Heteroatom compounds, petroleum

In very general terms, petroleum is a mixture of (1) hydrocarbon types, (2) nitrogen compounds, (3) oxygen compounds, (4) sulfur compounds, and (5) metallic constituents. Petrolenm prodncts are less well defined in terms of heteroatom compounds and are better defined in terms of the hydrocarbon types present. However, this general definition is not adequate to describe the true composition as it relates to the behavior of the petroleum, and its products, in the environment. For example, the occnrrence of amphoteric species (i.e., compounds having a mixed acid-base natnre) is not always addressed, nor is the phenomenon of molecnlar size or the occnrrence of specific functional types that can play a major role in petrolenm behavior. 

Although the focus of many tests is analysis of the hydrocarbon constituents of naphtha and other petroleum fractions, heteroatoms compounds that contain sulfur and nitrogen atoms cannot be ignored, and methods for their determination are available. The combination of gas chromatography with element-selective detection gives information about the distribution of the element. In addition, many individual heteroatomic compounds can be determined. 

Petroleum is a complex mixture of various organic compounds. It consists of different hydrocarbons and heteroatomic compounds. It is technically impossibly to separate petroleum into individual compounds. In any case, it is unnecessary to separate the petroleum to the component level in order to obtain a technological or industrial classification. 

After a plate has been exposed to the mobile-phase solvent for the required time, the compounds present can be viewed by several methods. Polynuclear aromatic hydrocarbons, other compounds with conjugated systems, and compounds containing heteroatoms (nitrogen, oxygen, or sulfur) can be viewed with long-and short-wave ultraviolet light. The unaided eye can see other material, or the plates can be developed in iodine. Iodine has an affinity for most petroleum compounds, including the saturated hydrocarbons, and stains the compounds a reddish-brown color. 

Cracking reactions Chemical reactions that occur during catagenesis and metagenesis in marine sediments and sedimentary rocks. During this process, petroleum compounds are formed as hydrocarbons are broken off heteroatomic macromolecules. 

The species which are unknown and have not been identified as one of the major chemical lump such as alkanes, phenols and aromatics are lumped together as unidentified. However, the species in this lump include saturated and unsaturated cycloalkanes with or without side chains, which resembles the naphthenes, a petroleum refinery product group. A number of well known species in coal liquid are not mentioned in this lumping scheme. Such as heterocyclic compounds with sulfur, nitrogen or oxygen as the heteroatom, and other heteroatora containing species. Some of these compounds appear with aromatics (e.g. thiophenes, quinolines) and with phenols (e.g. aromatic amines), and most of them are lumped with the unidentified species lump. 

Heterocycle A compound which contains a closed ring system in which the atoms are of more than one kind. Sulfur, nitrogen, and oxygen are common heteroatoms found in petroleum heterocycles. 

Compound type analysis was not conducted in this work, but it is instructive to look at some literature results. With respect to heteroatoms, tar sand bitumen and petroleum asphaltenes have been variously reported as containing predominantly polar heteroatoms, principally oxygen types (18) or nonpolar heteroatoms, principally nitrogen types (14). The difference in these reported results apparently relates to the method of analysis in which the former is a direct determination, the latter an indirect determination. 

Separating a whole sample of a coal liquid or shale oil into classes poses special problems since these materials contain high concentrations of heteroatomic species compared with natural petroleums. Many of these compounds are quite polar and can cause emulsification, precipitation, and may even react to produce artifactual compounds at some stage during a separation procedure. Many liquid chromatographic techniques have been useful in class separations and analyses of petroleums. More often, these have been applied to particular analytical scale operations with fossil-derived liquids. The most common applications are for aromatic-aliphatic and molecular weight types of separations. 

A wide variety of compounds that contain a heteroatom as well as carbon and hydrogen also occur in petroleum but generally to a lesser extent. Hydrogen sulfide and a variety of thiols, sulfides, and thiophenes are some examples of the sulfur compounds present [6] (Eq. 18.6). 

The most abundant heteroatom is invariably sulfur, appearing in concentrations from below 0.1 wt. % in North African or Indonesian light crudes to over 5 wt. % in Venezuelan heavy crudes (Boscan) or Canadian tar sands. A wide variety of sulfur containing compounds are present in petroleum and refinery fractions, ranging from thiols to thiophenes the most important classes of organosulfur compounds of interest for our purposes are represented in Fig. 1.1. 

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