268
The Chemistry and Technology of Petroleum
A magnetic field causes all liquids to exhibit optical rotation, usually in the same direction as
that of the magnetizing current; this phenomenon is known as the Faraday effect (θ) and it may be
expressed by the relation
q = pth
where
θ is the total angle of rotation
t is the thickness of substance through which the light passes
h is the magnetic field
the constant p is an intrinsic property of the substance, usually termed the Verdet constant (minutes
of arc/cm per G); there have been some attempts to use the Verdet constant in studying the constitution of hydrocarbons by physical property correlation.
10.7 SPECTROSCOPIC METHODS
Spectroscopic studies have played an important role in the evaluation of petroleum and of petroleum
products for the last three decades and many of the methods are now used as standard methods of
analysis for refinery feedstocks and products. Application of these methods to feedstocks and products is a natural consequence for the refiner.
The methods include the use of mass spectrometry to determine the (1) hydrocarbon types in middle distillates (ASTM D2425), (2) hydrocarbon types of gas oil saturate fractions (ASTM D2786), (3)
hydrocarbon types in low-olefin gasoline (ASTM D2789), and (4) aromatic types of gas oil aromatic
fractions (ASTM D3239). Nuclear magnetic resonance spectroscopy has been developed as a standard method for the determination of hydrogen types in aviation turbine fuels (ASTM D3701). X-ray
fluorescence spectrometry has been applied to the determination of lead in gasoline (ASTM D2599) as
well as to the determination of sulfur in various petroleum products (ASTM D2622; ASTM D4294).
Infrared spectroscopy is used for the determination of benzene in motor and/or aviation gasoline
(ASTM D4053), whereas ultraviolet (UV) spectroscopy is employed for the evaluation of mineral oils
(ASTM D2269) and for determining the naphthalene content of aviation turbine fuels (ASTM D1840).
Other techniques include the use of flame emission spectroscopy for determining trace metals in
gas turbine fuels (ASTM D3605) and the use of absorption spectrophotometry for the determination of the alkyl nitrate content of diesel fuel (ASTM D4046). AA has been employed as a means
of measuring the lead content of gasoline (ASTM D3237) and also for the manganese content of
gasoline (ASTM D3831) as well as for determining the barium, calcium, magnesium, and zinc
contents of lubricating oils (ASTM D4628). Flame photometry has been employed as a means of
measuring the lithium/sodium content of lubricating greases (ASTM D3340) and the sodium content of residual fuel oil (ASTM D1318).
Nowhere is the contribution of spectroscopic studies more emphatic than in application to the
delineation of structural types in the heavier feedstocks. This has been necessary because of the
unknown nature of these feedstocks by refiners. One particular example is the n.d.M. method (ASTM
D3238) which is designed for the carbon distribution and structural group analysis of petroleum oils.
Later investigators have taken structural group analysis several steps further than the n.d.M. method.
It is also appropriate at this point to give a brief description of other methods that are used for the
identification of the constituents of petroleum (Yen, 1984).
It is not intended to convey here that any one of these methods can be used for identification
purposes. However, although these methods may fall short of complete acceptability as methods
for the characterization of individual constituents of feedstocks, they can be used as methods
by which an overall evaluation of the feedstock may be obtained in terms of molecular types.
The Chemistry and Technology of Petroleum
A magnetic field causes all liquids to exhibit optical rotation, usually in the same direction as
that of the magnetizing current; this phenomenon is known as the Faraday effect (θ) and it may be
expressed by the relation
q = pth
where
θ is the total angle of rotation
t is the thickness of substance through which the light passes
h is the magnetic field
the constant p is an intrinsic property of the substance, usually termed the Verdet constant (minutes
of arc/cm per G); there have been some attempts to use the Verdet constant in studying the constitution of hydrocarbons by physical property correlation.
10.7 SPECTROSCOPIC METHODS
Spectroscopic studies have played an important role in the evaluation of petroleum and of petroleum
products for the last three decades and many of the methods are now used as standard methods of
analysis for refinery feedstocks and products. Application of these methods to feedstocks and products is a natural consequence for the refiner.
The methods include the use of mass spectrometry to determine the (1) hydrocarbon types in middle distillates (ASTM D2425), (2) hydrocarbon types of gas oil saturate fractions (ASTM D2786), (3)
hydrocarbon types in low-olefin gasoline (ASTM D2789), and (4) aromatic types of gas oil aromatic
fractions (ASTM D3239). Nuclear magnetic resonance spectroscopy has been developed as a standard method for the determination of hydrogen types in aviation turbine fuels (ASTM D3701). X-ray
fluorescence spectrometry has been applied to the determination of lead in gasoline (ASTM D2599) as
well as to the determination of sulfur in various petroleum products (ASTM D2622; ASTM D4294).
Infrared spectroscopy is used for the determination of benzene in motor and/or aviation gasoline
(ASTM D4053), whereas ultraviolet (UV) spectroscopy is employed for the evaluation of mineral oils
(ASTM D2269) and for determining the naphthalene content of aviation turbine fuels (ASTM D1840).
Other techniques include the use of flame emission spectroscopy for determining trace metals in
gas turbine fuels (ASTM D3605) and the use of absorption spectrophotometry for the determination of the alkyl nitrate content of diesel fuel (ASTM D4046). AA has been employed as a means
of measuring the lead content of gasoline (ASTM D3237) and also for the manganese content of
gasoline (ASTM D3831) as well as for determining the barium, calcium, magnesium, and zinc
contents of lubricating oils (ASTM D4628). Flame photometry has been employed as a means of
measuring the lithium/sodium content of lubricating greases (ASTM D3340) and the sodium content of residual fuel oil (ASTM D1318).
Nowhere is the contribution of spectroscopic studies more emphatic than in application to the
delineation of structural types in the heavier feedstocks. This has been necessary because of the
unknown nature of these feedstocks by refiners. One particular example is the n.d.M. method (ASTM
D3238) which is designed for the carbon distribution and structural group analysis of petroleum oils.
Later investigators have taken structural group analysis several steps further than the n.d.M. method.
It is also appropriate at this point to give a brief description of other methods that are used for the
identification of the constituents of petroleum (Yen, 1984).
It is not intended to convey here that any one of these methods can be used for identification
purposes. However, although these methods may fall short of complete acceptability as methods
for the characterization of individual constituents of feedstocks, they can be used as methods
by which an overall evaluation of the feedstock may be obtained in terms of molecular types.