Homogeneous liquid-phase flow

Reactive distillation was soon extended to other types of reactions, as nitrations, sulfonations, and sap-onifications [3], All of these reactions were homogeneously catalyzed, i.e. the catalyst was in the liquid phase, flowing down the column, and had to be recovered from the residue. 

Example 5-4 A first-order homogeneous (liquid-phase) reaction is carried out in an ideal stirred-tank reactor. The concentration of reactant in the feed is 3.0 g moles/liter and the volumetric flow rate is 60 cm /sec. The density and specific heat of the reaction mixture are constant at I.O g/cm and 1.0 cal/(g)(°C), respectively. The reactor volume is 18 liters. There is no product in the feed stream and the reactor operates adiabatically. The heat and rate of the irreversible reaction are... 

The limitations and boundary conditions of this concept, which were mentioned in the introduction, mainly refer to the question of extrapolation of the results obtained. The application of this concept remains comparatively simple as long as the process to be safety technically assessed belongs to the group of homogeneous liquid phase reactions. In heterogeneous processes, the thermal conversion obtained reflects the flow conditions of the measuring apparatus. Here, special care has to be taken in the experimental design in order to obtain results which, under full observation of all rules of the similarity theory, may be used for plant scale assessment. 

Eldridge J. W., Piret E.L. Gontinuous-flow stirred-tank reactor system I, Design equations for homogeneous liquid phase reactions. Experimental data, Chem. Eng. Prog., 1950 46 290. 

Figure 3 Phase diagram-type plot of reduced pressure analog versus the volume analog at constant reduced gas flow analog. Note similarities of strand flow to liquid phase, flow above strand flow to vapor phase, and homogeneous flow to gas phase.

Most of the previously used expressions to account for incomplete catalyst wetting in trickle-beds are summarized in Table I. All of these, with the exception of the last one, are based on the assumptions of a) plug flow of liquid, b) no external mass transfer limitations, c) isothermal conditions, d) first order irreversible reaction with respect to the liquid reactant, e) nonvolatile liquid reactant, f) no noncatalytic homogeneous liquid phase reaction. 

Because flashing steam-condensate lines represent two-phase flow, with the quantity of liquid phase depending on die system conditions, these can be designed following the previously described two-phase flow methods. An alternate by Ruskin [28] uses the concept but assumes a single homogeneous phase of fine liquid droplets dispersed in the flashed vapor. Pressure drop was calculated by the Darcy equation ... 

Weekman and Myers (W3) measured wall-to-bed heat-transfer coefficients for downward cocurrent flow of air and water in the column used in the experiments referred to in Section V,A,4. The transition from homogeneous to pulsing flow corresponds to an increase of several hundred percent of the radial heat-transfer rate. The heat-transfer coefficients are much higher than those observed for single-phase liquid flow. Correlations were developed on the basis of a radial-transport model, and the penetration theory could be applied for the pulsing-flow pattern. 

Fine suspensions are reasonably homogeneous and segregation of solid and liquid phases does not occur to any significant extent during flow. The settling velocities of the particles are low in comparison with the liquid velocity and the turbulent eddies within the fluid are responsible for the suspension of the particles. In practice, turbulent flow will always be used, except when the liquid has a very high viscosity or exhibits non-Newtonian characteristics. The particles may be individually dispersed in the liquid or they may be present as floes. 

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