High aromatic content

Monoaromatic, diaromatic and polycyclic aromatic compounds can all be found in fuels. Although concentrations vary in different fuels, the presence of these aromatics can have both desirable and undesirable consequences. Examples include the following  

As a general rule, low-molecular-weight aromatic compounds help to improve the low-temperature flow properties of fuels and oils. 

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. 

Aromatic hydrocarbons do not have good performance in the cetane engine. Compared to paraffins of the same carbon number, aromatic compounds have a very low cetane number. 

If a diesel fuel is reported to have a lower than expected cetane number, the first place to look for an explanation would be the total aromatic content of the fuel. A comparison of the approximate cetane number of various pure hydrocarbons is provided in TABLE 5-2. 

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Lubricants with a high aromatic content (LVI and some MVI oils) tend to oxidise to give sludge-forming compounds, although some naphthenic... 

Some polymers like PE and NR get cross-linked on exposure to radiation while others like those based on vinylidene polymers, e.g., polymethylmethacrylate (PMMA), polyisobutylene, degrade. Certain other types of polymer stmctures (high aromatic content or thermoset) resist degradation by high-energy radiation. Coating polymers usually contain acrylic, methacryUc, or fumaric vinyl unsaturation along or attached to the backbone. 

Aromatics are typically included in gasolines to increase octane number. However, high aromatic content increases engine-out hydrocarbons and NOx emissions.16 Moreover, aromatics are the main precursors of exhaust benzene, a known carcinogenic, via dealkylation of substituted aromatics.17 Therefore, reduction of total aromatic content, together with olefin content, is an important part of California phase III reformulated gasoline specifications,18 with respect to the current allowed concentrations of benzene and total aromatics of 0.8 and 25 percent of volume, respectively. 

It appears that the main reasons for the high thermal stability ofPNT-N and PNT-F arise from their inherent rigid-rod polymer structure and the high aromatic content of the repeating unit. However, the fact that the thermal stability of PNT-F is higher than PNT-N might be the result of strong intermolecular interaction between chains because of dipole-dipole interactions. 

Chapter 18 - The determination region of solubility of methanol with gasoline of high aromatic content was investigated experimentally at temperature of 288.2 K. A type 1 liquid-liquid phase diagram was obtained for this ternary system. These results were correlated simultaneously by the UNIQUAC model. By application of this model and the experimental data the values of the interaction parameters between each pair of components in the system were determined. This revealed that the root mean square deviation (RMSD) between the observed and calculated mole percents was 3.57% for methylcyclohexane + methanol + ethylbenzene. The mutual solubility of methylcyclohexane and ethylbenzene was also demostrated by the addition of methanol at 288.2 K. 

Benzene is a clear, colorless, flammable liquid with a distinct, sweet odor. It burns with a smolcy flame, as do other hydrocarbons with high aromatic concent. (That s why kerosenes with high aromatic content do not make good jet fuel or burning grade kerosene—too much black smoke.) Benzene is only slightly soluble, in water. 

The fuel oils coming out of olefin plants are also characterized by an abundance of polynuclear aromatic molecules, (Same definition as for Figure 2—1). They are sometimes inaccurately referred to as having a high aromatics content. Nomenclature aside, because of this, the burning characteristics of pyrolysis gas oil and pyrolysis pitch are poor. They are smoky, sooty, and gum formers they rend to be more viscous, and because of their polynuclear aromatic concent, they are suspected carcinogens. They are basically a witchs brew of unsavory hydrocarbons.. ... 

Uses. Gasoline additive, especially to aviation and premium grades with high aromatic content... 

The coefficient of determination, for the model prediction is 0.97 and the maximnm error is less than 0.7%. Figure 12.5 shows refractive index (n) observed versus that estimated from H-NMR spectra. The model shows the largest discrepancies for either low aromatic content feeds (triangles), or high aromatic content feeds (circle). 

Jet fuels are blended primarily from straight-run distillate components and contain virtually no olefins. Aromatics in jet fuel are also limited. High aromatic content can cause smoke to form during combustion and can lead to carbon deposition in engines. A total aromatic content >30% can cause deterioration of aircraft fuel system elastomers and lead to fuel leakage. 

Blend with higher-specific-gravity fuel components such as high-aromatic-content heating oil or stabilized FCC cycle oil. These components will improve fuel BTU ratings. 

Murray (4I) has recommended that, so far as film stability of larvicidal mixtures is concerned, the oil should have either a small or a very high aromatic content (it should not contain 50% of aromatics unless they are very high boiling—e.g., of lubricating base fraction) consist of a mixture of wide and overlapping cuts of oil and should not contain fats or fatty acids added as spread-aiders. If a spreading agent is desired, resins should be employed. 

Substitute for Conventional Vulcanized Rubbers, For this application, the products are processed by techniques and equipment developed for conventional thermoplastics, ie, injection molding, extrusion, etc. The S—B—S and S—EB—S polymers are preferred (small amounts of S—EP—S are also used). To obtain a satisfactory balance of properties, they must be compounded with oils, fillers, or other polymers compounding reduces costs. Compounding ingredients and their effects on properties are given in Table 8. Oils with high aromatic content should be avoided because they plasticize the polystyrene domains. Polystyrene is often used as an ingredient in S—B—S-based compounds it makes the products harder and improves their processibility. In S—EB—S-based compounds, crystalline polyolefins such as polypropylene and polyethylene are preferred. Some work has been reported on blends of liquid polysiloxanes with S—EB—S block copolymers. The products are primarily intended for medical and pharmaceutical-type applications and hardnesses as low as 5 on the Shore A scale have been reported (53). 

Remarkable increases in the aromatics content of gasolines and the octane number were obtained with synthetic-aluminum-silicate-supported catalysts (43), as shown in Table XXI. The experiments were made at 250 atm. pressure with petroleum gas oil of 0.846 sp. gr. and a boiling range of 187° to 330°C. Temperatures around 400°C. were used and were adjusted to obtain approximately the same conversion for both catalysts. The silicate catalyst is less active. The high aromatics content obtained with the aluminum silicate catalyst is especially evident in the higher fractions. The amount of branched-chain paraffin hydrocarbons is not greatly different, as shown by the octane number of the aromatic free fractions, used as an index. 

Phenolic resins have a low flammability by themselves due to the high aromatic content which leads to a high char formation on thermal degradation. However, end-capped brominated epoxy resins are used when necessary. Decabromodiphenyl ether in combination with antimony oxide is also used. 

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