without major revamp of conventional deep
hydrodesulfurization unit. “CoMo/NiMo Catalyst Relay” system has been developed
based on considering reaction conditions in detail for each part in a desulfurization unit,
particularly sulfur-containing compound types to be desulfurized and catalyst
poisoning by produced H2S and NH3. Fundamental experimental results for
“CoMo/NiMo Catalyst Relay” systems are reported.
Introduction
Further tightening of diesel sulfur specifications has been decided and proposed in
worldwide. The focus of the new specifications is reduction of suspended particulate
matters (SPM) and NOx emission from diesel-fueled vehicles.
In December, 2000, Ministry of the Environment, Japan announced a new sulfur
specification for diesel fuel.
According to the specifications, the maximum
permissible sulfur content of diesel will be 50ppm from the end of 20041).
Substantially “sulfur-free” diesel (10-15ppm or less) has been proposed as future
diesel specifications.
In June, 2000, Environmental Protection Agency, USA
proposed 15ppm or less as a new diesel sulfur specification from 20062). In March,
2001, German government announced a new incentive tax policy to encourage clean
fuel supply. According to the announcement, incentive tax (0.03DM/L) is given to
10ppm or less sulfur diesel from January, 20033). EU has already accepted the new
German policy. In May, 2001, the European Commission proposed a mandatory
“zero sulfur” specification (10ppm or less) from 20114). Japan is also considering a
lower sulfur diesel specification than 50ppm1). Thus much attention is given to
effective technological solutions for ultra-low sulfur diesel, particularly sulfur-free
diesel production.
Features of HDS reaction of gas oil fraction are summarized in the following5).
(1) The feedstock contains various sulfur compounds with widely different
reactivities. Sulfides, benzothiophenes, and dibenzothiophene (DBT) (reactive
sulfur compounds) are relatively easy to be desulfurized.
Conversely,
4-methyldibenzothiophene (4-MDBT) and 4,6-dimethyldibenzothiophene
(4,6-DMDBT) (refractory sulfur compounds) are very hard to be desulfurized.
(2) Hydrogen sulfide and ammonia, gaseous products of HDS and
hydrodenitrogenation (HDN) reactions seriously inhibit HDS reaction.
(3) The reaction conditions around the inlet and the outlet of an HDS reactor are
greatly different. In the reaction zone near the inlet, both reactive and
refractory sulfur compounds coexist, and the concentrations of poisoning
gaseous compounds are relatively low. In the reaction zone near the outlet,
however, refractory sulfur compounds selectively remain, and the concentrations
of poisoning gaseous compounds are very high.
The outlook of diesel HDS is shown in Figure 1.
We have developed “CoMo/NiMo Catalyst Relay” for ultra-low sulfur diesel
production considering the above-mentioned three key points.
“CoMo/NiMo Catalyst Relay” system can achieve 50ppm sulfur diesel production
without major revamp of conventional deep HDS units. In “CoMo/NiMo Catalyst
Relay” system, the first bed catalyst is CoMo type. CoMo catalyst is the pretreatment
catalyst for ultra deep HDS over the main NiMo catalyst and plays a role of HDS of
reactive sulfur compounds such as DBT. In “CoMo/NiMo Catalyst Relay” system,
the second bed catalyst is NiMo type. NiMo catalyst is the main catalyst for
ultra-low sulfur diesel production and achieves HDS of refractory sulfur compounds
such as 4-MDBT and 4,6-DMDBT, in the presence of high concentrations of catalyst
poisoning materials such as hydrogen sulfide and ammonia.
Experimental
Catalysts
Conventional diesel deep HDS catalyst, HOP-463 (CoMo)
Conventional diesel deep HDS catalyst, HOP-413 (NiMo)
Newly developed catalyst, HOP-467 (CoMo)
Newly developed catalyst, HOP-414 (NiMo)
All the catalysts are provided by Orient Catalyst Co., Ltd.
Single-stage Hydrotreating Experiments
A fixed bed flow reactor was used for single-stage hydrotreating experiments. All
the experiments were performed under the conditions of P(H2) 5.0 MPa and H2/Oil 200
NL/L. LHSV and reaction temperature were variables to obtain various product
sulfur levels. The hydrotreating experiments were carried out after presulfiding with
diesel fuel containing CS2 (S: 1wt%). Gaseous contaminants in product oils were
removed by contacting with nitrogen gas.
Feedstock
Properties of feedstock used for the hydrotreating experiments were summarized in
Table 1.
Feed 1, Feed 2 and Feed 3 are Middle-east straight-run gas oil fraction.
Feed 4 is hydrotreated gas oil. Feed 4S (Feed 4 spiked with CS2: 1.6wt%-sulfur) was
also used to demonstrate hydrogen sulfide inhibiting conditions. CS2 is quantitatively
converted into hydrogen sulfide at the inlet of the reactor.
Analysis
Sulfur content of product oil was determined by XRF. GC-AED analysis was also
conducted to determine DBT, 4-MDBT, and 4,6-DMDBT.
Results and Discussion
Sulfur Compound Type Analysis of Different Sulfur Content Diesels
Sulfur compound type analysis was carried out in order to know what type of sulfur
compounds must be desulfurized to obtain ultra-low sulfur diesel. Table 2 shows the
analytical results of Feed 1 and product oils hydrotreated over HOP-463 (CoMo).
The case of 316wtppm total product sulfur meets the current 500ppm-sulfur
regulation. In this case, a large amount of "Refractory Sulfur Compounds" such as
4-MDBT and 4,6-DMDBT are allowed to remain. Conversely, in the case to meet the
50ppm-sulfur regulation, "Refractory Sulfur Compounds" are allowed not to remain
substantially (see total sulfur = 46wtppm). Another important information is that
"Reactive Sulfur Compound" such as DBT is substantially removed by HDS upto about
2000ppm.
Sulfur Compound Distribution in the Conventional Deep HDS Reactor
Conceptual diagram of the sulfur compound distribution in the conventional gas oil
deep HDS reactor is demonstrated in Figure 2. In the first bed of the reactor, HDS of
the "Reactive Sulfur Compounds" is perfectly carried out. As a result, a high
concentration of hydrogen sulfide is fed to the second bed of the reactor.
Achievement of 50ppm product sulfur by using conventional CoMo catalyst seems to
be hard. Effective HDS of "Refractory Sulfur Compounds" is needed in the second
bed. CoMo catalyst primarily takes Direct HDS Route. However, Direct HDS
Route is less effective for HDS of "Refractory Sulfur Compounds" than Hydrogenation
HDS Route.
Reactivities for "Reactive Sulfur Compounds"
The reactivities of CoMo and NiMo catalysts for "Reactive Sulfur Compounds" with
Feed 2 were characterized (Figure 3). HOP-463 (CoMo) showed a higher HDS
activity than HOP-413 (NiMo) under the condition of HDS upto around
2000ppm-sulfur level in product oil.
Reactivities for "Refractory Sulfur Compounds"
The reactivities of CoMo and NiMo catalysts for "Refractory Sulfur Compounds"
with Feed 4 and Feed 4S were characterized (Figure 4). HOP-413 (NiMo) showed a
higher HDS activity than HOP-463 (CoMo) regardless of CS2 spiking.
Concept of “CoMo/NiMo Catalyst Relay” 6)
Conceptual Diagram of the sulfur compound distribution in “CoMo/NiMo Catalyst
Relay” is shown in Figure 5. The first bed CoMo catalyst achieves HDS of reactive
sulfur compounds. The second bed NiMo catalyst plays a role of the main catalyst for
ultra-low sulfur diesel production. The NiMo catalyst desulfurizes “Refractory Sulfur
Compounds” in the presence of a large amount of poisoning materials such as
hydrogen sulfide and ammonia.
Performance of “CoMo / NiMo Catalyst Relay”
We have developed CoMo catalyst (HOP-467) and NiMo catalyst (HOP-414) based
on the “CoMo/NiMo Catalyst Relay” concept. Figure 6 shows that the combined use
of HOP-467 and HOP-414 is superior to HOP-463 (Conventional CoMo) to achieve
50ppm-sulfur diesel. Under the evaluation conditions, combination of HOP-467 /
HOP-414 achieves 50ppm-sulfur diesel production at 341oC, that is, 14oC lower
reaction temperature than HOP-463 does.
Conclusions
The “CoMo/NiMo Catalyst Relay” system achieves ultra-low-sulfur diesel production
(S = 50ppm or less) without major revamp of conventional deep HDS unit. The first
bed CoMo catalyst achieves HDS of reactive sulfur compounds. The second bed
NiMo catalyst plays a role of the main catalyst for ultra-low sulfur diesel production.
Literature Cited
1) http://www.env.go.jp/press/file_view.php3?serial=791&hou_id=1243.pdf
(November 1, 2000, Japanese).
2) http://www.epa.gov/fedrgstr/EPA-AIR/2000/June/Day-02/ (June 2, 2000).
3) http://www.bmu.de/presse/2001/pm599.htm (March 13, 2001).
4) http://europa.eu.int/rapid/start/cgi/guesten.ksh?p_action.gettxt=gt&doc=IP/01/681|0|A
GED&lg=EN (May 11, 2001).
5) Kabe, T.; Ishihara, A.; Qian, W. “Hydrodesulfurization and Hydrodenitrogenation
Chemistry and Engineering”, Kodansha, Tokyo (1999) and cited therein.
6)
Koide, R.; Goto, Y.; Kawabata, M.; Ishida, K. Prepr. Div. Petrol. Chem., Am. Chem.
Soc., 2001, 46, 398-401.
Table 1. Feed Properties
Item
Unit
Density@15℃
[g/cm3]
Sulfur
[wtppm]
Nitrogen
[wtppm]
Distillation (ASTM D 86)
IBP
[oC]
T10%
[oC]
T50%
[oC]
T90%
[oC]
EP
[oC]
Table 2.
Feed 1
0.8604
17160
216
Feed 2
0.8569
16230
119
Feed 3
0.8490
16900
61
Feed 4
0.8383
303
2
221.5
281.5
309.5
352.5
367.5
221.0
272.5
303.0
351.0
375.5
223.0
256.5.
287.0
331.5
347.0
229.0
272.0
301.5
337.5
357.0
Sulfur Composition of Feed 1 and Product Oils Hydrotreated over HOP-463
Sulfur [wtppm]
Total
DBT
4-MDBT 4,6-DMDBT
17160(Feed 1)
268
624
435
2230
4
137
126
316
0
11
27
46
0
0
3
Feed
S > 10,000ppm
Target Desulfurized Compounds
H2
S
Dibenzothiophene (DBT)
Easy HDS Type
H2S Rich
NH3 Rich
S
4-Methyl-DBT
(4-MDBT)
Hard HDS Type
Product
Figure 1.
S
4,6-Dimethyl-DBT
(4,6-DMDBT)
Outlook of diesel hydrodesulfurization
Feed
Easy
Hard
CoMo
H2S
Product
50
2,000
Sulfur [wtppm]
17,000
Figure 2. Conceptual diagram of the sulfur compound distribution in the conventional
gas oil deep HDS reactor.
HOP-463
HOP-413
0
1000
2000
Product Sulfur [wtppm]
3000
Figure 3. HDS activity comparison of CoMo and NiMo catalysts. (Feed 2, P(H2) 5.0
MPa, H2/Oil 200 NL/L, LHSV 2.0 h-1, Temp. 320oC)
HOP-463
Feed 4S
Feed 4
HOP-413
0
50
100
Product Sulfur [wtppm]
150
Figure 4. HDS activity comparison of CoMo and NiMo catalysts. (P(H2) 5.0 MPa,
H2/Oil 200 NL/L, LHSV 2.0 h-1, Temp. 310oC)
Feed
Easy
CoMo
Hard
H2S
NiMo
Product
50
2,000
Sulfur [wtppm]
17,000
Figure 5. Conceptual diagram of “CoMo/NiMo Catalyst Relay” for 50ppm-sulfur
diesel production.
Easy:
Reactive Sulfur Compounds including DBT
Hard:
Refractory Sulfur Compounds including 4-MDBT and 4,6-DMDBT.
1000
HOP-463
S in product, ppm
HOP-467 / HOP-414
100
50ppm
o
341 C
o
355 C
10
310
320
330
340
350
o
Reaction temperature, C
360
Figure 6. Improvement of HDS activity with “CoMo/NiMo Catalyst Relay”
Feed 1, P(H2) 5.0 MPa, H2/Oil 200 NL/L, LHSV 1.0 h-1