15
History and Terminology
A series of ring-shaped hydrocarbons, known as the naphthenes, range from volatile liquids such as
naphtha to high-molecular-weight substances isolated as the asphaltene fraction. Another group of
ring-shaped hydrocarbons is known as the aromatics; the chief compound in this series is benzene,
a popular raw material for making petrochemicals.
Nonhydrocarbon constituents of petroleum include organic derivatives of nitrogen, oxygen, sulfur, and the metals nickel and vanadium. Most of these impurities are removed during refining.
Geologic techniques (Chapter 6) can determine only the existence of rock formations that are
favorable for oil deposits, not whether oil is actually there. Drilling is the only sure way to ascertain
the presence of oil. With modern rotary equipment, wells can be drilled to depths of more than
30,000 ft (9,000 m). Once oil is found, it may be recovered (brought to the surface) by the pressure
created by natural gas or water within the reservoir. Crude oil can also be brought to the surface
by injecting water or steam into the reservoir to raise the pressure artificially, or by injecting such
substances as carbon dioxide, polymers, and solvents to reduce crude oil viscosity. Thermal recovery methods are frequently used to enhance the production of heavy crude oils, whose extraction is
impeded by viscous resistance to flow at reservoir temperatures.
Crude oil is transported to refineries by pipelines, which can often carry more than 500,000
barrels/day, or by ocean-going tankers. The basic refinery process is distillation (Chapters 15
and 17), which separates the crude oil into fractions of differing volatility. After the distillation,
other physical methods are employed to separate the mixtures, including absorption, adsorption,
solvent extraction, and crystallization. After physical separation into such constituents as light and
heavy naphtha, kerosene, and light and heavy gas oils, selected petroleum fractions may be subjected to conversion processes, such as thermal cracking (i.e., coking, Chapter 18) and catalytic
cracking (Chapter 19). In the most general terms, cracking breaks the large molecules of heavier gas
oils into the smaller molecules that form the lighter, more valuable naphtha fractions.
Reforming (Chapter 24) changes the structure of straight-chain paraffin molecules into branchedchain iso-paraffins and ring-shaped aromatics. The process is widely used to raise the octane number of gasoline (Chapter 26) obtained by distillation of paraffinic crude oils.
1.4.2 oPPortunIty Crudes And HIgH-ACId Crudes
There is also the need for a refinery to be configured to accommodate opportunity crude oils and/or
high-acid crude oils, which, for many purposes, are often included with heavy feedstocks.
Opportunity crude oils are often dirty and need cleaning before refining by removal of undesirable constituents such as high-sulfur, high-nitrogen, and high-aromatics (such as polynuclear aromatic) components. A controlled visbreaking treatment would clean up such crude oils by removing
these undesirable constituents (which, if not removed, would cause problems further down the refinery sequence) as coke or sediment.
On the other hand, high-acid crude oils cause corrosion in the refinery—corrosion is predominant at temperatures in excess of 180°C (355°F) (Ghoshal and Sainik, 2013)—and occur
particularly in the atmospheric distillation unit (the first point of entry of the high-acid crude
oil) and also in the vacuum distillation units. In addition, overhead corrosion is caused by the
mineral salts, magnesium, calcium, and sodium chloride that are hydrolyzed to produce volatile
hydrochloric acid, causing a highly corrosive condition in the overhead exchangers. Therefore,
these salts present a significant contamination in opportunity crude oils. Other contaminants in
opportunity crude oils that are shown to accelerate the hydrolysis reactions are inorganic clays
and organic acids.
In addition to taking preventative measures for the refinery to process these feedstocks without
serious deleterious effects on the equipment, refiners will need to develop programs for detailed
and immediate feedstock evaluation so that they can understand the qualities of a crude oil very
quickly and it can be valued appropriately and management of the crude processing can be planned
meticulously.
History and Terminology
A series of ring-shaped hydrocarbons, known as the naphthenes, range from volatile liquids such as
naphtha to high-molecular-weight substances isolated as the asphaltene fraction. Another group of
ring-shaped hydrocarbons is known as the aromatics; the chief compound in this series is benzene,
a popular raw material for making petrochemicals.
Nonhydrocarbon constituents of petroleum include organic derivatives of nitrogen, oxygen, sulfur, and the metals nickel and vanadium. Most of these impurities are removed during refining.
Geologic techniques (Chapter 6) can determine only the existence of rock formations that are
favorable for oil deposits, not whether oil is actually there. Drilling is the only sure way to ascertain
the presence of oil. With modern rotary equipment, wells can be drilled to depths of more than
30,000 ft (9,000 m). Once oil is found, it may be recovered (brought to the surface) by the pressure
created by natural gas or water within the reservoir. Crude oil can also be brought to the surface
by injecting water or steam into the reservoir to raise the pressure artificially, or by injecting such
substances as carbon dioxide, polymers, and solvents to reduce crude oil viscosity. Thermal recovery methods are frequently used to enhance the production of heavy crude oils, whose extraction is
impeded by viscous resistance to flow at reservoir temperatures.
Crude oil is transported to refineries by pipelines, which can often carry more than 500,000
barrels/day, or by ocean-going tankers. The basic refinery process is distillation (Chapters 15
and 17), which separates the crude oil into fractions of differing volatility. After the distillation,
other physical methods are employed to separate the mixtures, including absorption, adsorption,
solvent extraction, and crystallization. After physical separation into such constituents as light and
heavy naphtha, kerosene, and light and heavy gas oils, selected petroleum fractions may be subjected to conversion processes, such as thermal cracking (i.e., coking, Chapter 18) and catalytic
cracking (Chapter 19). In the most general terms, cracking breaks the large molecules of heavier gas
oils into the smaller molecules that form the lighter, more valuable naphtha fractions.
Reforming (Chapter 24) changes the structure of straight-chain paraffin molecules into branchedchain iso-paraffins and ring-shaped aromatics. The process is widely used to raise the octane number of gasoline (Chapter 26) obtained by distillation of paraffinic crude oils.
1.4.2 oPPortunIty Crudes And HIgH-ACId Crudes
There is also the need for a refinery to be configured to accommodate opportunity crude oils and/or
high-acid crude oils, which, for many purposes, are often included with heavy feedstocks.
Opportunity crude oils are often dirty and need cleaning before refining by removal of undesirable constituents such as high-sulfur, high-nitrogen, and high-aromatics (such as polynuclear aromatic) components. A controlled visbreaking treatment would clean up such crude oils by removing
these undesirable constituents (which, if not removed, would cause problems further down the refinery sequence) as coke or sediment.
On the other hand, high-acid crude oils cause corrosion in the refinery—corrosion is predominant at temperatures in excess of 180°C (355°F) (Ghoshal and Sainik, 2013)—and occur
particularly in the atmospheric distillation unit (the first point of entry of the high-acid crude
oil) and also in the vacuum distillation units. In addition, overhead corrosion is caused by the
mineral salts, magnesium, calcium, and sodium chloride that are hydrolyzed to produce volatile
hydrochloric acid, causing a highly corrosive condition in the overhead exchangers. Therefore,
these salts present a significant contamination in opportunity crude oils. Other contaminants in
opportunity crude oils that are shown to accelerate the hydrolysis reactions are inorganic clays
and organic acids.
In addition to taking preventative measures for the refinery to process these feedstocks without
serious deleterious effects on the equipment, refiners will need to develop programs for detailed
and immediate feedstock evaluation so that they can understand the qualities of a crude oil very
quickly and it can be valued appropriately and management of the crude processing can be planned
meticulously.