Chemical classification of petroleum

Chemical classifications of petroleums relate to the molecular structures of the molecules in the oil. Of course the smaller molecules, six carbon atoms and less, are predominately paraffins. So chemical classification is usually based on analysis of the petroleum after most of the light molecules are removed. 

It is necessary to make a chemical classification of petroleum since chemical properties are very crucial in selecting the right method for processing the oil. There are many classifications with regard to fractions and chemical compositions of petroleum. In this chapter we will present the basis for these classification methods. 

The chemical classification of petroleum that distinguishes between oils of a paraffin base from those of an asphaltene base was introduced into petroleum chemistry to distinguish the oils that separate paraffin on cooling from those that separate asphaltenes. The presence of paraffins is usually reflected in the paraffinic nature of the constituent fractions whereas a high asphaltic content corresponds with the naphthenic properties of the fractions. This could lead to the misconception that paraffin-base petroleum consists mainly of paraffins and that asphalt-base petroleum consists mainly of cyclic (or naphthenic) hydrocarbons. In order to avoid confusion, a mixed base has been introduced for those oils that leave a mixture of asphaltic petroleum and paraffins as residue from nondestruc-... 

Classification of petroleum lubricating oils according to the type of crude they come from or the refining procedures used to obtain them is neither illogical nor grossly empirical. The physical and chemical properties of an oil depend on its composition, which in the last analysis is determined by the composition of the crude. Thus the nature... 

Various classifications of petroleum are reported in the literature, which take into consideration crude oil properties, distillates properties, chemical structure, origin, etc. Given the great amount of effort that experts around the world have put into these definitions, it is not necessary to generate new criteria. 

As a starting point, the book reviews the general properties of the raw materials. This is followed by the different techniques used to convert these raw materials to the intermediates, which are further reacted to produce the petrochemicals. The first chapter deals with the composition and the treatment techniques of natural gas. It also reviews the properties, composition, and classification of various crude oils. Properties of some naturally occurring carbonaceous substances such as coal and tar sand are briefly noted at the end of the chapter. These materials are targeted as future energy and chemical sources when oil and natural gas are depleted. Chapter 2 summarizes the important properties of hydrocarbon intermediates and petroleum fractions obtained from natural gas and crude oils. 

In addition, a method of petroleum classification based on other properties as well as the density of selective fractions has been developed. The method consists of a preliminary examination of the aromatic content of the fraction boiling up to 145°C (295°F), as well as that of the asphaltene content, followed by a more detailed examination of the chemical composition of the naphtha (bp < 200°C < 390°F). For this examination a graph is nsed that is a composite of cnrves expressing the relation among the percentage distillate from the naphtha. 

In terms of waste definition, there are three basic approaches (as it pertains to petroleum, petroleum products, and nonpetroleum chemicals) to defining petroleum or a petroleum product as hazardous (1) a qualitative description of the waste by origin, type, and constituents (2) classification by characteristics based on testing procedures and (3) classification as a result of the concentraUon of specific chemical substances. 

The Statistical Abstract of the United States is published annually by the U.S. Census Bureau, which groups all the economic activities in the United States into 11 divisions by the Standard Industrial Classification (SIC). The manufacturing division is divided into 20 sections designated by two-digit numbers. The manufacturers that involve chemistry intensively are listed in table 9.1, by two 2-digit numbers, such as 20 Food, 28 Chemicals, and 29 Petroleum Refining. The table lists the number of establishments, the number of employees and value of shipment in 1996. The SIC 28,... 

A common method of classification for petroleum is the PONA system (PONA is an acronym for paraffins, olefins, naphthenes, and aromatics). Paraffins are straight-chain or branched hydrocarbons in which there are no double or triple bonds between carbon atoms. Olefins are similar to paraffins, but they contain at least one multiple bond in their chemical structure. Naphthenes are saturated hydrocarbons, just like paraffins, but they incorporate a ring of carbon atoms into their chemical structure. Aromatics contain a benzene ring in their structure. 

As a consequence of its recent development the petrochemical industry is relatively much younger than the major inorganic chemicals industry. However, one can easily be misled by the classification of products that are termed petrochemical . Basically a petrochemical is derived directly or indirectly from a petroleum or natural gas fraction. It may be organic, such as ethylene, benzene, or formaldehyde, or it may be inorganic, such as ammonia, nitric acid, and ammonium nitrate (Chap. 11). So a petrochemical is not synonymous with an organic chemical, although most petrochemicals are also organic chemicals. 

Because of the wide range of chemical and physical properties, a wide range of tests have been (and continue to be) developed to provide an indication of the means by which a particular feedstock should be processed. Initial inspection of the nature of the petroleum will provide deductions about the most logical means of refining or correlation of various properties to structural types present and hence attempted classification of the petroleum. Proper interpretation of the data resulting from the inspection of crude oil requires an understanding of their significance. 

Petroleum lubricating oils are sometimes characterized by their density. As will be seen when we come to the examination of chemical structures in lubricating oils later in this chapter, density is associated with structural type. Paraffinic oils are lower in density than naphthenic or aromatic oils. Since paraffinic oils show more desirable viscosity-temperature behavior and better thermal stability than naphthenic oils, in the past density was widely used as an easily measured indicator of oil quality. With the development of additives to improve viscosity and thermal stability behavior, classification of oils by their density ratings has lost much of its former importance. 

Eventually, the need arose to describe each individnal sample of coal in terms that would accurately (even adequately) depict the physical and/or chemical properties (Kreulen, 1948 Van Krevelen and Schuyer, 1957 Francis, 1961). Conseqnently, the terminology that came to be applied to coal essentially came into being as part of a classification system and it is difficult (if not impossible) to separate terminology from classification to treat each as a separate subject. This is, of course, in direct contrast to the systems nsed for the nomenclature and terminology of petroleum, natural gas, and related materials (Speight, 1990, 2007). Indeed, the coal classification stands apart in the field of fossil fuel science as an achievement that is second to none insofar as the system(s) allow classification of all the coals that are known on the basis of standardized parameters. 

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