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The Chemistry and Technology of Petroleum
for nitrogen. Metals cause particular problems because they poison catalysts used for sulfur and
nitrogen removal as well as other processes such as catalytic cracking.
A variety of tests (ASTM D1026, D1262, D1318, D1368, D1548, D1549, D2547, D2599, D2788,
D3340, D3341, and D3605) have been designated for the determination of metals on petroleum
products. At the time of writing, the specific test for the determination of metals in whole feeds has
not been designated. However, this task can be accomplished by combustion of the sample so that
only inorganic ash remains. The ash can then be digested with an acid and the solution examined
for metal species by atomic absorption (AA) spectroscopy or by inductively coupled argon plasma
(ICP) spectrometry.
Heavy oils and residua contain relatively high proportions of metals either in the form of salts
or as organometallic constituents (such as the metallo-porphyrins), which are extremely difficult to
remove from the feedstock. Indeed, the nature of the process by which residua are produced virtually dictates that all the metals in the original crude oil are concentrated in the residuum (Speight,
2000). Those metallic constituents that may actually volatilize under the distillation conditions and
appear in the higher boiling distillates are the exceptions here. The deleterious effect of metallic
constituents on the catalyst is known, and serious attempts have been made to develop catalysts that
can tolerate a high concentration of metals without serious loss of catalyst activity or catalyst life.
10.3.6 totAl ACId numBer
Another characteristic of crude oil is the TAN, which represents a composite of acids present in the
crude oil (ASTM D664) and is often also expressed as the neutralization number. Crude oils having
a high acid number (high TAN number) account for an increasing percentage of the global crude oil
market, and, in fact, the increase in world production of heavy, sour, and high TAN crude oils will
impact many world (especially the United States) refineries (Shafizadeh et al., 2003; Sheridan, 2006).
In the test method, the sample normally dissolved in toluene/isopropyl alcohol/water is titrated
with potassium hydroxide and the results are expressed as milligrams of potassium hydroxide per
gram of sample (mg KOH/g). Crude oils having high acid numbers have a high potential to cause
corrosion problems in the refineries, especially in the atmospheric and vacuum distillation units
where the hot crude oil first comes into contact with hot metal surfaces. Crude oil typically has a
TAN value on the order of 0.05–6.0 mg KOH/g of sample.
High acid crude oils are considered to be those with an acid content >1.0 mg KOH/g sample
(many refiners consider TAN number greater than 0.5 mg KOH/g to be high) and refiners looking
for discounted crude supplies will import and use greater volumes of high TAN crude oils.
In the United States, using California as the example, Wilmington crude oil and Kern crude
oil have a TAN ranging from 2.2 to 3.2 mg, respectively. However, some acids are relatively inert
and the TAN number does not always give a true reflection of the corrosive properties of the crude
oil. Furthermore, different naphthenic acids (a broad group of organic acids in crude oil) will react
at different temperatures—making it difficult to pinpoint the processing units within the refinery
that will be affected by a particular high TAN crude oil. Nonetheless, high TAN crude oils contain
naphthenic acids and these acids corrode the distillation unit in the refinery and form sludge and
gum that can block pipelines and pumps entering the refinery.
The impact of corrosive, high TAN, crude oils can be overcome by blending higher and lower
TAN crude oils, installing or retrofitting equipment with anticorrosive materials, or by developing
low temperature catalytic decarboxylation processes using metal catalysts such as copper.
10.4 THERMAL PROPERTIES
The thermal properties of petroleum are those properties (or characteristics) that determine
how petroleum will behave (or react) when it is subjected to excessive heat, or heat fluctuations
over time.
The Chemistry and Technology of Petroleum
for nitrogen. Metals cause particular problems because they poison catalysts used for sulfur and
nitrogen removal as well as other processes such as catalytic cracking.
A variety of tests (ASTM D1026, D1262, D1318, D1368, D1548, D1549, D2547, D2599, D2788,
D3340, D3341, and D3605) have been designated for the determination of metals on petroleum
products. At the time of writing, the specific test for the determination of metals in whole feeds has
not been designated. However, this task can be accomplished by combustion of the sample so that
only inorganic ash remains. The ash can then be digested with an acid and the solution examined
for metal species by atomic absorption (AA) spectroscopy or by inductively coupled argon plasma
(ICP) spectrometry.
Heavy oils and residua contain relatively high proportions of metals either in the form of salts
or as organometallic constituents (such as the metallo-porphyrins), which are extremely difficult to
remove from the feedstock. Indeed, the nature of the process by which residua are produced virtually dictates that all the metals in the original crude oil are concentrated in the residuum (Speight,
2000). Those metallic constituents that may actually volatilize under the distillation conditions and
appear in the higher boiling distillates are the exceptions here. The deleterious effect of metallic
constituents on the catalyst is known, and serious attempts have been made to develop catalysts that
can tolerate a high concentration of metals without serious loss of catalyst activity or catalyst life.
10.3.6 totAl ACId numBer
Another characteristic of crude oil is the TAN, which represents a composite of acids present in the
crude oil (ASTM D664) and is often also expressed as the neutralization number. Crude oils having
a high acid number (high TAN number) account for an increasing percentage of the global crude oil
market, and, in fact, the increase in world production of heavy, sour, and high TAN crude oils will
impact many world (especially the United States) refineries (Shafizadeh et al., 2003; Sheridan, 2006).
In the test method, the sample normally dissolved in toluene/isopropyl alcohol/water is titrated
with potassium hydroxide and the results are expressed as milligrams of potassium hydroxide per
gram of sample (mg KOH/g). Crude oils having high acid numbers have a high potential to cause
corrosion problems in the refineries, especially in the atmospheric and vacuum distillation units
where the hot crude oil first comes into contact with hot metal surfaces. Crude oil typically has a
TAN value on the order of 0.05–6.0 mg KOH/g of sample.
High acid crude oils are considered to be those with an acid content >1.0 mg KOH/g sample
(many refiners consider TAN number greater than 0.5 mg KOH/g to be high) and refiners looking
for discounted crude supplies will import and use greater volumes of high TAN crude oils.
In the United States, using California as the example, Wilmington crude oil and Kern crude
oil have a TAN ranging from 2.2 to 3.2 mg, respectively. However, some acids are relatively inert
and the TAN number does not always give a true reflection of the corrosive properties of the crude
oil. Furthermore, different naphthenic acids (a broad group of organic acids in crude oil) will react
at different temperatures—making it difficult to pinpoint the processing units within the refinery
that will be affected by a particular high TAN crude oil. Nonetheless, high TAN crude oils contain
naphthenic acids and these acids corrode the distillation unit in the refinery and form sludge and
gum that can block pipelines and pumps entering the refinery.
The impact of corrosive, high TAN, crude oils can be overcome by blending higher and lower
TAN crude oils, installing or retrofitting equipment with anticorrosive materials, or by developing
low temperature catalytic decarboxylation processes using metal catalysts such as copper.
10.4 THERMAL PROPERTIES
The thermal properties of petroleum are those properties (or characteristics) that determine
how petroleum will behave (or react) when it is subjected to excessive heat, or heat fluctuations
over time.