Interfadal area

OS 10] [R 10] [P 9] The specific interfadal area was varied for a phase-transfer reaction for four amide formations from two amines and two acid chlorides [23[. This was done by filling the solutions in normal test-tubes of varying diameter (1-5 X cm ) and using a micro reactor which had the largest specific interface (45 X cm ). The yields of all foiu reactions are highly and similarly dependent on... 

Haverkamp, V., Emig, G., Hessel, V., Liauw, M.A. and Lowe, H. (2001) Characterization of a gas/liquid microreactor, the micro bubble column determination of specific interfadal area, in Microreaction Technology- IMRET 5 Proceedings of the 5th International Conference on Microreaction Technology (eds M. Matlosz, W. Ehrfeld and J.P. Baselt), Springer-Verlag, Berlin, pp. 202-214. 

The ability to predict drop size is critical to determining both the interfadal area for mass transfer and the state of dispersion of the system. In dilute systems and in moderately concentrated systems where coalescence can be neglected, the following equation describes the maximum equilibrium (i.e., after a long time) drop diameter of an inviscid or low viscosity dispersed phase ... 

For a stable interface y is positive that is, if the interfadal area increases G increases. Note that y is energy per unit area (mj m ), which is dimensionally equivalent to force per unit length (mN m ), the unit usually used to define surface or interfadal tension. 

O/W nanoemulsions with droplet radii in the range 26-66 nm could be obtained at surfactant concentrations between 4% and 8%. The nanoemulsion droplet size and polydispersity index was shown to decrease with increases in surfactant concentration this effect was considered due to the to the increase in surfactant interfadal area and the decrease in interfacial tension, y. 

Emulsification—imbibition greatly increases the oil—aqueous contact area in the foam and is possibly an important process when constant quality foam injection into waterflooded media at residual oil saturation is practiced, and when the amount of interfadal area constituted by pseudoemulsion films is a rate-determining factor for foam sensitivity. This emulsification—imbibition can act in favor of or against foam stability, depending upon whether the pseudoemulsion films, once formed, are quite stable or quite unstable. 

The interfacial areas do not appear explicitly in the correlations of equations (8-125) and (8-127), but they present another correlation problem in themselves. One is easy one is more difficult. The easy one is Up, the interfadal area between the catalyst particles and the liquid making up the slurry phase. Here, if the particle size (or average particle size) is known and the weight loading of catalyst is known. 

Figure 8.13 (a) Correlation of interfadal area (gas-liquid) with holdup in slurry bubble columns. [After M. Fukuma, K. Muroyama and A. Yashnishi, J. Chem. Eng. Japan, 20, 321, with permission of the Japanese Society of Chemical Engineers, (1987).]... 

Figure 8.13 (b) Correlation of interfadal area (gas-liquid) with bubble velocity in slurry... 

Sp.Sf, interfadal areas for liquid-solid and gas-liquid in slurry reactor, area/ volume... 

In the second type of syston, the dispersed phase is assumed to be pure substrate therefore, the substrate concentration in the dispersed phase remains constant but the interfadal area decreases as substrate is consumed. The growth of yeast on n-alkanes is one example of this type. 

Aiba, Moritz, Someya, and Haung (1969) also recognized that a favorable contact in the cultivation between cells and n-alkane droplets seemed indispensable to produce a normal pattern of yeast growth. They studied yeast growth kinetics in a fermenter, coupled with an empirical correlation between the interfadal area per unit volume of liquid and the operation condition, and obtained the following equation. 

In the BHJ polymer solar cells, efficient exciton dissociation requires large interfadal area between polymer and PCBM. On the other hand, fast charge... 

Stirrer type Specific interfadal area, uniformity of phase dispersion, emulsification Conversion n/i ratio 15]... 

The effect of aqueous phase hold-up on the rate of hydroformylation for 900 and 1500 rpm is shown in Figure 3. At 1500 rpm, the rate versus (aqueous phase hold-up) plot shows a maximum. For kinetic control, the rate is expected to vary linearly with catalyst loading. However, in a case where the reaction occurs essentially at the liquid-liquid interphase, it would depend on the liquid-liquid interfacial area even though liquid-liquid mass transfer is not rate limiting. For > 0.4, phase inversion occurs and the interfadal area would be determined by the dispersed phase, which would be the organic phase. Since, for > 0.5, will decrease with an increase in ei, a reduction in liquid-liquid interfacial area is expected. Hence, the observed results of a decrease in the rates with an increase in indicate a possibility of interfacial reaction rather than a bulk aqueous-phase reaction [7]. For di < 0.3 mm, a very large interfadal area (a = (> e d j d ) in the range (4—5) 10, 1/m is likely to exist compared to the volume of the aqueous phase. 

The addition of various surfactants and micelle-forming agents in the biphasic hydroformylation of olefins was also considered as a tool for enhancement of the reaction rates (see Section 2.3.4). Whereas the presence of a surfactant leads to a lower droplet size in the dispersed phase, thus increasing the liquid-liquid interfadal area and hence the mass-transfer rate, the formation of emulsions is considered as a maj or drawback of this system. Mass-transfer effects in biphasic hydroformylation of 1-octene in the presence of cetyltrimethylammonium bromide (CTAB) was studied by Lekhal et al. [37]. A mass-transfer model based on Higbie s penetration theory was proposed to predict the rate of hydroformylation in a gas-liquid-liquid system. 

We have seen how the concept of surface energy in principle relates to adhesion. The surface energy terms discussed (e.g., Eqs. (1) to (7)) are all energies per unit area. We now need to consider carefully what we mean by the interfadal area. 

Equipment design information also must be specified in the NEQ model so that mass-transfer coefficients, interfadal areas, liquid hold-ups, and pressure drops can be calculated. 

In colloidal dispersions a thin intermediate region or boundary, known as the interface, lies between the dispersed and continuous phases. Each of emulsions, foams, suspensions, and aerosols represent colloidal systems in which interfacial properties are very important because droplets, bubbles and particles can have very large interfadal areas. 

The specific surface is an important characteristic parameter of each porous body. It is defined as the interfadal area per gram of a solid phase, s = Splin, or as the interfadal area... 

This rather simple equation contains three cracial quantities that depend on design and operation of the packed colunm These quantities are the effective interfadal area, the gas side mass transfer coefficient /5q, and the liquid side mass transfer coefficient. According to the present state of the art, no models based on first principles are available for the prediction of these rather cracial quantities. Only some empirical correlations have been published so far (e.g., in Kister 1992). 

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