Page 117 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

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3. CHARACTERIZATION OF PETROLEUM FRACTIONS 97
stream may be analyzed every 20 min and automatic adjust-
Feedstock
ment can be made to the refinery unit. In crude assay anal-
n-Heptane
ysis distillation is being replaced by chromatography tech-
niques. The LC method is used for less volatile mixtures such
as heavy petroleum fractions and residues. Use of LC for sepa-
ration of saturated and aromatic hydrocarbons is described in
Asphaltenes Deasphaltened Oil ASTM D 2549 test method. Various forms of chromatography
techniques have been applied to a wide range of petroleum
Alumina products for analysis, such as PONA, PIONA, PNA, and SARA.
One of the most useful types of liquid chromatography is
high performance liquid chromatography (HPLC), which can
be used to identify different types of hydrocarbon groups.
Polar Aromatics Oils One particular application of HPLC is to identify asphaltene
(Resins) and resin type constituents in nonvolatile feedstocks such as
Alumina residua. Total time required to analyze a sample by HPLC is
just a few minutes. One of the main advantages of HPLC is
that the boiling range of sample is immaterial. A HPLC ana-
lyzer is shown in Fig. 3.15.
The accuracy of chromatography techniques mainly
Naphthene Aromatics Saturates
(Aromatics) depends on the type of detector used [7]. In Section 3.1.1.3,
flame ionization (FID) and thermal conductivity (TCD) detec-
FIG. 3.14—Separation of asphaltenes and resins from tors are described, which are widely used in GC. For LC the
petroleum fractions. Reprinted from Ref. [7], p. 281, by cour- most common detectors are refractive index detector (RID)
tesy of Marcel Dekker, Inc. and wavelength UV (ultraviolet) detector. UV spectroscopy is
particularly useful to identify the types of aromatics in asphal-
liquid mobile phase it is called a liquid chromatograph (LC). tenic fractions. Another spectroscopy method is conventional
As discussed earlier, components can be separated by their infrared (IR) spectroscopy, which yields information about
boiling points through GC analysis. In advanced petroleum the functional features of various petroleum constituents.
refineries automatic online GCs are used for continuous anal- For example, IR spectroscopy will aid in the identification of
ysis of various streams to control the quality of products. A N H and O H functions and the nature of polymethylene

FIG. 3.15—A HPLC instrument (courtesy of Chemical Engineering Department at KU).

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