Reduction multiphasic systems

Note that filter aid selection must be based on planned laboratory tests. Guidelines for selection may only be applied in the broadest sense, since there is almost an infinite number of combinations of filter media, filter aids, and suspensions that will produce varying degrees of separation. The hydrodynamics of any filtration process are highly complex filtration is essentially a multiphase system in which interaction takes place between solids from the suspension, filter aid, and filter medium, and a liquid phase. Experiments are mandatory in most operations not only in proper filter aid selection but in defining the method of application. Some general guidelines can be applied to such studies the filter aid must have the minimum hydraulic resistance and provide the desired rate of separation an insufficient amount of filter aid leads to a reduction in filtrate quality — excess amounts result in losses is filtration rate and it is necessary to account for the method of application and characteristics of filter aids. 

The use of Zn powder in a multiphase system is a way to solve many of the difficulties involved in the operation of electroorganic processes under a low maximum current density [513-516]. A three-phase system, water/organic, substrate/metal powder can be used for the reduction of halides and nitro compounds under a high... 

Figure 6.20 Selective reduction of haloaromatic ketones in the multiphasic system using Pd/C.

Polychlorobenzenes in the presence of a Pd/C catalysts can be debalogenated with sodium hypophosphite [49] or hydrogen [50, 51] in a multiphase system (eq. (3)). 1,2,4,5-Tetrachlorobenzene gives a quantitative yield of benzene using H2 or NaH2P02 as reductant. 

Acoustic irradiation appears to be able not only to boost chemical reactions but also to intensify mass transfer processes in multiphase systems. A twofold increase of k a using ultrasound has been observed [150], but depends strongly on the reaction conditions. Other authors have reported instead higher intensification factors. The enhancement is probably related to a reduction of the boundary layer thickness due to the microscale turbulence and reduction of the viscosity in the boundary layer. 

Further consequences of the yield stress [i.e., the plug flow] are (i) a drastic reduction of the extrudate swell, B = d/d (d is diameter of the extrudate, d that of the die) [see, e.g., Crowson and FoUces, 1980 Utracki et al, 1984], and (ii) significant increase of the entrance-exit pressure drop, Pg (also known as Bagley correction). For single-phase fluids, these parameters have been related to elasticity by molecular mechanisms [Tanner, 1970 Cogswell, 1972 Laun and Schuch, 1989]. However, in multiphase systems, both B and P depend primarily on the inter-domain interactions and morphology, not on deformation of the macromolecular coils. Thus, in multiphase systems [i.e., blends, filled systems, or composites], only direct measures of elasticity, such as that of Nj, or G should be used. It is customary to plot the measure of the elastic component versus that of the shear components, viz., vs. 

Homogenization, e.g., reduction of differences of concertUations (micro-, meso-, macromixing, see later) and/or temperatures in liqttids or multiphase systems, further the distribution of solid or fluid particles in sohd/liquid systems (suspensions) or fluid/flttid systems (emulsions, gas in hqttid dispersions)... 

Mass transfer with chemical reaction in multiphase systems" covers, indeed, a large area. Table 1 shows a general classification of the systems encountered. From the possible two-phase systems, solid-solid reactions, liquid-solid (reactive or catalytic) and gas-solid (reactive or catalytic) reactions are not discussed here. The first one was reviewed by Tamhankar and Doraiswamy (2) and gas-solid (reactive) systems, such as, coal gasification, calcination of limestone, reduction of ores, etc. have been treated in some detail in recent reviews (3-5). The industrially important fluid-solid catalytic processes were the topic of a previous Advanced Study Institute (6) and have been also discussed authoritatively elsewhere (5,7). Concerning solid (reactive)-liquid two-phase systems, only some interesting examples are presented in Table 2 (1). 

The dependence holds in steady-state as well as dynamic flowin shear or elongation, it is easy to use, and the extracted parameters calculated from equation fitting to experimental data agree with the directiy measured values. The magnitude of ay increases with aspect ratio, p, their rigidity, and concentration. Some consequences of Oy are the plug flow [77,78], reduction of the extrudate swell. Be [7,79], and increase of the entrance-exit pressure drop, Pe [80, 81]. In multiphase systems both Be and Pe depend mainly on the inter-domain interactions and morphology. 

As it is well known [1] that the interlacial interaction role in multiphase systems, including polymer composites, is very great. In polymer composites such interactions (interfacial adhesion) absence results in sharp reduction of their reinforcement degree [2]. For polymer nanocomposites interfacial adhesion existence in the first place means the formation of interfacial regions, which are the same reinforcing element for these materials, as nanofiller actually [3], Proceeding from the said above, it is necessary to know the conditions and mechanisms of interfacial regions formation in polymer nanocomposites for their structure control. The present paper purpose is these mechanism definition and the indicated researeh is performed on the example of three particulate-filled nanocomposites on the basis of butadiene-styrene rubber. 

Conclusions. In tubular multiphase reactors with an exothermic reaction where one phase with a high throughput serves to carry the heat of reaction out of the reactor, a sudden flow reduction in this phase (whether accompanied by a similar reduction in the other phases or not) can lead to a considerable transient temperature rise, well above the new steady state temperature. The maximum excess temperature depends in a complex way upon the rate of the flow reduction, the flow rates in the different phases, the heat capacities and the reaction rates of the system. 

The lacking special description of the Gibbs phase rule in MEIS that should be met automatically in case of its validity is very important for solution of many problems on the analysis of multiphase, multicomponent systems. Indeed, without information (at least complete enough) on the process mechanism (for coal combustion, for example, it may consist of thousands of stages), it is impossible to specify the number of independent reactions and the number of phases. Prior to calculations it is difficult to evaluate, concentrations of what substances will turn out to be negligibly low, i.e., the dimensionality of the studied system. Besides, note that the MEIS application leads to departure from the Gibbs classical definition of the notion of a system component and its interpretation not as an individual substance, but only as part of this substance that is contained in any one phase. For example, if water in the reactive mixture is in gas and liquid phases, its corresponding phase contents represent different parameters of the considered system. Such an expansion of the space of variables in the problem solved facilitates its reduction to the CP problems. 

---