Aromatic diesel fuel

Moreover, the increasing industrial demand for low-aromatic diesel fuels [2] stimulated by the discovery that diesel exhaust particles generate various respiratory allergies, contributes to developing this area of research area [3-5]. 

The oxygenate should be soluble in low aromatic diesel fuel at temperatures down to 6 °C. 

Since highly aromatic fuels have little wax, they possess better natural low-temperature handling properties than paraffinic fuels. Also, the cloud point, pour point and low-temperature filtration of aromatic diesel fuel will typically be much lower than a paraffinic diesel fuel. 

The chemistry of diesel fuel processing has evolved significantly around the central issue of how to produce ultra-low sulfur diesel fuels and low-aromatic diesel fuels in a more efficient and environmentally friendly fashion. New design approaches are necessary for making affordable ultra-clean diesel and gasoline. 

The field of application for liquid chromatography in the petroleum world is vast separation of diesel fuel by chemical families, separation of distillation residues (see Tables 3.4 and 3.5), separation of polynuclear aromatics, and separation of certain basic nitrogen derivatives. Some examples are given later in this section. 

As we have shown previously, obtaining both good cold operation characteristics and sufficient cetane numbers constitutes the principal objective for the refiner in the formulation of diesel fuel. To this is added the need for deep desulfurization and, perhaps in the future, limitations placed on the chemical nature of the components themselves, e.g., aromatics content. 

The properties of straight run diesel fuels depend on both nature of the crude oil and selected distillation range. Thus the paraffinic crudes give cuts of satisfactory cetane number but poorer cold characteristics the opposite will be observed with naphthenic or aromatic crudes. The increasing demand for diesel fuel could lead the refiner to increase the distillation end point, but that will result in a deterioration of the cloud point. It is generally accepted that a weight gain in yield of 0.5% could increase the cloud point by 1°C. The compromise between quantity and quality is particularly difficult to reconcile. 

The gas oil cut from catalytic cracking called Light Cycle Oil (LCO), is characterized by a very low cetane number (about 20), high contents in aromatics, sulfur and nitrogen, all of which strongly limit its addition to the diesel fuel pool to a maximum of 5 to 10%. 

The level of injector fouling is most often illustrated in terms of residual flow (RF) expressed as a percentage of the flow under new conditions for a given needle lift. An RF on the order of 20% for a lift of 0.1 mm is a good compromise. This level may not be achieved with certain aromatic or naphthenic diesel fuels. The best recourse is then detergent additive addition. 

Finally it is likely that attention will be focused on emissions of polynuclear aromatics (PNA) in diesel fuels. Currently the analytical techniques for these materials in exhaust systems are not very accurate and will need appreciable improvement. In conventional diesel fuels, emissions of PNA thought to be carcinogenic do not exceed however, a few micrograms per km, that is a car will have to be driven for several years and cover at least 100,000 km to emit one gram of benzopyrene for example These already very low levels can be divided by four if deeply hydrotreated diesel fuels are used. 

The elimination of lead, the reduction of aromatics in gasoline, and the desulfurization of diesel fuels are oing to require significant reformulations of these products that will irripiy development of specific additives that allow the refiner to optimize costs while meeting the required specifications. 

Methanol use would also reduce pubHc exposure to toxic hydrocarbons associated with gasoline and diesel fuel, including ben2ene, 1,3-butadiene, diesel particulates, and polynuclear aromatic hydrocarbons. Although pubHc formaldehyde exposures might increase from methanol use in garages and tunnels, methanol use is expected to reduce overall pubHc exposure to toxic air contaminants. 

Methanol is more soluble in aromatic than paraffinic hydrocarbons. Thus varying gasoline compositions can affect fuel blends. At room temperature, the solubiUty of methanol in gasoline is very limited in the presence of water. Generally, cosolvents are added to methanol—gasoline blends to enhance water tolerance. Methanol is practically insoluble in diesel fuel. 

The cetane number of a fuel depends on its hydrocarbon composition. In general, normal paraffins have high cetane numbers, isoparaffins and aromatics have low cetane numbers, and olefins and cycloparaffins fall somewhere in between. Diesel fuels marketed in the United States have cetane numbers ranging between 35 and 65. Most manufacturers specify a minimum cetane number of 40—45. 

Aromatics Content. Aromatic compounds have very poor ignition quahty and, although they are not specifically limited in ASTM D975, there are practical limitations to using high aromatic levels in highway diesel fuel. In the United States, where gasoline demand represents about one-half of the... 

Diesel Fuel. Eederal diesel specifications were changed to specify a maximum of 0.05% sulfur and a minimum cetane index of 40 or a maximum aromatics content of 35 vol % for on-road diesel. Eor off-road diesel, higher sulfur is allowed. CARB specifications require 0.05% sulfur on or off road and 10% aromatics maximum or passage of a qualification test. Process technologies chosen to meet these specifications include hydrotreating, hydrocracking, and aromatics saturation. 

European countries, including the UK, and covers about 5% of the total European diesel market. It contains less than 5 vol%. of mono-ring aromatics and less than 0.1 vol%. of di- and higher-ring aromatics. Eurthermore it is low in sulfur. Both EC and SEC methods have been developed for the rapid analysis of aromatics in diesel fuel. 

Figure 14.16 Typical cliromatograms of LC (a) and SFC (b) analysis of aromatics in diesel fuel. Peak identification is as follows 1, total saturates 2, total aromatics 3, mono-aromatics 4, higher-ring aromatics.

I. L. Davies, K. D. Battle, P. T. Williams and G. E. Andrews, On-line fractionation and identification of diesel fuel polycyclic aromatic compounds by two-dimensional microbore liigh-peiformance liquid-cliromatography/capillary gas-cliiomatography . Anal. Chem. 60 204-209 (1988). 

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