Cetane number improvers

Conventional Hydrofining of diesel oils does not improve octane number because octane number improvement, like smoke point improvement in kerosenes, requires samration of aromatics. Higher pressures are needed to gain appreciable aromatics samration and cetane number improvement. 

The greatest boost in cetane number improvement is obtained within the first 1,000 ppm of additive treatment. This is also demonstrated in FIGURE 4-9. 

The second and most promising approach is based on the fact that certain emulsifiers function by themselves as cetane number improvers. Observed cetane numbers of microemulsion fuels produced by this type... 

Figure 4, Cetane numbers of microemulsion fuels in which the emulsifiers act as cetane number improvers,...

The engine performance additives improve engine performance. Different members of this class are used to improve engine performance in different time Games. Any benefit that is provided by a cetane number improver is immediate, whereas that provided by detergent additives or lubricity additives is typically seen over the long term. 

Cetane number improvers or diesel ignition improvers reduce combustion noise and smoke. The magnitude of the benefit varies among engine designs and operating modes, ranging from no effect to readily perceptible improvement. 

Ethylhexyl nitrate (EHN) is the most widely used cetane number improver. It is also sometimes called, octyl nitrate . EHN is thermally unstable and decomposes rapidly at the high temperatures in the combustion chamber. The products of decomposition help initiate fuel combustion and, thus, shorten the ignition delay period as compared with that of the fuel without the additive. 

Other alkyl nitrates as well as ether nitrates and some nitroso compounds, have also been found to be effective cetane number improvers. However, they are not currently used commercially. Di-tertiary butyl peroxide has recently been introduced as a commercial cetane number improver. 

Petroleum-based diesel fuel is commonly treated with a large number of additives to enhance cetane number, improve cold flow and oxidative stability, lessen corrosive-... 

Hu Y, Lv J, Liu X et al (1997) Cetane number improvers in diesel fuel (l)-synthesis of isooctyl nitrate. J Petro Chem Univ 10(4) 16-18... 

Wang C, Li H (2005) New synthesizing technique for diesel cetane number improver. Chem Eng 11 58-59... 

Anti-oxidation Cetane improvement Dispersion Anti-icing Detergent Metal passivation Corrosion inhibition Cold-flow improvement Minimize oxidation and gum formation during storage Increase cetane number Improve behavior in fuel injectors Minimize ice formation during cold weather Control deposition of carbon in the engine Deactivate trace metals that can accelerate oxidation Minimize rust throughout the diesel fuel supply chain Improve flow characteristics in cold weather... 

The additives for improving the cetane number, called pro-cetane, are particularly unstable oxidants, the decomposition of which generates free radicals and favors auto-ignition. Two families of organic compounds have been tested the peroxides and the nitrates. The latter are practically the only ones being used, because of a better compromise between cost-effectiveness and ease of utilization. The most common are the alkyl nitrates, more specifically the 2-ethyl-hexyl nitrate. Figure 5.12 gives an example of the... 

Effectiveness of DtI3 additive in improving the cetane number. Source (Umelman, 1984). 

Improving the cetane number by additives results in better engine behavior, as would be predicted by the combustion mechanisms in the diesel engine (noise reduction, better operating characteristics, particularly when cold). Nevertheless, concerning certain items such as pollution emissions, it may be better to obtain a higher cetane number rather by modification of the... 

Diesel fuels, like gasoline, are formulated with additives that affect the process of combustion, in this case to improve the cetane number. Diesel fuels also contain detergents for irijection systems as well as compounds for improving the fuel s low tempierature rheology. Finally, decreasing particulate emissions is a problem of increasing concern, but the mechanism of action to promote this effect is not clearly understood. 

Unlike spark-induced combustion engines requiring fuel that resists autoignition, diesel engines require motor fuels, for vhich the reference compound is cetane, that are capable of auto-igniting easily. Additives improving the cetane number will promote the oxidation of paraffins. The only compound used is ethyl-2-hexyl nitrate. 

The trend in d and has also been accompanied by improvements in product quality illustratisd by the increases in gasoline octane numbers and diesel oil cetane numbers. 

Hydrotreating processes are applied to finished products to improve their characteristics sulfur content, cetane number, smoke point and the aromatics and olefins contents. 

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

Improving the cetane number as well as lowering the aromatics content requires higher partial pressures as well as higher hydrogen consumption. 

We cite isomerization of Cs-Ce paraffinic cuts, aliphatic alkylation making isoparaffinic gasoline from C3-C5 olefins and isobutane, and etherification of C4-C5 olefins with the C1-C2 alcohols. This type of refinery can need more hydrogen than is available from naphtha reforming. Flexibility is greatly improved over the simple conventional refinery. Nonetheless some products are not eliminated, for example, the heavy fuel of marginal quality, and the conversion product qualities may not be adequate, even after severe treatment, to meet certain specifications such as the gasoline octane number, diesel cetane number, and allowable levels of certain components. 

Santana, R.C. et alv Evaluation of different reaction strategies for the improvement of cetane number in diesel fuels, Fuel, 85,643,2006. 

The Syn technology is oriented to the production of ULSD, to the saturation of aromatics and to the improvement of cetane number. These processes can be run in a single reactor unit, in which case, the initial part of the reactor is fed in a co-current way,... 

Dan Resasco (with colleagues Phuong Do, Steven Crossley, Malee Santikuna-porn University of Oklahoma) examine strategies for improving important fuel properties catalytically—e.g., cetane number and threshold soot index. They show that proper choice of catalysts and reaction conditions can significantly improve these widely used measures of fuel performance. 

Fig. 1 Gradual improvement in cetane number of naphthalene caused by hydrogenation and subsequent selective ring opening. Adapted from ref. 12.

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