Carbon-forming propensity

Carbon residue the amount of carbonaceous residue remaining after thermal decomposition of petroleum, a petroleum fraction, or a petroleum product in a limited amount of air also called the coke- or carbon-forming propensity, often prefixed by the terms Conradson or Ramsbottom in reference to the inventor of the respective tests. 

The use of fuel oil (ASTM No. 2) for heating has resulted in the availability of different types of burners that are classified according to the manner in which the fuel oil is combusted. Any carbonaceous residue formed during the thermal decomposition of the fuel oil that is deposited in, or near, the inlet surface, reduces the fuel oil flow, with resultant loss in burner efficiency. Therefore, fuel oil should have low carbon-forming propensities. Other petroleum products that are lower boiling than distillate fuel oil do not usually reference the carbon residue in the specifications. 

Mineral oils are usually considered to have a high propensity for carbon formation and deposition under thermal conditions. Nevertheless, the tests that are applied to determine the carbon-forming propensity of fuel oil (and other petroleum products) are also available for application to mineral oils. The test methods for the carbon residue should not be confused with the test method for carbonizable substances (ASTM D-565). The former test methods are thermal in nature, whereas the latter test method involves the use of sulfuric acid in a search for specific chemical entities within the oil. 

For example, all of the carbon in coal is determined by ultimate analysis and it is not an indication (or determination) of the carbon-forming propensity (i.e., the coke-producing ability) of the coal as is the case with the test for the volatile matter content of coal. Thus, just as there has been the need to develop standard methods for the proximate analysis of coal, there has also been the necessity to develop standard methods for the ultimate analysis of coal. 

Data reporting (i.e., the statement of the results of the proximate analysis test methods) usually includes (in some countries but not in all countries) descriptions of the color of the ash and of the coke button. As an interesting comparison, the test for determining the carbon residue (Conradson), the coke-forming propensity of petroleum fractions and petroleum products (ASTM D-189 ASTM D-2416), advocates the use of more than one crucible. A porcelain crucible is used to contain the sample, and this is contained within two outer iron crucibles. This corresponds to the thermal decomposition of the sample in a limited supply of air (oxygen) and the measurement of the carbonaceous residue left at the termination of the test. 

The carbon residue (ASTM D-189 and ASTM D-524) of a crude oil is a property that can be correlated with several other properties (Figure 2-14). The carbon residue presents indications of the volatility or gasoline-forming propensity of the feedstock and, for the most part in this text, the coke-forming propensity of a feedstock. Tests for carbon residue are sometimes used to evaluate the carbonaceous depositing characteristics of fuels used in certain types of oil-burning equipment and internal combustion engines. 

As noted, in any of the carbon residue tests, ash-forming constituents (ASTM D-482) or nonvolatile additives present in the sample will be included in the total carbon residue reported, leading to higher carbon residue values and erroneous conclusions about the coke-forming propensity of the sample. 

Thus a feedstock map can be used to show where a particular physical or chemical property tends to concentrate on the map. For example, the coke-forming propensity, that is, the amount of the carbon residue, is shown for various regions on the map for a sample of atmospheric residuum (Fig. 2.7 Long and Speight, 1998). In addition, a feedstock map can be very useful for predicting the effectiveness of various types of separations processes as applied to petroleum (Fig. 2.8 Speight, 2001). 

Carbon Residue—amount left after evaporation and pyrolysis to provide some indication of relative coke-forming propensity (ASTM Test Method D189, Conradson Carbon Residue of Petroleum Products, ASTM Test Method D524, Ramsbottom Carbon Residue of Petroleum Products, or ASTM Test Method D4530, Determination of Carbon Residue (Micro Method)), ASTM Method D4530 having gained wide acceptance. 

This test method covers the determination of the amount of carbon residue (Note 1) left after evaporation and pyrolysis of an oil, and is intended to provide some indication of relative coke-forming propensity. This test method is generally applicable to relatively nonvolatile petroleum products which partially decompose on distillation at atmospheric pressure. Petroleum products containing ash-forming contituents as determined by Test Method D 482, will have an erroneously high carbon residue, depending upon the amount of ash formed (Notes 2 and 3). 

Note 3— In diesd fuel, the presence of alkyl nitrates such as amyl nitrate, hexyl nitrate, or octyl nitrate, causes a higher carbon residue value than observed in untreated fud, which can lead to erroneous condusioiis as to the coke-forming propensity of the fuel. The presence of alkyl nitrate in the fiiel can be detected by Test Method D 4046. 

The propensity of nitriles to release cyanide subsequent to metaboHsm is the basis of their acute toxicity. Nitriles that form tertiary radicals at their alpha carbon atoms (eg, isobutyronitrile, 2-methylbutyronitrile) are substantially more acutely lethal than nitriles that form secondary radicals at their alpha carbons (eg, butyronitrile, propionitnle). Cyanohydrins are acutely toxic because they are unstable and release cyanide quickly. Alpha-aminonitriles are also acutely toxic, presumably by analogy with cyanohydrins. 

Boron is a unique and exciting element. Over the years it has proved a constant challenge and stimulus not only to preparative chemists and theoreticians, but also to industrial chemists and technologists. It is the only non-metal in Group 13 of the periodic table and shows many similarities to its neighbour, carbon, and its diagonal relative, silicon. Thus, like C and Si, it shows a marked propensity to form covalent, molecular compounds, but it differs sharply from them in having one less valence electron than the number of valence orbitals, a situation sometimes referred to as electron deficiency . This has a dominant effect on its chemistry. 

The short lifetimes of carbon-centered monoradicals are generally reduced in the case of diradicals due to their propensity to form covalent bonds. It has been suggested that stable diradicals may be observable from highly strained bicyclic molecules where the TS for inversion is a diradical. Unfortunately, only persistent diradicals have been obtained in this way. Akin to this approach, in a recent attempt to generate the oxyallyl diradical, Sorensen and co-workers synthesized two substituted bicyclobutanones hoping to stretch and homolytically break the central bond using bulky substituents, which would also stabilize the diradical. Though the bicyclobutanones did not yield the desired oxyallyl derivative, the X-ray structures showed... 

When EO is formed, single bonds from two adjacent carbons are connected to an oxygen atom. A three-member ring is always in a strained condition, due to the geometry of the molecule. Because of the propensity to relieve the strain, epoxides are very reactive. Practically all the EO produced is converted to chemical intermediates as a result of a ring opening reaction. 

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