Sulfur, and aromatization

For gas oil sulfur and aromatics reduction serves to increase the cetane number and to improve color and thermal stability. 

A fuel closely related to gasoline is naphtha, which is also a potential fuel cell fuel. Naphtha is already produced in large quantities at refineries and is a cheaper fuel than gasoline, which must have octaneboosting additives blended into it. Unlike methanol, naphtha can be distributed in the same pipelines as gasoline. From the fuel cell s perspective, it has a higher H C ratio and lower sulfur and aromatics content than gasoline. 

A number of refiners split the debutanized gasoline into light and heavy gasoline. This optimizes the refinery gasoline pool when blending is constrained by sulfur and aromatics. In a few gasoline splitters, a third heart cut is withdrawn. This intermediate cut is low in octane and it is processed in another unit for further upgrading. 

The synthetic fuels that can be produced by low-temperature Fischer-Tropsch synthesis inherently have a high quality (being sulfur- and aromatics-free) and can therefore be used as quality improvers with conventional components. 

Biodiesel is a olean burning alternative fuel produced from domestic, renewable resources. Biodiesel contains no petroleum, but it can be blended at any level with petroleum diesel to oreate a biodiesel blend. It can be used in compression-ignition (diesel) engines with little or no modifications. Biodiesel is simple to use, biodegradable, non-toxic, and essentially free of sulfur and aromatics. 

Clean diesel is a term that applies to diesel fuel that has low sulfur and aromatic content, along with other characteristics that facilitate low emissions from diesel engines. 

Fatty acid mono-ester diesel fuel (or biodiesel) has advantage over petroleum-based fuel in being a renewable source of energy, virtually free of sulfur and aromatic compounds (Bagley et al., 1998). Biodiesel fuel reduces total particle volume concentration and does not increase any of the potentially toxic, health related emissions. 

In developed markets, cleaner-fuel issues revolve around several product specifications. The fuels market is at various stages of removing sulfur and aromatics from gasoline and diesel. For global organizations, formulating a clean-fuels agenda is a very market-dependent issue, as shown in Table 18.4. 

Fuel standards for the year 2000 were set by the European community, with plans for more stringent specifications on sulfur and aromatics for the year 2005 (Table 7.1). 

The Fischer-Tropsch (FT) synthesis leads to a broad range of products, i.e. hydrocarbons, alcohols, acids, esters, etc. The increasingly stringent regulations on the sulfur and aromatics content in fuels are the reasons for renewed interest in this reaction [1]. More efficient catalysts are required to improve FT activity and selectivity to the desired products. Cobalt catalysts have been found to be most suitable for the production of higher hydrocarbons [2]. Optimization of the metal function (Co, Fe, Ru, Mo) in supported FT catalysts has been studied in a large number of papers [3-6]. 

Official methods of chemical analysis of conventional diesel are often not adequate to characterize biodiesel. Tests for the levels of sulfur and aromatic components in biodiesel are useful but usually reveal that the concentrations of compounds containing these atoms or functional groups are very low. Analysis of biodiesel chemistry can reveal characteristics conferred by the source of the oU, the method of manufacture, and duration of storage (20, 21). For example, free and bound glycerol is measured to ascertain if biodiesel has been completely formed during synthesis. Fatty acid content, residual soaps, iodine value, peroxide value, and fatty acid composition all may reflect the quality of biodiesel (Table 1) but are unimportant and inapplicable in conventional diesel fuel quality determination. 

Typical examples of the first approach, upgrading or improving the fiiel, are the catalytic removal of sulfur and aromatic compounds in automotive fuels [8,9]. A shift from the use of coal to the use of natural gas as a fuel in many industrial applications has led to reduced emissions, due to the favorable composition of natural gas as compared to coal. However, future developments of combustion processes will most likely include the use of more low-grade fuels, such as heavy fuel oils [10]. The use of coal will increase again, which can be related to its relative abundance. Finally, low-Btu fuels, such as gasified biomass or gasified coal will play an important role [11]. 

The objective of the Synsat process is to convert feedstocks boiling between 200 and 360°C to high quality diesel oils low in sulfur and aromatics. 

Synthetic ultra-clean fuels are produced from simple chemical building blocks derived from the breakdown of natural gas, coal, petroleum coke, or biomass. Unlike traditional fuel products, which naturally have substantial impurities such as sulfur and aromatic material which must be removed, the synthetic fuels are produced by building up from molecules which are free of... 

A recent paper by EIA (Energy Information Administration) within DOE (U.S. Department of Energy) indicates that CTL (coal-to-liquids) fuels, under the High Price B Case, could become a viable supplement to the petroleum liquids supply in U.S. by 2010 (1). CTL fuels made from the indirect liquefaction technology are free of sulfur and aromatics, and also have clean combustion properties. These fuels are compatible with the petroleum-based ultra-clean transportation fuels mandated by EPA (U.S. Environmental Protection Agency) for 2006 and beyond to help meet the new stringent specifications for vehicle emissions. The CTL fuels can be used either as a blending component or as neat fuel. 

Jochum,73 however, working with various mixtures of carbon monoxide and hydrogen ranging from a composition of 1 1 and 1 5, respectively, found that gas velocity over the nickd catalyst had practically no effect on the composition of the exit gases. With a ratio of carbon monoxide and hydrogen of 1 3 the best operation was obtained at 270° to 280° C., and with a ratio of 1 5 the preferred temperature was 300° to 350° C. Sulfur and aromatic compounds were found to destroy catalyst activity. 

Base stock specifications, as defined by the producer or the purchaser, largely enumerate the physical properties required for the fluid—typically density, viscosity at two temperatures, viscosity index (VI), low temperature performance measures, flash and volatility properties, and solubility information from aniline point or viscosity-gravity constant (VGC)—the latter two are usually for naphthenic base stocks. While chemical composition is responsible for physical properties, it usually only surfaces as measurements of heteroatom content—sulfur and nitrogen—and aromatics content (or conversely that of saturates). Sulfur and aromatics levels in paraffinic base stocks are now criteria for American Petroleum Institute (API) classifications. However, detailed chemical compositional information is needed to understand the chemistry of the unit processes, the effects of changes in feeds, catalysts, and operating conditions, and behaviors of finished lubricant products. 

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