Asphaltene content

The asphaltene content is found either directly by precipitation using n-heptane (NF T 60-115 or ASTM D 32), or indirectly by correlation with the Conradson Carbon. It can vary from 4 or 5% to as much as 15 or 20% in extreme cases. 

The different cuts obtained are collected their initial and final distillation temperatures are recorded along with their weights and specific gravities. Other physical characteristics are measured for the light fractions octane number, vapor pressure, molecular weight, PONA, weight per cent sulfur, etc., and, for the heavy fractions, the aniline point, specific gravity, viscosity, sulfur content, and asphaltene content, etc. 

The conversion to lighter products is limited by the asphaltenes content (C insolubles). At high conversions, the residual asphaltenes —no longer being soluble in their environment— tend to precipitate, resulting in the production of unstable residues that are unmarketable. 

Aromaticity is the most important property of a carbon black feedstock. It is generally measured by the Bureau of Mines Correlation Index (BMCI) and is an indication of the carbon-to-hydrogen ratio. The sulfur content is limited to reduce corrosion, loss of yield, and sulfur in the product. It may be limited in certain locations for environmental reasons. The boiling range must be low enough so that it will be completely volatilized under furnace time—temperature conditions. Alkane insolubles or asphaltenes must be kept below critical levels in order to maintain product quaUty. Excessive asphaltene content results in a loss of reinforcement and poor treadwear in tire appHcations. 

Asphaltic—contain relatively a large amount of polynuclear aromatics, a high asphaltene content, and relatively less paraffins than paraffinic crudes. 

Residues containing high levels of heavy metals are not suitable for catalytic cracking units. These feedstocks may be subjected to a demetallization process to reduce their metal contents. For example, the metal content of vacuum residues could be substantially reduced by using a selective organic solvent such as pentane or hexane, which separates the residue into an oil (with a low metal and asphaltene content) and asphalt (with high metal content). Demetallized oils could be processed by direct hydrocatalysis. 

Solvent extraction may also be used to reduce asphaltenes and metals from heavy fractions and residues before using them in catalytic cracking. The organic solvent separates the resids into demetallized oil with lower metal and asphaltene content than the feed, and asphalt with high metal content. Figure 3-2 shows the IFP deasphalting process and Table 3-2 shows the analysis of feed before and after solvent treatment. Solvent extraction is used extensively in the petroleum refining industry. Each process uses its selective solvent, but, the basic principle is the same as above. 

The heptane insoluble (ASTM D-3279) method is commonly used to measure the asphaltene content of the feed. Asphaltenes are clusters of polynuclear aromatic sheets, but no one has a clear understanding of their molecular structure. They are insoluble in C3 to paraffins. The amount of asphaltenes that precipitate varies from one solvent to another, so it is important that the reported asphaltene values be identified with the appropriate solvent. Both normal heptane and... 

Cap Gas. Both crude and asphaltene-free oil were used to determine the consequences of low-temperature oxidation. It was found that the oxygen content in an artificial gas cap was completely consumed by chemical reactions (i.e., oxidation, condensation, and water formation) before the asphaltene content had reached equilibrium. 

In this zone, the quantity of extracted oil is generally sufficient to obtain the distribution of the different structural groups (SARA analysis) except for oil A (Fig. 6 to 9) For oil B (Fig. 6), for the first two samples, the amount of extracted products is too low and the analysis is uncertain. It can only be noticed that the asphaltene content is null. On the contrary, just beyond the coke zone (samples III-IV), the asphaltene content respectively reaches 12.9 and 5 4 whereas the asphaltene content of the initial oil is only 0.3. This effect is also observed for oil C (10 versus 6.3%) (Fig. 7), D 24% versus 13.8 ) (Fig. 8), E (24 4 versus 8.1 ) (Fig. 9) For all the oils, the amount of resins+asphaltenes generally remains constant and the amount of saturates increases... 

For crude oils C and D, some lighter hydrocarbons are formed during the cracking reactions but the composition of the 210 fraction is hardly modified. In particular, it can be noticed that the asphaltene contents of both of the recovered oils remain high. 

Aromatics Resins — Asphaltenes — coke where the resin + asphaltene content remains constant and asphaltenes are the main precursors of coke. The same observations have been made in low-temperature oxidation experiments (6). 

Table II. Resin and Asphaltene Content of Crude Oils (11)...

The high viscosity of heavy crude oils is essentially due to the high levels of asphaltene content. Asphaltene is the highest MW component of crude oil, is a friable, amorphous dark solid, which is colloidally dispersed, in the oily portion of the crude. Asphaltenes are considered to be heavily condensed aromatic molecules with aliphatic side chains and with high heteroatom content (S, N, and O) as well as high-metal content. The asphaltene fraction is physically defined as that fraction insoluble in n-alkanes, but soluble in toluene and is the most polar fraction of oil. 

Brunnock et al. [67] have also determined beach pollutants. They showed that weathered crude oil, crude oil sludge, and fuel oil can be differentiated by the n-paraffin profile as shown by gas chromatography, wax content, wax melting point, and asphaltene content. The effects of weathering at sea on crude oil were studied parameters unaffected by evaporation and exposure are the contents of vanadium, nickel, and n-paraffins. The scheme developed for the identification of certain weathered crude oils includes the determination of these constituents, together with the sulfur content of the sample. 

In addition, a method of petroleum classification based on other properties as well as the density of selective fractions has been developed. The method consists of a preliminary examination of the aromatic content of the fraction boiling up to 145°C (295°F), as well as that of the asphaltene content, followed by a more detailed examination of the chemical composition of the naphtha (bp < 200°C < 390°F). For this examination a graph is nsed that is a composite of cnrves expressing the relation among the percentage distillate from the naphtha. 

The precipitation number is often equated to the asphaltene content, but there are several issues that remain obvious in its rejection for this purpose. For example, the method to determine the precipitation number (ASTM D91) advocates the use of naphtha for use with black oil or lubricating oil, and the amount... 

The road asphalt used in this study was obtained from the road as a fresh sample. The road asphalt is composed of asphaltenes (GPC peak at lOOA and petroleum residual oils (15) (GPC peak at n-C QHgo). The GPC of road asphalt is shown in Figure 9. Since petroleum asphaltenes cannot be separated by a lOOA pore size gel column, the asphaltene appears without any separation at the total size exclusion limit of the column. But the nonasphaltene components are separated showing a peak at n-C QHg2. The performance of the road asphalt depends on the asphaltene content as well as on the molecular size distribution of the nonasphaltenic fraction. 

When the powdered coal is mixed intimately with a catalyst such as 1% (of the dry coal) of ferrous sulfate or 0.2% of ammonium molybdate, the oil yield is increased, and its asphaltene content is reduced. 

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