710
1.2 Crude Oil Characteristics and Properties
Crude oil characterization is of primary importance in the refinery (industry). As
discussed in the previous section, crude oil is a complex mixture of an organic compound. Therefore, there is a need to understand the physical and chemical characteristics of crude before further processing. There exist many such properties and
characteristics, but here a few are discussed in brief.
1.2.1 API Gravity
American Petroleum Institute (API) gravity and specific gravity (S g ) are a standard
in trading of crude oil. Specific gravity (density) with respect to water is one of the
important properties widely used in industry for preliminary assessment of crude oil
quality and character. API gravity of crude is calculated by the Eq. (1) given below:
DegreeAPI =
-
141 5 131 5
.
.
S g
(1)
According to API gravity grade, the crudes are further classified as light, medium,
and heavy crude oil. API gravity greater than 31.1° (S g  < 0.867 g/cm
3
) is called light
crude, API value in between 22.3° and 31.1° (S g  = 0.917 – 0.867 g/cm
3
) is called
medium crude, while API value below 22.3° (S g  > 0.917 g/cm
3
) is termed as heavy
Table 2 Classifications of
hydrocarbons in crude oil
Hydrocarbon
Weight % (average)
Paraffins (alkanes) 30%
Naphthenes
49%
Aromatics
15%
Asphaltics
6%
Fig. 1 SARA-separation scheme
V. Anand and R. M. Thaokar