crude oil definition

Petroleum is a fossilized mass that has accumulated below the earth’s surface from time immemorial. Raw petroleum is known as crude (petroleum) oil or mineral oil, It is a mixture of various organic substances and is the source of hydrocarbons, such as methane, ethane, propane, butane, pentane, and various other paraffinic, naphthenic, and aromatic hydrocarbons, Various petroleum products, such as gaseous and liquid fuels, lubricating oil, solvents, asphalts, waxes, and coke, are derived from refining crude oil. Many lighter hydrocarbons and other organic chemicals are synthesized by thermal and catalytic treatments of these hydrocarbons. Refineries produce cooking gas (liquified petroleum gas or LPG), motor spirit (also known as petrol or gasoline), naphtha, kerosene, aviation turbine fuel (ATF), high-speed diesel (HSD), lubricating base oils, wax, coke, bitumen (or asphalt), etc.

In a petrochemical plant (where one or more petrochemicals are produced) or in a petrochemical complex (where many petrochemical products are produced), pure hydrocarbons or other organic chemicals with a definite number and type of constituent element or compound are produced from the products in refineries. Thus, petrochemicals are derived from petroleum products obtained from refineries products from a petrochemical complex are plastics, rubbers, synthetic fibers, raw materials for soap and detergents, alcohols, paints, pharmaceuticals, etc. Since petroleum is the mixture of hundreds of thousands of hydrocarbon compounds, there is a possibility of synthesizing many new compounds. 

crude oil definition 

what is crude oil made of?:

The compounds in crude petroleum oil are essentially hydrocarbons or substituted hydrocarbons in which the major elements are carbon at 85%–90% and hydrogen at 10%–14%, and the rest with non-hydrocarbon elements—sulfur (0.2%–3%), nitrogen (< 0.1–2%), oxygen (1%–1.5%), and organometallic compounds of nickel, vanadium, arsenic, lead, and other metals in traces (in parts per million or parts per billion concentration) inorganic salts of magnesium chloride, sodium chlorides, and another mineral salts are also accompanied with crude oil from the well either because of water from formation or water and chemicals injected during drilling and production.

ORIGIN OF HYDROCARBONS:

The word petroleum is derived from the Latin words for rock (petra) and oleum (oil), it is found in the form of gas and/or liquid phases in porous rock structures. Both gases and liquids are rich mixtures of organic components consisting of carbon and hydrogen and hence are known as hydrocarbons in general. Usually, these are available in the sub-surface of Earth in the porous rocks known as sedimentary basins. In the majority of the basins, gas, oil, and water coexist under pressure with methane gas at the cap, and oil is sandwiched between the gas and water.

origin of oil

 Physical properties of crude oil:

Crude oil is classified as a paraffinic base, naphthenic base, or asphaltic base, according to the prevalence of the hydrocarbon groups. But various physical properties are required in addition to this classification to characterize a crude oil. API gravity is expressed as the relationship developed by the American Petroleum Institute:

API = 141.5/s − 131.5

where is the specific gravity of oil measured concerning water, both at 60°F (15.5°C), Since oil is lighter than water, API gravity is always greater than 10. The lighter the oil, the larger the API gravity. However, gravity is not the only measurement of crude oil, but a mere indicator of lightness. Since crude oil is, in fact, a mixture of various hydrocarbons varying from gases to semi-solid asphalts, it is convenient to separate these into various boiling fractions rather than as individual chemical species. Crude is distilled in a laboratory distillation apparatus and the boiling fractions are collected. Boiling fractions are a mixture of hydrocarbons.

 boiling in a certain range of temperatures. For a particular crude oil, each boiling fraction separated has a certain average boiling point. A characterization factor of crude oil has been related with the average (molal average) boiling point (TB in Rankine) of all the fractions separated and its specific gravity:

CF = (TB)1/3 /s.

Characterization factor (CF) is universally accepted as the identity of crude oil and its products. Various other properties, such as molecular weight, density, viscosity, and thermodynamic properties, are available for any oil product if its characterization factor is determined. Since crude oil is always associated with water and settleable solids, it is essential to determine the relative amount of bottom sludge and water (BSW) after the necessary settling period. Water is separated by the solvent extraction method in the laboratory. Ultimate analysis of crude oil is a method to determine the amount of carbon, hydrogen, and other constituent elements in it. Combustion of crude oil yields ashes of metallic oxides that are analyzed for the metallic components present in crude oil.

Hydrocarbon groups:

Compounds solely made of carbon and hydrogen are called hydrocarbons. These hydrocarbons are grouped in general into 4 groups paraffin, naphthene, aromatics, and olefins. Crude oil contains these hydrocarbons in different proportions, except olefins, which are produced during processing.

 

1.  Paraffins: Paraffins are saturated hydrocarbons, a saturated hydrocarbon is a compound where all four bonds of a carbon atom are linked to four separate atoms. Examples are methane, ethane, propane, butane, pentane, hexane, with the generic molecular formula of CnH2n+2, where n is the number of carbon atoms in that compound. The homologous series of these hydrocarbons are called alkanes.

paraffin hydrocarbons

 

2.  Naphthene: are cyclic saturated hydrocarbons with the general formula, like olefins, of CnH2n, also known as cyclo-alkanes. Since they are saturated, they are relatively inactive, like paraffins, naphthenes are desirable compounds for the production of aromatics and good quality lube oil base stocks.

naphthene hydrocarbons

3.  Aromatics: often called benzenes, are chemically very active as compared to other groups of hydrocarbons. Their general formula is CnH2n-6. These hydrocarbons in particular are attacked by oxygen to form organic acids. Naphthene can be dehydrogenated to aromatics in the presence of a platinum catalyst. Lower aromatics, such as benzene, toluene, and xylenes, are good solvents and precursors for many petrochemicals. Aromatics from petroleum products can be separated by extraction with solvents such as phenol, furfurol, and diethylene glycol.

aromatics hydrocarbons

 

4.  Olefins: are unsaturated hydrocarbons, i.e., the double bond is present between the two carbon atoms in the formula. The generic formula is CnH2n, and the lowest member of this homologous series is ethylene, C2H4. This series is known as alkenes. these are highly reactive and can react to themselves to mono olefins Olefins are not present in crude oil, but they are produced by thermal and catalytic decomposition or dehydrogenation of normal paraffins.

olefin hydrocarbons

Complex Hydrocarbons:

Crude oil also contains a large number of hydrocarbons that do not fall into the category of paraffin, olefins, naphthenes, or aromatics, but maybe the combined group of any two or more groups of paraffin, naphthenes, or aromatic hydrocarbons. By joining two or more naphthene rings or combining naphthene and aromatic rings, paraffin “n” chains with aromatic rings (alkyl-aromatics), etc., a vast array of complex hydrocarbons may be formed, examples of these compounds are decalin, naphthalene, and diphenyl. Heavier fractions of crude oil contain these types of hydrocarbons, multinuclear (multi-ring) aromatics or polynuclear aromatics (PNA) are well known in crude oil and its residual products.

 

polynuclear hydrocarbons

Non-Hydrocarbons or Hetero-Atomic Compounds :

Common hetero atoms in hydrocarbons are sulfur, oxygen, nitrogen, and metallic atoms. Sulfur compounds are present in crude oil as mercaptans, mono- and disulfides with the general formula R-SH, R-S-R1, R-S-S-R1, where R and R1 are the alkyl radicals. Mercaptans are very corrosive whereas mono- and disulfides are not. Examples of cyclic sulfur compounds are thiophenes and benzothiophene.

 

hetero-atomic hydrocarbons

1.    Hydrogen sulfide (H2S): gas is associated with crude oil in dissolved form and is released when heated. H2S is corrosive at high temperatures and in the presence of moisture. Crude oil that contains large amounts of H2S is called sour crude. Sulfur present in petroleum fuel products also forms various oxides of sulfur (SOx) during combustion, which are strong environmental pollutants H2S can be removed from gases by absorption in an amine solution. the sulfur atom is very stable and non-reactive. As a result, sulfur from heavier petroleum cannot be removed without a destructive reaction, such as severe thermal or catalytic reactions. Nowadays, sulfur is recovered during refining and sold as a product. Sulfur also has a poisoning effect on various catalysts.

 

2.    Nitrogen compounds: hydrocarbons are usually found in the heavier parts of crude oil. These are responsible for color and color instability and poisoning of certain catalysts. Nitrogen in petroleum fuels causes the generation of oxides of nitrogen (NOx), which are also strong pollutants in the atmosphere. Nitrogen can be eliminated from petroleum products by catalytic hydrogenation. Like sulfur, nitrogen in the heavier parts of petroleum cannot be removed without severe cracking or hydrogenation reactions.

 

3.    Oxygen compounds: crude oil may contain oxygen-containing compounds, such as naphthenic acids, phenols, and cresols, which are responsible for corrosive activities. Oxygen also acts as a poison for many catalysts. This can be removed by catalytic hydrogenation. Excess oxygen compounds may even lead to explosions.

 

4.    Metallic compounds: of vanadium, nickel, lead, arsenic, etc., are also found in crude oil. Vanadium and nickel are found in the form of organometallic compounds mostly in the heavier fractions of crude oil where the metal atoms are distributed within the compound in a complex form called porphyrins. Petroleum fuels containing these metallic compounds may damage the burners, lines, and walls of the combustion chambers.