350
The Chemistry and Technology of Petroleum
Thus, most of those substances with greater molecular weight and with the most pronounced aromatic
nature are situated closest to the nucleus and are surrounded by lighter constituents of lesser aromatic
nature. The transition of the intermicellar (dispersed or oil) phase is gradual and almost continuous.
And, there is no reason to reject this hypothesis. It has survived the test of time and the current
discussion focuses on the actual mechanics of micelle structure.
It is also known that, in the absence of the resins, the asphaltenes are incompatible with the
remainder of the crude oil (Swanson, 1942; Witherspoon and Munir, 1960; Koots and Speight, 1975).
This indicates that the resin fraction is, under normal operating conditions, essential for the dispersability of the asphaltene constituents and represents one of several factors that need to be taken
into account when attempting to resolve the issues of incompatibility and sediment formation
(Mushrush and Speight, 1995).
Continued attention to this aspect of asphaltene chemistry has led to the postulate that asphaltene–
asphaltene clusters form the center of the micelle but other options such as a single asphaltene–resin
cluster at the center of the micelle have also been proposed.
The relationships of petroleum constituents are an essential factor in determining the structure
of petroleum systems. There is a multitude of structural types in petroleum and much effort has
been given to the identification of these constituents (Chapters 10 and 11). However, it is not only
the structures of the constituents that determine the structure of petroleum but also the means by
which these constituents relate to one another. Remembering that the asphaltene constituents are not
soluble or dispersible in the de-resined deasphaltened oil, this involves the transition from one phase
to another to present a homogenous mixture.
For example, while the reactivity of molecular species can be assessed on the basis of bond energies, the reactivity of a particular bond is also subject to its environment and can change the order
of reactivity that has been assessed on the basis of relative bond energy. In the present context, the
relationships of petroleum constituents to one another are also subject to the environment. And a
major determinant of this relationship is stereochemistry of the constituents as they relate to one
another. It must be appreciated that the stereochemistry of organic compounds is often a major factor in determining reactivity and properties (Eliel and Wilen, 1994).
The evidence available in the literature appears to indicate that the hydrocarbon structures
and some features, such as the various condensed ring systems, in different crude oils are similar
(from the asphaltenes and resins to the constituents of the oil fraction). A wide variety of source
materials are involved in petroleum genesis (Chapter 3). Thus, on a molecular scale, there are
substantial structural differences between the constituents of different crude oils as dictated by
regional variations in the composition of the first-formed protopetroleum and the maturation
conditions.
The structural differences in different crude oils are reflected in the difficulty with which resins
from one crude oil peptize asphaltenes from a different crude oil and the instability of the blend
(Koots and Speight, 1975). For reference, in asphaltene science as in colloid science, the terms
peptized, dispersed, and solubilized are often used interchangeably to describe the means by which
asphaltenes exist within petroleum.
Some researchers, in addition to deriving broad generalities from the use of a variety of analytical
techniques, are attempting to assign specific molecular configurations to the asphaltene constituents.
Perhaps, it is of little value to petroleum technology and is certainly beyond the scope of the available methods to derive such formulae.
However, a variety of structures exist in the asphaltene fraction (in which there is a decided
hydrogen deficiency). But the close relationships of the various hydrocarbon series comprising
the asphaltene constituents, resin constituents, and oil constituents give rise to overlapping of
fractions into neighboring series, both in molecular weight and in the atomic hydrogen-to-carbon
atomic ratio.
The asphaltene constituents have been proposed to be the final (excluding carbenes and carboids,
those organic fractions of petroleum that are insoluble in toluene or benzene) maturation products
The Chemistry and Technology of Petroleum
Thus, most of those substances with greater molecular weight and with the most pronounced aromatic
nature are situated closest to the nucleus and are surrounded by lighter constituents of lesser aromatic
nature. The transition of the intermicellar (dispersed or oil) phase is gradual and almost continuous.
And, there is no reason to reject this hypothesis. It has survived the test of time and the current
discussion focuses on the actual mechanics of micelle structure.
It is also known that, in the absence of the resins, the asphaltenes are incompatible with the
remainder of the crude oil (Swanson, 1942; Witherspoon and Munir, 1960; Koots and Speight, 1975).
This indicates that the resin fraction is, under normal operating conditions, essential for the dispersability of the asphaltene constituents and represents one of several factors that need to be taken
into account when attempting to resolve the issues of incompatibility and sediment formation
(Mushrush and Speight, 1995).
Continued attention to this aspect of asphaltene chemistry has led to the postulate that asphaltene–
asphaltene clusters form the center of the micelle but other options such as a single asphaltene–resin
cluster at the center of the micelle have also been proposed.
The relationships of petroleum constituents are an essential factor in determining the structure
of petroleum systems. There is a multitude of structural types in petroleum and much effort has
been given to the identification of these constituents (Chapters 10 and 11). However, it is not only
the structures of the constituents that determine the structure of petroleum but also the means by
which these constituents relate to one another. Remembering that the asphaltene constituents are not
soluble or dispersible in the de-resined deasphaltened oil, this involves the transition from one phase
to another to present a homogenous mixture.
For example, while the reactivity of molecular species can be assessed on the basis of bond energies, the reactivity of a particular bond is also subject to its environment and can change the order
of reactivity that has been assessed on the basis of relative bond energy. In the present context, the
relationships of petroleum constituents to one another are also subject to the environment. And a
major determinant of this relationship is stereochemistry of the constituents as they relate to one
another. It must be appreciated that the stereochemistry of organic compounds is often a major factor in determining reactivity and properties (Eliel and Wilen, 1994).
The evidence available in the literature appears to indicate that the hydrocarbon structures
and some features, such as the various condensed ring systems, in different crude oils are similar
(from the asphaltenes and resins to the constituents of the oil fraction). A wide variety of source
materials are involved in petroleum genesis (Chapter 3). Thus, on a molecular scale, there are
substantial structural differences between the constituents of different crude oils as dictated by
regional variations in the composition of the first-formed protopetroleum and the maturation
conditions.
The structural differences in different crude oils are reflected in the difficulty with which resins
from one crude oil peptize asphaltenes from a different crude oil and the instability of the blend
(Koots and Speight, 1975). For reference, in asphaltene science as in colloid science, the terms
peptized, dispersed, and solubilized are often used interchangeably to describe the means by which
asphaltenes exist within petroleum.
Some researchers, in addition to deriving broad generalities from the use of a variety of analytical
techniques, are attempting to assign specific molecular configurations to the asphaltene constituents.
Perhaps, it is of little value to petroleum technology and is certainly beyond the scope of the available methods to derive such formulae.
However, a variety of structures exist in the asphaltene fraction (in which there is a decided
hydrogen deficiency). But the close relationships of the various hydrocarbon series comprising
the asphaltene constituents, resin constituents, and oil constituents give rise to overlapping of
fractions into neighboring series, both in molecular weight and in the atomic hydrogen-to-carbon
atomic ratio.
The asphaltene constituents have been proposed to be the final (excluding carbenes and carboids,
those organic fractions of petroleum that are insoluble in toluene or benzene) maturation products