272
The Chemistry and Technology of Petroleum
The sample size used in gas chromatography may vary upward from a microliter, and there is
no theoretical upper limit to the size of the sample that may be handled if the equipment is built
to accommodate it. The technique can be used for the analysis of mixtures of volatile vaporizable
compounds boiling at any temperature between absolute zero (−273°C, 459°F) and 450°C (840°F).
Identification of any substance that can be heated sufficiently without decomposing to give a vapor
pressure of a few millimeters mercury is also possible.
The use of GLC for direct component analysis in the higher boiling fractions of petroleum,
such as residua, beset by many problems, not the least of which is the low volatility (Chapter 10)
and tendency for adsorption on solids by the higher molecular weight constituents (Chapter 9).
The number of possible components in any given molecular weight range increases markedly with
the molecular weight (Speight, 2002), and there is a significant drop in the differences in physical
properties among similar structural entities. This limits the ability of GLC, and unless the sample
has been fractionated by other techniques to reduce the complexity, complete component analysis
is difficult, if not impossible.
The mass spectrometer identifies chemical compounds principally in terms of molecular type
and molecular weight, and for many problems, therefore, it becomes necessary to use additional
means of identification; the integrated GLC infrared system is a very valuable complement to the
mass spectrometer technique.
Considerable attention has also been given to trapping devices to collect gas chromatographic
fractions for examination by one or more of the spectroscopic techniques. At the same time, developments in preparative GLC have contributed even more to the compositional studies of petroleum
and its products. With column size of 4–6 in. in diameter and capable of dealing with sample sizes
of 200 mL or more, there is every possibility that GLC will replace distillation in such areas as
standard crude oil assay work.
GLC also provides a simple and convenient method for determining n-paraffin distribution
throughout the petroleum distillate range. In this method the n-paraffins are first separated by activated chemical destruction of the sieve with hydrofluoric acid, and the identity of the individual
paraffins is determined chromatographically. This allows n-paraffin distribution throughout the
boiling range 170°C–500°C (340°F–930°F) to be determined.
Gas chromatographic process analyzers have become very important in petroleum refineries.
In some refineries more samples are analyzed automatically by process chromatographs than are
analyzed with laboratory instruments. These chromatographs are usually fully automatic. In some
cases, after an analysis the instrument even makes automatic adjustments to the refinery unit. The
chromatographs usually determine from 1 to 10 components, and the analyses are repeated at short
intervals (15–20 min) over 24 h.
A more recent, very important development in gas chromatography is its combination with a
mass spectrometer as the detector. The technique in which gas chromatography is combined with
spectrometry (GC/MS) has proved to be a powerful tool for identifying many compounds at very
low levels in a wide range of boiling matrix. By the combination of the two techniques in one instrument, the onerous trapping of fractions from the gas chromatographic column is avoided and higher
sensitivities can be attained. In passing through the gas chromatographic column, the sample is
separated more or less according to its boiling point.
In view of the molecular characterizing nature of spectrometric techniques, it is not surprising
that considerable attention has been given to the combined use of GLC and these techniques. In
recent years the use of the mass spectrometer to monitor continuously the effluent of a chromatographic column has been reported, and considerable progress has been made in the development of
rapid scan infrared spectrometers for this purpose. The mass spectrometer, however, has the advantage that the quantity of material required for the production of a spectrum is considerably less than
that necessary to produce an infrared spectrum.
Although insufficient component resolution is observed in most cases, the eluting compounds
at any time are usually closely related to each other in boiling point and molecular weight or both
The Chemistry and Technology of Petroleum
The sample size used in gas chromatography may vary upward from a microliter, and there is
no theoretical upper limit to the size of the sample that may be handled if the equipment is built
to accommodate it. The technique can be used for the analysis of mixtures of volatile vaporizable
compounds boiling at any temperature between absolute zero (−273°C, 459°F) and 450°C (840°F).
Identification of any substance that can be heated sufficiently without decomposing to give a vapor
pressure of a few millimeters mercury is also possible.
The use of GLC for direct component analysis in the higher boiling fractions of petroleum,
such as residua, beset by many problems, not the least of which is the low volatility (Chapter 10)
and tendency for adsorption on solids by the higher molecular weight constituents (Chapter 9).
The number of possible components in any given molecular weight range increases markedly with
the molecular weight (Speight, 2002), and there is a significant drop in the differences in physical
properties among similar structural entities. This limits the ability of GLC, and unless the sample
has been fractionated by other techniques to reduce the complexity, complete component analysis
is difficult, if not impossible.
The mass spectrometer identifies chemical compounds principally in terms of molecular type
and molecular weight, and for many problems, therefore, it becomes necessary to use additional
means of identification; the integrated GLC infrared system is a very valuable complement to the
mass spectrometer technique.
Considerable attention has also been given to trapping devices to collect gas chromatographic
fractions for examination by one or more of the spectroscopic techniques. At the same time, developments in preparative GLC have contributed even more to the compositional studies of petroleum
and its products. With column size of 4–6 in. in diameter and capable of dealing with sample sizes
of 200 mL or more, there is every possibility that GLC will replace distillation in such areas as
standard crude oil assay work.
GLC also provides a simple and convenient method for determining n-paraffin distribution
throughout the petroleum distillate range. In this method the n-paraffins are first separated by activated chemical destruction of the sieve with hydrofluoric acid, and the identity of the individual
paraffins is determined chromatographically. This allows n-paraffin distribution throughout the
boiling range 170°C–500°C (340°F–930°F) to be determined.
Gas chromatographic process analyzers have become very important in petroleum refineries.
In some refineries more samples are analyzed automatically by process chromatographs than are
analyzed with laboratory instruments. These chromatographs are usually fully automatic. In some
cases, after an analysis the instrument even makes automatic adjustments to the refinery unit. The
chromatographs usually determine from 1 to 10 components, and the analyses are repeated at short
intervals (15–20 min) over 24 h.
A more recent, very important development in gas chromatography is its combination with a
mass spectrometer as the detector. The technique in which gas chromatography is combined with
spectrometry (GC/MS) has proved to be a powerful tool for identifying many compounds at very
low levels in a wide range of boiling matrix. By the combination of the two techniques in one instrument, the onerous trapping of fractions from the gas chromatographic column is avoided and higher
sensitivities can be attained. In passing through the gas chromatographic column, the sample is
separated more or less according to its boiling point.
In view of the molecular characterizing nature of spectrometric techniques, it is not surprising
that considerable attention has been given to the combined use of GLC and these techniques. In
recent years the use of the mass spectrometer to monitor continuously the effluent of a chromatographic column has been reported, and considerable progress has been made in the development of
rapid scan infrared spectrometers for this purpose. The mass spectrometer, however, has the advantage that the quantity of material required for the production of a spectrum is considerably less than
that necessary to produce an infrared spectrum.
Although insufficient component resolution is observed in most cases, the eluting compounds
at any time are usually closely related to each other in boiling point and molecular weight or both