Chemical Engineering Use of Catalyzed Sulfite Oxidation Kinetics for the Determination of Mass Transfer Characteristics of Gas-Liquid Contactors

Mechanically agitated gas-liquid reactors

Limitations of oxygen transfer in fermentation can be solved using auxiliary liquids immiscible in the aqueous phase The liquids (called oxygen-vectors) used in this study were hydrocarbon (n-dodecane) and perfluorocarbon (forane F66E) in which oxygen is highly soluble (549 mg/L in n-dodecane and 118 mg/L in forane F66E at 35 degrees C in contact with air at atmospheric pressure) It has been demonstrated that the use of n-dodecane emulsion in a culture of Aerobacter aerogenes enabled a 3 5-fold increase of the volumetric oxygen transfer coefficient(k(L)a) calculated on a per-liter aqueous phase basis The droplet size of the vector played a crucial role in the phenomena When a static contact between gas bubble and vector droplet was established in water, the vector covered the bubble, in agreement with positive values of the spreading coefficient for these fluids The determination of the oxygen transfer coefficients (k(L)) in a reactor with a definite interfacial area enabled the main resistance to be located in the boundary layer of the waterside either for a gas-water or a vector-water interface Because oxygen consumption by weakly hydrophobic cells can only occur in the aqueous phase, the oxygen transfer is achieved according to the following pathway: gas-vector-water-cell Finally, a mechanism for oxygen transfer within this four-phased system is proposed

Mechanism of enhanced oxygen transfer in fermentation using emulsified oxygen-vectors.

Mathematical models for design of bioreactors: applications of Kolmogoroff's theory of isotropic turbulence

Etude experimentale de quatre contacteurs a boucle externe, dont le rapport des sections du trop plein et du tube de montee se situe dans le domaine 0,11≤A d /A r ≤0,69 et de trois contacteurs a tubes concentriques, ce rapport se situant dans la gamme 0,13≤A d /A r ≤0,56. Resultats concernant la vitesse du liquide dans la colonne de montee, le nombre de Bodenstein de la phase liquide et le temps de melange

Liquid circulation and mixing characteristics of airlift contactors

Gas holdup and the ratio of the turbulent regime mechanical power consumed in aerated compared to that in nonaerated aqueous phases were measured in two laboratory sized tanks. Standard six-blade turbine (D/T = 1/3), six-blade paddle (D/T = 1/3), and four-blade paddle (D/T = 2/3) impellers were used over a wide range of impeller rotational speed and gas sparging rate. For all systems, the power ratio results were found to fit a semitheoretical correlation (derived from dimensional analysis) involving the impeller Weber number, the aeration number, and the ratio of dispersion and liquid densities. Empirical correlations for gas holdup in water, aqueous solutions of nonelectrolytes, and an aqueous electrolyte solution are given. The overall results lead to the conclusion that power ratio and gas holdup correlations are highly specific to a particular impeller type and are also dependent on the tank size and the liquid phase physicochemical properties.

Stirred-tank mechanical power requirement and gas holdup in aerated aqueous phases

The effect of dispersed n ‐dodecane or n ‐hexadecane on the air‐to‐aqueous phase overall volumetric oxygen transfer coefficient in a simulated (cell‐free) stirred‐tank fermentor is described. The oil volume fraction ranged from zero to 0.10; the ionic strength of the aqueous phases was varied from 0 to 0.45. The air‐to‐aqueous phase coefficients in both oil‐free (KLa) and oil‐bearing (KLa*) systems were evaluated from unsteady‐state experiments using a membrane‐covered probe to follow the aqueous phase dissolved oxygen tension.

Oxygen transfer in mechanically agitated aqueous systems containing dispersed hydrocarbon

The oxygen transfer characteristics of gas-aqueous electrolyte solution dispersions have been studied in a laboratory-size, mechanically-agitated tank equipped with a 6-flat blade turbine of standard dimensions (DI/T = 1/3). The effects of mechanical agitation power input per unit volume (Pg/V), gas superficial velocity (vS) and aqueous-phase ionic strength (Γ) upon the overall volumetric mass transfer coefficient (kL a) and the liquid-phase mass transfer coefficient (kL) are presented. In the range of 0.2 ≤ Γ ≤ 1.2 kmol(ions)/m3, the results of this study indicate that kL increases with increasing Γ is independent of P/V for Pg/V < 2000 W/m3 but decreases with increasing Pg/V above that level and is independent of vs over the range of gas velocities studied. On the other hand, KL a was found to be dependent on all three variables (Pg/V, vg, and Γ).



On a etudie les caracteristiques du transfert d'oxygene dans le cas de dispersions de gaz dans des solutions aqueuses d'elec-trolytes, dans une cuve a l'echelle du laboratoire, agitee mecaniquement et munie d'une turbine a 6 pales plates de dimensions standards (Dt/T = 1/3). On presente les effets de la puissance d'agitation mecanique utilisee par unite de volume (Pg/V), de la vitesse superficielle du gaz (va) et de la force ionique (Γ) de la phase aqueuse sur le coefficient volumetrique (kL a) de transfert de masse global, et le coefficient (kL) de transfert de niasse en phase liquide. Dans le cas 0.2 ≤ Γ ≤ 1.2 k mole(ions)/m3, les resultats de Γetude indiquent que kL augmente avec V et est independant de Pg/V lorsque ce rapport est inferieur a 2000 W/m3; toutefois, kL decroit lorsque Pg/V croit au-dessus de cette valeur, et est independant de vS sur la gamme de vitesses du gaz etudiee. Par contre, on a constate que KL a dependait des trois variables (Pg/V, vs et Γ).

Ibrahim T. M. Hassan

Papers

Stirred-tank mechanical power requirement and gas holdup in aerated aqueous phases

Oxygen transfer in mechanically agitated aqueous systems containing dispersed hydrocarbon

Mass transfer coefficients in mechanically agitated gas—aqueous electrolyte dispersions

Mass-transfer-effective bubble coalescence frequency and specific interfacial area in a mechanically agitated gas-liquid contactor