295
Structural Group Analysis
The method assumes that atoms other than carbon and hydrogen are not major components,
olefins are absent, the number of rings is greater than one, and the rings are the fused naphthalene
type rather than biphenyl type.
11.2.2 sPeCtrosCoPIC metHods
A decrease in the volatility of the petroleum constituents in residua precludes the use of gas–liquid
chromatography for identification purposes, and it is at this stage that methods of structural analysis
involving physical property determinations become more predominant.
With the startling advances in spectroscopic techniques after World War II, chemists and technologists have been able to gain a better understanding of the chemical nature of petroleum and, therefore,
of the chemical changes which occur during refining. Consequently, new fields of research nave been
opened involving the structural determinations of fossil fuels, and their derived products, by a variety
of physical, chemical, and spectroscopic techniques. Indeed, a large number of the individual constituents of petroleum have been identified; this has been an aid not only to the refiner but also to the
chemist and geochemist whose interests lie in the ways and means by which petroleum was formed
from its precursors. Scientifically interesting as this may be, the real message lies in understanding the
formation of petroleum and the types of formations where more reserves might be discovered.
The application of spectroscopic methods to structural analysis is a fairly recent innovation but
has received considerable attention, nevertheless. As composition studies in petroleum advance to
the higher molecular weight ranges, the physical nature of the material often requires that the structural analysis be performed by a more convenient and suitable technique. For example, gas–liquid
chromatography may well suffice for the identification of the volatile constituents of petroleum, as
well as for volatile petroleum products.
However, a point will certainly be reached at which even the determination of the various
physical properties, outlined in the previous section, may become tedious and impractical, if not
impossible. Such a point is usually reached when investigators turn their attention to the asphaltic
constituents of petroleum; the asphaltenes, the resins, and the higher boiling or even nonvolatile
portion of the oily constituents.
It is perhaps for this reason that spectroscopic methods of structural analysis have come into
fairly common usage. This is not to say that distinct divisions should be made and a particular
method for structural analysis be assigned to a particular fraction. It is in fact preferred that as many
methods of structural analysis as possible be applied to any particular fraction to gain an overall
picture of the structural entities present. However, it is expected that the chemical and physical
nature of the various fractions will most certainly preclude the use of one or more of the methods
proposed for structural analysis.
It is also appropriate at this point to give a brief description of other methods that are used for the
identification of the constituents of petroleum. It is not intended to convey here that any one of these
methods can be used for identification purposes. However, although these methods may fall short
of acceptability as methods for the identification of individual constituents, they are recognized as
methods by which an overall evaluation of the feedstock may be obtained in terms of molecular
types. It is appropriate to describe these methods briefly at this point to place them in their context
relative to the other methods already described.
11.2.2.1 Infrared Spectroscopy
Infrared absorption spectroscopy is an excellent method for providing detailed information about
the chemical constitution of organic materials. Infrared absorption spectroscopy is one of the most
widely used techniques for examining the chemical constitution of organic materials. Whether the
material being examined is a single compound or a mixture, infrared absorption spectroscopy offers
valuable information about the hydrocarbon skeleton and about the functional groups in petroleum
(Wen et al., 1978).
Structural Group Analysis
The method assumes that atoms other than carbon and hydrogen are not major components,
olefins are absent, the number of rings is greater than one, and the rings are the fused naphthalene
type rather than biphenyl type.
11.2.2 sPeCtrosCoPIC metHods
A decrease in the volatility of the petroleum constituents in residua precludes the use of gas–liquid
chromatography for identification purposes, and it is at this stage that methods of structural analysis
involving physical property determinations become more predominant.
With the startling advances in spectroscopic techniques after World War II, chemists and technologists have been able to gain a better understanding of the chemical nature of petroleum and, therefore,
of the chemical changes which occur during refining. Consequently, new fields of research nave been
opened involving the structural determinations of fossil fuels, and their derived products, by a variety
of physical, chemical, and spectroscopic techniques. Indeed, a large number of the individual constituents of petroleum have been identified; this has been an aid not only to the refiner but also to the
chemist and geochemist whose interests lie in the ways and means by which petroleum was formed
from its precursors. Scientifically interesting as this may be, the real message lies in understanding the
formation of petroleum and the types of formations where more reserves might be discovered.
The application of spectroscopic methods to structural analysis is a fairly recent innovation but
has received considerable attention, nevertheless. As composition studies in petroleum advance to
the higher molecular weight ranges, the physical nature of the material often requires that the structural analysis be performed by a more convenient and suitable technique. For example, gas–liquid
chromatography may well suffice for the identification of the volatile constituents of petroleum, as
well as for volatile petroleum products.
However, a point will certainly be reached at which even the determination of the various
physical properties, outlined in the previous section, may become tedious and impractical, if not
impossible. Such a point is usually reached when investigators turn their attention to the asphaltic
constituents of petroleum; the asphaltenes, the resins, and the higher boiling or even nonvolatile
portion of the oily constituents.
It is perhaps for this reason that spectroscopic methods of structural analysis have come into
fairly common usage. This is not to say that distinct divisions should be made and a particular
method for structural analysis be assigned to a particular fraction. It is in fact preferred that as many
methods of structural analysis as possible be applied to any particular fraction to gain an overall
picture of the structural entities present. However, it is expected that the chemical and physical
nature of the various fractions will most certainly preclude the use of one or more of the methods
proposed for structural analysis.
It is also appropriate at this point to give a brief description of other methods that are used for the
identification of the constituents of petroleum. It is not intended to convey here that any one of these
methods can be used for identification purposes. However, although these methods may fall short
of acceptability as methods for the identification of individual constituents, they are recognized as
methods by which an overall evaluation of the feedstock may be obtained in terms of molecular
types. It is appropriate to describe these methods briefly at this point to place them in their context
relative to the other methods already described.
11.2.2.1 Infrared Spectroscopy
Infrared absorption spectroscopy is an excellent method for providing detailed information about
the chemical constitution of organic materials. Infrared absorption spectroscopy is one of the most
widely used techniques for examining the chemical constitution of organic materials. Whether the
material being examined is a single compound or a mixture, infrared absorption spectroscopy offers
valuable information about the hydrocarbon skeleton and about the functional groups in petroleum
(Wen et al., 1978).