Page 62 - Petroleum and Gas Field Processing

of these cyclic compounds in the naphtha range has its
significance in the production of aromatic compounds. Naphtha
cuts with a high percentage of naphthenes would make an
excellent feedstock for aromatization.
3. Alkenes or Olefins: Alkenes are unsaturated hydrocarbon
compounds having the general formula C n H n . They are
practically not present in crude oils, but they are produced
during processing of crude oils at high temperatures.
Alkenes are very reactive compounds. Light olefinic
hydrocarbons are considered the base stock for many
petrochemicals. Ethylene, the simplest alkene, is an important
monomer in this regard. For example, polyethylene is a well-
known thermoplastic polymer and polybutadiene is the most
widely used synthetic rubber.
4. Aromatics: Aromatic compounds are normally present in crude
oils. Only monomolecular compounds in the range of C6–C8
(known as B-T-X) have gained commercial importance.
Aromatics in this range are not only important petrochemical
feedstocks but are also valuable for motor fuels.
Dinuclear and polynuclear aromatic compounds are present
in heavier petroleum fractions and residues. Asphaltenes, which
are concentrated in heavy residues and in some asphaltic crude
oils, are, in fact, polynuclear aromatics of complex structures. It
has been confirmed by mass spectroscopic techniques that
condensed-ring aromatic hydrocarbons and heterocyclic com-
pounds are the major compounds of asphaltenes.

Nonhydrocarbon Compounds
So far, a brief review of the major classes of the hydrocarbon compounds
that exist in crude oils and their products was presented. For
completeness, we should mention that other types of nonhydrocarbon
compound occur in crude oils and refinery streams. Most important are
the following:

Sulfur compounds
Nitrogen compounds
Oxygen compounds
Metallic compounds

Sulfur Compounds. In addition to the gaseous sulfur compounds in
crude oil, many sulfur compounds have been found in the liquid phase
in the form of organosulfur. These compounds are generally not acidic.

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.