Liquid-vapour

When oil and gas are produced simultaneously into a separator a certain amount (mass fraction) of each component (e.g. butane) will be in the vapour phase and the rest in the liquid phase. This can be described using phase diagrams (such as those described in section 4.2) which describe the behaviour of multi-component mixtures at various temperatures and pressures. However to determine how much of each component goes into the gas or liquid phase the equilibrium constants (or equilibrium vapour liquid ratios) K must be known. 

Statistical mechanical theory and computer simulations provide a link between the equation of state and the interatomic potential energy functions. A fluid-solid transition at high density has been inferred from computer simulations of hard spheres. A vapour-liquid phase transition also appears when an attractive component is present hr the interatomic potential (e.g. atoms interacting tlirough a Leimard-Jones potential) provided the temperature lies below T, the critical temperature for this transition. This is illustrated in figure A2.3.2 where the critical point is a point of inflexion of tire critical isothemr in the P - Vplane. 

For a one-component fluid, the vapour-liquid transition is characterized by density fluctuations here the order parameter, mass density p, is also conserved. The equilibrium structure factor S(k) of a one component fluid is... 

Mdller D and Fisoher J 1990 Vapour liquid equilibrium of a pure fluid from test partiole method in oombination with NpTmoleoular dynamios simulations Mol. Phys. 69 463-73... 

Lotfi A, Vrabeo J and Fisoher J 1992 Vapour liquid equilibria of the Lennard-Jones fluid from the NpT plus test partiole method Mol. Phys. 76 1319-33... 

Boda D, Liszi J and Szalai I 1995 An extension of the NpT plus test partiole method for the determination of the vapour-liquid equilibria of pure fluids Chem. Phys. Lett. 235 140-5... 

Compiled from Daubert, T. E., R. P. Danner, H. M. Sibul, and C. C. Stebbins, DIPPR Data Compilation of Pure Compound Properties, Project 801 Sponsor Release, July, 1993, Design Institute for Physical Property Data, AlChE, New York, NY and from Ambrose, D. Vapour-Liquid Critical Properties , Report Chem 107, National Physical Laboratory, Teddiugtou, UK, October, 1979. 

Solids processes clearly differ from vapour liquid systems in two main ways. Firstly and most obviously, solid systems have a particle size or size distribution added to their specification. Secondly, solids processing systems use different... 

Cantor (1895) has indicated that the deiv-point, or temperature at which vapour condenses on a solid surface, must be different from the saturation temperature for the vapour over the surface of its own liquid, because of the different surface tensions between (vapour)/(solid) and (vapour)/(liquid). 

Some of the important features of the flow of two-phase mixtures composed of a liquid together with a gas or vapour are discussed in this section. There are many applications in the chemical and process industries, ranging from the flow of mixtures of oil and gas from well heads to flow of vapour-liquid mixtures in boilers and evaporators. 

In interface evaporation, the bubbles of vapour formed on the heated surface move to the vapour-liquid interface by natural convection and exert very little agitation on the liquid. The results are given by ... 

It should be noted that the curves of humidity plotted against either temperature or enthalpy have a discontinuity at the point corresponding to the freezing point of the humidifying material. Above the temperature 90 the lines are determined by the vapour liquid equilibrium and below it by the vapour-solid equilibrium. 

Figure 5.2-2. Typical vapour-liquid equilibrium curves a) system obeying Henry s law b) regular system c) system of close-boiling components d) azeotrope.

In general, the only problem in the scale-up of distillation is to obtain reliable vapour-liquid equilibrium (VLB) data. Computer programs cover the vast majority of physical systems and data banks for VLB are included in these programs. However, VLB data are not available for... 

Equilibrium in multiphase and/or multireaction systems. If more than one phase is present in the system, a criterion of phase equilibria has to be satisfied together with the chemical equilibrium criterion. For instance, in a gas-liquid system components are in chemical equilibrium in the phase where the reaction occurs, but vapour-liquid equilibria between the gas and the liquid phases must also be taken into account. To determine the equilibrium composition of a reacting mixture in both phases, chemical equilibrium constants as well as data concerning vapour-liquid equilibria for all components of the reaction mixture should be known. In the equilibrium state ... 

Problems with the determination of chemical equilibria in multiphase systems are solved in practice by assuming that the reaction takes place in any phase and all components are also equilibrated between phases. Accordingly, for a single reaction any of Eqns. (5.4-32) and (5.4-33) must be solved, while the relationships of Eqn. (5.4-31) must also be fulfilled. Since vapour-liquid equilibrium coefficients are functions of the compositions of both phases, the search for the solution is an iterative procedure. Equilibrium compositions are assumed, vapour-liquid equilibrium coefficients are then estimated, and new equilibrium compositions are evaluated. If the new equilibrium compositions are close to those assumed initially one may consider the assumed values to be the solution of the problem. Otherwise the evaluated compiositions are taken as the start for repetition of the procedure until a reasonable agreement between tissumed and evaluated comfiositions has been reached. 

Tochigi, K., Minami, S., Kojima, K. Prediction of vapour-liquid equilibria with chemical reaction by analytical solutions of groups./. Chem. Eng. Jpn. 1977, 10, 349-354. 

Steam distillation is a process whereby organic liquids may be separated at temperatures sufficiently low to prevent their thermal decomposition or whereby azeotropes may be broken. Fats or perfume production are examples of applications of this technique. The vapour-liquid equilibria of the three-phase system is simplified by the usual assumption of complete immiscibility of the liquid phases and the validity of the Raoult and Dalton laws. Systems containing more than one volatile component are characterised by complex dynamics (e.g., boiling point is not constant). 

Touching on drawbacks of vapour-liquid method, we should note that among those there is a lack of control of the thickness of condensed liquid layer on detector surface which may result (for fairly thick liquid layers) in diffusion retardation of oxygen chemisorbtion. The diffusion... 

In drying a water-wet solid, free liquid water may or may not be present. If it is, there are in all three phases-vapour, liquid and solid- and three components, so F = 2. At constant... 

Calculate the binary parameters for the UNIQUAC equation by using the vapour-liquid equilibrium data for benzene(l)-i-propyl alcohol (2) at 760 mmHg (Tassios, 1993). The following values for other UNIQUAC parameters are available from Tassios (1993) ri=3.19, qi=2.40, r2=2.78, q2=2.51. The data are given in Table 15.6. 

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