Hydrocarbons, classes

Hydrocarbons, compounds of carbon and hydrogen, are stmcturally classified as aromatic and aliphatic the latter includes alkanes (paraffins), alkenes (olefins), alkynes (acetylenes), and cycloparaffins. An example of a low molecular weight paraffin is methane [74-82-8], of an olefin, ethylene [74-85-1], of a cycloparaffin, cyclopentane [287-92-3], and of an aromatic, benzene [71-43-2]. Cmde petroleum oils [8002-05-9], which span a range of molecular weights of these compounds, excluding the very reactive olefins, have been classified according to their content as paraffinic, cycloparaffinic (naphthenic), or aromatic. The hydrocarbon class of terpenes is not discussed here. Terpenes, such as turpentine [8006-64-2] are found widely distributed in plants, and consist of repeating isoprene [78-79-5] units (see Isoprene Terpenoids). 

The important hydrocarbon classes are alkanes, alkenes, aromatics, and oxygenates. The first three classes are generally released to the atmosphere, whereas the fourth class, the oxygenates, is generally formed in the atmosphere. Propene will be used to illustrate the types of reactions that take place with alkenes. Propene reactions are initiated by a chemical reaction of OH or O3 with the carbon-carbon double bond. The chemical steps that follow result in the formation of free radicals of several different types which can undergo reaction with O2, NO, SO2, and NO2 to promote the formation of photochemical smog products. 

The large number of individual hydrocarbons in the atmosphere and the many different hydrocarbon classes make ambient air monitoring a very difficult task. The ambient atmosphere contains an ubiquitous concentration of methane (CH4) at approximately 1.6 ppm worldwide (9). The concentration of all other hydrocarbons in ambient air can range from 100 times less to 10 times greater than the methane concentration for a rural versus an urban location. The terminology of the concentration of hydrocarbon compounds is potentially confusing. Hydrocarbon concentrations are referred to by two units—parts per million by volume (ppmV) and parts per million by carbon (ppmC). Thus, 1 fx of gas in 1 liter of air is 1 ppmV, so the following is true ... 

The principal constituents of most crude oils are hydrocarbon compounds. All hydrocarbon classes are present in the crude mixture, except alkenes and alkynes. This may indicate that crude oils originated under a reducing atmosphere. The following is a brief description of the different hydrocarbon classes found in all crude oils. 

Appreciable property differences appear between crude oils as a result of the variable ratios of the crude oil components. For a refiner dealing with crudes of different origins, a simple criterion may be established to group crudes with similar characteristics. Crude oils can be arbitrarily classified into three or four groups depending on the relative ratio of the hydrocarbon classes that predominates in the mixture. The following describes three types of crudes ... 

Natural gas and crude oils are the main sources for hydrocarbon intermediates or secondary raw materials for the production of petrochemicals. From natural gas, ethane and LPG are recovered for use as intermediates in the production of olefins and diolefms. Important chemicals such as methanol and ammonia are also based on methane via synthesis gas. On the other hand, refinery gases from different crude oil processing schemes are important sources for olefins and LPG. Crude oil distillates and residues are precursors for olefins and aromatics via cracking and reforming processes. This chapter reviews the properties of the different hydrocarbon intermediates—paraffins, olefins, diolefms, and aromatics. Petroleum fractions and residues as mixtures of different hydrocarbon classes and hydrocarbon derivatives are discussed separately at the end of the chapter. 

FIGURE 13.5 ASF plot for hydrocarbon classes as determined by full analysis of the FT product. 

The parent triafulvene, 104, is the sole representative of this hydrocarbon class for which there is a suggested enthalpy of formation75, namely 423 kJ mol 1. If the conjugative interactions of the exo-methylene with cyclopropene and cyclopentadiene were the same, then equation 39 would be thermoneutral. 

In a model for catalytic reforming of gasoline, cited in problem P2.03.26, some 300 chemical species are identified, broken up in one case into 13 lumps characterized by carbon number and hydrocarbon class. The kinetic characteristics of such lumps are proprietary information. 

Assuming that some of the physical and chemical mechanisms just reviewed are predominant in the formation of organic aerosol, various schemes can be derived that permit a more quantitative description of the time evolution of atmospheric organic aerosol. For example, a kinetic scheme has been proposed recently (Grosjean and Friedlander, unpublished data) for aerosol formation from ole ic precursors that may be applied in principle to other hydrocarbon classes. Starting with this system. 

From these simple gas products, which correspond to a very large portion of the reacted feed stock, two basic cracking patterns are postulated the first is applicable to aliphatics and alicyclics (I) (thus including paraffins, olefins, and naphthenes), the second to substituted aromatics (II). These two basic patterns are best illustrated by Figures 1 and 2, which show the molar distribution of the principal cracked products according to the number of carbon atoms in the fragments, per 100 moles of feed stock cracked, for selected representatives of the four major hydrocarbon classes, all at 500° C. (see Table II for experimental conditions and product analyses). 

Study of the primary cracking step of the four major hydrocarbon classes leads to an important generalization, which may be seen from the following type reactions ... 

As discussed in the previous section, gas oils are complicated mixtures of several different hydrocarbon classes contaminated with small amounts of sulfur-containing species that lower product quality and limit marketability of the whole gas oil (see Fig. 1). The concentration of these sulfur species must be lowered significantly to meet present standards and, in the future, they must be nearly completely removed. To understand the difficulties in such conversions, it is helpful to consider the detailed composition of gas oils, from both the viewpoint of the desirable components of gas oils which are not to be converted and that of the sulfur-containing species which must be treated to extinction. 

About 800 aniline points or CST of hydrocarbons with aniline are listed. Since CST of hydrocarbons with nitrobenzene are about 50° C. lower than aniline points with the same hydrocarbons, nitrobenzene CST can be estimated easily for these 800 hydrocarbons. CST of many other aromatic solvents with the same hydrocarbons may be approximated similarly. Nonaromatic solvents are not so nearly parallel in this respect, but certain generalities are apparent among similar groups of components (139, 140). Moreover, many more aniline points (and from them other CST) of unknown isomeric hydrocarbons could be estimated with reasonable confidence by one of six equations for aniline points of hydrocarbon classes (that section of Table I). Altogether this table might furnish a basis for estimates of about a million CST. Even so, combinations are encountered frequently which are not predictable from this table, and new observations are required. 

TABLE 6.4.1 Coefficients Bm0 and Bmt and Correlation Coefficient r in Relationship 6.4.6a for Various Hydrocarbon Classes ... 

Solubility-Molar Volume Relationships The correlation between aqueous solubility at room temperature and the molar volume has been studied by McAuliffe [5] for different hydrocarbon classes. He discusses linear relationships, presented as graphs, describing the decrease in solubility with increasing molar volume for the homologous series of alkanes, alkenes, alkandienes, alkynes, and cycloalkanes. 

Fig. 1. Relative quantities and boiling range of major hydrocarbon classes in the crude oil from Ponca City Field (Venuto and Habib, 1978).

A nearly equally good linear correlation is observed for the aromatic hydrocarbon class consisting of fluorene, acenaphthene, and phenanthrene. The rate constants exhibit a positive correlation to log P ... 

Liquid chromatography (also called adsorption chromatography) has helped to characterize the group composition of crude oils and hydrocarbon products since the beginning of this century. The type and relative amount of certain hydrocarbon classes in the matrix can have a profound effect on the quality and performance of the hydrocarbon product. The fluorescent indicator adsorption (FIA) method (ASTM D-1319) has been used to measure the paraffinic, olefinic, and aromatic content of gasoline, jet fuel, and liquid products in general (Suatoni and Garber, 1975 Miller et al., 1983 Norris and Rawdon, 1984). 

Kelly, T.J. Allar, W.J. Premuzic, E. Tanner, R. Gaffney, J. "Temperature dependence of ozone-hydrocarbon chemiluminescence. Possible hydrocarbon class monitor. Presented at the Symp. on Atmospheric Chemistry, 182nd ACS National Meeting, New York, NY, 1981. 

Lockey, K.H. (1991). Insect hydrocarbons classes implication for chemotaxonomy. Insect Biochem., 21, 91-97. 

The only practical method for the measurement of specific hydrocarbons is by gas chromatography (GC), which can be automated, but is expensive and often used as a laboratory analyzer. Certain specially prepared columns can be used to adsorb specific hydrocarbon classes. For atmospheric hydrocarbons, a common method is to pass a sample of air through a small freeze-out trap, sweep out the air with helium, and then warm the trap and introduce the condensables into the GC column in one concentrated slug. 

NDIR sensors can only identify hydrocarbon classes, whereas two-wave-length IR detectors are able to identify individual hydrocarbon species. The GC analyzers that are capable of identifying specific classes of hydrocarbons are complex and are less precise or reliable. 

The definition of the sea boundary of the mouth area is related to the term mouth-mixing zone. Water salinity within this zone increases from the salinity inherent in river water (usually 0.2-0.5%o) to the salinity of seawater (usually 10-40%o in different seas). The salt composition of water radically changes within the mixing zone river water of hydrocarbonate class and calcium group transforms into seawater of chloride class and sodium group. 

The results in Figure 1 can be interpreted in terms of general ring structures with the hydrocarbon classes. The peak for the polypolar aromatic fraction at 160° C probably is caused by polar-monocyclic compounds and the peak at 240° C is probably the result of polar dicyclic compounds. The broad curve in the monoaromatics centering at 275°C is probably mainly caused by alkyl-substituted tetralins while the peaks... 

Hydrocarbon Class Analysis. The hydrocarbon class or type separation of the pentane-soluble fraction was performed on a silica gel-alumina column according... 

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