Physical Properties of Petroleum Oil

Oil is a general term that describes a wide variety of natural substances of plant, animal, or mineral origin, as well as a range of synthetic compounds. The many different types of oil are made up of hundreds of major compounds and thousands of minor ones. As their composition varies, each type of oil or petroleum product has certain unique characteristics or properties. These properties influence how the oil behaves when it is spilled and determine the effects of the oil on living organisms in the environment. These properties also influence the efficiency of cleanup operations. This book deals specifically with crude oils and petroleum products derived from crude oils. The chemical composition and physical properties of these oils are described in this chapter. 

Petroleum consists of four hydrocarbon-t3 es (saturates, aromatics, resins, and asphaltenes) that may be defined in terms of solubility, polarity, and MW. Of these structural t)q)es, asphaltenes have markedly adverse effects on the processability of petroleum and play a significant role in the physical properties of heavy oils and bitumen. Because of these effects, in this chapter, asphaltenes will be discussed in detail in terms of their properties, composition, and thermal chemistry during upgrading, as well as their influence on instability/incompatibility during the production, transportation and upgrading of petroleum. 

The effect of asphaltenes on the physical properties of heavy oils and bitumen has been studied extensively. It has been demonstrated that the viscosity of petroleum is significantly influenced by the presence and concentration of asphaltenes. Storm et al. demonstrated that when the relative viscosity of heavy oils was plotted versus asphaltenes concentration in both toluene (at room temperature) and vacuum residue (at 93°C), a straight line resulted. Thus, it was concluded that toluene is as good a solvent for asphaltenes as for vacuum resid. However, the amount of solvation is temperature dependent. By analyzing the temperature dependency of solvation. Storm et al. showed that the forces holding asphaltenes in the resid are very weak. Moreover, the fact that the solvation constant is the same for toluene at 25 °C as in a vacuum resid at 93°C implies that the forces between asphaltene colloidal particles and toluene are weaker. 

The material in this section is divided into three parts. The first subsection deals with the general characteristics of chemical substances. The second subsection is concerned with the chemistry of petroleum it contains a brief review of the nature, composition, and chemical constituents of crude oil and natural gases. The final subsection touches upon selected topics in physical chemistry, including ideal gas behavior, the phase rule and its applications, physical properties of pure substances, ideal solution behavior in binary and multicomponent systems, standard heats of reaction, and combustion of fuels. Examples are provided to illustrate fundamental ideas and principles. Nevertheless, the reader is urged to refer to the recommended bibliography [47-52] or other standard textbooks to obtain a clearer understanding of the subject material. Topics not covered here owing to limitations of space may be readily found in appropriate technical literature. 

However, die major purpose of this chapter is to define and describe the five types of petroleum reservoir fluids. Each will be defined by reference to the shape of its typical phase diagram. Several rales of thumb will be given to assist in determining fluid type from normally available production data. Many of the producing characteristics of each type of fluid will be discussed. Ensuing chapters will address the physical properties of these five reservoir fluids,with emphasis on black oils, dry gases, and wet gases. 

The term physical composition (or bulk composition) refers to the composition of crude oil as determined by various physical techniques. For example, the separation of petroleum using solvents and adsorbents (Altgelt and Boduszynski, 1994 Speight, 1999) into various bulk fractions (Figure 3-8) determines the physical composition of crude oil. However, in many instances, the physical composition may not be equivalent to the chemical composition. These methods of separation are not always related to chemical properties and the terminology applied to the resulting fractions is often a terminology of convenience. 

The term oil and grease refers to a broad class of organic substances recovered from the sample matrices by extraction with an appropriate solvent. Such recovery, therefore, is characteristic of certain physical properties of the compounds, primarily the volatility of the compounds and their solubility in the extraction solvent. The solvent must be immiscible in water and volatile, as well as readily distilled on a water bath. Many solvents or mixed-solvent systems should be suitable for the extraction of oil and grease in aqueous and nonaqueous samples. These include petroleum ether, w-hexanc, methylene chloride, methyl ter/-butyl ether, and trichlorotrifhroroethan (freon). These solvents are listed in Table 1. 

Bio-oil from rapid pyrolysis is usually a dark brown, free-flowing liquid having a distinctive smoky odor. It has significantly different physical and chemical properties compared to the liquid from slow pyrolysis processes, which is more like a tar. Bio-oils are multicomponent mixtures comprised of different size molecules derived primarily from depolymerization and fragmentation reactions of the three key biomass building blocks cellulose, hemicellulose, and lignin. Therefore, the elemental composition of biooil resembles that of biomass rather than that of petroleum oils. Basic properties of biooils are shown in Table 33.7. More detail on fuel-related characteristics is provided in the literature.571... 

The classic definition of asphaltenes is based on the solution properties of petroleum residuum in various solvents. This generalized concept has been extended to fractions derived from other carbonaceous sources, such as coal and oil shale. 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. This effort is summarized by Speight and Moschope-dis (i) in their chapter in this volume along with a good summary of the current thinking. Thus, there are petroleum asphaltenes, coal tar asphaltenes, shale oil asphaltenes, tar sands bitumen asphaltenes, and so on. In this chapter I will attempt to show how these materials are special cases of an overall concept based directly on the physical chemistry of solutions and that the idea that they have a specific chemical composition and molecular weight is incorrect even for different crude oil sources. 

Petroleum asphaltenes are commonly viewed as an undesired component of crude oil that creates serious difficulties in upgrading of petroleum heavy ends. However, it is not often recognized that processing of petroleum residua also includes production of asphalts where asphaltenes are not only a very desired component but the component that determines, to a great extent, the physical properties of an asphalt. 

Chemicul and Physical Properties of the ParafRns. The parafSns are very important constituents of crude oil Pennsylvania petroleum seems to be largely composed of hydrocarbons of this series while other petroleums contain them to a lesser extent. Natural gas consists of the more volatile members of this series. 

In the early 1930s, tests were developed which characterized petroleum oils and petroleum fractions, so that various physical characteristics of petroleum products could be related to these tests. Details of the tests can be found in Petroleum Products and Lubricants, an annual publication of the Committee D-2 of the American Society for Testing Materials. These tests are not scientifically exact, and hence the procedure used in the tests must be followed faithfully if reliable results are to be obtained. However, the tests have been adopted because they are quite easy to perform in the ordinary laboratory and because the properties of petroleum fractions can be predicted from the results. The specifications for fuels, oils, and so on, are set out in terms of these tests plus many other properties, such as the flashpoint, the percent sulfur, and the viscosity. 

Differences in the physical properties of creosote and oils may also affect PNA distributions. When creosote was mixed with seawater In the laboratory, three phases were formed one more dense than seawater, one dissolved in seawater, and one less dense than seawater. Analysis of the phase more dense than seawater produced a gas chromatogram indistinguishable from that of Intact creosote. At a spill site, the phase with a density greater than seawater may be rapidly removed to the sediments with only slight alteration. The water-soluble compounds may then be slowly leached into the water column and act as a chronic PNA source. Petroleum,... 

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