316
The Chemistry and Technology of Petroleum
that this allows modifications to the various processes resulting in easy elimination of these atoms. It
will also allow evaluation of the structural types present in the hydrocarbon portions of these molecules in the hope of deriving as much benefit as possible during processing of these complex materials.
Whether these reasons are sufficiently valid remains to be seen, but considerable work has been
done and is even now in progress to evaluate the influence of these high-molecular-weight materials
during petroleum recovery and petroleum refining (Speight, 1994; Yan et al., 1997).
12.2 SEPARATION
The asphalt constituents of petroleum usually appear as a dark brown to black, sticky, semisolid fraction that is the result of various refining processes, but what constitutes the asphalt fraction of petroleum
is a matter of conjecture. The residuum from vacuum distillation is most frequently referred to as the
asphalt portion of petroleum, as is the material precipitated by liquid propane–liquid butane mixtures
during the deasphalting stage of petroleum refining (Chapters 15 and 20). In both cases, the residue usually consists of asphaltene constituents, resin constituents, and possibly a heavy gas oil fraction, which
may be lubricating stock material and cannot be distilled. Hence, for the purposes of this chapter, the
asphalt constituents of petroleum are considered asphaltene constituents, resin constituents, and the portion of the oil fraction that cannot be distilled without the onset of thermal decomposition.
Separation of the asphalt portion of petroleum can be achieved by a variety of methods
(Chapters 10 and 26). Further discussion about these techniques is not warranted here. However,
it should be noted that, unless otherwise stated, the asphalt materials described in this chapter
are those materials separated by nondestructive distillation or by solvent–adsorbent treatment.
Materials separated by chemical methods or by methods that could involve substantial structural
changes within the molecular framework of the constituents are not considered here.
The asphaltene fraction is, by definition, a solubility class (Chapters 9 and 10) and is the fraction
precipitated from feedstocks by the addition of 40 volumes of the liquid hydrocarbon (Table 12.1;
Chapters 1 and 10; Girdler, 1965; Mitchell and Speight, 1973; Speight et al., 1982, 1984; Andersen
and Birdi, 1990; Andersen, 1994; Speight, 1994; Cimino et al., 1995).
The asphaltene fraction is a dark brown to black friable solid that has no definite melting point
and usually foams and swells on heating to leave a carbonaceous residue. They are obtained from
petroleum by the addition of a nonpolar solvent (such as a hydrocarbon) with a surface tension
lower than 25 dyne/cm at 25°C (77°F) such as low-boiling petroleum naphtha, petroleum ether,
n-pentane, iso-pentane, n-heptane, liquefied petroleum gases, and the like (Chapter 10) (Mitchell
and Speight, 1973) and, in fact, propane is used commercially in processing petroleum residua
TABLE 12.1
Standard Methods for Asphaltene Separation
Method
Precipitant
Volume Precipitant Per
Gram of Sample (mL)
ASTM D893
n-Pentane
10
ASTM D2006
n-Pentane
50
ASTM D2007
n-Pentane
10
ASTM D3279
n-Heptane
100
ASTM D4124
n-Heptane
100
IP 143
n-Heptane
30
Source: ASTM, Annual Book of Standards, American Society
for Testing and Materials, West Conshohocken, PA,
1980–2012.
The Chemistry and Technology of Petroleum
that this allows modifications to the various processes resulting in easy elimination of these atoms. It
will also allow evaluation of the structural types present in the hydrocarbon portions of these molecules in the hope of deriving as much benefit as possible during processing of these complex materials.
Whether these reasons are sufficiently valid remains to be seen, but considerable work has been
done and is even now in progress to evaluate the influence of these high-molecular-weight materials
during petroleum recovery and petroleum refining (Speight, 1994; Yan et al., 1997).
12.2 SEPARATION
The asphalt constituents of petroleum usually appear as a dark brown to black, sticky, semisolid fraction that is the result of various refining processes, but what constitutes the asphalt fraction of petroleum
is a matter of conjecture. The residuum from vacuum distillation is most frequently referred to as the
asphalt portion of petroleum, as is the material precipitated by liquid propane–liquid butane mixtures
during the deasphalting stage of petroleum refining (Chapters 15 and 20). In both cases, the residue usually consists of asphaltene constituents, resin constituents, and possibly a heavy gas oil fraction, which
may be lubricating stock material and cannot be distilled. Hence, for the purposes of this chapter, the
asphalt constituents of petroleum are considered asphaltene constituents, resin constituents, and the portion of the oil fraction that cannot be distilled without the onset of thermal decomposition.
Separation of the asphalt portion of petroleum can be achieved by a variety of methods
(Chapters 10 and 26). Further discussion about these techniques is not warranted here. However,
it should be noted that, unless otherwise stated, the asphalt materials described in this chapter
are those materials separated by nondestructive distillation or by solvent–adsorbent treatment.
Materials separated by chemical methods or by methods that could involve substantial structural
changes within the molecular framework of the constituents are not considered here.
The asphaltene fraction is, by definition, a solubility class (Chapters 9 and 10) and is the fraction
precipitated from feedstocks by the addition of 40 volumes of the liquid hydrocarbon (Table 12.1;
Chapters 1 and 10; Girdler, 1965; Mitchell and Speight, 1973; Speight et al., 1982, 1984; Andersen
and Birdi, 1990; Andersen, 1994; Speight, 1994; Cimino et al., 1995).
The asphaltene fraction is a dark brown to black friable solid that has no definite melting point
and usually foams and swells on heating to leave a carbonaceous residue. They are obtained from
petroleum by the addition of a nonpolar solvent (such as a hydrocarbon) with a surface tension
lower than 25 dyne/cm at 25°C (77°F) such as low-boiling petroleum naphtha, petroleum ether,
n-pentane, iso-pentane, n-heptane, liquefied petroleum gases, and the like (Chapter 10) (Mitchell
and Speight, 1973) and, in fact, propane is used commercially in processing petroleum residua
TABLE 12.1
Standard Methods for Asphaltene Separation
Method
Precipitant
Volume Precipitant Per
Gram of Sample (mL)
ASTM D893
n-Pentane
10
ASTM D2006
n-Pentane
50
ASTM D2007
n-Pentane
10
ASTM D3279
n-Heptane
100
ASTM D4124
n-Heptane
100
IP 143
n-Heptane
30
Source: ASTM, Annual Book of Standards, American Society
for Testing and Materials, West Conshohocken, PA,
1980–2012.