Facts of Petroleum

COMPOSITION:-
The proportion of hydrocarbons in the mixture of crude oil is highly variable and ranges from as much as 97% by weight in the lighter oils to as little as 50% in the heavier oils.
The hydrocarbons in crude oil are mostly alkanes, cycloalkanes and various aromatic hydrocarbons while the other organic compounds contain nitrogen, oxygen and sulfur,

and trace amounts of metals such as iron, nickel, copper and vanadium. The exact molecular composition varies widely from formation to formation but the proportion of chemical elements vary over fairly narrow limits as follows:
1) Carbon -- 83-87%
2) Hydrogen --10-14%
3) Nitrogen--0.1-2%
4) Oxygen--0.1-1.5%
5) Sulfur--0.5-6%
6) Metals-- <1000ppm

Crude oil varies greatly in appearance depending on its composition. It is usually black or dark brown (although it may be yellowish or even greenish). It is mainly garlic in smell. In the reservoir it is usually found in association with natural gas, which being lighter forms a gas cap over the petroleum, and saline water which being heavier generally floats underneath it. Petroleum is used mostly, by volume, for producing fuel oil and gasoline (petrol), both important "primary energy" sources. 84% by volume of the hydrocarbons present in petroleum is converted into energy-rich fuels (petroleum-based fuels), including gasoline, diesel, jet, heating, and other fuel oils, and liquefied petroleum gas.
Due to its high energy density, easy transportability and relative abundance, it has become the world's most important source of energy since the mid-1950s. Petroleum is also the raw material for many chemical products, including pharmaceuticals, solvents, fertilizers, pesticides, and plastics; the 16% not used for energy production is converted into these other materials.

CHEMISTRY:-
Petroleum is a mixture of a very large number of different hydrocarbons; the most commonly found molecules are alkanes (linear or branched), cycloalkanes, aromatic hydrocarbons, or more complicated chemicals like asphaltenes. Each petroleum variety has a unique mix of molecules, which define its physical and chemical properties, like color and viscosity.
The alkanes, also known as paraffins, are saturated hydrocarbons with straight or branched chains which contain only carbon and hydrogen and have the general formula CnH2n+2 They generally have from 5 to 40 carbon atoms per molecule. The alkanes from pentane (C5H12) to octane (C8H18) are refined into gasoline (petrol), the ones from nonane (C9H20) to hexadecane (C16H34) into diesel fuel and kerosene (primary component of many types of jet fuel), and the ones from hexadecane upwards into fuel oil and lubricating oil. At the heavier end of the range, paraffin wax is an alkane with approximately 25 carbon atoms, while asphalt has 35 and up.

The cycloalkanes, also known as napthenes, are saturated hydrocarbons which have one or more carbon rings to which hydrogen atoms are attached according to the formula CnH2n. Cycloalkanes have similar properties to alkanes but have higher boiling points.
The aromatic hydrocarbons are unsaturated hydrocarbons which have one or more planar six-carbon rings called benzene rings, to which hydrogen atoms are attached with the formula CnHn. They tend to burn with a sooty flame, and many have a sweet aroma.

CLASSIFICATION:-
The petroleum industry generally classifies crude oil by the geographic location it is produced in , its API gravity , and by its sulfur content.
API ( American Petroleum Institute) Gravity:- It is a mathematical equation which is used to measure crude oil’s density. It is given by:-
API Gravity = 141.5/ specific gravity – 131.5
Eg:- API of water = 10. (Because specific gravity of water=1). API values of some other crude oils are:-
1) Crude from Bombay High 40
2) Gulf 25-28
3) Venezuela 15
Crude oil may be considered light if it has low density or heavy if it has high density; and it may be referred to as sweet if it contains relatively little sulfur or sour if it contains substantial amounts of sulfur. The geographic location is also important because it affects transportation costs to the refinery. Light crude oil is more desirable than heavy oil since it produces a higher yield of gasoline, while sweet oil commands a higher price than sour oil because it has fewer environmental problems and requires less refining to meet sulfur standards imposed on fuels in consuming countries.

USES:-
The chemical structure of petroleum is composed of hydrocarbon chains of different lengths. Because of this, petroleum may be taken to oil refineries and the hydrocarbon chemicals separated by distillation and treated by other chemical processes, to be used for a variety of purposes. The most common distillations of petroleum are as various fuels. These include:

Ethane and other short-chain alkanes
Diesel fuel (petrodiesel)
Fuel oils
Gasoline
Jet fuel
Kerosene
Liquefied petroleum gas (LPG)
Natural gas
Bitumen
Aviation Turbine Fuel(ATF)
Naptha
Parrafin Wax
Asphalt