283
11
Structural Group Analysis
11.1 INTRODUCTION
Petroleum processing requires knowledge of feedstock properties (Chapters 9, 10, and 15) because
petroleum varies markedly in properties and composition according to the source. Knowledge
of petroleum properties is required for optimization of existing processes as well as for the development and design of new processes.
In the early days of petroleum processing, there was a lesser need to understand the character
and behavior of petroleum in the detail that is currently required. Refining involved distillation of
the valuable kerosene fraction that was required as an illuminant. After the commercialization
of the internal combustion engine, the desired product became gasoline and it was also obtained
by distillation. Even when crude oil that contained little natural gasoline was used, cracking
(i.e., thermal decomposition with simultaneous removal of distillate) became the modus operandi.
However, with the startling demands on the petroleum industry during and after World War II,
and the emergence of the age of petrochemicals and plastics, the petroleum industry needed to
produce materials not even considered as products in the decade before the war. Thus, petroleum
refining took on the role of technological innovator as new and better processes were invented and
advances in the use of materials for reactors were developed. In addition, there became a necessity
to find out more about petroleum so that refiner might be able to enjoy the luxury of predictability
and plan a product slate that was based on market demand—an often difficult task when the character of the crude oil was unknown! The idea that petroleum refining should be a hit-and-miss affair
was not acceptable.
Valuable information can be obtained from the true boiling point (TBP) curve, which is a function of percent weight distilled and temperature, that is, a boiling point distribution (Figure 11.1).
However, there are boiling point limitations on this function that are well below the final boiling
point (FBP) of a crude oil. In addition to the boiling point distribution, it is possible to measure bulk
physical properties such as specific gravity and viscosity that have assisted in the establishment of
certain empirical relationships for petroleum processing from the true boiling point curve. Many
of these relationships include assumptions that are based on experience with a range of feedstocks.
However, movement of the refining industry to feedstocks that contain higher proportions of cokeforming materials emphasizes the need for more definitive data that would enable more realistic
predictions to be made of crude oil behavior in refinery operations.
The history of analysis of the constituents in petroleum started more than 150 years ago and the
rapid advances in analytic techniques have allowed the identification of large numbers of petroleum
constituents. At this time, the major chemical types of compounds that exist in crude oil have been
identified and many members of the various homologous series have been separated or conclusively
identified by various techniques (Table 11.1; Chapter 8; see Rossini et al., 1953 for historical details).
Since the publication of the first edition of this book in 1980, researchers have made advances in
areas relating to the use of petroleum and the environmental aspects of petroleum use. However, and
there are those who will sorely disagree with me, very little progress has been made on the so-called
average structure of the petroleum asphaltene fraction—because the complex asphaltene fraction
does not have an average structure.
During the 1960s and 1970s, the postulation of average structure, for example, the asphaltene fraction, was a serious area of study. As the studies evolved, it became clear that the asphaltene fraction
11
Structural Group Analysis
11.1 INTRODUCTION
Petroleum processing requires knowledge of feedstock properties (Chapters 9, 10, and 15) because
petroleum varies markedly in properties and composition according to the source. Knowledge
of petroleum properties is required for optimization of existing processes as well as for the development and design of new processes.
In the early days of petroleum processing, there was a lesser need to understand the character
and behavior of petroleum in the detail that is currently required. Refining involved distillation of
the valuable kerosene fraction that was required as an illuminant. After the commercialization
of the internal combustion engine, the desired product became gasoline and it was also obtained
by distillation. Even when crude oil that contained little natural gasoline was used, cracking
(i.e., thermal decomposition with simultaneous removal of distillate) became the modus operandi.
However, with the startling demands on the petroleum industry during and after World War II,
and the emergence of the age of petrochemicals and plastics, the petroleum industry needed to
produce materials not even considered as products in the decade before the war. Thus, petroleum
refining took on the role of technological innovator as new and better processes were invented and
advances in the use of materials for reactors were developed. In addition, there became a necessity
to find out more about petroleum so that refiner might be able to enjoy the luxury of predictability
and plan a product slate that was based on market demand—an often difficult task when the character of the crude oil was unknown! The idea that petroleum refining should be a hit-and-miss affair
was not acceptable.
Valuable information can be obtained from the true boiling point (TBP) curve, which is a function of percent weight distilled and temperature, that is, a boiling point distribution (Figure 11.1).
However, there are boiling point limitations on this function that are well below the final boiling
point (FBP) of a crude oil. In addition to the boiling point distribution, it is possible to measure bulk
physical properties such as specific gravity and viscosity that have assisted in the establishment of
certain empirical relationships for petroleum processing from the true boiling point curve. Many
of these relationships include assumptions that are based on experience with a range of feedstocks.
However, movement of the refining industry to feedstocks that contain higher proportions of cokeforming materials emphasizes the need for more definitive data that would enable more realistic
predictions to be made of crude oil behavior in refinery operations.
The history of analysis of the constituents in petroleum started more than 150 years ago and the
rapid advances in analytic techniques have allowed the identification of large numbers of petroleum
constituents. At this time, the major chemical types of compounds that exist in crude oil have been
identified and many members of the various homologous series have been separated or conclusively
identified by various techniques (Table 11.1; Chapter 8; see Rossini et al., 1953 for historical details).
Since the publication of the first edition of this book in 1980, researchers have made advances in
areas relating to the use of petroleum and the environmental aspects of petroleum use. However, and
there are those who will sorely disagree with me, very little progress has been made on the so-called
average structure of the petroleum asphaltene fraction—because the complex asphaltene fraction
does not have an average structure.
During the 1960s and 1970s, the postulation of average structure, for example, the asphaltene fraction, was a serious area of study. As the studies evolved, it became clear that the asphaltene fraction