348
The Chemistry and Technology of Petroleum
13.2.3.1 Composition
Elemental constitutions of a suite of petroleum resins (Koots and Speight, 1975), isolated by the
same procedure and therefore comparable, show that the proportions of carbon and hydrogen, like
those of the asphaltene constituents, vary over a narrow range: 85% ± 3% carbon and 10.5% ± 1%
hydrogen. The proportions of nitrogen (0.5% ± 0.15%) and oxygen (1.0% ± 0.2%) also appear to vary
over a narrow range, but the amount of sulfur (0.4%–5.1%) varies over a much wider range.
There are notable increases in the H/C ratios of the resins relative to those of the asphaltene constituents (Chapter 12; Speight, 1994). Presumably, this indicates that aromatization is less advanced
in the resins than in the asphaltenes. It may actually be that the asphaltenes are maturation products
of the resins, and if this is the case, it indicates that one of the maturation processes involves aromatization of the nonaromatic portion of the resin. There is also a tendency to increased proportions of
nitrogen, oxygen, and sulfur in the resins relative to the asphaltenes. There are, however, exceptions
to this trend, notably in the proportions of sulfur present in the asphaltenes and resins.
13.2.3.2 Structure
Initial postulates of resin structure invoked the concept of long paraffinic chains with naphthenic
rings interspersed throughout. Other structures used the idea of condensed aromatic and naphthenic ring systems and allowed the interspersion of heteroatoms throughout the molecule.
Structural investigations of resin fractions have not been carried out to the same extent as they
have been on the asphaltene fractions. Nevertheless, the data available from, for the most part, the
molecular magnetic resonance method indicate that the resin molecules are lower molecular weight
than the asphaltenes from the same crude oil.
Infrared spectroscopic investigation of the resins also indicates the presence of hydrogen-bonded
hydroxyl groups. In addition, at high concentrations (10%), a band is evident at 3490 cm −1 that
is assigned to N–H functions in pyrrole(s) or indole(s). Acetylation of the resins, combined with
detailed infrared spectroscopic examination, has also established the presence of ester and acid
functions as well as carbonyl (ketone or quinone) functions. As with the asphaltenes, the presence
of ether or sulfur–oxygen functions cannot be discounted on the basis of the available evidence.
There is also evidence that the structural aspects of the constituents of the resin fraction may differ
very little from those of the corresponding asphaltene fraction, the main difference being the proportion of aromatic carbon within each fraction (Koots and Speight, 1975; Selucky et al., 1981). It has
been postulated that resins and asphaltenes are small fragments of kerogen (Tissot, 1984) or at least
have the same origins as the kerogen (Chapter 5) and, therefore, a relationship might be anticipated.
Identification of the constituents of complex mixtures (such as petroleum residua) by molecular
type may be achieved by a variety of methods (Chapters 10 and 11). These methods can be generally
classified into three groups:
1. Spectroscopic techniques
2. Physical property methods
3. Chemical techniques
Using these methods, various structural parameters are derived from a particular property by a
sequence of mathematical manipulations. It is difficult to completely separate these three methods
of structural elucidation and there must, by virtue of need and relationship, be some overlap.
The end results of the application of these methods are indications of the structural types present
in the material. However, there is the unfortunate tendency of researchers to then attempt to interrelate these structural types into a so-called average structure and there is caution advised in the
use of average structures (Chapter 11).
Much work has been carried out on the application of the spectroscopic and physical property methods to the deduction of the structural types in the high boiling fractions of petroleum.
Application of chemical reactivity to the elucidation and description of the structural types in
The Chemistry and Technology of Petroleum
13.2.3.1 Composition
Elemental constitutions of a suite of petroleum resins (Koots and Speight, 1975), isolated by the
same procedure and therefore comparable, show that the proportions of carbon and hydrogen, like
those of the asphaltene constituents, vary over a narrow range: 85% ± 3% carbon and 10.5% ± 1%
hydrogen. The proportions of nitrogen (0.5% ± 0.15%) and oxygen (1.0% ± 0.2%) also appear to vary
over a narrow range, but the amount of sulfur (0.4%–5.1%) varies over a much wider range.
There are notable increases in the H/C ratios of the resins relative to those of the asphaltene constituents (Chapter 12; Speight, 1994). Presumably, this indicates that aromatization is less advanced
in the resins than in the asphaltenes. It may actually be that the asphaltenes are maturation products
of the resins, and if this is the case, it indicates that one of the maturation processes involves aromatization of the nonaromatic portion of the resin. There is also a tendency to increased proportions of
nitrogen, oxygen, and sulfur in the resins relative to the asphaltenes. There are, however, exceptions
to this trend, notably in the proportions of sulfur present in the asphaltenes and resins.
13.2.3.2 Structure
Initial postulates of resin structure invoked the concept of long paraffinic chains with naphthenic
rings interspersed throughout. Other structures used the idea of condensed aromatic and naphthenic ring systems and allowed the interspersion of heteroatoms throughout the molecule.
Structural investigations of resin fractions have not been carried out to the same extent as they
have been on the asphaltene fractions. Nevertheless, the data available from, for the most part, the
molecular magnetic resonance method indicate that the resin molecules are lower molecular weight
than the asphaltenes from the same crude oil.
Infrared spectroscopic investigation of the resins also indicates the presence of hydrogen-bonded
hydroxyl groups. In addition, at high concentrations (10%), a band is evident at 3490 cm −1 that
is assigned to N–H functions in pyrrole(s) or indole(s). Acetylation of the resins, combined with
detailed infrared spectroscopic examination, has also established the presence of ester and acid
functions as well as carbonyl (ketone or quinone) functions. As with the asphaltenes, the presence
of ether or sulfur–oxygen functions cannot be discounted on the basis of the available evidence.
There is also evidence that the structural aspects of the constituents of the resin fraction may differ
very little from those of the corresponding asphaltene fraction, the main difference being the proportion of aromatic carbon within each fraction (Koots and Speight, 1975; Selucky et al., 1981). It has
been postulated that resins and asphaltenes are small fragments of kerogen (Tissot, 1984) or at least
have the same origins as the kerogen (Chapter 5) and, therefore, a relationship might be anticipated.
Identification of the constituents of complex mixtures (such as petroleum residua) by molecular
type may be achieved by a variety of methods (Chapters 10 and 11). These methods can be generally
classified into three groups:
1. Spectroscopic techniques
2. Physical property methods
3. Chemical techniques
Using these methods, various structural parameters are derived from a particular property by a
sequence of mathematical manipulations. It is difficult to completely separate these three methods
of structural elucidation and there must, by virtue of need and relationship, be some overlap.
The end results of the application of these methods are indications of the structural types present
in the material. However, there is the unfortunate tendency of researchers to then attempt to interrelate these structural types into a so-called average structure and there is caution advised in the
use of average structures (Chapter 11).
Much work has been carried out on the application of the spectroscopic and physical property methods to the deduction of the structural types in the high boiling fractions of petroleum.
Application of chemical reactivity to the elucidation and description of the structural types in