Page 64 - Petroleum and Gas Field Processing

It has to be stated that the presence of nitrogen in petroleum is of
much greater significance in refinery operations than might be expected
from the very small amounts present. It is established that nitrogen
compounds are responsible for the following:
1. Catalyst poisoning in catalytic processes
2. Gum formation in some products such as domestic fuel oils

Oxygen Compounds. Oxygen compounds in crude oils are more
complex than sulfur compounds. However, oxygen compounds are not
poisonous to processing catalysts. Most oxygen compounds are weakly
acidic, such as phenol, cresylic acid and naphthenic acids. The oxygen
content of petroleum is usually less than 2%, although larger amounts
have been reported.

Metallic Compounds. Many metals are found in crude oils; some of
the more abundant are sodium, calcium, magnesium, iron, copper,
vanadium, and nickel. These normally occur in the form of inorganic salts
soluble in water—as in the case of sodium chloride—or in the form of
organometallic compounds—as in the case of iron, vanadium, and nickel.
The occurrence of metallic constituents in crude oils is of
considerably greater interest to the petroleum industry than might be
expected from the very small amounts present. The organometallic
compounds are usually concentrated in the heavier fractions and in crude
oil residues. The presence of high concentration of vanadium compounds
in naphtha streams for catalytic reforming feeds will cause permanent
poisons. These feeds should be hydrotreated not only to reduce the
metallic poisons but also to desulfurize and denitrogenate the sulfur and
nitrogen compounds.
Hydrotreatment may also be used to reduce the metal content in
heavy feeds to catalytic cracking.

2.2.2 Physical Methods
Having discussed the various chemicals found in crude oils and realizing
not only the complexity of the mixture but the difficulty of specifying a
crude oil as a particular mixture of chemicals, we can understand why the
early petroleum producers adopted the physical methods generally used for
classification.
As may be seen, crude oils from different locations may vary in
appearance and viscosity and also vary in their usefulness as producers for
final products. It is possible by the use of certain basic tests to identify the

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