(39b) Advanced Hydro-Desulfurization Catalysts for Hydrocarbon Fuels

Sulfur is a natural component in crude oil and therefore is also present in diesel and other hydrocarbon fuels. All of the on-highway diesel fuel sold at gas stations in the United States is ultra-low-sulfur diesel (ULSD), for which the allowable sulfur content is 15 ppm. Meanwhile, the International Maritime Organization (IMO) has decided to cut the allowable sulfur content of marine bunker fuels from 3.5 to 0.5%, and this new sulfur cap will be implemented from 2020.[1] Consequently, refineries are facing major challenges to meet this fuel sulfur specification. In this study, Advanced Energy Materials, LLC. (ADEM) developed a group of metal oxides alloyed nanowires catalysts for removal of thiophenic sulfur from liquid fuels through hydrodesulfurization (HDS) process. The operation conditions of this process are milder than the typical conditions applied in industrial applications. The metal oxides alloyed nanowires consist bimetals or trimetals from Ni, Co, Mo, W and Cu. These alloy nanowires can be used directly unsupported or supported on the high surface area substrates such as porous alumina or titania for various HDS applications. The presence of alloyed phase nanowires highly improved the HDS activity and reduced the sintering effect. Consequently, the sulfur removal efficiency increases. For small to medium scale oil refineries, the newly invented catalyst products strongly help them to meet the EPA regulations of sulfur level in fuels. For the IMO 2020 regulation, this new catalyst product is highly active on the toughest refractory sulfur species, so it will benefit on the deep desulfurization of the marine diesel, gas oil, fuel oil and their segregation.

ADEM’s patented technology of making metal oxide and mixed metal oxide nanowires is used to make highly active HDS catalysts. The composition of mixed metal oxide nanowires was controlled. On average, the diameter of the NWs ranges from 10 to 50 nm, and the length is 200-1000 nm. This method is highly scalable and ADEM has extensive experience on the customized catalyst formulation, extrusion, packaging and transportation.

For the HDS activity testing, Ni-Mo-O3 alloy nanowires (AdE-Scat-200) mixed with high surface gamma alumina, and extruded into 1.25 to 3 mm diameter extrudates in cylindrical and trilobed shapes. 50 to 100 gram catalyst extrudates was mixed with inert material and then packed in the high pressure fixed-bed reactor. The feed contains 1100 to 3400 ppm sulfur including thiophene and refractory sulfur compounds such as benzothiophene, dibenzothiophene, methyl dibenzothiophene and 4,6-DMDBT. Table 1 summarized the HDS activity testing results of different catalysts. AdE-Scat-110 is another HDS catalysts product developed by ADEM, using conventional co-impregnation method. The alloyed NiMo nanowires based product (AdE-Scat-200) shows excellent ultra deep desulfurization performance under much lower pressure comparing to the commercially available HDS catalysts.

Table 1. Summary of HDS testing results using ADEM catalyst formulations (AdE-Scat series)

Catalyst	Synthesis	Time on stream (h)	Temperature (C)	Pressure (bar)	Sulfur outlet (ppm)
AdE-Scat-201	Alloyed NWs	200	350	15	40±10
AdE-Scat-200	Alloyed NWs on high SA alumina	200	350	15	12±5
AdE-Scat-110	Co-impregnation on NWs	200	350	20	15±10
A commercial catalyst NiMo-Al2O3)	Commercially available	200	400	30	55±10

Significance

The use of alloyed nanowires as HDS catalysts has multi-fold advantages for catalyst applications: (1) allows for uniform and high level of dispersion; (2) the single-crystal nature and faceting improves the properties of the alloyed catalytically-active metals; (3) an ability to produce well-defined surface facets yields a higher concentration of desired sites; (4) the nanowire morphology presents an easier diffusion pathway for sulfur transfer from supported clusters to the underlying support, thereby maintaining a high surface concentration of active nickel and other precious metallic sites for deep desulfurization and hydrotreating activity; (5) nanowire morphology prevents further sintering with a long catalyst life time. ADEM has been working with local oil refineries and customized the HDS catalyst formulation based on the operation conditions and limitations; (6) in 2020, ADEM will conduct a pilot-scale testing using skid-mounted unit at one of the refineries.

References

1. IMO 2020: Taking bold action to clean up shipping emissions by reducing the sulfur content in ship’s fuel oil http://www.imo.org/en/MediaCentre/HotTopics/Documents/Sulphur%202020%20infographic%202%20page.pdf
2. Sunkara, S. Vasireddy, J. He, and V. Kumar; US Patent Application No: 62440937 The application has been assigned serial number PCT/US18/12006.