Petroleum structural elements

Azaarenes are structural elements of coal and petroleum, and are found in products derived from them by pyrolysis and distillation. They are components of creosote, which has been widely used as a timber preservative. 

Gabrielsen, R.H., Faerseth, R.B., Jensen, L.N., Kalheim, J.E. and Riis, F. 1990. Structural elements of the Norwegian Continental Shelf Part I the Barents Sea Region. Norwegian Petroleum Directorate Bulletin No. 6, 33 pp. 

Historically, a BCGS has been defined in terms of the fundamental petroleum system elements and processes associated with development and formation of this resource. Similar to conventional hydrocarbon reservoirs, the BCGS process requirements generally include deposition of the reservoir rock, hydrocarbon generation, migration and entrapment by geological structural elements and/or seal capacity genesis. 

When it comes to the hydrophobic part of a surfactant, the natural oleochemical source predominantly offers straight hydrophobic chains with even amounts of carbon atoms. These structures are not always optimal and it has been shown that some branching that does not destroy the biodegradability is preferable from a performance point of view in many applications like cleaning, wetting, etc. On the hydrophilic side, one of the most interesting structural elements that forms the non-ionic surfactants as well as some of the anionic surfactants is ethylene oxide, which at present is made from petroleum sources, i.e. ethylene. 

The viscosity-gravity constant (VGC) is a useful function for the approximate characterization of the viscous fractions of petroleum. It is relatively insensitive to molecular weight and is related to a fluids composition as expressed in terms of certain structural elements. Values of VGC near 0.800 indicate samples of paraffinic character, while values close to 1.00 indicate a preponderance of aromatic structures. Like other indicators of hydrocarbon composition, the VGC should not be indiscriminately applied to residual oils, asphaltic materials, or samples containing appreciable quantities of nonhydrocarbons. 

Even if all of the elements described so far have been present within a sedimentary basin an accumulation will not necessarily be encountered. One of the crucial questions in prospect evaluation is about the timing of events. The deformation of strata into a suitable trap has to precede the maturation and migration of petroleum. The reservoir seal must have been intact throughout geologic time. If a leak occurred sometime in the past, the exploration well will only encounter small amounts of residual hydrocarbons. Conversely, a seal such as a fault may have developed early on in the field s history and prevented the migration of hydrocarbons into the structure. 

The natural world is one of eomplex mixtures petroleum may eontain 10 -10 eomponents, while it has been estimated that there are at least 150 000 different proteins in the human body. The separation methods necessary to cope with complexity of this kind are based on chromatography and electrophoresis, and it could be said that separation has been the science of the 20th century (1, 2). Indeed, separation science spans the century almost exactly. In the early 1900s, organic and natural product chemistry was dominated by synthesis and by structure determination by degradation, chemical reactions and elemental analysis distillation, liquid extraction, and especially crystallization were the separation methods available to organic chemists. 

In modern terms, asphaltene is conceptually defined as the normal-pentane-insoluble and benzene-soluble fraction whether it is derived from coal or from petroleum. The generalized concept has been extended to fractions derived from other carbonaceous sources, such as coal and oil shale (8,9). With this extension there has been much effort to define asphaltenes in terms of chemical structure and elemental analysis as well as by the carbonaceous source. It was demonstrated that the elemental compositions of asphaltene fractions precipitated by different solvents from various sources of petroleum vary considerably (see Table I). Figure 1 presents hypothetical structures for asphaltenes derived from oils produced in different regions of the world. Other investigators (10,11) based on a number of analytical methods, such as NMR, GPC, etc., have suggested the hypothetical structure shown in Figure 2. 

In terms of the elemental composition of petroleum, the carbon content is relatively constant it is the hydrogen and heteroatom contents that are responsible for the major differences. Nitrogen, oxygen, and sulfur are present in only trace amounts in some petroleum, which thus consists primarily of hydrocarbons. On the other hand, a crude oil containing 9.5% heteroatoms may contain essentially no true hydrocarbon constituents insofar as the constituents contain at least one or more nitrogen, oxygen, and/or sulfur atoms within the molecular structures. 

Being the third most common element (after carbon and hydrogen) in petroleum product, sulfur has been analyzed extensively. Analytical methods range from elemental analyses to functional group (sulfur-type) analyses to structural characterization to molecular speciation (Speight, 2001). Of the methods specified for the... 

Sulfur constitutes about 0.052 wt % of the earth s crust. The forms in which it is ordinarily found include elemental or native sulfur in unconsolidated volcanic rocks, in anhydrite over salt-dome structures, and in bedded anhydrite or gypsum evaporate basin formations combined sulfur in metal sulfide ores and mineral sulfates hydrogen sulfide in natural gas organic sulfur compounds in petroleum and tar sands and a combination of both pyritic and organic sulfur compounds in coal (qv). 

She finds that both A and B are white, diamagnetic, crystalline compounds lhat gve elemental aialyses for empirical formula PtCI>polar solvents, such as ethanol, while B is soluble in petroleum ether (a mixture of hydrocarbons) and carbon tetrachloride Draw the structures of A and B. 

Petroleums also contain compounds in which sulfur, oxygen, and/or nitrogen atoms are combined with carbon and hydrogen. These elements usually are combined with the complex ring structures that make up the larger molecules of petroleums. These larger nonhydrocarbon compounds form a class of chemicals generally called resins and asphal-tanes. The quantity of these compounds in petroleum is often very small however, as much as 50% of the total molecules in some heavy crude oils are resins and asphaltines. 

Table III shows elemental composition of typical sour petroleum, coal syncrudes or shale oils. Compared with typical sour petroleum, the coal syncrude is lower in sulfur content but significantly higher in nitrogen. Compared with shale oil, coal syncrude is lower boiling and contains only about one half the nitrogen. A major difference between the two liquids is the highly aromatic structure of coal liquids and the absence of long paraffinic structures. Shale oil is more aromatic than petroleum but significantly less aromatic than coal liquids. This is mirrored by the hydrogen contents which were shown in Table I.

To better understand the structure and the inner workings of an environmental laboratory, we need to familiarize ourselves with laboratory functional groups and their responsibilities. Figure 4.2 shows an example of a typical full service environmental laboratory organization chart. A full service laboratory has the capabilities to perform analysis for common environmental contaminants, such as VOCs and SVOCs (including petroleum fuels and their constituents, pesticides, herbicides, and PCBs), trace elements (metals), and general chemistry parameters. Analysis of dioxins/furans, explosives, radiochemistry parameters, and analysis of contaminants in air are not considered routine, and are performed at specialized laboratories. 

As you will learn in Unit 5, the term organic refers to most compounds structured around the element carbon. Toluene belongs to a large class of petroleum-related compounds called hydrocarbons. 

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