Prediction of phase behavior

S 2] The result was a prediction of phase behavior of the ternary system H20/HI/I2 given in Figure 4.83 together with experimental data. The direct application of this tool to micro technology is uncritical as this simulation only considers thermodynamic and chemical model assumptions. It does not make any assumptions such as the neglect of axial heat transfer. 

Richardson, C. J., Mbanefo, A., Aboofazeli, R., Lawrence, M. J., and Barlow, D. J. (1997), Prediction of phase behavior in microemulsion systems using artificial neural networks,... 

From the predictive category, we bring some examples of the application of the UNIFAC model. In one study, this model has been used to predict the solubility of naphtalene, anthracene, and phenanthrene in various solvents and their mixtures [8], They showed the applicability of the UNIFAC model in prediction of the phase behavior of solutes in solvents. There have been efforts to make the UNIFAC model more robust and powerful in the prediction of phase behaviors [14], In one study, the solubility of buspirone-hydrochloride in isopropyl alcohol was measured and evaluated by the modified UNIFAC model [15]. It was concluded that for highly soluble pharmaceutics, the modified form of the UNIFAC model was not suitable. In another study, the solubility of some chemical species in water and some organic solvents was predicted by the UNIFAC model [16]. For some unknown functional groups, they used other known groups which had chemical structures that were similar to unknown ones. 

Coleman, M.M. Painter, P.C. Intramolecular screening and functional group accessibility effects in polymer blends the prediction of phase behavior. Macromol. Chem. Phys. 1998, 199, 1307-1314. 

Wong, J. M., R. S. Pearlman, and K. P. Johnston. 1985. Supercritical fluid mixtures Prediction of phase behavior. J. Phys. Chem. 89 2671-2675. 

An additional complication with SCF processes is the possibility of complex phase behavior. A thorough understanding of the phase behavior of each reaction mixture is desirable, but not always possible. There is an extensive literature devoted to the investigation and prediction of phase behavior of SCFs [11], and the subject is introduced in chapter 1.2. Spectroscopic monitoring can provide at least an indication of phase behavior for example, which compounds are dissolved in which phase, as well as a method for monitoring the progress of reactions and identifying intermediates and products. It is best to resist the temptation to treat a supercritical reactor as a black box, and simply... 

Comments The agreement with the experimental data is not veiy good. UNIFAC indeed predicts an azeotrope at x, = 0.33 (compared to x. = 0.275 from the experimental data) but its pressure is under-predicted by about 0.1 bar. We must note, however, that as a predictive model, UNIFAC has no adjustable parameters. The next example demonstrates a case in which UNIFAC produces a much better prediction of phase behavior. 

Avila-Mendez, G.A., Justo-Garci a, D.N., Garcta-Sdnchez, F., Garcta-Ftores, B.E., n.d. Prediction of phase behavior for the system methane-carbon dioxide-hydrogen sulfide-water with the PR and PC-SAFT equations of state. 

Asphaltene precipitation results in removal of heavier fractions of the crude leaving behind lighter deasphalted crude. This indicates that in a miscible process, the alteration of crude composition needs to be accounted for in prediction of phase behavior, compositional path and miscibility conditions for solvent-oil systems. 

Since eqs (1) and (2) are more convenient to use than eqs (3) and (4), the distinction between critical, spinodal and coexisting phase points is sometimes ignored [4-7]. Though incorrect, such an approximation may still be useful provided it allows predictions of phase behavior that can be proven reasonably accurate. In this paper we discuss examples of that approach and also present a case in point where the approximation mentioned can be analyzed quantitatively and shown to involve negligible errors only. 

Numerous equations of state for polymer liquids have been developed. These equations provide valuable thermodynamic information that can be used to predict properties of polymer blends and polymer solutions. The predictions of phase behavior of polymer blends vary considerably from one equation of state to another. EOS theories for polymer liquids can be roughly grouped into three kinds ... 

Mi J, Tang Y, Zhong C, Li Y-G Prediction of phase behavior of nanoconfined Lennard-Jones fluids with density functional theory based on the first-order mean spherical approximation, J Chem Phys 124(14) 144709, 2006. 

The phase rule is a mathematical expression that describes the behavior of chemical systems in equilibrium. A chemical system is any combination of chemical substances. The substances exist as gas, liquid, or solid phases. The phase rule applies only to systems, called heterogeneous systems, in which two or more distinct phases are in equilibrium. A system cannot contain more than one gas phase, but can contain any number of liquid and solid phases. An alloy of copper and nickel, for example, contains two solid phases. The rule makes possible the simple correlation of very large quantities of physical data and limited prediction of the behavior of chemical systems. It is used particularly in alloy preparation, in chemical engineering, and in geology. 

This paper reviews the experiences of the oil industry in regard to asphaltene flocculation and presents justifications and a descriptive account for the development of two different models for this phenomenon. In one of the models we consider the asphaltenes to be dissolved in the oil in a true liquid state and dwell upon statistical thermodynamic techniques of multicomponent mixtures to predict their phase behavior. In the other model we consider asphaltenes to exist in oil in a colloidal state, as minute suspended particles, and utilize colloidal science techniques to predict their phase behavior. Experimental work over the last 40 years suggests that asphaltenes possess a wide molecular weight distribution and they may exist in both colloidal and dissolved states in the crude oil. 

One major question of interest is how much asphaltene will flocculate out under certain conditions. Since the system under study consist generally of a mixture of oil, aromatics, resins, and asphaltenes it may be possible to consider each of the constituents of this system as a continuous or discrete mixture (depending on the number of its components) interacting with each other as pseudo-pure-components. The theory of continuous mixtures (24), and the statistical mechanical theory of monomer/polymer solutions, and the theory of colloidal aggregations and solutions are utilized in our laboratories to analyze and predict the phase behavior and other properties of this system. 

Calculations for all three cases have been performed for the system described in Tables VII and VIII and Figure 6. In this case the raw feed gas was flashed at 66°C and 138 bars with sufficient water to assure that the gas leaving the separator was water saturated. Each of the calculational philosophies described above was used to predict the phase behavior of the systems at each pressure temperature point in the pipeline. The results of these calculations are summarized in Tables IX through XI and Figures 7 through 10. 

In an earlier paper Q ), the authors presented an efficient procedure for predicting the phase behavior of systems exhibiting a water - rich liquid phase, a hydrocarbon - rich liquid phase, and a vapor phase. The Peng-Robinson equation of state (2) was used to reDresent the behavior of all three phases. It has the following form ... 

An analogy may be drawn between the phase behavior of weakly attractive monodisperse dispersions and that of conventional molecular systems provided coalescence and Ostwald ripening do not occur. The similarity arises from the common form of the pair potential, whose dominant feature in both cases is the presence of a shallow minimum. The equilibrium statistical mechanics of such systems have been extensively explored. As previously explained, the primary difficulty in predicting equilibrium phase behavior lies in the many-body interactions intrinsic to any condensed phase. Fortunately, the synthesis of several methods (integral equation approaches, perturbation theories, virial expansions, and computer simulations) now provides accurate predictions of thermodynamic properties and phase behavior of dense molecular fluids or colloidal fluids [1]. 

A. A. Petraukas and V. K. Svedas, Hydrophobicity of /3-lactam antibiotics Explanation and prediction of their behavior in various partitiong solvent systems and reversed-phase chromatography, J. Chromatogr., 585 3 (1991). 

We know the most about cuticular hydrocarbons, because they are abundant and because it is relatively easy to isolate and identify them. They are also the most hydrophobic lipid components, and so should provide the best barrier to water-loss. -Alkanes isolated from insect cuticles typically have chain lengths of 20-40 carbons. These can be modified by insertion of cis double bonds, or addition of one or more methyl groups. Relatively polar surface lipids include alcohols, aldehydes, ketones and wax esters (see Chapter 9). Given this diversity, is it possible to predict lipid phase behavior (and, by extension, waterproofing characteristics) from composition alone If so, a large body of literature would become instantly interpretable in the context of water balance. Unfortunately, this is not the case. 

CO2 is an important industrial gas, consequently, the study of phase behavior of C02/n-alkane systems is necessary. Though they are nonpolar systems, the predictive accuracies of MHV2(Dahl and Michelsen, 1990) and PSRK(Holderbaum and Gmehling, 1991, using MHV1) are dramatically bad for large n-alkanes (Boukouvalas et al., 1994). So, it is necessary to do some modification to improve the predictive accuracy for them, which is the motive of this work. 

We consider a reactor with a bed of solid catalyst moving in the direction opposite to the reacting fluid. The assumptions are that the reaction is irreversible and that adsorption equilibrium is maintained everywhere in the reactor. It is shown that discontinuous behavior may occur. The conditions necessary and sufficient for the development of the internal discontinuities are derived. We also develop a geometric construction useful in classification, analysis and prediction of discontinuous behavior. This construction is based on the study of the topological structure of the phase plane of the reactor and its modification, the input-output space. 

A novel approach to reduce the experimental effort associated with constructing pseudoternary phase diagrams is by using expert systems to predict the phase behavior of multicomponent ME-forming systems. Artificial neural networks have been investigated and were shown to be promising in phase behavior studies [17,35,36] as well as in the process of ingredient selection [37]. 

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