Liquid Film Mass Transfer Research Articles

Effects of hydrocarbon additions on gas-liquid mass transfer coefficients in biphasic bioreactors

The effects of aliphatic hydrocarbons (n-hexadecane andn-dodecane) on the volumetric oxygen mass transfer coefficient (k L a) were studied in flat alveolar airlift reactor and continuous stirred tank reactors (CSTRs). In the flat alveolar airlift reactor, high aeration rates (>2 vvm) were required in order to obtain efficient organic-aqueous phase dispersion and reliablek L a measurements. Addition of 1% (v/v)n-hexadecane orn-dodecane increased thek l a 1.55-and 1.33-fold, respectively, compared to the control (superficial velocity: 25.8×10−3 m/s, sparger orifice diameter: 0.5 mm). Analysis of the gas-liquid interfacial areaa and the liquid film mass transfer coefficientk L suggests that the observedk L a increase was a function of the media's liquid film mass transfer. Addition of 1% (v/v)n-hexadecane orn-dodecane to analogous setups using CSTRs led to ak L a increase by a factor of 1.68 and 1.36, respectively (superficial velocity: 2.1×10−3 m/s, stirring rate: 250 rpm). These results propose that low-concentration addition of oxygen-vectors to aerobic microbial cultures has additional benefit relative to incubation in purely aqueous media.

Aspects of estimating parameter dependencies in a detailed chromatography model based on frontal experiments

A methodology for estimation of the dependency on flow rate and bead size of the axial dispersion coefficient and the film mass transfer coefficient in a detailed model for chromatographic processes is proposed. The model describes the concentration of the solute in the mobile phase and considers external/internal mass transfer resistance. The flow rate dependency of the mixing effect in the external volume is also considered. The unknown model parameters estimated are the bed void, the axial dispersion coefficient, the liquid film mass transfer coefficient, the effective diffusion coefficient and the apparent bead porosity. All the parameters in the model and the parameter dependencies were subsequently determined in three classes of experiments, i.e. the external mixing behaviour, the mobile phase behaviour and the stationary phase behaviour. The estimates are based on the sum of the least squares of the residuals between the experimental breakthrough curves and the model response. The methodology is exemplified by frontal experiments with blue dextran and bovine serum albumin in a well-defined column set-up. The results show that it is possible to estimate the unknown physical parameters in the detailed model, and their dependencies on flow rate and bead size, using the proposed methodology.

Batch study of liquid-phase adsorption of methylene blue using cedar sawdust and crushed brick

This paper presents a study on the batch adsorption of basic dye, methylene blue, from aqueous solution (40 mg L −1) onto cedar sawdust and crushed brick in order to explore their potential use as low-cost adsorbents for wastewater dye removal. Adsorption isotherms were determined at 20 °C and the experimental data obtained were modelled with the Langmuir, Freundlich, Elovich and Temkin isotherm equations. Adsorption kinetic data determined at a temperature of 20 °C were modelled using the pseudo-first and pseudo-second-order kinetic equations, liquid-film mass transfer and intra-particle diffusion models. By considering the experimental results and adsorption models applied in this study, it can be concluded that equilibrium data were represented well by a Langmuir isotherm equation with maximum adsorption capacities of 142.36 and 96.61 mg g −1 for cedar sawdust and crushed brick, respectively. The second-order model best describes adsorption kinetic data. Analysis of adsorption kinetic results indicated that both film- and particle-diffusion are effective adsorption mechanisms. The Influence of temperature and pH of the solution on adsorption process were also studied. The extent of the dye removal decreased with increasing the solution temperature and optimum pH value for dye adsorption was observed at pH 7 for both adsorbents. The results indicate that cedar sawdust and crushed brick can be attractive options for dye removal from dilute industrial effluents.

Validation of bubble breakage, coalescence and mass transfer models for gas–liquid dispersion in agitated vessel

Bubble breakage and coalescence phenomena and multicomponent gas–liquid mass transfer were studied in a 194dm3 Rushton turbine agitated vessel. Local bubble size distributions (BSD) were measured from air–tap water system at several agitation conditions with capillary suction probe (CSP) technique. The CSP was compared to the digital imaging (DI) and phase Doppler anemometry (PDA) techniques in a 14dm3 stirred vessel. The volumetric BSDs between the CSP and DI were in agreement, but number BSDs showed notable deviation. The limitations of measurement techniques seem to be the main reason.A multiblock stirred tank model with discretized population balances for bubbles and two-film Maxwell–Stefan multicomponent mass transfer between gas and liquid was created for the 194dm3 agitated vessel. The model considers local mass transfer conditions in the vessel and is simple enough for the mathematical optimization of unknown model parameters. Unknown parameters in the mechanistic bubble breakage and coalescence models were fitted against measured local BSDs. After this, a parameter in the liquid film mass transfer correlation was adjusted against absorption and desorption experiments of oxygen. Local gas–liquid mass transfer areas were calculated from the population balance model. The simulations with the validated models show good agreement against experiments. On the other hand, the fitted parameters deviate from the theoretical values, which emphasizes the need of model validation against accurate experiments. Due to their fundamental character and the validation process, the fitted models seem to be useful tools for the design and scale-up of agitated gas–liquid reactors.

Modeling of Falling Film Molecular Distillator

On the basis of the kinetic equation, a mathematic model for two‐components in the presence of an inert gas was developed to describe the falling film molecular distillation process. The heat and mass transfer in liquid film on the evaporating surface and the mass transfer in the vapor phase in the distillation gap are taken into account. This model may show the profiles of temperature and concentration of film and the profiles of density, temperature, and velocity of vapor in consideration of the feed rate, evaporation temperature, and inert gas pressure. The model can be applicable to simulating various operational situations in a falling film molecular distillator. The comparison of the experiment results with the model study results shows a satisfactory qualitative agreement between the experiment and the theory.

Estimation of adsorption parameters in a detailed affinity chromatography model based on shallow bed experiments

A method for estimation of unknown adsorption parameters in a detailed chromatography model including the Langmuir adsorption expression is proposed. The model describes the concentration of the solute in the mobile phase and considers external/internal mass transfer resistance and adsorption dynamics. The external volume and its mixing effect are also considered. The unknown model parameters estimated are the bed void, the axial dispersion coefficient, the liquid film mass transfer coefficient, the effective diffusion coefficient, the apparent bead porosity, the adsorption/desorption rate coefficients and the Langmuir isotherm. All the parameters in the model were subsequently determined in four classes of experiments, the external mixing behaviour, the mobile phase behaviour, the stationary phase behaviour and the adsorption behaviour. The estimates are based on the sum of the least squares of the residuals between the experimental breakthrough curves and the model response. The methodology is exemplified by frontal experiments with bovine serum albumin in a shallow packed bed. The results show that it is possible to estimate the adsorption parameters using the proposed methodology, and to replace the Langmuir adsorption dynamic expression with the corresponding isotherm when high inlet concentrations are used. It was also investigated at what inlet concentration this model simplification resulted in satisfactory results. It was possible to estimate adsorption parameters using several experimental breakthrough curves simultaneously, i.e. multiple data responses, to obtain single parameters that are valid within the interval of inlet concentrations used.

A Methodology for Estimation of Mass Transfer Parameters in a Detailed Chromatography Model Based on Frontal Experiments

A methodology for estimation of the unknown physical parameters in a detailed model for chromatographic processes is proposed. The model describes the concentration of the solute in the mobile phase and considers external/internal mass transfer resistance. The external volume and its mixing effect are also considered. The unknown model parameters estimated are the bed void, the axial dispersion coefficient, the liquid film mass transfer coefficient, the effective diffusion coefficient and the apparent bead porosity. All the parameters in the model were subsequently determined in three classes of experiments, the external mixing behaviour, the mobile phase behaviour and the stationary phase behaviour. The estimates are based on the sum of the least squares of the residuals between the experimental breakthrough curves and the model response. The methodology is exemplified by frontal experiments with lysozyme, bovine serum albumin and immuno globulin γ on a well-defined column set-up. When the mixing properties in the external volume had to be accounted for, to avoid adding broadening behaviour to the dispersion coefficient, the film mass transfer coefficient and the diffusion coefficient were also investigated. The results show that it is possible to estimate the unknown parameters using the proposed methodology.

Mass transfer phenomena during sorption of hydrophilic volatile organic compounds into aqueous suspensions of activated carbon

A new process combining the two conventional control techniques absorption and adsorption, which consists in scrubbing the gases with an aqueous slurry of fine-powdered activated carbon, was studied to reduce the emission of some hydrophilic volatile organic compounds (VOCs). The collection of airborne isopropyl alcohol (IPA) and acetone vapors, the concentrations of which being in the range 1–5 g/m 3, was carried out with aqueous suspensions containing up to 8 % (w/w) activated carbon, in a cables contactor operating at ambient temperature in a semi-continuous way with recycle of the slurry. To interpret the experiments, a model was developed on the basis of the two-film theory of absorption, a Henry’s law for the solubility of organic compounds in water, and the assumption of a linear relationship between the instantaneous VOC contents of the solid and liquid phases. This model allows determining the overall gas–liquid height of transfer unit of the absorption column. Experimental results clearly reveal the increase of the global uptake capacity of VOC due to the presence of carbon particles in the absorbent. Nevertheless, it appears that the gas–liquid mass transfer rate is reduced, contrary to the expected enhancement due to the so-called grazing effect or shuttle movement of carbon particles reported in the literature. Same kinds of runs performed with slurries of non-adsorbing fine particles of silica resulted in a net increase of the overall gas–liquid and particularly of the liquid film mass transfer resistance. These runs show that, in the kind of absorber used, a substantial hindering influence of the solid particles accumulation in the liquid film also occurs when adsorbing particles are added to the liquid. The lack of enhancement in presence of activated carbon was attributed moreover to an inefficient shuttle effect caused by a too small adsorption capacity of the soluble VOCs on the activated carbon. This was confirmed by some tests carried out with an hydrophobic compound which being strongly adsorbed led to an appreciable enhancement.

1341 流下液膜・対向気流における界面波動と物質輸送に関する数値解析

1341 流下液膜・対向気流における界面波動と物質輸送に関する数値解析

Determination of the effective diffusion coefficient of Zn(II) on a macroporous resin XAD-2 impregnated with di-2-ethylhexyl phosphoric acid (DEHPA): Influence of metal concentration and particle size

In this work the experimental and numerical techniques employed to estimate the diffusion coefficient, D e, of Zn(II) adsorption on a macroporous resin XAD-2 impregnated with di-(2-ethylhexyl) phosphoric acid (DEHPA) have been reported. The influence of initial metal concentration and particle size on the D e has been studied. In the studied initial metal concentration range (37–248 mg/dm 3), D e was found to vary when increasing the initial feed concentration from 2.30×10 −13 to 14.05×10 −13 m 2/s for the particle size 840–630 μm, and from 1.63×10 −13 to 7.32×10 −13 m 2/s for the particle size 630–400 μm. When comparing the effect of particle size, the values of D e and k f corresponding to the biggest size showed a clear correlation with the step governing the adsorption, liquid film mass transfer or intraparticle diffusion.

B209 界面波を伴う流下液膜における熱物質輸送に関する数値解析(オーガナイズドセッション3 : 界面における輸送現象の物理)

B209 界面波を伴う流下液膜における熱物質輸送に関する数値解析(オーガナイズドセッション3 : 界面における輸送現象の物理)

Mass transfer with gas desorption from the surface of a liquid film in the presence of a cocurrent flow

Results of a thcoretical and experimental study of dynamics and mass transfer during desorption of a gas from a liquid film in the presence of a cocurrent air flow are presented. The calculation model is based on solving integral momentum and diffusion relations for the gaseous and liquid phascs. Both laminar and turbulent regimes of the film flow are analyzed. The experimental study of mass transfer was conducted for carbon dioxide desorption from a water film. Criterial relations for mass transfer in the gaseous and liquid phases are obtained. The experiments showed that the heat-transfer coefficients for the case under study are one order of magnitude grcater than those for the flow of a smooth film. Possible mechanisms of such an appreciable intensification of the liquid-film mass transfer in a cocurrent gas flow are discussed.

Modelling of fractionation in a molecular evaporator with divided condenser

Fractionation in a one-stage film evaporator can only be done by draining the condensate from different heights of a divided condenser. We have shown the capabilities of this distillation in a short-path (molecular) evaporator with a falling liquid film in a model study, taking into account heat and mass transfer in both liquid films on the evaporating and condensing surfaces, and mass transfer in the vapour phase. The data on flows and compositions of fractions were obtained for a binary test mixture at various feed rates, feed compositions, evaporating and condensing temperatures, and at various condenser arrangements. This mode of short-path distillation in an evaporator with a divided condenser can be used for fractionation and in cases where recycling of some portion of distillate is required. The comparison of the experimental results with the model study results shows a satisfactory qualitative agreement between the experiment and the theory.

Liquid film mass transfer coefficients KL for O2 and C02 desorption from open thin-layer microalgal cultures into atmosphere

Liquid film mass transfer coefficients KL for O2 and C02 desorption from open thin-layer microalgal cultures into atmosphere

Mass transfer parameter estimation using optimization technique: Case study in CO2 absorption with chemical reaction

AbstractThis paper proposes a new approach of applying an optimization technique to simultaneously determine a physical liquid—film mass transfer coefficient (KoL) and effective interfacial area (av) from a pilot plant data. The mass transfer mechanism of the CO2‐NaOH system was modeled using the two‐film theory to represent the behaviors of packed absorbers. The model presents an overall absorption rate (Rv) as a function of KoL and av. The optimization algorithm used in this study follows a modified Levenberg‐Marquardt method with a trust region approach. The Rv predictions from the model are in good agreement with the experimental data, with an average error of 6.5%.

Balance Equations for Molecular Distillation

We have derived balanced equations for continuous molecular (short-path) distillation of a binary mixture in a falling film evaporator. The relation of heat and mass transfer in liquid films on both the evaporating and condensing surfaces were taken into account, as well as the mass transfer in the vapor phase in the distillation gap. Individual balance equations were coupled by boundary conditions into a closed set of partial differential equations. By introducing the streams, we have transformed partial differential equations into the simple form of ordinary differential equations. These were solved numerically or approximately for some selected problems in isothermal (e.g., for turbulent film on evaporation surface) and nonisothermal regimes and for the influence of reevaporation from the condenser. These developed mathematical formulations can be used to model various operational situations in a molecular evaporator or to evaluate the influence of some parameters on the molecular distillation process.

Onset of gas induction, power consumption, gas holdup and mass transfer in a new gas-induced reactor

A newly developed gas-induced reactor, characteristics of having a draft tube and dual turbines was studied. This paper presents the effects of operational variables on the onset of gas induction and power consumption post gas induction. Moreover, gas holdup and mass transfer were also investigated. It was found that all the impeller speed, the liquid level and the impeller diameter had significant effects on the onset of gas induction and the power consumption post gas induction. Two empirical equations which correlate the onset of gas induction and power consumption post gas induction with the operational variables were obtained, being successfully capable of predicting the data. The volumetric mass transfer coefficients (kLa) of 0.8–1.2/min and liquid-film mass transfer coefficients (kL) of 2.5 × 10−4−7.5 × 10−4 m/s were also obtained, being comparable to the cited values. Furthermore, regional bubble number and size distributions as well as an unique method for determining the gas holdup were also presented.

Liquid-Film Mass-Transfer Coefficient in a Column Equipped with Structured Packings

The effective mass-transfer efficiency in a column equipped with structured packings was investigated experimentally. The packings analyzed in the present work were Sulzer Mellapak 250Y, made of corrugated plastic or metal sheets, and Sulzer BX, made of plastic gauze. In the literature many works have been published on this topic, but they have mainly been oriented toward evaluating overall mass-transfer efficiency or the gas-side coefficient, leaving out closer examination of the liquid-side mass-transfer coefficient. The aim of the present work is to examine liquid film and to identify a relation that allows accurately evaluating the liquid film contribution to overall mass-transfer efficiency. Experimental results showed that column packing height affects the liquid-side mass-transfer coefficient at the usual industrial-scale liquid and gas flow rates. This result agrees with theoretical analysis on stable liquid rivulet flow.

A Simplified Analysis of Reaction and Mass Transfer in UASB and EGSB Reactors

The paper is focused on the study of the hydrodynamics, reaction kinetics and mass transfer in lab-scale Upflow Anaerobic Sludge Blanket (UASB) and Expanded Granular Sludge Bed (EGSB) reactors treating wastewaters with low volatile fatty acids concentrations. The fluid pattern in the UASB approached a plug-flow reactor because of the low turbulence provided by the upflow velocity and gas production. The EGSB behaved as a continuous-stirred tank reactor due to the effects of the high recirculation rate. Liquid film mass transfer resistance seemed negligible in the EGSB but important in the UASB reactor. This should be the consequence of the different hydrodynamic conditions in the two reactors. The rate of acetate degradation was best fitted by an apparent half-order kinetics in both reactors. Internal mass transfer limitations, associated to an intrinsic zero-order kinetics, was detected in the degradation of low acetate concentrations by the granular biomass.

Gas-liquid reactions in well-mixed reactors—A fresh perspective

Classification of gas-liquid reactions in the past has been based on comparison of characteristic times for diffusional mass transfer and chemical reaction in liquid film near the gas-liquid interface. The fast chemical reactions occur almost entirely in liquid film and the very slow reactions are confined to bulk liquid. Gas-liquid reactions that do not belong to either class have received less attention and have been in general assumed to be confined to either liquid film or bulk liquid for simplification of modeling and design of reactors. A unified approach for modeling of gas-liquid reactors is provided here considering a single reaction occurring over the entire liquid phase, with at least the reactant or the product being volatile. The two-way linkages between liquid film and bulk liquid, largely ignored previously, are properly accounted for in the present approach. The dispositions of concentration profiles for reactant and product in the liquid film are presented and discussed. A first-order reaction is considered as a specific example. Numerical illustrations for a perfectly mixed reactor demonstrate that an unwarranted confinement of liquid-phase reaction to either liquid film or bulk liquid can lead to incorrect design of and erroneous prediction of performance of gas-liquid reactors. Variation in relative importance of reaction in liquid film with respect to reaction in bulk liquid with variations in process parameters is investigated. The effectiveness of the liquid-phase reaction in the presence of mass transfer resistances is examined.