Composition of petroleum

Hydrocarbon Series. Of the many hydrocarbon series present in petroleum, only a few have been studied thoroughly enough to guide commercial development. The best known series are the paraffin, olefin, naphthene, aromatic, diolefin, and acetylene (Figs. 2-la to/are examples of the structural formulas of these types of compounds). 

The olefin or ethylene series (type formula C H2n) is composed of unsatu rated hydrocarbons i.e., the members of this series are capable of uniting directly with other materials such as chlorine, bromine, hydrochloric acid, and sulfuric acid, without displacing a hydrogen atom. The names of these hydrocarbons end in ene, as ethene (ethylene), propene (propylene), and butene (butylene). Unsaturated compounds react with and dissolve in sulfuric acid and may thus be removed from petroleum oils. The low-boiling olefins are probably not present in crude petroleum, but they are 

Isomeric Compounds. Confusion often arises because different compounds may have the same molecular formula. Isomeric compounds are those which have the same molecular formula but different internal structures. Compounds of the type formula C H2n may be either saturated or 

Carbon atoms Isomers Carbon atoms Isomers 

Determination of Series. Although chemists have not yet determined procedures and reagents for the isolation of each chemical series, a start toward this goal has been made. The proposed methods do not indicate the exact series of hydrocarbons that are present, but they do indicate groups of compounds that behave chemically in the same way as the lower Hill, J. B., Ind. Eng. Chem., 46, 1398 (1955). 

---

A. B. Brown and J. O. Knoblock, Symposium on Composition of Petroleum Oils, ASTM Technical Pubhcation No. 224, American Society for Testing and Materials, Philadelphia, Pa., June 1958, pp. 213—229. 

Considering the composition of petroleum and petroleum products (Speight, 1994, 1999), it is not surprising that petroleum and petroleum-derived chemicals are environmental pollutants (Loeher, 1992 Olschewsky and Megna, 1992). The world s economy is highly dependent on petroleum for energy production, and widespread use has led to enormous releases to the environment of petroleum, petroleum products, exhaust from internal combustion engines, emissions from oil-fired power plants, and industrial emissions where fuel oil is employed. 

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. 

The chemical composition of petroleum also varies over a wide range. A broad functional definition of petroleum hydrocarbons is that hydrocarbons are composed primarily of many organic compounds of natural origin and low water solubility. 

Petroleum products themselves are the source of the many components but do not adequately define total petroleum hydrocarbons. However, the composition of petroleum products assist in understanding the hydrocarbons that become environmental contaminants, but any ultimate exposure is also determined by how the product changes with use, by the nature of the release, and by the hydrocarbon s environmental fate. When petroleum products are released into the environment, changes occur that affect their potential effects significantly. Physical, chemical, and biological processes change the location and concentration of hydrocarbons at any particular site. 

Most investigations involving petrolenm hydrocarbons are regulated by various agencies that may require methodologies, action levels, and cleanup criteria that are different. Indeed, the complex chemical composition of petroleum and petroleum products can make it extremely difficult to select the most appropriate analytical test methods for evaluating environmental samples and to interpret and use the data accurately. 

As already noted, the chemical composition of petroleum and petroleum products is complex and may change over time following release into the environment. These factors make it essential that the most appropriate analytical methods are selected from a comprehensive hst of methods and techniques that are used for the analysis of environmental samples (Dean, 1998 Miller, 2000 Budde, 2001 Sunahara et al., 2002 Nelson, 2003 Smith and Cresset, 2003). But once a method is selected, it may not be the ultimate answer to solving the problem of identification and, hence, behavior (Patnaik, 2004). There are a significant number of petroleum hydrocarbon-affected sites, and evaluation and remediation of these sites may be difficult because of the complexity of the issues (analytical, scientific, and regulatory not to mention economic) regarding water and soil affected. 

Weisman, W. 1998. Analysis of Petroleum Hydrocarbons in Environmental Media. Total Petroleum Hydrocarbons Criteria Working Group Series, Vol. 1. Amherst Scientific Publishers, Amherst, MA.(See also Vol. 2, Composition of Petroleum Mixtures, 1998 Vol. 3, Selection of Representation Total Petroleum Hydrocarbons Fractions Based on Fate and Transport Considerations, 1997 Vol. 4, Development of Fraction-Specific Reference Doses and Reference Concentrations for Total Petroleum Hydrocarbons, 1997 and Vol. 5, Human Health Risk-Based Evaluation of Petroleum Contaminated Sites, Implementation of the Working Group Approach, 1999.)... 

Fractional composition the composition of petroleum as determined by fractionation (separation) methods. 

Five- and six-membered rings are quite common in organic compounds because of the tetrahedral geometry of the carbon atom. Hydrocarbons are reluctant to form new C—C bonds. Even so, five- and six-membered hydrocarbon rings can be created naturally, as proved by the composition of petroleum. This reaction was first achieved in research in 1936 by means of heterogeneous catalysts (7- ). 

The refractive index (n) of a feed sample is proportional to its aromatic content the higher the value the more aromatic compounds are present in the feed. There are many methods to predict composition of petroleum products based on refractive index measurements [11]. The best linear regression model to predict refractive index (n) based on H-NMR spectra has the form ... 

Until further information is obtained on the response of citrus trees to differences in the composition of petroleum oil, estimation of the practical value of the differences indicated between the two series of petroleum fractions on the basis of viscosity, in the control of citrus red mite, is limited. However, the conventional spray oils used in southern Califomia for the control of citrus red mite are applied at dosages six to seven times the LDm values indicated in Figiue 4 for oils having a molecular weight of 340 or above. Proper selection of oils with respect to molecular weight might make it possible to achieve good field control of citrus red mite with applications of much smaller amounts of oil. 

This paper presents a survey of our present knowledge of the composition of petroleum. Included in the presentation is a brief discussion of the nonhydrocarbon constituents of petroleum, covering sulfur, nitrogen, oxygen, and metallic constituents, together with more detailed information regarding the hydrocarbon constituents which comprise the bulk of crude petroleum. In addition to a discussion of the hydrocarbon compounds and types of hydrocarbon compounds occurring in one representative petroleum, the problem is considered of how different crude petroleums differ in their composition with respect to the hydrocarbon components. 

From the present state of our knowledge of the composition of petroleum, the following general conclusions may be drawn ... 

Compositions of petroleum mixtures sometimes are represented adequately in terms of some physical property. Three examples appear in Figure 14.5. Straight line combining of mixtures still is valid on such diagrams. 

Of the data that are available (Speight, 1999), the ultimate composition of petroleum and heavy oil vary over fairly narrow limits of elemental distribution ... 

The ultimate analysis (elemental composition) of petroleum is not reported to the same extent as it is for coal (Speight, 1994). Nevertheless, there are ASTM procedures (ASTM, 1995) for the ultimate analysis of petroleum and petroleum products but many such methods may have been designed for other materials. 

Specific gravity is influenced by the chemical composition of petroleum, but quantitative correlation is difficult to establish. Nevertheless, it is generally recognized that increased amounts of aromatic compounds result in an increase... 

Thus, investigations of the character of petroleum need to be focused on the influence of its character on refining operations and the nature of the products that will be produced. Furthermore, one means by which the character of petroleum has been studied is through its fractional composition. However, the fractional composition of petroleum varies markedly with the method of isolation or separation, thereby leading to potential complications (especially in the case of the heavier feedstocks) in the choice of suitable processing schemes for these feedstocks. 

---