376
The Chemistry and Technology of Petroleum
Therefore, appropriate emulsion-breaking agents have to be chosen very carefully, usually with
the help of previous laboratory evaluations. Water- or oil-soluble demulsifiers, the latter often being
nonionic surface-active alkylene oxide adducts, are used for this purpose. But, as had been said in
the foregoing, the most suitable demulsifier has to be chosen for each case from a large number of
such substances in the market by a prior laboratory evaluation.
14.3 FACTORS INFLUENCING INSTABILITY AND INCOMPATIBILITY
A number of experimental methods are available for estimation of the factors that influence instability/incompatibility. These factors have been explored and attempts made to estimate the character of
the fuel or product with varied results.
14.3.1 elementAl AnAlysIs
The ultimate analysis (elemental composition) of petroleum and its products is not reported to the
same extent as for coal (Speight, 2013). Nevertheless, there are ASTM procedures (ASTM, 2012)
for the ultimate analysis of petroleum and petroleum products (Chapter 10), but many such methods
may have been designed for other materials.
Of the data that are available, the proportions of the elements in petroleum vary only slightly
over narrow limits: carbon 83.0%–87.0% w/w, hydrogen 10.0%–14.0% w/w, nitrogen 0.10%–2.0%
w/w, oxygen 0.05%–1.5% w/w, and sulfur 0.05%–6.0% w/w (Chapters 8 and 10). And yet, there is a
wide variation in physical properties from the lighter more mobile crude oils at one extreme to the
extra heavy crude oil at the other extreme (Chapter 1). In terms of the instability and incompatibility
of petroleum and petroleum products, the heteroatom content appears to represent the greatest influence. In fact, it is not only the sulfur and nitrogen content of crude oil that are important parameters
in respect of the processing methods, which have to be used in order to produce fuels of specification sulfur concentrations, but also the type of sulfur and nitrogen species in the oil. There could
well be a relation between nitrogen and sulfur content and crude oil (or product) stability; higher
nitrogen and sulfur crude oils are suspect of higher sludge-forming tendencies.
14.3.2 densIty And sPeCIFIC grAvIty
In the earlier years of the petroleum industry, density and specific gravity (with the API gravity)
were the principal specifications for feedstocks and refinery products (Chapters 10, 24, and 26).
They were used to give an estimate of the most desirable product, that is, kerosene, in crude oil.
At the present time, a series of standard tests exist for determining density and specific gravity
(Chapter 10) (Speight, 2001, 2002).
There is no direct relation between the density and specific gravity of crude oils to their sludgeforming tendencies, but crude oil having a higher density (thus, a lower API gravity) is generally
more susceptible to sludge formation, presumably because of the higher content of the polar/
asphaltic constituents.
14.3.3 volAtIlIty
Petroleum can be subdivided by distillation into a variety of fractions of different boiling ranges or
cut points (Chapters 10 and 17). In fact, distillation was, and still is, the method for feedstock evaluation for various refinery options. Indeed, volatility is one of the major tests for petroleum products,
and it is inevitable that the majority of all products will, at some stage of their history, be tested for
volatility characteristics (Chapter 10).
As an early part of characterization studies, a correlation was observed between the quality
of petroleum fractions and their heteroatom content (Figure 14.1), since gasoline, kerosene, diesel
The Chemistry and Technology of Petroleum
Therefore, appropriate emulsion-breaking agents have to be chosen very carefully, usually with
the help of previous laboratory evaluations. Water- or oil-soluble demulsifiers, the latter often being
nonionic surface-active alkylene oxide adducts, are used for this purpose. But, as had been said in
the foregoing, the most suitable demulsifier has to be chosen for each case from a large number of
such substances in the market by a prior laboratory evaluation.
14.3 FACTORS INFLUENCING INSTABILITY AND INCOMPATIBILITY
A number of experimental methods are available for estimation of the factors that influence instability/incompatibility. These factors have been explored and attempts made to estimate the character of
the fuel or product with varied results.
14.3.1 elementAl AnAlysIs
The ultimate analysis (elemental composition) of petroleum and its products is not reported to the
same extent as for coal (Speight, 2013). Nevertheless, there are ASTM procedures (ASTM, 2012)
for the ultimate analysis of petroleum and petroleum products (Chapter 10), but many such methods
may have been designed for other materials.
Of the data that are available, the proportions of the elements in petroleum vary only slightly
over narrow limits: carbon 83.0%–87.0% w/w, hydrogen 10.0%–14.0% w/w, nitrogen 0.10%–2.0%
w/w, oxygen 0.05%–1.5% w/w, and sulfur 0.05%–6.0% w/w (Chapters 8 and 10). And yet, there is a
wide variation in physical properties from the lighter more mobile crude oils at one extreme to the
extra heavy crude oil at the other extreme (Chapter 1). In terms of the instability and incompatibility
of petroleum and petroleum products, the heteroatom content appears to represent the greatest influence. In fact, it is not only the sulfur and nitrogen content of crude oil that are important parameters
in respect of the processing methods, which have to be used in order to produce fuels of specification sulfur concentrations, but also the type of sulfur and nitrogen species in the oil. There could
well be a relation between nitrogen and sulfur content and crude oil (or product) stability; higher
nitrogen and sulfur crude oils are suspect of higher sludge-forming tendencies.
14.3.2 densIty And sPeCIFIC grAvIty
In the earlier years of the petroleum industry, density and specific gravity (with the API gravity)
were the principal specifications for feedstocks and refinery products (Chapters 10, 24, and 26).
They were used to give an estimate of the most desirable product, that is, kerosene, in crude oil.
At the present time, a series of standard tests exist for determining density and specific gravity
(Chapter 10) (Speight, 2001, 2002).
There is no direct relation between the density and specific gravity of crude oils to their sludgeforming tendencies, but crude oil having a higher density (thus, a lower API gravity) is generally
more susceptible to sludge formation, presumably because of the higher content of the polar/
asphaltic constituents.
14.3.3 volAtIlIty
Petroleum can be subdivided by distillation into a variety of fractions of different boiling ranges or
cut points (Chapters 10 and 17). In fact, distillation was, and still is, the method for feedstock evaluation for various refinery options. Indeed, volatility is one of the major tests for petroleum products,
and it is inevitable that the majority of all products will, at some stage of their history, be tested for
volatility characteristics (Chapter 10).
As an early part of characterization studies, a correlation was observed between the quality
of petroleum fractions and their heteroatom content (Figure 14.1), since gasoline, kerosene, diesel