Interface mass transfer

R. W. Schrage, Theoretical Study of Interface Mass Transfer, Columbia University, New York, 1953. 

In addition to the process steps described above involving mass transfer to and across interfaces, mass transfer by fluid flow through the reactor must also be taken into account. 

Such a model should take into account at least the following phenomena Mass transfer across gas-liquid interface, mass transfer to exterior particle surface, catalytic reaction, flow and axial mixing of gas phase, and flow and axial mixing of liquid phase. 

The experimental and theoretical work reported in the literature will be reviewed for each of the five major types of ga s-liquid-particle operation under the headings Mass transfer across gas-liquid interface mass transfer across liquid-solid interface holdup and axial dispersion of gas phase holdup and axial dispersion of liquid phase heat transfer reaction kinetics. 

Figure 5.18 Conversion as a function of reaction rate and interface mass transfer kR for, ub = 0.5 for a first-order gas-phase catalytic reaction.

One possible way to modify Eq. (75) was suggested in a paper by Scott, Tung, and Drickamer (S7), who proposed that the mass flux across the interface. (intJ be written as the product of an interface mass transfer coefficient fe[Pg.181]

The removal of one of more selected components from a mixture of gases by absorption into a suitable solvent (Mass Separating Agent, MSA) is the second major operation of chemical engineering after distillation. Absorption is based on interface mass transfer controlled largely by rates of diffusion. It is worth noting that absorption followed by a chemical reaction in the liquid phase is often used to get more removal of a solute from a gas mixture. 

Abstract The objective of this chapter is to present some recent developments on nonaque-ous phase liquid (NAPL) pool dissolution in water saturated subsurface formations. Closed form analytical solutions for transient contaminant transport resulting from the dissolution of a single component NAPL pool in three-dimensional, homogeneous porous media are presented for various shapes of source geometries. The effect of aquifer anisotropy and heterogeneity as well as the presence of dissolved humic substances on mass transfer from a NAPL pool is discussed. Furthermore, correlations,based on numerical simulations as well as available experimental data, describing the rate of interface mass transfer from single component NAPL pools in saturated subsurface formations are presented. 

The concentration of a dissolved NAPL in groundwater is governed mainly by interface mass-transfer processes that often are slow and rate-limited [7,8]. There is a relatively large body of available literature on the migration of NAPLs and dissolution of residual blobs [6,9-22], and pools [5,23-34]. Furthermore, empirical correlations useful for convenient estimation of NAPL dissolution... 

Numerous empirical correlations for the prediction of residual NAPL dissolution have been presented in the literature and have been compiled by Khachikian and Harmon [68]. On the other hand, just a few correlations for the rate of interface mass transfer from single-component NAPL pools in saturated, homogeneous porous media have been established, and they are based on numerically determined mass transfer coefficients [69, 70]. These correlations relate a dimensionless mass transfer coefficient, i.e., Sherwood number, to appropriate Peclet numbers, as dictated by dimensional analysis with application of the Buckingham Pi theorem [71,72], and they have been developed under the assumption that the thickness of the concentration boundary layer originating from a dissolving NAPL pool is mainly controlled by the contact time of groundwater with the NAPL-water interface that is directly affected by the interstitial groundwater velocity, hydrodynamic dispersion, and pool size. For uniform... 

The cloud chemistry simulation chamber (5,6) provides a controlled environment to simulate the ascent of a humid parcel of polluted air in the atmosphere. The cloud forms as the pressure and temperature of the moist air decreases. By controlling the physical conditions influencing cloud growth (i.e. initial temperature, relative humidity, cooling rate), and the size, composition, and concentration of suspended particles, chemical transformation rates of gases and particles to dissolved ions in the cloud water can be measured. These rates can be compared with those derived from physical/chemical models (7,9) which involve variables such as liquid water content, solute concentration, the gas/liquid interface, mass transfer, chemical equilibrium, temperature, and pressure. 

Table 9-3 Summary of gas-liquid interface mass transfer studies for cocurrent gas-liquid flow in a fluidized bed...

Recommendations The best up to date work on gas-liquid interface mass-transfer coefficients in a stirred three-phase column is by Joosten et al.51 For a three-phase fluidized bed, the data of Ostergaard and Fosbol, 03 Kito et al.,59 and Nishikawa et al.92 should be used wherever possible. Future work should include the derivation of a correlation for KLaL for the hydrocarbon systems. At present, the best available correlation for the gas-liquid interfacial area in a three-phase fluidized bed is that by Strumillo and Kudra [Eq. (9-44)]. 

Attempts to use the analytical result of Equation 3 to correlate experimental data have consistently failed (17). Consequently, empirical and semi-empirical models which include various factors to account for evaporation and non-Newtonian behavior have been proposed (17) but these too have not been able to satisfactorily fit the available data. We have considered the coating flow problem with simultaneous solvent evaporation (11). In the regime of interface mass transfer controlled evaporation, i.e. at high solvent concentration, the fluid mechanics problem can be decoupled from the mass transfer problem via an experimental parameter a which measures the changing time-dependent kinematic viscosity due to solvent evaporation. An analytical expression for the film thickness has been obtained (11) ... 

Assuming that the reaction rate, represented by Iq. (m g/(m ss)) is limited by the external gas-to-solid interface mass transfer to spherical particles, k,=kg a=kg 6/dp yielding ... 

At not-too-high current densities, the electrolyte flow induced by the interface mass transfer (the second equation in... 

Figure 19 illustrates that the difference in conversion at various reaction times in SC CO2 and in the CO2/IL mixture is not considerable. One of the main reasons may be that the catalysts are well dispersed in the IL-rich phase in the presence of the IL, which favors enhancement of the reaction rate in the CO2/IL system. On the other hand, the liquid/vapor interface exists in the CO2/IL system, which does not favor the increase of the reaction rate due to the interface mass transfer. The two opposite factors compensate each other, and thus the conversion is similar. The effect of reaction time on the selectivity in the tw o solvents is not significant, as can be seen from the figure. However, in the CO2/IL mixed solvent the selectivity to the desired product is much higher than that in SC CO2. Moreover, the selectivity in the mixed solvent increases slightly with reaction time, while the selectivity decreases slowly with reaction time in SC CO2. 

In this section we derive the drift-flux mixture model starting out from the time averaged multi-fluid model expressed in terms of phase- and mass weighted variables [112]. The relative moment of the phases is given in terms of drift velocities. This approach can be applied for systems where the phase densities are constants and the interface mass transfer can be neglected. 

The material balances are implemented based on Equation 13.2, written separately for each phase on a stage. Each phase equation is then expanded to include vapor-liquid interface mass transfer, Equations 15.11 or 15.12. 

The reaction engineering aspects of liquid-liquid reactions have been well studied ([86-88], cf. Section 4.1). The performance of these reactions depends on the hydrodynamics of the dispersion, the mixing of the two fluid phases, the interface mass-transfer steps, the phase equilibria and kinetics of the reactions involved. 

To determine the conditions at the interface for this point in the tower, solve simultaneously the equilibrium relationship (Raoult s law, in this case) and the interface mass-transfer condition given by an equation similar to (3-10) ... 

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