Page 120 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

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100 CHARACTERIZATION AND PROPERTIES OF PETROLEUM FRACTIONS

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FIG. 3.18—Leco made CHNS-932 model elemental analyzer (courtesy of Chemical Engi-
neering Department at KU).
the instrument depend on the type of sample. For Newto- for simplicity in experimental measurement and the need for
nian and high-shear fluids such as engine oils, viscosity can another type for its application requires conversion methods
be measured by a capillary U-type viscometer. An example of between various distillation curves. The tedious procedures
such viscometers is the Cannon–Fenske viscometer. The test necessary to obtain experimental EFV data have given im-
method is described in ASTM D 445, which is equivalent to petus to the development of correlations for predicting EFV
ISO 3104 method, and kinematic viscosity is measured at tem- data from the analytical ASTM and TBP distillations. Sim-
peratures from 15 to 100 C(∼60 to 210 F). In this method, ulated distillation by gas chromatography appears to be the
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repeatability and reproducibility are 0.35 and 0.7%, respec- most simple, reproducible, and consistent method to describe
tively [5]. Another type of viscometer is a rotary viscometer, the boiling range of a hydrocarbon fraction unambiguously.
which is used for a wide range of shear rates, especially for TBP is the most useful distillation curve, while available data
low shear rate and viscous fluids such as lubricants and heavy might be ASTM D 86, ASTM D 2887, or ASTM D 1160 distilla-
petroleum fractions. In these viscometers, fluid is placed be- tion curves. ASTM [4] has accepted this technique as a tenta-
tween two surfaces, one is fixed and the other one is rotating. tive method for the “Determination of Boiling Range Distribu-
In these viscometers absolute viscosity can be measured and tion of Petroleum Fractions by Gas Chromatography” (ASTM
an example of such viscometers is the Brookfield viscome- D 2887). In most cases distillation data are reported in terms
ter. Details of measurement and prediction of viscosity of of ASTM D 86 or SD. In this section methods of calculation of
petroleum fractions are given in Chapter 8. As the viscosity average boiling points, interconversion of various distillation
of petroleum fractions, especially the heavy oils, is one of the curves, and prediction of complete distillation curves from a
most difficult properties to estimate, its experimental value is limited data are presented.
highly useful and desirable.
3.2.1 Average Boiling Points
Boiling points of petroleum fractions are presented by distil-
3.2 PREDICTION AND CONVERSION lation curves such as ASTM or TBP. However, in prediction of
OF DISTILLATION DATA physical properties and characterization of hydrocarbon mix-
tures a single characteristic boiling point is required. Gener-
Various distillation curves are introduced in Section 3.1.1. ally an average boiling point for a fraction is defined to de-
For simplicity ASTM is used to refer to ASTM D 86 distilla- termine the single characterizing boiling point. There are five
tion curve, similarly TBP, SD, and EFV refer to true boiling average boiling points defined by the following equations [9].
point, simulated distillation (ASTM D 2887), and equilibrium Three of these average boiling points are VABP (volume aver-
flash vaporization, respectively. Petroleum fractions have a age boiling point), MABP (molal average boiling point) and
range of boiling points. To use the correlations introduced WABP (weight average boiling point), defined for a mixture
in Chapter 2, a single value for boiling point is required. For of n components as
this reason there is a need for the definition of an average
boiling point or a characteristic boiling point based on a dis- (3.3) ABP = n
tillation curve. Availability of one type of distillation curve x i T bi
i=1

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