Well-Mixed Liquid Phase

A majority of applications of venturi loop systems (Table 8.1) pertain to situations in which the gas-phase reactant is a pure gas. Further, the operating pressures are also high ( 1 MPa and above) therefore, partial pressure of the liquid under saturation conditions is also negligible. As a result, back mixing of the gas phase is inconsequential. 

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The froth on the tray is where mass transfer takes place between the phases, assumed to exist at equilibrium at the vapor-liquid interface. The well mixed liquid phase is at its bubble point temperature at equilibrium with the vapor interfacial composition Y. The vapor leaving tray j with composition Fy, is at temperature Ty, determined by heat transfer rates according to Equations 14.17 and 14.18. This temperature may be above the dew point. 

As can be easily derived from the concentration pattern, the reaction takes place either mainly in the bulk of the well-mixed liquid phase or in the liquid-phase boundary layer. In reactions which occur in the bulk of the liquid phase, the concentration of gaseous educts decreases only within the interfacial layer (thickness d) to the concentration cAj by physical diffusion processes. Only in the case of mass transport processes that are fast relative to the reaction rate is the latter proportional to the cAl j in the liquid phase. If the catalytic reaction is fast enough a reaction surface may develop within the boundary layer which may even move into the interface itself and, thus, neither the bulk of the liquid nor the liquid-phase boundary layer is utilized any more for the reaction. A simple approach in order to determine the regime of the overall reaction rate can be performed by comparison of the intrinsic kinetics with the rate of mass transfer according to Table 2 [22],... 

In the Dimersol process [22] a cationic nickel complex (Ni VAlEtCl2 and Table II) transforms propylene and/or w-butenes into a mixture of di, tri-, and tetramers of various structures (Tables III and IV), consisting of all possible olefinic isomers. The process works in a well mixed liquid phase. 

In the classical set-up of bulk liquid membranes, the membrane phase is a well-mixed bulk phase instead of an immobilized phase within a pore or film. The principle comprises enantioselective extraction from the feed phase to the carrier phase, and subsequently the carrier releases the enantiomer into the receiving phase. As formation and dissociation of the chiral complex occur at different locations, suitable conditions for absorption and desorption can be established. In order to allow for effective mass transport between the different liquid phases involved, hollow fiber... 

Piston Flow in Contact with a CSTR. A liquid-phase reaction in a spray tower is conceptually similar to the transpired-wall reactors in Section 3.3. The liquid drops are in piston flow but absorb components from a well-mixed gas phase. The rate of absorption is a function of as it can be in a transpired-wall reactor. The component balance for the piston flow phase is... 

Both gas as well as liquid phase are ideally mixed. 

The data can be evaluated using any commonly available non-linear regression program or with a linear regression, in which k,a is the slope from the plot of the natural log of the concentration difference versus time. Linearity of the logarithmic values over one decade is required for the validity of the measurement. Of course the assumptions inherent in the model must apply to the experimental system, especially in respect to completely mixed gas as well as liquid phases and reactions are negligible. Two common problems are discussed below. Other common pitfalls and problems are summarized in Table 3-3. 

For viscous or solid food the simplifying assumption of a well-mixed liquid is abandoned and finding an analytical solution for this two phase system... 

As discussed earlier, stirred tanks are desirable when the overall reaction rate is limited by liquid-phase reaction. Bubbling gas through well-mixed liquid in a stirred tank should minimize the thickness of the gas-liquid interface while maximizing the availability of the liquid volume (fi = lO -loV- Consequently, process conditions that achieve this objective are the first consideration in designing stirred tank gas-liquid contactors. 

We now discuss some of the main features of LLPTC models developed for reaction under neutral conditions. Evans and Palmer (1981) were among the first to consider the effect of diffusion and mass transfer inPTC. They considered PTC in liquid-liquid systems by considering two well-mixed bulk phases of uniform composition separated by a uniform stagnant mass-transfer layer at the interface, and set up equations for bulk phase species balance and mass conservation equations for simultaneous diffusion and reaction in the film. Dynamics of the interaction between reaction and diffusion were studied under these assumptions for two special cases (a) reaction which is pseudo-first-order in the quaternary ion-pair (b) mass-transfer controlled instantaneous reaction. 

Plug-flow gas and well-mixed liquid CFTR. From the general balance of equations (8-164) and (8-165), for the gas phase in steady state... 

Plug-flow gas, well-mixed liquid SFBR. Here, from the general phase balanee, for the gas... 

Consider a slurry reactor with a well-mixed slurry phase in which the reaction of Problem 6 is taking place. The gas-phase concentration of A is = 10 mol/cm, and the inlet liquid-phase concentration of B is Cs = 10 mol/cm It is assumed that the products have no effect on... 

Both the gas and the liquid phase can be divided into a stagnant film (thickness 5g and 5i) located near the interface and well-mixed bulk phases without concentration gradients. 

As already outlined in Section 4.4, interfacial mass transfer processes can be described by the two-film theory. To recapitulate this theory is based on the assumptions that (i) both the gas and liquid phase can be divided into a stagnant film near the interface and a well-mixed bulk phase without concentration gradients and that (ii) mass transfer is a steady-state process. 

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