Gas-Liquid Mass Transfer Coefficient

Liquid-phase mass transfer coefficient Gas-liquid interfacial area per unit volume of dispersion Gas volume fraction in dispersion Diffusivity of cyanogen in solution Henry law coefficient... 

The importance of gas-liquid mass transfer on the reactor performance depends upon the nature of the reaction system and the flow conditions in the reactor. Two important parameters characterizing the gas-liquid mass transfer are the gas-liquid mass-transfer coefficient and the gas-liquid interfacial area. Both of these parameters depend on the flow conditions and the nature and status of the solid packing. The relationships between gas-liquid mass-transfer coefficients, gas-liquid interfacial area, and the system conditions for various types of reactors are described in Chaps. 6 through 9. 

First, the overall mass transfer coefRcient k a of the microreactor was estimated to be 3-8 s [43]. For intensified gas liquid contactors, kj a can reach 3 s while bubble columns and agitated tanks do not exceed 0.2 s Reducing the flow rate and, accordingly, the liquid film thickness is a means of further increasing kj a, which is limited, however, by liquid dry-out at very thin films. Despite such large mass transfer coefficients, gas-liquid microreactors such as the falling film device may still operate between mass transfer and kinetic control regimes, as fundamental simulation studies on the carbon dioxide absorption have demonstrated [44]. Distinct concentration profiles in the liquid, and even gas, phase are predicted. 

Overall mass transfer coefficient (gas-liquid 4- solid-liquid) of A, B given by Equations 17.3 and 17.5, m/s. 

Intrinsic rate constant Mass transfer coefficient (gas, liquid phase)... 

The main transport parameters to be estimated are the mass transfer coefficients (gas-liquid (liquid side) fc , gas-liquid (gas side) kg, and liquid-solid fc )). Coupled to that is the estimation of the interfacial area per unit volume a, and often it is the combination (i.e., kia or kgO) that is estimated in a certain experimental procedure. Thermodynamic parameters, such as Henry s law constant (fZ) can be estimated in a simpler manner since their estimation on the flow or on any time-dependent phenomenon. Mass transfer coefticients may be evaluated in well-defined geometries with known flow fields using classical theories like film theory, penetration theory, surface renewal... 

Lemoine R, Morsi BI. Hydrodynamic and mass transfer parameters in agitated reactors. Part II gas-holdup, Sauter mean bubble diameters, volumetric mass transfer coefficients, gas-liquid interfa-dal areas, and liquid-side mass transfer coefficients. InL J. Chem. React. Eng. 2005 3 A20. 

Mass-transfer coefficient gas-liquid in liquid side, cm VCcm/ s) Overall mass-transfer coefficient gas-liquid, cmp/(cm, s) Mass-transfer coefficient liquid-solid, cmp/icmi s)... 

Volume mass transfer coefficient, gas to liquid (basis unit volume of reactor),... 

Molstad, M. C., McKinney, J. F. and Abbey, R. G. Trans. Am. Inst. Chem. Eng. 39 (1943) 605. Performance of drip-point grid tower packings, III. Gas-film mass transfer coefficients additional liquid-film mass transfer coefficients. 

Relationships between the gas-phase mass transfer coefficient the liquid-phase mass transfer coefficient and the overall mass transfer coefficients Kq and were discussed in Section 6.2. With the definitions used in this book, all of these coefficients have a simple dimension (L T ). 

There are two mass transfer coefficients that are significant, the gas/liquid mass transfer coefficient and liquid to solid coefficient. If the gas is a mixture, the gas/liquid coefficient is more difficult to estimate. 

In deriving the material balance equations, the dispersed plug flow model will first be used to obtain the general form but, in the numerical calculations, the dispersion term will be omitted for simplicity. As used previously throughout, the basis for the material balances will be unit volume of the whole reactor space, i.e. gas plus liquid plus solids. Thus in the equations below, for the transfer of reactant A kLa is the volumetric mass transfer coefficient for gas-liquid transfer, and k,as is the volumetric mass transfer coefficient for liquid-solid transfer. 

External surface area of particles per unit volume of reactor 1200 m-1 Mass transfer coefficient, liquid to particles 0.10 x 10"3 m/s Volume mass transfer coefficient, gas to liquid (basis unit volume of reactor) (ki.a) = 0.02 s l... 

Due to the complexity of mass transfer between gas-liquid-solid phases, it is difficult to evaluate the average value of mass transfer coefficient ki from the literature. A realistic way to evaluate ki is to use the algebraic expression of solution and by regression to obtain the experimental data rather than by regression with solving the set of non-linear differential equations. 

C concentration in liquid phase, mol/cur liquid C for concentration at equilibrium with the gas, mol/cm liquid k. liquid film mass transfer coefficient, cur liquid/cm2 bubble... 

Gas-liquid can operate countercurrently or cocurrently. Holdup volumetric liquid holdup per total reactor volume >0.7 and usually 0.95. Gas holdup = 0.05 to 0.4, increasing with increase in gas velocity. Superficial gas velocity 1 to 30 cm/s, although it has been as high as 50 cm/s. Mass transfer coefficients typical liquid mass transfer coefficient = kpa = 0.005 to 0.01 1/s ki = 0.6 to 0.7 10 m/s. For gas phase k(ja = 1 to 3 1/s. Surface area gas-liquid per volume of reactor 20 to 1000 m /m volume reactor depending on flow conditions. Surface area gas-liquid per volume... 

Mass transfer involves establishing a transfer between the elementary regions of the reactor and between individual phases (interfacial mass transfer coefficients gas phase mass transfer, liquid phase mass transfer, mass transfer with reaction, liquid-solid mass transfer), as well as other elementary phenomena and processes connected with mass transfer gas phase phenomena and processes (gas hold-up, bubble size, interfacial area and bubble coalescence/redispersion), volumetric mass transfer and power consumption during mass transfer (2). 

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