Review on Chemical Separation of Crude Oil and Analysis of Its Components

Crude oil is chemically composed of a complex mixture of hydrocarbons of different gaseous, liquid and solid states, the total of which may reach more than 17,000 organic compounds. At standard conditions of pressure and temperature the light hydrocarbons with carbon numbers 1 to 4 (methane, ethane, propane, butane) are present in gaseous form; Whereas pentane and the heavier hydrocarbons are found in liquid form, and in the heavy fractions with higher boiling points the hydrocarbons are in solid form. The ratio of gaseous, liquid and solid components depends on the conditions and the phase diagram of the subsurface oil mixture. The hydrocarbons in petroleum are composed predominantly of linear alkanes and to a lesser extent of cycloalkanes and aromatic hydrocarbons; with a small percentage of aromatic compounds containing heterogeneous atoms of nitrogen, oxygen and sulfur, in addition to trace amounts of metals such as iron, copper, nickel and vanadium. Many oil tanks also contain live bacteria in their mixtures. The exact molecular composition of crude oil varies greatly depending on the mixture from one place to another, but the difference in the proportion of chemical elements in the mixtures is relatively small.