Mass transfer coefficient enhancement

Thus the mass transfer coefficient, enhanced by chemical reaction, h D is given by ... 

D Mass transfer coefficient enhanced by chemical reaction m/s LT 1... 

Meyyappan, N. and Gandhi, N.N. Solubility and mass transfer coefficient enhancement of benzyl acetate in water through hydrotropy, 7 Chem. Eng. Data, 49(5) 1290-1294, 2004. 

This equation can be written Nco,s k[CCor where k[ = VA, Deo, and may be regarded as a liquid-film mass transfer coefficient enhanced oy the fast chemical reaction. This is very convenient because it allows us to use the expression in Volume 2, Chapter 12 for combining liquid-film and gas-film coefficients to give an overall gas-film coefficient ... 

Mass transfer coefficient Enhancement factor E Inlet mol fraction of CO2, yo Henry s constant, MPa 1/mol ... 

The enhanced rate expressions for regimes 3 and 4 have been presented (48) and can be appHed (49,50) when one phase consists of a pure reactant, for example in the saponification of an ester. However, it should be noted that in the more general case where component C in equation 19 is transferred from one inert solvent (A) to another (B), an enhancement of the mass-transfer coefficient in the B-rich phase has the effect of moving the controlling mass-transfer resistance to the A-rich phase, in accordance with equation 17. Resistance in both Hquid phases is taken into account in a detailed model (51) which is apphcable to the reversible reactions involved in metal extraction. This model, which can accommodate the case of interfacial reaction, has been successfully compared with rate data from the Hterature (51). 

Reaction between an absorbed solute and a reagent reduces the equilibrium partial pressure of the solute, thus increasing the rate of mass transfer. The mass-transfer coefficient hkewise is enhanced, which contributes further to increased absorption rates. Extensive theoretical analyses of these effects have been made, but rather less experimental work and design guidehnes. 

With a reactive solvent, the mass-transfer coefficient may be enhanced by a factor E so that, for instance. Kg is replaced by EKg. Like specific rates of ordinary chemical reactions, such enhancements must be found experimentally. There are no generalized correlations. Some calculations have been made for idealized situations, such as complete reaction in the liquid film. Tables 23-6 and 23-7 show a few spot data. On that basis, a tower for absorption of SO9 with NaOH is smaller than that with pure water by a factor of roughly 0.317/7.0 = 0.045. Table 23-8 lists the main factors that are needed for mathematical representation of KgO in a typical case of the absorption of CO9 by aqueous mouethauolamiue. Figure 23-27 shows some of the complex behaviors of equilibria and mass-transfer coefficients for the absorption of CO9 in solutions of potassium carbonate. Other than Henry s law, p = HC, which holds for some fairly dilute solutions, there is no general form of equilibrium relation. A typically complex equation is that for CO9 in contact with sodium carbonate solutions (Harte, Baker, and Purcell, Ind. Eng. Chem., 25, 528 [1933]), which is... 

Note that the tower height is inversely proportional to the enhanced mass-transfer coefficient, or to the enhancement factor itself. 

When liquid/liquid contactors are used as reacdors, values of their mass-transfer coefficients may be enhanced by reaction, analogously to those of gas/liquid processes, but there do not seem to be any published data of this nature. 

Hence, show that the enhancement, E, for the increase in value of the liquid-phase mass transfer coefficient is ... 

Steps 1 and 7 are highly dependent on the fluid flow characteristics of the system. The mass velocity of the fluid stream, the particle size, and the diffusional characteristics of the various molecular species are the pertinent parameters on which the rates of these steps depend. These steps limit the observed rate only when the catalytic reaction is very rapid and the mass transfer is slow. Anything that tends to increase mass transfer coefficients will enhance the rates of these processes. Since the rates of these steps are only slightly influenced by temperature, the influence of these processes... 

With a reactive solvent, the mass transfer coefficient may be enhanced by a factor E so that, for instance Kg is replaced by EKg. Like specific rates of ordinary chemical reactions, such enhancements must be found experimentally, although some theoretical relations for idealized situations have been found. Tables 8.1 and 8.2 show a few spot data. A particular... 

A reagent in solution can enhance a mass transfer coefficient in comparison with that of purely physical absorption. The data of Tables 8.1 and 8.2 have been cited. One of the simpler cases that can be analyzed mathematically is that of a pseudo-first order reaction that goes to completion in a liquid film, problem P8.02.01. It appears that the enhancement depends on the specific rate of reaction, the diffusivity, the concentration of the reagent and physical mass transfer coefficient (MTC). These quantities occur in a group called the Hatta number,... 

Table 9.3 gives data of common types of L-L contactors. Since the given range of kLa is more than 100/1, this information is not of direct value for sizing equipment. The efficiencies of various kinds of small liquid-liquid contactors for physical extraction are summarized on Figure 8.1. Larger units may have efficiencies less than half of these values. In some cases, however, enhancement of the L-L mass transfer coefficient by reaction may be as appreciable as in some gas-liquid cases. 

In this cell, mechanical vibration is applied to the cell housing to enhance the transfer in the parallel plate tank cell [248]. The vibrations are transfered to the electrolyte resulting in an increase of the mass-transfer coefficient. The cell is extensively used in industry for the pretreatment of higher and high metal concentrations which is finally purified by a packed bed electrolysor if the required conversion is not too high [247],... 

From the above it can be concluded that only the reaction with component B may enhance mass transfer of ozone substantially. And only if the Hatta number HaB is much higher than 1. Therefore it can be expected that whenever we have to deal with an enhancement of mass transfer due to chemical reactions, this influences the selectivity of the oxidation process in a negative way. The factor which has to be considered in this respect is the Hatta number for the reaction of ozone with component B (equation 29). HaB increases with increasing value of kB and CBb and with decreasing value of the mass transfer coefficient for ozone, kHq,... 

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