(39c) Adesulfur -- a High Capacity Catalytic Adsorbent for Ultra-Deep Desulfurization of Fuels

Sulfur content of fuels has been cut down to ultra-low levels by environmental regulations in many countries with the aim of reducing harmful emissions and improving air quality. The presence of sulfur compounds in fuel oils also influenced refining processes (due to catalyst deactivation and corrosion). Refiners often target 10 ppmw sulfur to allow additional sulfur impurities that may arise during transportation and storage.

To meet these ultra-low sulfur specifications, refiners needed to do costly revamping which typically require addition of significant catalyst volume (i.e. additional reactor), higher hydrogen consumption, higher operating severity, equipment modifications to increase the hydrogen purity and circulation rate, and installation of improved reactor internals¹. Especially for small to medium scale refineries which are remotely located had no access or low amounts of hydrogen for hydrodesulfurization process.

The development of a catalytic adsorbent system (AdESulfur) and process conditions for the ultra-deep desulfurization of hydrocarbon fuels such as naphtha, kerosene and diesel, specifically for ULSD production will be described. The sulfur breakthrough time and pickup capacity (g sulfur/ g of adsorbent) at different process conditions and feeds will be presented.

The conventional hydrodesulfurization catalysts such as Ni-Mo and Co-Mo require high temperature 330-400 °C, pressure 30-100 bar and high hydrogen requirement (900-1500 SCFbbl)^2,3. The HDS process also produce H₂S needs further treatment. The AdESulfur can produce clean fuels with <10 ppm sulfur for ULSD application and <1 ppm sulfur for fuel cell applications from the feed containing 50-100 ppmw sulfur at low to moderate process conditions and no H₂S produced in the process⁴. The AdESulfurâ„¢ is an advanced catalytic adsorbent technology for removing sulfur chemicals from naphtha, kerosene and diesel feedstocks. This is not a hydrodesulfurization process where H₂S will be produced. Rather, AdESulfurâ„¢ is a novel catalytic sorbent that specifically adsorbs ‘S’ containing chemicals and the ‘S’ atom will be retained in the sorbent and releases the hydrocarbon portion of the molecule. This process does not produce any H₂S gas which needs to be treated downstream. Also, implementing AdESulfurâ„¢ avoids problems associated with H₂S inhibition and recombination of olefins with H₂S forming mercaptans.

AdE-Sulfur is a catalytic adsorbent containing active metal nanoparticles deposited onto ZnO nanowires support. The ZnO nanowires of size 100-150 nanometers in dia and 2-3 µm in length were produced by ADEM’s patented dry manufacturing process using micron sized Zn metal powder as feedstock^5a,5b,5c. The active metals were then deposited onto nanowires by wet impregnation followed by drying, calcination and extrusion to get final form of the catalyst to apply in refineries with required crush strength (3 lbs/mm).

These materials were tested for several 100 hrs using different feed stocks received from a local refinery and gas station diesel spiked with various sulfur chemicals such as mercaptans, thiophene and most difficult to remove refractory sulfur compounds such as dibenzothiophene and mono- and di-alkyl substituted dibenzothiohenes. Table 1 shows the AdESulfur can effectively remove sulfur down to 10 ppm at LHSV as high as 4.2 h^-1 from feed having 1520 ppmw of sulfur and the sulfur pickup capacity was found to be as high as 25 wt%.

Table 1. Effect of feed LHSV on desulfurization of diesel

LHSV (hr-1)	Sulfur content in feed (ppm)	Sulfur content in treated diesel product (ppm)
		Trial 1	Trial 2
2.2	1520	0.7±0.5	0.5±0.1
3.2	1520	5.5±3	5.5±3
4.2	1520	10±5	10±5
5.2	1520	60±20	100±20

The fuel properties such as cetane number, cloud point, por point and cold filter plugging point were measure before and after treatment with AdESulfur. The aromatics content in the feed and product were measured by UV-Vis analysis.

Table 2. Cetane number and flow properties of Diesel before and after treatment with AdE-Sulfur

Sample	Process	Density (g/ml, at 5°C)	Cetane Number	Flow Properties
ULSD from small refinery	Use as received	0.825	58±1
ULSD from small refinery + 120ppm sulfur spiked	After treatment, using AdESulfur	0.825	60±1
LCO from a refinery (900 ppm sulfur)	Use as received	0.83	46 ±1
LCO from refinery (900 ppm sulfur)	After treatment using AdESulfur	0.82	55±1
ULSD from gas station	Use as received	0.84	47±1	CP: 6.3 CFPP: 0 PP: -8.7
ULSD from gas station + 120ppm sulfur spiked	After desulfurization treatment using AdESulfur	0.835	57±1	CP: 0.8 CFPP: -10 PP: -14.2

*CP: Cloud point (°F); CFPP: Cold filter plugging point (°F); PP: pour point (°F)

A clear improvement of cetane number and flow properties was observed (table 2) and this improvement in CN is due to the hydrogenation of aromatics and ring opening processes and selectivity.

Significance

This catalytic adsorbent (AdESulfur) technology relaxes the severity of operating conditions that are required by the conventional hydrotreaters to meet the ULSD specifications, allowing 50-100 ppmw sulfur in the exit diesel from HDS reactor which will be taken care by AdESulfurâ„¢ in the downstream reactor removing the sulfur down to <10 ppmw. This also improves the upstream HDS operation by 30-40 °C thereby increasing the lifetime of the HDS catalyst at least by an additional 1-2 years. AdESulfurâ„¢ can be operated at low severe process conditions, T – 200-290 °C, P – 5-20 bar, LHSV- 2-6 h^-1, H₂/oil – 50 SCCM/ml to 200 SCCM/ml.

References

1. 1. Kumar, V.P., Peddy, V.C.R. and Gandham, S.G., Reducing hydrogen consumption in diesel hydrotreating; https://www.digitalrefining.com/article_1001545.pdf, 2018.
2. Stanislaus, A., Marafi, A., and Rana, M.S. Recent advances in the science and technology of ultra low sulfur diesel (ULSD) production; Catal. Today 153 (2010) 1–68.

3. Song, C., An overview of new approaches to deep desulfurization for ultra-clean gasoline, diesel fuel and jet fuel; Catal. Today 86 (2003) 211-263.

4. Vasireddy, S., He, J., and Sunkara, M.K., Nanometal oxide Adsorbents for Desulfurization of Hydrocarbon Fuels; US patent application: 62/457,695.

5. a). Sunkara, M.K., Nguyen, T.Q., Guhy, L., and Paxton, W., US patent publication no: 20190193044; b) Sunkara, M.K., Kumar, V., Kim, J.H., and Clark, E.L., Methods for synthesizing metal oxide nanowires; US Patent publication No: 9,409,141 and c) Sunkara, M.K., Vaddiraju, S., Mozetic, M., and Cvelbar, U., Method for rapid synthesis of large quantities of metal oxide nanowires at low temperatures; US patent publication No: 7,591,897.