Petroleum• Petroleum (L. petroleum, from Latin: petra rock + oleum oil or crude oil is a naturally occurring, toxic, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights, and other organic compounds, that are found in geologic formations beneath the Earths surface.• Petroleum is recovered mostly through oil drilling.• It is refined and separated, most easily by boiling point, into a large number of consumer products, from gasoline and kerosene to asphalt and chemical reagents used to make plastics and pharmaceuticals.
Petroleum-composition• Petroleum includes only crude oil, but in common usage it includes both crude oil and natural gas.• Both crude oil and natural gas are predominantly a mixture of hydrocarbons.• Under surface pressure and temperature conditions, the lighter hydrocarbons methane, ethane, propane and butane occur as gases,• while the heavier ones from pentane and up are in the form of liquids or solids.• However, in the underground oil reservoir the proportion which is gas or liquid varies depending on the subsurface conditions, and on the phase diagram of the petroleum mixture.
Petroleum-compositionAn oil well produces predominantly crude oil, with some natural gas dissolved in it.Because the pressure is lower at the surface than underground, some of the gas will come out of solution and be recovered (or burned) as associated gas or solution gas.A gas well produces predominately natural gas.However, because the underground temperature and pressure are higher than at the surface, the gas may contain heavier hydrocarbons such as pentane, hexane, and heptane in the gaseous state.Under surface conditions these will condense out of the gas and form natural gas condensate, often shortened to condensate.Condensate resembles gasoline in appearance and is similar in composition to some volatile light crude oils.
Petroleum-composition• The proportion of light hydrocarbons in the petroleum mixture is highly variable between different oil fields and ranges from as much as 97% by weight in the lighter oils to as little as 50% in the heavier oils and bitumens.• 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.•
Petroleum-composition Composition by weight• The exact molecular Element Percent range composition varies widely from Carbon 83 to 87% formation to formation but the proportion of chemical Hydrogen 10 to 14% elements vary over fairly Nitrogen 0.1 to 2% narrow limits as follows: Oxygen 0.1 to 1.5% Sulfur 0.5 to 6% Metals < 0.1%• Four different types of hydrocarbon molecules appear Composition by weight in crude oil. The relative Hydrocarbon Average Range percentage of each varies from oil to oil, determining the Paraffins 30% 15 to 60% properties of each oil. Naphthenes 49% 30 to 60% Aromatics 15% 3 to 30% Asphaltics 6% remainder
Distillation of crude oil• An oil refinery or petroleum refinery is an industrial process plant where crude oil is processed and refined into more useful petroleum products, such as gasoline, diesel fuel, asphalt base, heating oil, kerosene, and liquefied petroleum gas.
• Crude oil is separated into fractions by fractional distillation. The fractions at the top of the fractionating column have lower boiling points than the fractions at the bottom. The heavy bottom fractions are often cracked into lighter, more useful products. All of the fractions are processed further in other refining units
• Petroleum products are usually grouped into three categories: light distillates (LPG, gasoline, naphtha), middle distillates (kerosene, diesel), heavy distillates and residuum (heavy fuel oil, lubricating oils, wax, asphalt). This classification is based on the way crude oil is distilled and separated into fractions•
Octane number• An octane number is a number which reflects a fuels resistance to knocking .• The octane rating is a measure of the resistance of petrol and other fuels to auto-ignition in spark-ignition internal combustion engines.• The octane number of a fuel is measured in a test engine, and is defined by comparison with the mixture of 2,2,4-trimethylpentane (iso-octane) and heptane which would have the same anti-knocking capacity as the fuel under test: the percentage, by volume, of 2,2,4- trimethylpentane in that mixture is the octane number of the fuel.• A value used to indicate the resistance of a motor fuel to knock. Octane numbers are based on a scale on which isooctane is 100 (minimal knock) and heptane is 0 (bad knock).•
Cetane Number• Cetane number or CN is a measurement of the combustion quality of diesel fuel during compression ignition. It is a significant expression of diesel fuel quality among a number of other measurements that determine overall diesel fuel quality.• Cetane number is actually a measure of a fuels ignition delay; the time period between the start of injection and start of combustion (ignition) of the fuel.• Cetane numbers are only used for the relatively light distillate diesel oils.• Generally, diesel engines run well with a CN from 40 to 55. Fuels with higher cetane number which have shorter ignition delays provide more time for the fuel combustion process to be completed.
Synthetic petrol• The petrol obtained artificially from coal as a mixture of alkanes resembling petroleum like aliphatic hydrocarbon fuels is called synthetic petrol.• Two important methods for producing synthetic petrol are the Fischer-Tropsch process and the Bergius process.• In Bergius process, powdered coal is mixed with heavy oil and heated with hydrogen under high pressure (200-250 atm) at about 748 K in presence of iron oxide as catalyst.• The vapours on condensation give a liquid resembling crude oil. This is called synthetic petroleum, which on fractional distillation gives petrol (gasoline).
Synthetic petrol• In this process, a mixture of water gas and hydrogen under pressure (5-10 atm) is passed over a cobalt catalyst at 450 - 475 K. The water gas required is obtained by passing steam over red-hot coke.• C(red hot) + H2O(g) CO + H2 water gas•• The product so obtained is fractionally distilled to obtain petrol, middle oil and heavy oil. Further hydrogenation of the middle oil fraction then produces petrol.