386
The Chemistry and Technology of Petroleum
Thus, the deposition of asphaltene constituents is the consequence of instability of the crude oil
or the crude oil product (e.g., fuel oil). The asphaltene constituents are stabilized by resin constituents (Chapter 12) and maintained in the crude oil due to this stabilization. Asphaltene dispersants
are substitutes for the natural resin constituents and are able to keep the asphaltene constituents
dispersed to prevent flocculation/aggregation and phase separation (Speight, 1994; Browarzik et al.,
1999). Dispersants will also clean up sludge in the fuel system and they have the ability to adhere to
surface of materials that are insoluble in the oil and convert them into stable colloidal suspensions.
At the other end of the molecular weight scale and refining, the heteroatoms (particularly nitrogen, sulfur, and trace metals) (Chapter 8) that are present in petroleum and might be also expected
to be present in liquid fuels and other products from petroleum. And, indeed, this is often the case,
although there may have been some skeletal changes induced by the refining process(es). Oxygen
is much more difficult to define in petroleum and liquid fuels. However, it must be stressed that
instability/incompatibility is not directly related to the total nitrogen, oxygen, or sulfur content.
The formation of color/sludge/sediment is a result of several factors. Perhaps the main factor is the
location and nature of the heteroatom which, in turn, determines reactivity (Por, 1992; Mushrush
and Speight, 1995).
The instability/incompatibility of petroleum products is a precursor to either the formation
of degradation products or the occurrence of undesirable changes in the properties of the fuel.
Individually, the components of a product may be stable and in compliance with specifications, but
their blend may exhibit poor stability properties, making them unfit for use.
Incompatibility in the distillate products is important to consumers as well as the producer.
Distillate products that are made from the refining process based on straight-run distillation show
very little incompatibility problems. However, at present and in the future, problems for refiners
will continue to increase as the quality of the available crude decreases worldwide. This decrease
coupled with the inevitable future use of fuel liquids from both coal and shale sources will exacerbate the present problems for the producers.
Incompatibility in petroleum products can be linked to the presence of several different deleterious heteroatomic compound classes (Mushrush and Speight, 1995). The incompatibility observed
in a fuel is dependent on the blending stocks employed in its production. The light cycle oils produced during catalytic process contain the unstable heteroatomic species that are responsible for the
observed deterioration in fuel. The solution is to use straight-run distillate product, but a deficiency
in supply and an option is to use chemical additives that overcome the incompatibilities of the variant chemical composition of the light cycle oil.
In general, the reaction sequence for sediment formation can be envisaged as being dependent
upon the most reactive of the various heteroatomic species that are present in fuels (Pedley et al.,
1986, 1988, 1989). The worst-case scenario would consist of a high olefin fuel with both high indole
concentration and a catalytic trace of sulfonic acid species. This reaction matrix would lead to
rapid degradation. However, just as there is no one specific distillate product, there is also no one
mechanism of degradation. In fact, the mechanism and the functional groups involved will give a
general but not specific mode of incompatibility (Cooney et al., 1985; Hiley and Pedley, 1986, 1987;
Mushrush et al., 1990, 1991). The key reaction in many incompatibility processes is the generation
of the hydroperoxide species from dissolved oxygen. Once the hydroperoxide concentration starts
to increase, macromolecular incompatibility precursors form in the fuel. Acid or base catalyzed
condensation reactions then rapidly increase both the polarity, incorporation of heteroatoms, and
the molecular weight.
When various feedstocks are blended at the refinery, incompatibility can be explained by the
onset of acid–base catalyzed condensation reactions of the various organo-nitrogen compounds in
the individual blending stocks. These are usually very rapid reactions with practically no observed
induction time period.
When the product is transferred to a storage tank or some other holding tank, incompatibility can
occur by the free-radical hydroperoxide-induced polymerization of active olefins. This is a relatively
The Chemistry and Technology of Petroleum
Thus, the deposition of asphaltene constituents is the consequence of instability of the crude oil
or the crude oil product (e.g., fuel oil). The asphaltene constituents are stabilized by resin constituents (Chapter 12) and maintained in the crude oil due to this stabilization. Asphaltene dispersants
are substitutes for the natural resin constituents and are able to keep the asphaltene constituents
dispersed to prevent flocculation/aggregation and phase separation (Speight, 1994; Browarzik et al.,
1999). Dispersants will also clean up sludge in the fuel system and they have the ability to adhere to
surface of materials that are insoluble in the oil and convert them into stable colloidal suspensions.
At the other end of the molecular weight scale and refining, the heteroatoms (particularly nitrogen, sulfur, and trace metals) (Chapter 8) that are present in petroleum and might be also expected
to be present in liquid fuels and other products from petroleum. And, indeed, this is often the case,
although there may have been some skeletal changes induced by the refining process(es). Oxygen
is much more difficult to define in petroleum and liquid fuels. However, it must be stressed that
instability/incompatibility is not directly related to the total nitrogen, oxygen, or sulfur content.
The formation of color/sludge/sediment is a result of several factors. Perhaps the main factor is the
location and nature of the heteroatom which, in turn, determines reactivity (Por, 1992; Mushrush
and Speight, 1995).
The instability/incompatibility of petroleum products is a precursor to either the formation
of degradation products or the occurrence of undesirable changes in the properties of the fuel.
Individually, the components of a product may be stable and in compliance with specifications, but
their blend may exhibit poor stability properties, making them unfit for use.
Incompatibility in the distillate products is important to consumers as well as the producer.
Distillate products that are made from the refining process based on straight-run distillation show
very little incompatibility problems. However, at present and in the future, problems for refiners
will continue to increase as the quality of the available crude decreases worldwide. This decrease
coupled with the inevitable future use of fuel liquids from both coal and shale sources will exacerbate the present problems for the producers.
Incompatibility in petroleum products can be linked to the presence of several different deleterious heteroatomic compound classes (Mushrush and Speight, 1995). The incompatibility observed
in a fuel is dependent on the blending stocks employed in its production. The light cycle oils produced during catalytic process contain the unstable heteroatomic species that are responsible for the
observed deterioration in fuel. The solution is to use straight-run distillate product, but a deficiency
in supply and an option is to use chemical additives that overcome the incompatibilities of the variant chemical composition of the light cycle oil.
In general, the reaction sequence for sediment formation can be envisaged as being dependent
upon the most reactive of the various heteroatomic species that are present in fuels (Pedley et al.,
1986, 1988, 1989). The worst-case scenario would consist of a high olefin fuel with both high indole
concentration and a catalytic trace of sulfonic acid species. This reaction matrix would lead to
rapid degradation. However, just as there is no one specific distillate product, there is also no one
mechanism of degradation. In fact, the mechanism and the functional groups involved will give a
general but not specific mode of incompatibility (Cooney et al., 1985; Hiley and Pedley, 1986, 1987;
Mushrush et al., 1990, 1991). The key reaction in many incompatibility processes is the generation
of the hydroperoxide species from dissolved oxygen. Once the hydroperoxide concentration starts
to increase, macromolecular incompatibility precursors form in the fuel. Acid or base catalyzed
condensation reactions then rapidly increase both the polarity, incorporation of heteroatoms, and
the molecular weight.
When various feedstocks are blended at the refinery, incompatibility can be explained by the
onset of acid–base catalyzed condensation reactions of the various organo-nitrogen compounds in
the individual blending stocks. These are usually very rapid reactions with practically no observed
induction time period.
When the product is transferred to a storage tank or some other holding tank, incompatibility can
occur by the free-radical hydroperoxide-induced polymerization of active olefins. This is a relatively