Characterization of Petroleum Fractions

We will use the term petroleum fraction to designate a mixture of hydrocarbons whose boiling points fall within a narrow temperature range, typically as follows  

In a general manner, the following expression should be obeyed ( h ) 

This is the average boiling temperature at atmospheric pressure (1.013 bar abs). This characteristic is obtained by direct laboratory measurement and is expressed in K or °C. 

When the boiling point is measured at a pressure other than normal atmospheric, the normal boiling point can be calculated by a method described in article 4.1.3.4. 

If the boiling temperature is not known, it is somewhat risky to estimate it. One could, if the Watson characterization factor is known, use the following 

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Characterization of Petroleum Fractions Based on Chemical Reactions... 

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. 

In many cases distribution functions are determined experimentally the characterization of petroleum fractions by true-boiling-point distillation or gas-chromatographically simulated distillation, and the characterization of polymers by gel-permeation chromatography. In principle, the integrals of continuous thermodynamics may be directly solved based on these experimentally determined distribution functions. However, this approach delicate numerical analyses and the assumption the complete distribution function has been obtained by experiment clearly this is no the case, for example, for some polymers only molar-mass averages are determined. Thus, there are numerous cases where smoothed or analytical distribution function provides more reliable phase equilibrium calculation than those obtained by use of the experimentally determined distribution function. When the integrals of continuous thermodynamics possess analytical solutions considerably numerical simplification is afforded and this is one motive for the desire to have analytical expressions for the distribution function. 

In process simulation software during the creation of pseudocomponents, which are used together with quadrature techniques for determining the optimal number of pseudocomponents for simulation purposes, for example, characterization of petroleum fractions (Whitson, 1983 Whitson et al.,... 

Table 2 Some Widely Used Parameter Estimation Methods for Characterization of Petroleum and its Fractions...

In the early 1930s, tests were developed which characterized petroleum oils and petroleum fractions, so that various physical characteristics of petroleum products could be related to these tests. Details of the tests can be found in Petroleum Products and Lubricants, an annual publication of the Committee D-2 of the American Society for Testing Materials. These tests are not scientifically exact, and hence the procedure used in the tests must be followed faithfully if reliable results are to be obtained. However, the tests have been adopted because they are quite easy to perform in the ordinary laboratory and because the properties of petroleum fractions can be predicted from the results. The specifications for fuels, oils, and so on, are set out in terms of these tests plus many other properties, such as the flashpoint, the percent sulfur, and the viscosity. 

Other averages for boiling points are used in evaluating K and the other physical properties in this Appendix. (Refer to Danbert or Maxwell S for details.) This factor has been related to many of the other simple tests and properties of petroleum fractions, such as viscosity, molecular weight, critical temperature, and percentage of hydrogen, so that it is quite easy to estimate the factor for any particular sample. Furthermore, tables of the UOP characterization factor are available for a wide variety of common types of petroleum fractions as shown in Table K.l for typical liquids. 

Proton Spectra—wAverage Molecule Parameters. Proton NMR has, of course, found considerable and important use in the characterization of petroleum constituents and fractions. In the case of isolated individual components, NMR can be a powerful tool in the elucidation of structure. However, this approach is obviously limited when we are dealing with immensely complex, multicomponent mixtures such as petroleum fractions. 

The ebullioscope of von Weber, shown in Fig. 32, operates in a similar manner. With this apparatus vapour pressure curves in the range of 10 to 760 mm Hg can be determined, whilst it can also be employed for other purposes, for instance for the calibration of thermometers, ebullioscopic measurements, the determination of vapour-liquid equilibria and the characterization of distillate fractions, such as those from petroleum and tar [33]. The apparatus consists of a vertical boiling tube A of 34 mm I.D. and 500 mm length. At its lower end the liquid is heated by an electric soldering iron element B of variable output, which is contained in a well C, the outer... 

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