261
Petroleum Analysis
The mechanical design and operating conditions of such equipment have such a profound influence on carbon deposition during service that comparison of carbon residues between oils should
be considered as giving only a rough approximation of relative deposit-forming tendencies. A more
precise relationship between carbon residue and hydrogen content, H/C atomic ratio, nitrogen content, and sulfur content has been shown to exist. These data can provide more precise information
about the anticipated behavior of a variety of feedstocks in thermal processes.
Because of the extremely small values of carbon residue obtained by the Conradson and
Ramsbottom methods when applied to the lighter distillate fuel oils, it is customary to distill such
products to 10% residual oil and determine the carbon residue thereof. Such values may be used
directly in comparing fuel oils, as long as it is kept in mind that the value is that for a residuum oil
and are not to be compared with the carbon residue of the whole feedstock.
There are two older methods for determining the carbon residue of a petroleum or petroleum
product: the Conradson method (ASTM D189) and the Ramsbottom method (ASTM D524). Both
are applicable to the relatively nonvolatile portion of petroleum and petroleum products, which partially decompose when distilled at a pressure of 1 atm. However, crude oil that contains ash-forming
constituents will have an erroneously high carbon residue by either method unless the ash is first
removed from the oil; the degree of error is proportional to the amount of ash.
A third method, involving micropyrolysis of the sample, is also available as a standard test
method (ASTM D4530). The method requires smaller sample amounts and was originally developed as a thermogravimetric method. The carbon residue produced by this method is often
referred to as the microcarbon residue (MCR). Agreements between the data from the three
methods are good, making it possible to interrelate all of the data from carbon residue tests (Long
and Speight, 1989).
Even though the three methods have their relative merits, there is a tendency to advocate use of
the more expedient microcarbon method to the exclusion of the Conradson and Ramsbottom methods because of the lesser amounts required in the microcarbon method, which is somewhat less
precise in practical technique.
10.4.4 AnIlIne PoInt
The aniline point of a liquid was originally defined as the consolute or critical solution temperature
of the two liquids, that is, the minimum temperature at which they are miscible in all proportions.
The term is now most generally applied to the temperature at which exactly equal parts of the two
are miscible. This value is more conveniently measured than the original value and is only a few
tenths of a degree lower for most substances.
Although it is an arbitrary index (ASTM D611), the aniline point is of considerable value in the
characterization of petroleum products. For oils of a given type it increases slightly with molecular weight; for those of given molecular weight it increases rapidly with increasing paraffinic
character. As a consequence, it was one of the first properties proposed for the group analysis of
petroleum products with respect to aromatic and naphthene content. It is used, alternately, even
in one of the more recent methods. The simplicity of the determination makes it attractive for the
rough estimation of aromatic content when that value is important for functional requirements,
as in the case of the solvent power of naphtha and the combustion characteristics of gasoline and
diesel fuel.
10.4.5 sPeCIFIC HeAt
Specific heat is defined as the quantity of heat required to raise a unit mass of material through one
degree of temperature (ASTM D2766).
Petroleum Analysis
The mechanical design and operating conditions of such equipment have such a profound influence on carbon deposition during service that comparison of carbon residues between oils should
be considered as giving only a rough approximation of relative deposit-forming tendencies. A more
precise relationship between carbon residue and hydrogen content, H/C atomic ratio, nitrogen content, and sulfur content has been shown to exist. These data can provide more precise information
about the anticipated behavior of a variety of feedstocks in thermal processes.
Because of the extremely small values of carbon residue obtained by the Conradson and
Ramsbottom methods when applied to the lighter distillate fuel oils, it is customary to distill such
products to 10% residual oil and determine the carbon residue thereof. Such values may be used
directly in comparing fuel oils, as long as it is kept in mind that the value is that for a residuum oil
and are not to be compared with the carbon residue of the whole feedstock.
There are two older methods for determining the carbon residue of a petroleum or petroleum
product: the Conradson method (ASTM D189) and the Ramsbottom method (ASTM D524). Both
are applicable to the relatively nonvolatile portion of petroleum and petroleum products, which partially decompose when distilled at a pressure of 1 atm. However, crude oil that contains ash-forming
constituents will have an erroneously high carbon residue by either method unless the ash is first
removed from the oil; the degree of error is proportional to the amount of ash.
A third method, involving micropyrolysis of the sample, is also available as a standard test
method (ASTM D4530). The method requires smaller sample amounts and was originally developed as a thermogravimetric method. The carbon residue produced by this method is often
referred to as the microcarbon residue (MCR). Agreements between the data from the three
methods are good, making it possible to interrelate all of the data from carbon residue tests (Long
and Speight, 1989).
Even though the three methods have their relative merits, there is a tendency to advocate use of
the more expedient microcarbon method to the exclusion of the Conradson and Ramsbottom methods because of the lesser amounts required in the microcarbon method, which is somewhat less
precise in practical technique.
10.4.4 AnIlIne PoInt
The aniline point of a liquid was originally defined as the consolute or critical solution temperature
of the two liquids, that is, the minimum temperature at which they are miscible in all proportions.
The term is now most generally applied to the temperature at which exactly equal parts of the two
are miscible. This value is more conveniently measured than the original value and is only a few
tenths of a degree lower for most substances.
Although it is an arbitrary index (ASTM D611), the aniline point is of considerable value in the
characterization of petroleum products. For oils of a given type it increases slightly with molecular weight; for those of given molecular weight it increases rapidly with increasing paraffinic
character. As a consequence, it was one of the first properties proposed for the group analysis of
petroleum products with respect to aromatic and naphthene content. It is used, alternately, even
in one of the more recent methods. The simplicity of the determination makes it attractive for the
rough estimation of aromatic content when that value is important for functional requirements,
as in the case of the solvent power of naphtha and the combustion characteristics of gasoline and
diesel fuel.
10.4.5 sPeCIFIC HeAt
Specific heat is defined as the quantity of heat required to raise a unit mass of material through one
degree of temperature (ASTM D2766).