273
Petroleum Analysis
and are free from interfering lower and higher molecular weight species. Because of the reduced
complexity of the gas chromatographic fractions, mass spectrometric scans carried out at regular
intervals yield simpler spectra from which compound classes can more easily be determined.
Pyrolysis gas chromatography can be used for information on the gross composition of heavy
petroleum fractions. In this technique, the sample under investigation is pyrolyzed and the products
are introduced into a gas chromatography system for analysis. There has also been extensive use of
pyrolysis gas chromatography by geochemists to correlate crude oil with source rock and to derive
geochemical characterization parameters from oil-bearing strata.
In the technique of inverse GLC, the sample under study is used as the stationary phase and a
number of volatile test compounds are chromatographed on this column. The interaction coefficient
determined for these compounds is a measure of certain qualities of the liquid phase. The coefficient is therefore indicative of the chemical interaction of the solute with the stationary phase. The
technique has been used largely for studies of asphalt.
10.8.2 sImulAted dIstIllAtIon
GLC has also been found useful for the preparation of simulated distillation curves. By integrating
increments of the total area of the chromatogram and relating these to the boiling points of the components within each increment, which are calculated from the known boiling points of the easily
recognizable n-paraffins, simulated boiling point data are produced.
Distillation is the most widely used separation process in the petroleum industry (Chapters 15
and 17). In fact, knowledge of the boiling range of crude feedstocks and finished products has been
an essential part of the determination of feedstock quality since the start of the refining industry.
The technique has been used for control of plant and refinery processes as well as for predicting
product slates. Thus it is not surprising that routine laboratory scale distillation tests have been
widely used for determining the boiling ranges of crude feedstocks and a whole slate of refinery
products (Chapter 26).
There are some limitations to the routine distillation tests. For example, although heavy crude
oils contain volatile constituents, it is not always advisable to use distillation for identification of
these volatile constituents. Thermal decomposition of the constituents of petroleum is known to
occur at approximately 350°C (660°F). Thermal decomposition of the constituents of the heavier,
but immature, crude oil has been known to commence at temperatures as low as 200°C (390°F),
however. Thus, thermal alteration of the constituents and erroneous identification of the decomposition products as natural constituents is always a possibility.
On the other hand, the limitations to the use of distillation as an identification technique may
be economic, and detailed fractionation of the sample may also be of secondary importance. There
have been attempts to combat these limitations, but it must be recognized that the general shape of a
one-plate distillation curve is often adequate for making engineering calculations, correlating with
other physical properties, and predicting the product slate.
However, a low-resolution, temperature-programmed gas chromatographic analysis has been
developed to simulate the time-consuming true boiling point distillation (ASTM D2887). The
method relies on the general observation that hydrocarbons are eluted from a nonpolar adsorbent in
the order of their boiling points. The method has been well researched in terms of method development and application (MacAllister and DeRuiter, 1985; Romanowski and Thomas, 1985; Schwartz
et al., 1987). The benefits of the technique include good comparisons with other ASTM distillation
data as well as application to higher boiling fractions of petroleum (Speight, 2001, 2002).
The full development of simulated distillation as a routine procedure has been made possible by
the massive expansion in gas chromatographic instrumentation (such as the introduction of automatic temperature programming) since the 1960s. In fact, a fully automated simulated distillation
system, under computer control, can operate continuously to provide finished reports in a choice of
formats that agree well with true boiling point data. For example, data output includes the provision
Petroleum Analysis
and are free from interfering lower and higher molecular weight species. Because of the reduced
complexity of the gas chromatographic fractions, mass spectrometric scans carried out at regular
intervals yield simpler spectra from which compound classes can more easily be determined.
Pyrolysis gas chromatography can be used for information on the gross composition of heavy
petroleum fractions. In this technique, the sample under investigation is pyrolyzed and the products
are introduced into a gas chromatography system for analysis. There has also been extensive use of
pyrolysis gas chromatography by geochemists to correlate crude oil with source rock and to derive
geochemical characterization parameters from oil-bearing strata.
In the technique of inverse GLC, the sample under study is used as the stationary phase and a
number of volatile test compounds are chromatographed on this column. The interaction coefficient
determined for these compounds is a measure of certain qualities of the liquid phase. The coefficient is therefore indicative of the chemical interaction of the solute with the stationary phase. The
technique has been used largely for studies of asphalt.
10.8.2 sImulAted dIstIllAtIon
GLC has also been found useful for the preparation of simulated distillation curves. By integrating
increments of the total area of the chromatogram and relating these to the boiling points of the components within each increment, which are calculated from the known boiling points of the easily
recognizable n-paraffins, simulated boiling point data are produced.
Distillation is the most widely used separation process in the petroleum industry (Chapters 15
and 17). In fact, knowledge of the boiling range of crude feedstocks and finished products has been
an essential part of the determination of feedstock quality since the start of the refining industry.
The technique has been used for control of plant and refinery processes as well as for predicting
product slates. Thus it is not surprising that routine laboratory scale distillation tests have been
widely used for determining the boiling ranges of crude feedstocks and a whole slate of refinery
products (Chapter 26).
There are some limitations to the routine distillation tests. For example, although heavy crude
oils contain volatile constituents, it is not always advisable to use distillation for identification of
these volatile constituents. Thermal decomposition of the constituents of petroleum is known to
occur at approximately 350°C (660°F). Thermal decomposition of the constituents of the heavier,
but immature, crude oil has been known to commence at temperatures as low as 200°C (390°F),
however. Thus, thermal alteration of the constituents and erroneous identification of the decomposition products as natural constituents is always a possibility.
On the other hand, the limitations to the use of distillation as an identification technique may
be economic, and detailed fractionation of the sample may also be of secondary importance. There
have been attempts to combat these limitations, but it must be recognized that the general shape of a
one-plate distillation curve is often adequate for making engineering calculations, correlating with
other physical properties, and predicting the product slate.
However, a low-resolution, temperature-programmed gas chromatographic analysis has been
developed to simulate the time-consuming true boiling point distillation (ASTM D2887). The
method relies on the general observation that hydrocarbons are eluted from a nonpolar adsorbent in
the order of their boiling points. The method has been well researched in terms of method development and application (MacAllister and DeRuiter, 1985; Romanowski and Thomas, 1985; Schwartz
et al., 1987). The benefits of the technique include good comparisons with other ASTM distillation
data as well as application to higher boiling fractions of petroleum (Speight, 2001, 2002).
The full development of simulated distillation as a routine procedure has been made possible by
the massive expansion in gas chromatographic instrumentation (such as the introduction of automatic temperature programming) since the 1960s. In fact, a fully automated simulated distillation
system, under computer control, can operate continuously to provide finished reports in a choice of
formats that agree well with true boiling point data. For example, data output includes the provision