37
Classification
Indeed, investigation of crude oils from worldwide sources showed that 85% fell into one of the
three classes: paraffin, intermediate, or naphthene base.
It also has been proposed to classify heavy oils according to characterization gravity. This is
defined as the arithmetic average of the instantaneous specific gravity of the distillates boiling at
177°C (350°F), 232°C (450°F), and 288°C (550°F) vapor line temperature at 25 mm pressure in a
true boiling point distillation.
In addition, a method of petroleum classification based on other properties, as well as the density, of selective fractions has been developed. The method consists of a preliminary examination of the aromatic content of the fraction boiling up to 145°C (295°F), as well as that of the
asphaltene content, followed by a more detailed examination of the chemical composition of the
naphtha (b.p. < 200°C < 390°F). For this examination, a graph is used that is a composite of curves
expressing the relation between percentage distillate from the naphtha, the aniline point, refractive
index, specific gravity, and the boiling point. The aniline point after acid extraction is included to
estimate the paraffin–naphthene ratio.
2.2.5 API grAvIty
Conventional crude oil and heavy oil have also been defined very generally in terms of physical properties. For example, heavy oils were considered those petroleum-type materials that had
gravity somewhat less than 20°API, with the heavy oils falling into the API gravity range 10°–15°
(e.g., Cold Lake crude oil = 12°API) and bitumen falling into the 5°–10°API range (e.g., Athabasca
bitumen = 8°API). Residua vary depending upon the temperature at which distillation is terminated.
Atmospheric residua are usually in the 10°–15°API range, and vacuum residua are in the range
2°–8°API (Speight, 2000).
There have been several recent noteworthy attempts to classify crude oil (Bestougeff et al., 1984;
Danyluk et al., 1984; Gibson, 1984; Khayan, 1984) using one or more of the general physical properties of crude oils. One method uses divisions by API gravity, which is already accepted by most workers, and also uses viscosity data (Khayan, 1984). This method is essentially a more formal attempt in
which specific numbers are applied without recognition of the implications of these numbers.
In the author’s experience, the assignment of specific numbers to the classification of petroleum
is fraught with difficulty. For example, heavy oil was considered those petroleum-type materials
that had gravity somewhat less than 20°API, and generally fell into the API gravity range 10°–15°
with tar sand bitumen falling into the 5°–10°API range (Speight, 2000). Using such lines of demarcation does not circumvent the question that must arise when one considers a material having an
TABLE 2.2
Classification according to API Gravity
Fraction
Classification
250°C–270°C 480°F–520°F 275°C–300°C 525°F–570°F
API Gravity
Type
API Gravity
Type
>40.0
Paraffin
>30.0
Paraffin
Paraffin
>40.0
Paraffin
20.1–29.9
Intermediate
Paraffin-intermediate
33.1–9.9
Intermediate
20.1–29.9
Paraffin
Intermediate-paraffin
33.1–39.9
Intermediate
20.1–29.9
Intermediate
Intermediate
33.1–39.9
Intermediate
<20.0
Naphthene
Intermediate-naphthene
<33.0
Naphthene
20.1–29.9
Intermediate
Naphthene-intermediate
<33.0
Naphthene
<20.0
Naphthene
Naphthene
>44.0
Paraffin
<20.0
Naphthene
Paraffin-naphthene
33.0
Naphthene
>30.0
Paraffin
Naphthene-paraffin
Classification
Indeed, investigation of crude oils from worldwide sources showed that 85% fell into one of the
three classes: paraffin, intermediate, or naphthene base.
It also has been proposed to classify heavy oils according to characterization gravity. This is
defined as the arithmetic average of the instantaneous specific gravity of the distillates boiling at
177°C (350°F), 232°C (450°F), and 288°C (550°F) vapor line temperature at 25 mm pressure in a
true boiling point distillation.
In addition, a method of petroleum classification based on other properties, as well as the density, of selective fractions has been developed. The method consists of a preliminary examination of the aromatic content of the fraction boiling up to 145°C (295°F), as well as that of the
asphaltene content, followed by a more detailed examination of the chemical composition of the
naphtha (b.p. < 200°C < 390°F). For this examination, a graph is used that is a composite of curves
expressing the relation between percentage distillate from the naphtha, the aniline point, refractive
index, specific gravity, and the boiling point. The aniline point after acid extraction is included to
estimate the paraffin–naphthene ratio.
2.2.5 API grAvIty
Conventional crude oil and heavy oil have also been defined very generally in terms of physical properties. For example, heavy oils were considered those petroleum-type materials that had
gravity somewhat less than 20°API, with the heavy oils falling into the API gravity range 10°–15°
(e.g., Cold Lake crude oil = 12°API) and bitumen falling into the 5°–10°API range (e.g., Athabasca
bitumen = 8°API). Residua vary depending upon the temperature at which distillation is terminated.
Atmospheric residua are usually in the 10°–15°API range, and vacuum residua are in the range
2°–8°API (Speight, 2000).
There have been several recent noteworthy attempts to classify crude oil (Bestougeff et al., 1984;
Danyluk et al., 1984; Gibson, 1984; Khayan, 1984) using one or more of the general physical properties of crude oils. One method uses divisions by API gravity, which is already accepted by most workers, and also uses viscosity data (Khayan, 1984). This method is essentially a more formal attempt in
which specific numbers are applied without recognition of the implications of these numbers.
In the author’s experience, the assignment of specific numbers to the classification of petroleum
is fraught with difficulty. For example, heavy oil was considered those petroleum-type materials
that had gravity somewhat less than 20°API, and generally fell into the API gravity range 10°–15°
with tar sand bitumen falling into the 5°–10°API range (Speight, 2000). Using such lines of demarcation does not circumvent the question that must arise when one considers a material having an
TABLE 2.2
Classification according to API Gravity
Fraction
Classification
250°C–270°C 480°F–520°F 275°C–300°C 525°F–570°F
API Gravity
Type
API Gravity
Type
>40.0
Paraffin
>30.0
Paraffin
Paraffin
>40.0
Paraffin
20.1–29.9
Intermediate
Paraffin-intermediate
33.1–9.9
Intermediate
20.1–29.9
Paraffin
Intermediate-paraffin
33.1–39.9
Intermediate
20.1–29.9
Intermediate
Intermediate
33.1–39.9
Intermediate
<20.0
Naphthene
Intermediate-naphthene
<33.0
Naphthene
20.1–29.9
Intermediate
Naphthene-intermediate
<33.0
Naphthene
<20.0
Naphthene
Naphthene
>44.0
Paraffin
<20.0
Naphthene
Paraffin-naphthene
33.0
Naphthene
>30.0
Paraffin
Naphthene-paraffin