Mass transfer with fast chemical reaction in drops

Mass transfer with a fast second-order chemical reaction inside a drop has been studied photographically. Measured flow patterns and the reaction surface position have been compared with predictions of solutions of transport equations. The agreement is within experimental error.     

Mass transfer with chemical reaction: the slow reaction regime revisited

A simple calculation procedure for the case of absorption with chemical reaction in case of the slow reaction regimes is presented. It is based on film theory and concerns reactors open to the liquid and to the gas. The influence of the reactor type and of reaction orders is shown.     

Mass transfer with chemical reaction in liquid foam reactors

Mass transfer studies were conducted in a stable liquid foam reactor under various operating conditions to evaluate gas holdup, effective interfacial area, liquid-phase mass transfer coefficient and a modified interfacial mass transfer coefficient to include the surface-active agents employed. Gas holdup and effective interfacial area were evaluated experimentally. The interfacial mass transfer coefficient was evaluated semitheoretically, by considering the interfacial region as a separate phase and using the experimental data developed for mass transfer accompanied by a fast first-order chemical reaction. The liquid-phase mass transfer coefficient was also evaluated semitheoretically, using Danckwert's theory for the liquid phase and the experimental data on mass transfer accompanied by a slow pseudofirst-order chemical reaction. An experimental unit was set up to provide a stable flowing foam column, simulating the foam reactor. Mass transfer rates were studied for superfacial gas velocities in the range from 1.5 × 10⁻² m/s to 5 × 10⁻² m/s, giving gas residence times in the range from 20 to 55 seconds. A cationic and nonionic surface-active agent and three different wire mesh sizes, giving bubble size distributions in the range from 2.2 to 5.4 mm Sauter mean diameters, were employed. It is observed that gas holdup is insensitive to the type of surface-active agent; it is however, dependent on wire mesh size and gas velocity. The bubble diameter and, hence, the interfacial area are found to be insensitive to gas velocity in the range studied; they are, however, strong functions of wire mesh size. The liquid-phase mass transfer coefficient increases with increase in gas velocity. The surface-active agent introduces additional resistance to mass transfer in both reaction cases, this being the controlling one in the case of the fast reaction. A comparison with conventional packed bed contactors indicates the mass transfer rates to be about 8 times lower for the foam reactor, for the fast reaction case; for slow reactions, the foam reactor has mass transfer rates approximately 2-4 times higher than those for conventional packed bed contactors.     

Mass transfer with chemical reaction in a foam bed contactor

On the basis of dodecahedral structure of a foam bed, a model to predict conversion in a foam bed contactor with mass transfer with chemical reaction has been developed. To verify the proposed model, experiments have been carried out in a semi-batch apparatus for the absorption of lean CO₂ gas in a foam of sodium hydroxide solution. The proposed model predicts fairly well the experimentally found absorption values.     

Mass transfer and chemical reaction in fluid two-phase systems

Steady-state concentrations of the transferred reactant in the bulk phase and the non-flowing diffusion boundary layer of an isothermal, isobaric two-phase reactor with an irreversible first-order reaction and constant composition of one phase.     

Mass transfer without and with chemical reaction in dispersed gas-liquid two-phase flows

Using a concentric sphere model, velocity profiles around bubbles in a bubble swarm were derived for clean and for relatively contaminated gas bubbles. The theoretical Sherwood numbers were calculated, including the effect of void fraction. These mass transfer predictions were compared with experimental results for the absorption with reaction of carbon dioxide into monoethanolamine solutions. The results indicated an appreciable contamination of the bubbles by surface active material.     

Mass transfer without and with chemical reaction from single free gas bubbles

Rates of mass transfer of carbon dioxide bubbles into water and into monoethanolamine solutions are reported. The apparatus used located the free bubble in an inverted small angle funnel through which the continuous phase flowed. An appreciable wall effect was expected and was included in the analysis of the results by a concentric sphere potential flow model.     

Mass transfer with chemical reaction during gas absorption on a sieve plate

On the basis of measurements of the rate of absorption of carbon dioxide into potassium carbonate—potassium bicarbonate buffer solutions, containing sodium hypochlorite and potassium chloride, and into sodium hydroxide solutions it has been proved that the Danckwerts' pseudo-first order reaction method may be successfully used for the determination of interfacial area and mass transfer coefficients on sieve plates.The values of interfacial area and mass transfer coefficient have been measured by this method for sieve plates of various geometry, at different gas velocities and clear liquid heads. It was found that the interfacial area per unit volume of the froth is almost independent of these parameters.A method of computation of the plate efficiency for absorption with reaction process has been suggested and tested experimentally.The results of investigations of the kinetics of the chemical reactions involved are also given.     

Mass transfer with mth order chemical reaction for multi-particle systems

The steady-state diffusion equation with convective term and mth order chemical reaction term was numerically solved by the finite difference method. The penetration theory agreed only with the numerical solution around single spheres in an infinite potential flow field. The enhancement factor varies with the values of the Reynolds number, void fraction and contamination factor.     

Mass transfer with chemical reaction inside single droplets and gas bubbles: Mathematical mechanisms

The effect of a first order homogeneous chemical reaction on the rate of mass transfer inside liquid droplets and gas bubbles was determined. One of the models presented assumes the non-oscillating dispersed phase is moving in the creeping flow region and the Hadamard stream functions are applicable. The results of the numerical solution of this model are presented graphically as a function of the Peclet number, reaction number, and dimensionless contact time. An oscillating droplet model is also presented which considers the effect of reaction within the dispersed phase.     

Mass transfer with chemical reaction from spherical one or two component bubbles or drops

Unsteady state mass transfer between a one or two component bubble (or drop) and the continuous phase with a chemical reaction occuring either in the continuous or in the dispersed phase is examined. The main assumption for binary bubbles is that the rate determining step is diffusion in the continuous phase. Two limiting velocity fields. Hadamard flow (Re?:1) and potential flow (Re?:1) are used in the calculations.     

Mass transfer accompanied by chemical reaction at the surface of a single droplet

Mass transfer accompanied by chemical reaction at the surface of a droplet in the free-rise period has been studied. Theoretical analysis was carried out on the basis of two typical models; one is the stagnant spherical drop model proposed by Newman, and the other is the model which accounts for the turbulent circulation in a droplet proposed by Handlos and Baron. Diffusion equations for these models were numerically solved under the boundary conditions which accounts for the chemical reaction at the drop surface. Two cases were discussed. One is the case in which mass transfer resistance in the continuous phase can be ignored, and the other is the case in which it should be accounted for. In the former case, it was found that the mass transfer rate increased with an increase of the initial concentration of reaction component in a droplet when the reaction order is greater than unity.The reverse case occurs when the reaction order is smaller than unity. In the latter case, it was revealed that the mass transfer rate increased with an increase of the initial concentration of the dispersed phase component when it is small but decreased when it is large.On the basis of these results of the theoretical analysis, the extraction rate of acetic acid by Amberlite LA-2, secondary long-chain alkylamine, was examined. As a result of the examination, the experimental results were fairly well explained by the model which takes account of the interfacial reaction of first order with respect to either acetic acid or amine.     

Mass transfer with Nth order chemical reaction around spheres in the presence of surfactants

A numerical technique has been used to solve the nonlinear equation describing the mass transfer taking place for single and multiple particles for Nth order chemical reactions in the presence of a surfactant. A generalized form is given for the Sherwood number as a function of the Peclet number for reaction orders of 1/2, 1 and 2 in the presence of surfactants, (Sh = aPe^b). The parameters (a) and (b) are dependent on the reaction orders and the amount of surfactant present. The coefficient (b) had an average value of 0.46 with the parameter (a) increasing with larger reaction rate constants. The numerical technique involved DISPL, a computer software package for the solution of partial differential equations by the method of lines.