Ultra-low sulfur

NiMo and NiW formulations have succeeded in desulfurizing the sterically hindered compounds, by fully hydrogenating at least one of the lateral rings, facilitating their elimination. From this point of view, the need for a high hydrogenation activity when producing ultra-low sulfur fuel is explained. Consequently, the preferential application of a Ni-Mo(W) for the manufacture of ULS fuels can be easily understood, as well. 

An overview of the commercially available technologies for the manufacturing of ultra-low sulfur light-fuels has been published, and includes hydroprocessing technologies, as well as some other means of production of ULS fuels [40],... 

Tippett, T. Knudsen, K. G., and Cooper, B., Ultra Low Sulfur Diesel Catalyst and Process Options, in NPRA Annual Meeting, 1999., Paper 99-06. 

Mukai, Y., and Mizutani, Y., Survey of Petroleum Refining Technology for High-quality (Ultra-low Sulfur Content) Diesel Fuel. Petroleum Energy Center. 01 Survey 4-3, 2001. 

Energy Information Agency. The Transition to Ultra-Low-Sulfur Diesel Fuel Effects on Prices and Supply. Special Report. 2001 May. Available from http //www.eia.doe.gov/oiaf/ servicerpt/ulsd/pdf/ulsd.pdf. 

Hydroprocessing is utilized to reduce fuel sulfur concentrations. Fuels classed as high-sulfur diesel typically contain up to 5000 ppm of sulfur. Fuels classed as low-sulfur diesel typically contain up to 500 ppm of sulfur. Ultra-low sulfur or sulfur-free fuels typically have sulfur values of 15 ppm or less. 

Severely hydroprocessed ultra-low sulfur diesel fuel can differ in properties and performance from higher-sulfur-content diesel fuels. Some important differences are described here. 

Severe hydroprocessing required to produce ultra-low sulfur fuel removes most of the polar organic compounds from the fuel. The resulting product is virtually unable to effectively dissipate static charge as it builds in moving fuel. Instead, electrical discharge into pockets of gas within a pipeline or into air and vapors as fuel is being dispensed can occur. An explosion may result. Low levels of a fuel-soluble electrical conductivity improver to ultra-low sulfur fuel can help restore fuel electrical conductivity to safe levels. 

Ultra-low sulfur fuel has little ability to prevent water-initiated corrosion of metal since most of the naturally occurring, film-forming inhibitors have been removed by hydroprocessing. Water-initiated corrosion can occur readily in ultra-low sulfur fuel systems. The addition of a traditional film-forming corrosion inhibitor will provide good protection against water-initiated corrosion. 

Severely hydroprocessed ultra-low sulfur diesel fuel has poorer lubricity properties than higher-sulfur-content fuels. Many of the compounds that contribute to providing adequate lubricity have been removed. Metal wear and loss of fuel pump pressure can occur if fuel with poor lubricity is used. 

Conversion of heterocyclic aromatic compounds or other aromatic fuel components to paraffins by hydroprocessing can help increase the cetane number of diesel fuel. Fuel paraffins have significantly higher cetane number values than fuel aromatics. For this reason, the cetane number of ultra-low sulfur diesel fuel will typically be one to five numbers greater than higher-sulfur grade fuels. 

Although hydroprocessing will remove most of the naturally occurring antioxidants contained in fuel, other less stable, more reactive components will also be reduced. As a whole, ultra-low sulfur diesel fuel will be much less prone to color degradation and deposit formation than earlier-era diesel fuels. 

Severe hydroprocessing required to refine ultra-low sulfur fuel grades generates hydrogen sulfide as a by-product. If low levels of hydrogen sulfide remain soluble in the finished fuel, the possibility exists for hydrogen sulfide-initiated corrosion of copper and the resulting failure of the ASTM D-130 specification for finished fuel. 

Because of the low-sulfur, -nitrogen, and -aromatic content of Fischer-Tropsch fuels, there is renewed interest in these products. In two recent studies, Fischer-Tropsch diesel was evaluated and compared to an ultra-low sulfur California diesel and to a 49 cetane number, low-sulfur diesel. In the two studies, carbon monoxide, nitrogen oxide, hydrocarbon, particulate, and carbon dioxide emissions were reduced in vehicles fuels by Fischer-Tropsch diesel. The fuel economy, however, was also reduced. The low aromatic content and high concentration of waxlike hydrocarbons in Fischer-Tropsch diesel can lead to the need for special handling and treatment of the fuel to prevent gelling when used in cold-temperature conditions. 

Meanwhile, ultra-low-sulfur diesel fuel was introduced at retail pumps in October 2006 in the U.S. New EPA emissions rules will be in effect across America in 2009 requiring that diesel engines meet exacting standards for low air pollution. The new clean diesel fuel eliminates 97% of sulfur... 

Total removal of phosphorus and sulfur would require the use of synthetic base-oils and new additive systems to provide antiwear antioxidation protection. Synthetic base-oil PAOs or esters have high values of viscosity improver VI and low temperature operating properties. The lubricants in diesel engines require a reduction in Ca carbonate-sulfonate concentrations. This may be less of a problem when ultra low sulfur diesel fuel is widely deployed, since a significant part of the requirement for these additives arises from the need to neutralize sulfur oxides from combustion processes. 

TABLE 1.17. Effect of blending or additization on HFRR data (60 °C) of ultra-low sulfur petrodiesel fuel (ULSD). For data of the neat petrodiesel fuels, see Table 1.16. 

So how much investment will be made to process low-sulfur fuels A recent Energy Information Administration (EIA) report estimates that U.S. refiners will invest 6.3-9.3 billion to reach full compliance with the ultra-low sulfur diesel (ULSD) rule through 201 1.33 For Europe, refiners made investments of nearly 22.9 billion from 1997 to 2005 to meet gasoline and diesel specifications. From 2005 to 2015, an additional 9.7-14 billion may be spent on improving the quantity and quality of middle distillates in Europe.15 Thus, considerable investment will be necessary to bring cleaner fuels to market. 

EIA, The Transition to Ultra-low Sulfur Diesel Effects on Process and Supply, May 2001. 

Min W. S., A unique way to make ultra low sulfur diesel, KIChE annual meeting... 

Rock, K.L. Ultra-low sulfur gasoline via catalytic distillation. The Fifth International Conference on Refinery Processing, AIChE Spring National Meeting. New Orleans, LA, 2002. 

Knudsen, K.G., Cooper, B.H., and Topsoe, H. Catalyst and process technologies for ultra low sulfur diesel. Applied Catalysis. A, General, 1999, 189, 205. 

Meijburg, G. Production of ultra-low-sulfur diesel in hydrocracking with the latest and future generation catalysts. Catalyst Courier, 2001, No. 46, Akzo Nobel. 

Nero, V.P., Decanio, S.J., Rappas, A.S., Levy, R.E., and Lee, F.M. Oxidative process for ultra-low sulfur diesel. Preprints of Papers—American Chemical Society, Division of Petroleum Chemistry, 2002, 47, 41. 

A major challenge even for advanced diesel engines is the array of impending U.S. federal Tier 2 and California LEV II emissions standards. Work is ongoing to achieve these standards and to ensure that the exhaust after-treatment devices required will meet the necessary durability standards. Two things are certain Diesel fuel quality must improve dramatically, at least to the 2006 ultra low sulfur diesel requirements and preferably well beyond, and the cost of a Tier 2 Bin 5 or LEV II compliant diesel system will be substantial, rivaling the cost of hybrid electric gasoline fueled vehicle systems. 

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