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       #Post#: 747--------------------------------------------------
       Petroleum fractions
   DIR By: Michel
       Date: September 27, 2012, 9:05 am
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       Hydrocarbons can exist in all three phases (gas, liquid and
       solid). Petroleum generally contains 83-87% Carbon,
       10-14%Hydrogen, with trace amounts of other elements like
       Oxygen, Sulfur,Nitrogen, etc. For petroleum to be useful as a
       source of energy and raw materials for chemical industries, it
       has to be separated into its component fractions. This is done
       by fractional distillation ofcrude oil in an oil refinery.
       Crude oil typically contains fourdifferent types of
       hydrocarbon molecules. The relative percentageof each fraction
       varies from oil to oil. The four typical hydrocarbon molecules
       found in crude oil include; Paraffins (15-60%), Naphthalenes
       (30-60%), aromatics (3-30%), Asphaltics/Asphaltenes (~6%)
       Alkanes:  They are compounds with single carbon to carbon bonds
       with the general formula CnH2n+2. Apart from ethane, all alkanes
       have isomers. Natural gas is mainly ethane and methane. Higher
       molecular weight alkanes may exist as vapor or liquid depending
       on reservoir conditions.
       Cycloalkanes: Just as the name suggests, they are alkanes with
       one or more ring structures. Examples include cyclobutane,
       cyclopentane, etc. cycloalkanes have properties similar to
       alkanes but they have higher boiling points.
       Aromatics: The aromatic hydrocarbons are unsaturated
       hydrocarbons with one or more benzene rings. The benzene ring
       has six carbon atoms bonded in ahexagonal geometry. X-ray
       diffraction studies show that the electrons for the C-C bonds in
       benzene are equally distributed and that the bond lengths of the
       C-C  bonds are all equal and intermediate in length. The high
       degree of unsaturation in aromatics make them burn with asooty
       flame. Aromatics such as benzene, toluene, xylene etc are useful
       industrial chemicals.
       Asphaltics: Asphaltics are a sub class of aromatics. They are
       otherwise called resins. Asphaltene precipitation is more common
       in large to medium oils. Asphaltene precipitation may occur as a
       result of hydrocarbon injection.
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