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Petroleum Processing

Chemical Constitution of Crude Oil

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Chemical Constitution of Crude Oil

Crude oil contains organic compounds, heteroatom compounds (S,N,O), hydrocarbons (C, H), metals and organic (Ni, V, Fe) and inorganic (Na+, Ca++, Cl-) compounds as listed in Figure 1.7. Compounds that contain only elements of carbon and hydrogen are called hydrocarbons and constitute the largest group of organic compounds found in petroleum. There might be as many as several thousand different hydrocarbon compounds in crude oil. Hydrocarbon compounds have a general formula of CxHy, where x and y are integer numbers.

Constituents of Crude Oil. More in text above
Figure 1.7. Constituents of crude oil.
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Triangle labeled Crude Oil. On each corner is:

Inorganic Compounds (Na+, Ca2+, Cl-)

Organic Compounds (Ni, V, Fe)

Organic Compounds

On each side they are labeled:

Between organic and inorganic compounds: Heteroatom compounds (S,N,O)

Between organic and Organic (Ni, V, Fe) compounds: Hydrocarbons (C,H)

Between Organic (Ni, V, Fe) and inorganic compounds: Metals

Source: Dr. Semih Eser

Hydrocarbons are generally divided into four groups: (1) paraffins, (2) olefins, (3) naphthenes, and (4) aromatics (Figure 1.8). Among these groups, paraffins, olefins, and naphthenes are sometimes called aliphatic compounds, as different from aromatic compounds. The lightest hydrocarbon found as a dissolved gas is methane (CH4), the main component of natural gas. Olefins are not usually found in crude oils, but produced in a number of refining processes.

Hydrocarbon
Figure 1.8. Chemical bonding in hydrocarbons.
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Essential components of petroleum

-CH compounds based on quadrivalency of carbon atoms

-linked by a single bond (alkanes)

-liked by a double bond (alkenes)

-linked by conjugated double bonds in a ring structure (aromatics)

Saturated Aliphatic HC (n-alkanes or n-paraffins)

-straight chains of C atoms each with 2, 3 H atoms (except CH4)

-general formula: CnH2n+2

-CH3-(CH2)n-(CH3): Ex) n-pentane: CH3-CH2-CH2-CH2-CH3

Source: Dr. Semih Eser