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The Chemistry and Technology of Petroleum
hydrocarbon species cannot be expected to remain in operation. It must also be recognized that the
lack of realistic standards of known number average molecular weight distribution and of chemical
nature similar to that of the constituents of petroleum for calibration purposes may also be an issue.
However, GPC has been employed in the study of petroleum constituents, especially the heavier
constituents, and has yielded valuable data (Baltus and Anderson, 1984; Reynolds and Biggs, 1988;
Speight, 2001, 2002).
The adoption of GPC represents a novel approach to the identification of the constituents since
the method is not limited by the vapor pressure of the constituents. However, the situation is different with heavy petroleum samples. These are not homologous mixtures differing only in molecular
weight. In any particular crude oil a large variety of molecular species, varying from paraffinic
molecules to the polynuclear aromatic ring systems, may not follow the assumed physical relationships that the method dictates from use with polymers.
GPC is the separation method that comes closest to differentiating by molecular weight only, and
is almost unaffected by chemical composition (hence the alternate name SEC). The method actually, it separates by molecular size and has been used to measure molecular weights (Altgelt and
Guow, 1979) although there is some question about the value of the data when the method is applied
to asphaltenes (Speight et al., 1985).
SEC is usually practiced with RI detection and yields a mass profile (concentration vs. time or
elution volume) that can be converted to a mass versus molecular weight plot by means of a calibration curve. The combination of SEC with element-specific detection has widened this concept
to provide the distribution of heterocompounds in the sample as a function of elution volume and
molecular weight.
The use of SEC with reverse phase high-performance liquid chromatography (HPLC) with a
graphite furnace atomic absorption (GFAA) detector has been described for measuring the distribution of vanadium and nickel in high molecular weight petroleum fractions, including the asphaltene fraction. Using variants of this technique, inductively coupled and direct current plasma (ICP
and DCP) atomic emission spectroscopy, the method was extended and improved the former SECGFAA method allowing the separation to be continuously monitored.
The combination of GPC with another separation technique also allows the fractionation of a
sample separately by molecular weight and by chemical structure. This is particularly advantageous
for the characterization of the heavier fractions of petroleum materials because there are limitations
to the use of other methods. Thus, it is possible to obtain a matrix of fractions differing in molecular
weight and in chemical structure. It is also considered advisable to first fractionate a feedstock by
GPC to avoid overlap of the functionality that might occur in different molecular weight species in
the separation by other chromatographic methods.
The combination of GPC with another separation technique also allows the fractionation of a
sample separately by molecular weight and by chemical structure. This is particularly advantageous
for the characterization of the heavier fractions of petroleum materials because there are limitations
to the use of other methods. Thus, it is possible to obtain a matrix of fractions differing in molecular
weight and in chemical structure. It is also considered advisable to first fractionate a feedstock by
GPC to avoid overlap of the functionality that might occur in different molecular weight species in
the separation by other chromatographic methods.
In short, the gel permeation chromatographic technique concentrates all of a specific functional
type into one fraction, recognizing that there will be a wide range of molecular weight species in
that fraction. This is especially true when the chromatographic feedstock is a whole feed rather than
a distillate fraction.
10.8.5 Ion-exCHAnge CHromAtogrAPHy
Ion-exchange chromatography is widely used in the analyses of petroleum fractions for the
isolation and preliminary separation of acid and basic components (Speight, 2001). This
The Chemistry and Technology of Petroleum
hydrocarbon species cannot be expected to remain in operation. It must also be recognized that the
lack of realistic standards of known number average molecular weight distribution and of chemical
nature similar to that of the constituents of petroleum for calibration purposes may also be an issue.
However, GPC has been employed in the study of petroleum constituents, especially the heavier
constituents, and has yielded valuable data (Baltus and Anderson, 1984; Reynolds and Biggs, 1988;
Speight, 2001, 2002).
The adoption of GPC represents a novel approach to the identification of the constituents since
the method is not limited by the vapor pressure of the constituents. However, the situation is different with heavy petroleum samples. These are not homologous mixtures differing only in molecular
weight. In any particular crude oil a large variety of molecular species, varying from paraffinic
molecules to the polynuclear aromatic ring systems, may not follow the assumed physical relationships that the method dictates from use with polymers.
GPC is the separation method that comes closest to differentiating by molecular weight only, and
is almost unaffected by chemical composition (hence the alternate name SEC). The method actually, it separates by molecular size and has been used to measure molecular weights (Altgelt and
Guow, 1979) although there is some question about the value of the data when the method is applied
to asphaltenes (Speight et al., 1985).
SEC is usually practiced with RI detection and yields a mass profile (concentration vs. time or
elution volume) that can be converted to a mass versus molecular weight plot by means of a calibration curve. The combination of SEC with element-specific detection has widened this concept
to provide the distribution of heterocompounds in the sample as a function of elution volume and
molecular weight.
The use of SEC with reverse phase high-performance liquid chromatography (HPLC) with a
graphite furnace atomic absorption (GFAA) detector has been described for measuring the distribution of vanadium and nickel in high molecular weight petroleum fractions, including the asphaltene fraction. Using variants of this technique, inductively coupled and direct current plasma (ICP
and DCP) atomic emission spectroscopy, the method was extended and improved the former SECGFAA method allowing the separation to be continuously monitored.
The combination of GPC with another separation technique also allows the fractionation of a
sample separately by molecular weight and by chemical structure. This is particularly advantageous
for the characterization of the heavier fractions of petroleum materials because there are limitations
to the use of other methods. Thus, it is possible to obtain a matrix of fractions differing in molecular
weight and in chemical structure. It is also considered advisable to first fractionate a feedstock by
GPC to avoid overlap of the functionality that might occur in different molecular weight species in
the separation by other chromatographic methods.
The combination of GPC with another separation technique also allows the fractionation of a
sample separately by molecular weight and by chemical structure. This is particularly advantageous
for the characterization of the heavier fractions of petroleum materials because there are limitations
to the use of other methods. Thus, it is possible to obtain a matrix of fractions differing in molecular
weight and in chemical structure. It is also considered advisable to first fractionate a feedstock by
GPC to avoid overlap of the functionality that might occur in different molecular weight species in
the separation by other chromatographic methods.
In short, the gel permeation chromatographic technique concentrates all of a specific functional
type into one fraction, recognizing that there will be a wide range of molecular weight species in
that fraction. This is especially true when the chromatographic feedstock is a whole feed rather than
a distillate fraction.
10.8.5 Ion-exCHAnge CHromAtogrAPHy
Ion-exchange chromatography is widely used in the analyses of petroleum fractions for the
isolation and preliminary separation of acid and basic components (Speight, 2001). This