Fractions, petroleum

The most common method for GC/MS analysis of semivolatile compounds (EPA SW-846 8270) includes 16 polycyclic aromatic compounds, some of which commonly occur in middle distillate to heavy petroleum products. The method also quantifies phenols and cresols, compounds that are not hydrocarbons but may occur in petroleum products. Phenols and cresols are more likely found in crude oils and weathered petroleum products. 

To reduce the possibility of false positives, the intensities of one to three selected ions are compared to the intensity of a unique target ion of the same spectrum. The sample ratios are compared to the ratios of a standard. If the sample ratios fall within a certain range of the standard, and the retention time matches the standard within specifications, the analyte is considered present. Quantification is performed by integrating the response of the target ion only. 

Mass spectrometers are among the most selective detectors, but they are still susceptible to interferences. Isomers have identical spectra, whereas many other compounds have similar mass spectra. Heavy petroleum products can contain thousands of major components that are not resolved by the gas chromatograph. As a result, multiple compounds enter the mass spectrometer simultaneously. Different compounds may share many of the same ions, confusing the identification process. The probability of misidentiflcation is high in complex mixtures such as petroleum products. 

Rather than quantifying a complex total petroleum hydrocarbon mixture as a single number, petroleum hydrocarbon fraction methods break the mixture into discrete hydrocarbon fractions, thus providing data that can be used in a risk assessment and in characterizing product type and compositional changes such as may occur during weathering (oxidation). The fractionation methods can be used to measure both volatile and extractable hydrocarbons. 

In contrast to traditional methods for total petroleum hydrocarbons that report a single concentration number for complex mixtures, the fractionation methods report separate concentrations for discrete aliphatic and aromatic fractions. The petroleum fraction methods available are GC-based and are thus sensitive to a broad range of hydrocarbons. Identification and quantification of aliphatic and aromatic fractions allows one to identify petroleum products and evaluate the extent of product weathering. These fraction data also can be used in risk assessment. 

As is true with all naturally occurring feed stocks, the composition or boiling range of crude oil varies greatly from production field to production field. This variability results in a very significant dynamic control problem in a refinery that feeds crude oil from a variety of sources, which is often the case. 

The book by Nelson provides a thorough discussion of many aspects of the petroleum industry, such as types and sources of crude, characterization of petroleum fraction, and types of refinery operations. 

TABLE 11.1 Comparison of Boiling Point Methods for Naphtha 

The properties of a petroleum stream are not specified in terms of compositions. Instead, properties are used, such as 5% point, final boiling point, Reid vapor pressure, flash point, and octane number. 

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Benzene was first isolated by Faraday in 1825 from the liquid condensed by compressing oil gas. It is the lightest fraction obtained from the distillation of the coal-tar hydrocarbons, but most benzene is now manufactured from suitable petroleum fractions by dehydrogenation (54%) and dealkylation processes. Its principal industrial use is as a starting point for other chemicals, particularly ethylbenzene, cumene, cyclohexane, styrene (45%), phenol (20%), and Nylon (17%) precursors. U.S. production 1979 2-6 B gals. 

Edeleanu process An extraction process utilizing liquid sulphur dioxide for the removal of aromatic hydrocarbons and polar molecules from petroleum fractions. 

It is produced from petroleum fractions rich in naphthenes by catalytic reforming in the presence of hydrogen (hydroforming) in this process dehydrogenation .nd dealkylation... 

D 2887, applies to products and petroleum fractions whose final boiling points are equal to or below 538°C (1000°F), and have boiling points above 38°C (100°F). The results obtained are equivalent to those obtained from the TBP distillation, ASTM D 2892. 

D 3710, applies to products and petroleum fractions whose final boiling points are equal to or less than 260°C (500°F). 

Chapter 3. ChARACTERIZA VON OF CRUDE OlLS AND PETROLEUM FRACTIONS... 

To extend the applicability of the characterization factor to the complex mixtures of hydrocarbons found in petroleum fractions, it was necessary to introduce the concept of a mean average boiling point temperature to a petroleum cut. This is calculated from the distillation curves, either ASTM or TBP. The volume average boiling point (VABP) is derived from the cut point temperatures for 10, 20, 50, 80 or 90% for the sample in question. In the above formula, VABP replaces the boiling point for the pure component. 

Characterization of Crude Oils and Petroleum Fractions Based on Structural Analysis... 

Characterization of a Petroleum Fraction by Carbon Atom Distribution... 

Using Infrared Spectrometry to Characterize Petroleum Fractions according to the Nature of the Carbon Atoms... 

Chapter 3. CHARACTERIZATION OF CRUDE OILS AND PETROLEUM FRACTIONS 63... 

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