277
Petroleum Analysis
technique has the advantage of greatly improving the quality of a complex operation, but it
can be a very time-consuming separation.
Ion-exchange resins are prepared from aluminum silicates, synthetic resins, and polysaccharides. The most widely used resins have a skeletal structure of polystyrene cross-linked with varying amounts of divinylbenzene. They have a loose gel structure of cross-linked polymer chains
through which the sample ions must diffuse to reach most of the exchange sites. Since ion-exchange
resins are usually prepared as beads that are several hundred micrometers in diameter, most of the
exchange sites are located at points quite distant from the surface. Because of the polyelectrolyte
nature of these organic resins, they can absorb large amounts of water or solvents and swell to volumes considerably larger than the dried gel. The size of the species that can use through the particle
is determined by the intermolecular spacing between the polymeric chains of the three-dimensional
polyelectrolyte resin.
Cation-exchange chromatography is now used primarily to isolate the nitrogen constituents in a
petroleum fraction. The relative importance of these compounds in petroleum has arisen because of
their deleterious effects in many petroleum refining processes. They reduce the activity of cracking
and hydrocracking catalysts and contribute to gum formation, color, odor, and poor storage properties of the fuel. However, not all basic compounds isolated by cation-exchange chromatography are
nitrogen compounds. Anion-exchange chromatography is used to isolate the acid components (such
as carboxylic acids and phenols) from petroleum fractions.
10.8.6 HIgH-PerFormAnCe lIQuId CHromAtogrAPHy
High-performance liquid chromatography (HPLC), particularly in the normal phase mode, has
found great utility in separating different hydrocarbon group types and identifying specific constituent types (Miller et al., 1983). However, a severe shortcoming of most HPLC approaches to a hydrocarbon group type of analysis is the difficulty in obtaining accurate response factors applicable to
different distillate products. Unfortunately, accuracy can be compromised when these response
factors are used to analyze hydrotreated and hydrocracked materials having the same boiling range.
In fact, significant changes in the hydrocarbon distribution within a certain group type causes the
analytic results to be misleading for such samples because of the variation in response with carbon
number exhibited by most routinely used HPLC detectors.
Of particular interest is the application of the HPLC technique to the identification of the molecular types in nonvolatile feedstocks such as residua. The molecular species in the asphaltene fraction
have been of particular interest (Felix et al., 1985) leading to identification of the size of polynuclear
aromatic systems in the asphaltene constituents (Speight, 1987).
Several recent HPLC separation schemes are particularly interesting since they also incorporate
detectors not usually associated with conventional hydrocarbon group types of analyses (Matsushita
et al., 1981; Miller et al., 1983; Norris and Rawdon, 1984; Rawdon, 1984; Schwartz and Brownlee,
1986). The ideal detector for a truly versatile and accurate hydrocarbon group type of analysis is one
that is sensitive to hydrocarbons but demonstrates a response independent of carbon number. More
recent work (Hayes and Anderson, 1987) has demonstrated the merits of the dielectric constant
detector as an integral part of a hydrocarbon group analyzer system.
In general, the amount of information that can be derived from any chromatographic separation,
however effective, depends on the detectors. As the field of application for HPLC has increased,
the limitations of commercially available conventional detectors, such as UV/VIS absorption and
RI have become increasingly restrictive to the growth of the technique. This has led a search for
detectors capable of producing even more information. The so-called hyphenated techniques are the
outcome of this search.
The general advantages of HPLC method are (1) each sample is analyzed as received, (2) the
boiling range of the sample is generally immaterial, (3) the total time per analysis is usually of the
order of minutes, and (4) the method can be adapted for on-stream analysis.
Petroleum Analysis
technique has the advantage of greatly improving the quality of a complex operation, but it
can be a very time-consuming separation.
Ion-exchange resins are prepared from aluminum silicates, synthetic resins, and polysaccharides. The most widely used resins have a skeletal structure of polystyrene cross-linked with varying amounts of divinylbenzene. They have a loose gel structure of cross-linked polymer chains
through which the sample ions must diffuse to reach most of the exchange sites. Since ion-exchange
resins are usually prepared as beads that are several hundred micrometers in diameter, most of the
exchange sites are located at points quite distant from the surface. Because of the polyelectrolyte
nature of these organic resins, they can absorb large amounts of water or solvents and swell to volumes considerably larger than the dried gel. The size of the species that can use through the particle
is determined by the intermolecular spacing between the polymeric chains of the three-dimensional
polyelectrolyte resin.
Cation-exchange chromatography is now used primarily to isolate the nitrogen constituents in a
petroleum fraction. The relative importance of these compounds in petroleum has arisen because of
their deleterious effects in many petroleum refining processes. They reduce the activity of cracking
and hydrocracking catalysts and contribute to gum formation, color, odor, and poor storage properties of the fuel. However, not all basic compounds isolated by cation-exchange chromatography are
nitrogen compounds. Anion-exchange chromatography is used to isolate the acid components (such
as carboxylic acids and phenols) from petroleum fractions.
10.8.6 HIgH-PerFormAnCe lIQuId CHromAtogrAPHy
High-performance liquid chromatography (HPLC), particularly in the normal phase mode, has
found great utility in separating different hydrocarbon group types and identifying specific constituent types (Miller et al., 1983). However, a severe shortcoming of most HPLC approaches to a hydrocarbon group type of analysis is the difficulty in obtaining accurate response factors applicable to
different distillate products. Unfortunately, accuracy can be compromised when these response
factors are used to analyze hydrotreated and hydrocracked materials having the same boiling range.
In fact, significant changes in the hydrocarbon distribution within a certain group type causes the
analytic results to be misleading for such samples because of the variation in response with carbon
number exhibited by most routinely used HPLC detectors.
Of particular interest is the application of the HPLC technique to the identification of the molecular types in nonvolatile feedstocks such as residua. The molecular species in the asphaltene fraction
have been of particular interest (Felix et al., 1985) leading to identification of the size of polynuclear
aromatic systems in the asphaltene constituents (Speight, 1987).
Several recent HPLC separation schemes are particularly interesting since they also incorporate
detectors not usually associated with conventional hydrocarbon group types of analyses (Matsushita
et al., 1981; Miller et al., 1983; Norris and Rawdon, 1984; Rawdon, 1984; Schwartz and Brownlee,
1986). The ideal detector for a truly versatile and accurate hydrocarbon group type of analysis is one
that is sensitive to hydrocarbons but demonstrates a response independent of carbon number. More
recent work (Hayes and Anderson, 1987) has demonstrated the merits of the dielectric constant
detector as an integral part of a hydrocarbon group analyzer system.
In general, the amount of information that can be derived from any chromatographic separation,
however effective, depends on the detectors. As the field of application for HPLC has increased,
the limitations of commercially available conventional detectors, such as UV/VIS absorption and
RI have become increasingly restrictive to the growth of the technique. This has led a search for
detectors capable of producing even more information. The so-called hyphenated techniques are the
outcome of this search.
The general advantages of HPLC method are (1) each sample is analyzed as received, (2) the
boiling range of the sample is generally immaterial, (3) the total time per analysis is usually of the
order of minutes, and (4) the method can be adapted for on-stream analysis.