Numerical solutions to the unaveraged mass balance equation for the case of a flat mobile interface reveal that both high-and low-frequency velocity fluctuations can contribute to mass transfer. This is in contrast to transport to a solid boundary where only low-frequency fluctuations, normal to the wall, are important. The average mass transfer coefficient is found to depend on Schmidt number to the -0.5 power, in agreement with classical theories. It is related to the velocity field in the liquid primarily through the mean-square value of the gradient of normal velocity fluctuations at the interface. SCOPEThe absorption of a slightly soluble gas in a concurrent, turbulent gas-liquid flow is controlled by flow fluctuations in the liquid through mechanisms that are not yet understood. This is a situation where the Schmidt number is large, and as a consequence the concentration boundary layer in the liquid is confined to a very thin region near the interface. Shear, caused by the gas flow, induces wave formation and also greatly enhances mass transfer rates. Mass transfer coefficients measured by Aisa et al. (1981) and McCready and Hanratty (1 984b) are about one order of magnitude larger than those found for turbulent mass transfer at a solid boundary. The fundamental problem that must be considered in order to understand mass transfer in these complex flows is how the gas and liquid velocity fields interact to control the transport rate. The work presented here addresses this question by numerically solving the unaveraged mass balance equations for a randomly varying velocity.A similar approach was taken previously by Campbell and Hanratty (1983) in their studies of mass transfer between a turbulent fluid and a solid boundary. These yielded the surprising result that mass transfer is controlled by low-frequency velocity fluctuations normal to the surface that contain only a small fraction of the turbulent energy.The principal hydrodynamic difference between the case considered here and the case considered by Campbell and Hanratty is that near a mobile boundary the velocity normal to the boundary varies linearly with distance from the boundary, rather than quadratically. The goal of this work has been to explore the consequences of this difference. CONCLUSIONS AND SIGNIFICANCEMass transfer at a mobile boundary (a clean gas-liquid interface) is found to be fundamentally different from mass transfer at an immobile boundary (a contaminated gas-liquid interface or a solid), in that velocity fluctuations of all frequencies are playing an important role. This is reflected in the equations for the massThe presentaddressof Eleni Vassiliadou is KoninklijkeShell Lab.. Amsterdam, Holland. transfer coefficient that are derived from computer experiments.The velocity normal to mobile and immobile surfaces are given respectively by u = p ( x , z, t ) y, and u = p ( x , z, t ) y', where all terms have been made dimensionless using a friction velocity and the kinematic viscosity. Campbell and Hanratty (1983) T h e importanc...

The reaction kinetics between CO2 and trihexyl(tetradecyl)phosphonium ([P66614])-based ionic liquids (ILs) with prolinate ([Pro]), 2-cyanopyrrolide ([2-CNpyr]), and 3-(trifluoromethyl)pyrazolide ([3-CF3pyra]) anions are studied at temperatures from 22-60 °C. The absorption of CO2 is carried out in a stirred reactor under pseudo first order conditions. ILs are diluted to concentrations of 0.05, 0.1 and 0.15 M with tetraglyme--a nonreactive, low volatility solvent with much lower viscosity than the ILs. Physical solubility of CO2 in the mixtures is calculated using correlations developed from CO2 solubility measurements in tetraglyme and the N2O-analogy for ILs and dilute IL solutions. The diffusivity of CO2 is estimated from viscosity-dependent correlations chosen after a thorough literature review. The results indicate partial first order reaction kinetics with respect to IL with values ranging from 19,500 L mol(-1) s(-1) ([P66614][Pro]) to 3200 L mol(-1) s(-1) ([P66614][3-CF3pyra]) at 22 °C. The second order reaction rate constants follow Arrhenius behavior with the highest activation energy of 43 kJ mol(-1) measured for [P66614][Pro]. ILs with aprotic heterocylic anions (AHA), on the other hand, show small activation energies of 18 and 11 kJ mol(-1) for [P66614][3-CF3pyra] and [P66614][2-CNpyr], respectively. The ILs studied in this work exhibit reactivity comparable to or higher than common aqueous amines. High reaction rates and tunable capacity make ILs, and AHA ILs in particular, attractive solvents for CO2 separations.

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The kinetics of phenylacetylene hydrogenation over Pt/γ-Al 2 O 3 catalyst was investigated using stirred semibatch reactors over a range of temperatures, pressures, and initial phenylacetylene concentrations. Analysis verified that the results were obtained in the absence of transport limitations. Equations for the rates of change for phenylacetylene, styrene, and ethylbenzene were derived from a system of elementary reactions and tested against experimental data. The model was found to accurately predict rate dependencies on catalyst weight, initial concentration, and pressure. The kinetic parameters were determined by minimizing the error between the model predictions and the experimental results, and the obtained activation energy values compared favorably with those reported in the literature.

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