Hydrocarbon mixtures, behavior

Dror I, Gerstl Z, Prost R, Yaron B (2000a) Behavior of neat and enriched volatile petroleum hydrocarbons mixture in the subsurface during leaching. Land Contam Reclam 8 341-348... 

Physical chemistry and related sciences have played an increasingly important role in the explanation and prediction of physical phenomena which are useful in the production and processing of petroleum. Knowledge of the volumetric and phase behavior of hydrocarbons has so developed that such properties may be predicted with reasonable accuracy at most of the states of interest except those near retrograde dew point. The inability to describe with certainty the composition of many hydrocarbon mixtures in terms of their components places a severe limitation on the prediction of the volumetric and phase behavior of petroleum and of mixtures of its components. 

In this chapter we will consider methods of calculating the behavior of hydrocarbon mixtures in this two-phase region. Three types of calculations will be examined ... 

The phase behavior of hydrocarbon + water mixtures differs significantly from that of normal hydrocarbon mixtures. Differences arise from two effects, both of which have their basis in hydrogen bonding. First, the hydrate phase is a significant part of all hydrocarbon + water phase diagrams for hydrocarbons with a molecular size lower than 9 A. Second, water and hydrocarbon molecules are so different that, in the condensed state, two distinct liquid phases form, each with a very low solubility in the other. 

The first requisite for practical use was achieved by the synthesis of callosobruchusic acid, and the substitution of a complex hydrocarbon mixture by octadecane. Only the (E) form was active. Synthesis of the two optical forms was also achieved, but both forms showed the same activity as the natural callosobruchusic acid, thus making it impossible to assign the absolute configuration (5). The second requirement has been pursued by selecting different dummies. When an amount of erectin equivalent to that of one female was applied to a glass rod, the male attempted copulation, but did not ejaculate. However, the male did show the insertion and ejaculation behavior with a dummy of aluminum foil tube bearing erectin. 

For a pure supercritical fluid, the relationships between pressure, temperature and density are easily estimated (except very near the critical point) with reasonable precision from equations of state and conform quite closely to that given in Figure 1. The phase behavior of binary fluid systems is highly varied and much more complex than in single-component systems and has been well-described for selected binary systems (see, for example, reference 13 and references therein). A detailed discussion of the different types of binary fluid mixtures and the phase behavior of these systems can be found elsewhere (X2). Cubic ecjuations of state have been used successfully to describe the properties and phase behavior of multicomponent systems, particularly fot hydrocarbon mixtures (14.) The use of conventional ecjuations of state to describe properties of surfactant-supercritical fluid mixtures is not appropriate since they do not account for the formation of aggregates (the micellar pseudophase) or their solubilization in a supercritical fluid phase. A complete thermodynamic description of micelle and microemulsion formation in liquids remains a challenging problem, and no attempts have been made to extend these models to supercritical fluid phases. 

No solution is ideal but when the components rraemble one another closely the resulting solution is likely to approach the behavior of an ideal solution. Consequently many of the hydrocarbon mixtures which are of particular interest to the petroleum engineer can be expected to follow ideal solution behavior more or less closely under ordinary conditions of temperature and relatively low pressures. 

To summarize, then, we require a mechanism which (1) describes reaction rate phenomena accurately over a specified range of concentrations, (2) is a parsimonious representation of the actual atmospheric chemistry, in the interest of minimizing computation time, and (3) can be written for a general hydrocarbon species, with the inclusion of variable stoichiometric coefflcients to permit simulation of the behavior of the complex hydrocarbon mixture that actually exists in the atmosphere. Thus, we seek a mechanism which incorporates a balance between accuracy of prediction and ease of computation. 

The dynamic model proposed proved to represent well the separation in a DWC of a ternary hydrocarbon mixture. The values of internal flows and temperature distributions along the trays reached at steady state were in good agreement with the simulations obtained in the frame of commercial simulators. The use as control variables the reflux ratio or the side-stream flowrate proved to enable a reduction of the startup time with about 70 % compared with classical startup procedures. The complex technique developed can be a useful tool in studying dynamic behavior and startup optimization for complex columns and can be easily extended to various mixtures. 

Burris DR, MacIntyre WG. 1984. Water solubility behavior of hydrocarbon mixtures — Implications for petroleum dissolution. In Vandermeulen JH, Hrudey SE, eds. Oil in freshwater Chemistry, biology, countermeasure technology. New York,NY Pergamon Press, 85-94. 

Fig. 1 Multiphase, fluid-only behaviors exhibited by hydrocarbon mixtures. Dashed phase boundaries indicate critically identical phases.

Measurement and prediction of transitions from one type of phase behavior to another are key to our understanding of the physical properties of hydrocarbon mixtures. One can examine phase behavior type transitions for binary mixtures from the perspective of the solute or the solvent while varying the other. Both approaches are found in the literature. The solvent fixed approach is shown in Fig. 5 for carbon dioxide + n-alkane binary mixtures. The anthracene... 

The theory and conditions for phase equilibrium are well established. If more than one phase is present, then the chemical potential of a component is the same in all phases present. As chemical potential is linked functionally to the concepts of fugacity and activity, models for phase behavior prediction and correlation based on chemical potentials, fugacities, and activities have been developed. Historically, phase equilibrium calculations for hydrocarbon mixtures have been fragmented with liquid-vapor, liquid-liquid, and other phase equilibrium calculations, subject to separate and diverse treatments depending on the temperature, pressure, and component properties. Many of these methods and approaches arose to meet specific needs in the chemical process industries. Poling, Prausnitz,... 

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