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 H 2 S and NH 3. 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 2004 1). 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 2006 2). 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, 2003 3). EU has already accepted the new German policy. In May, 2001, the European Commission proposed a mandatory zero sulfur specification (10ppm or less) from 2011 4). Japan is also considering a lower sulfur diesel specification than 50ppm 1). 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 following 5). (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(H 2 ) 5.0 MPa and H 2 /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 CS 2 (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 CS 2 : 1.6wt%-sulfur) was also used to demonstrate hydrogen sulfide inhibiting conditions. CS 2 is quantitatively converted into hydrogen sulfide at the inlet of the reactor. Analysis Sulfur content of product oil was determined by XRF. conducted to determine DBT, 4-MDBT, and 4,6-DMDBT. GC-AED analysis was also 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 CS 2 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 341 o C, that is, 14 o C 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 Feed 1 Feed 2 Feed 3 Feed 4 Density@15 [g/cm 3 ] 0.8604 0.8569 0.8490 0.8383 Sulfur [wtppm] 17160 16230 16900 303 Nitrogen [wtppm] 216 119 61 2 Distillation (ASTM D 86) IBP [ o C] 221.5 221.0 223.0 229.0 T10% [ o C] 281.5 272.5 256.5. 272.0 T50% [ o C] 309.5 303.0 287.0 301.5 T90% [ o C] 352.5 351.0 331.5 337.5 EP [ o C] 367.5 375.5 347.0 357.0 Table 2. 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 H 2 S Dibenzothiophene (DBT) Easy HDS Type H 2 S Rich NH 3 Rich Product S 4-Methyl-DBT (4-MDBT) S 4,6-Dimethyl-DBT (4,6-DMDBT) Hard HDS Type Figure 1. Outlook of diesel hydrodesulfurization Feed Easy Hard CoMo H 2 S Product 50 2,000 17,000 Sulfur [wtppm] Figure 2. Conceptual diagram of the sulfur compound distribution in the conventional gas oil deep HDS reactor. HOP-463 HOP-413 0 1000 2000 3000 Product Sulfur [wtppm] Figure 3. HDS activity comparison of CoMo and NiMo catalysts. (Feed 2, P(H 2 ) 5.0 MPa, H 2 /Oil 200 NL/L, LHSV 2.0 h -1, Temp. 320 o C)
HOP-463 HOP-413 Feed 4S Feed 4 0 50 100 150 Product Sulfur [wtppm] Figure 4. HDS activity comparison of CoMo and NiMo catalysts. (P(H 2 ) 5.0 MPa, H 2 /Oil 200 NL/L, LHSV 2.0 h -1, Temp. 310 o C) Feed Easy CoMo Hard NiMo H 2 S Product 50 2,000 17,000 Sulfur [wtppm] 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 HOP-467 / HOP-414 S in product, ppm 100 50ppm 10 341 o C 355 o C 310 320 330 340 350 360 Reaction temperature, o C Figure 6. Improvement of HDS activity with CoMo/NiMo Catalyst Relay Feed 1, P(H 2 ) 5.0 MPa, H 2 /Oil 200 NL/L, LHSV 1.0 h -1