Gas-liquid interphase mass transfer

The reported study on gas-liquid interphase mass transfer for upward cocurrent gas-liquid flow is fairly extensive. Mashelkar and Sharma19 examined the gas-liquid mass-transfer coefficient (both gas side and liquid side) and effective interfacial area for cocurrent upflow through 6.6-, 10-, and 20-cm columns packed with a variety of packings. The absorption of carbon dioxide in a variety of electrolytic and ronelectrolytic solutions was measured. The results showed that the introduction of gas at high nozzle velocities ( 20,000 cm s ) resulted in a substantial increase in the overall mass-transfer coefficient. Packed bubble-columns gave some improvement in the mass-transfer characteristics over those in an unpacked bubble-column, particularly at lower superficial gas velocities. The value of the effective interfacial area decreased very significantly when there was a substantial decrease in the superficial gas velocity as the gas traversed the column. The volumetric gas-liquid mass-transfer coefficient increased with the superficial gas velocity. 

Specchia et al.32 measured gas liquid interfacial area and liquid-phase mass-transfer coefficients in an 8-cm-diameter packed column. Three types of packing, glass spheres, Berl saddles, and ceramic rings, all of 6 mm, were examined. Superficial velocities of 14 through 221 cm s 1 and 0.25 through 4.3 cm s 1 were used for the gas and liquid phase, respectively. The gas-liquid interfacial area was correlated to the pressure drop by an expression 

aL is the interfacial area per unit volume of column in m x, as in m 1, and (AP/AZ)Lg in kg, m 3. The relative mean quadratic error for the above correlation is 6.2 percent. A comparison between Eq. (7-26) and a similar relation for the downflow conditions is illustrated in Fig. 7-17. The liquid-side mass-transfer coefficient was similarly correlated to the energy parameter by an expression 

fcL is in m s , /0l is in m s-1, gc is in kgm m kgf 1 s 2, pL is in kg in-3, and u9 is in m 1. The above relation is graphically illustrated and compared with a similar relation for the downflow conditions in Fig. 7-18. Better values of kL are obtained for slower liquid velocities in upflow compared to downflow, presumably due to an increase in circulation inside the liquid drops, caused, among other things, by the greater slip velocity between the liquid and the gas phase. It should be noted.that the estimation of aL and kL from the above relations requires a prior knowledge of (AP/AZ)LG. 

Saada25 measured the gas liquid mass-transfer coefficients for absorption of carbon dioxide into NaOH solutions for cocurrent upflow. Goto et al.8 evaluated the liquid-gas mass-transfer coefficients for the desorption of oxygen from water into nitrogen in a 2.58-cm-i.d. glass tube packed with CuO-ZnO particles 

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The reaction kinetics is of first order with respect to hydrogen and almost of zero order with respect to A. The reactor itself can be described by the plug flow model, but both internal and external (at the gas-liquid interphase) mass transfers limit the hydrogenation rate. The gas phase consists of pure hydrogen, which flows in a large excess. The density of the liquid phase is assumed to be constant. Give the balance equations of the components. 

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