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The superior electrocatalytic hydrodechlorination (EHDC) performance on Pd/U-TiO 2 catalyst is attributed to the electron-rich Pd regulated by urchin-like yolk/shell TiO 2 support, enhanced adsorption and activation of 2,4-dichlorophenol, faster mass diffusion behavior and high current efficiency toward EHDC. [Display omitted] • Pd supported on urchin-like yolk/mesoporous shell TiO 2 (Pd/U-TiO 2) is prepared. • Pd/U-TiO 2 affords high efficiency and durability in EHDC of 2,4-DCP. • Pd/U-TiO 2 affords a higher H* utilization efficiency of 48.6 % than single Pd. • U-TiO 2 support boosts the mass diffusion of 2,4-DCP around Pd nanoparticles. • The pollutant adsorption and activation are enhanced on U-TiO 2 -supported Pd. Improving the utilization of hydrogen radicals (H*) is of great significance for effective Pd-mediated electrocatalytic hydrodechlorination (EHDC) in detoxifying chlorinated organic pollutants (COPs). However, the limited H* utilization by single Pd arises from its inadequate performance in adsorbing/activating COPs and inferior mass transfer of low-concentration COPs. In this study, an urchin-like yolk/shell TiO 2 spheres with mesoporous structure are developed for supporting Pd nanoparticles (Pd/U-TiO 2), which exhibits superior EHDC activity and selectivity for 2,4-DCP reduction. Notably, the prepared Pd/U-TiO 2 catalyst achieves a mass activity of 4.2 min−1 g Pd -1 and a specific activity of 1.94 min−1 mol Pd -1 when detoxifying 50 mg/L of 2,4-DCP at −0.85 V, surpassing the most reported catalysts. Furthermore, the Pd/U-TiO 2 catalyst consistently demonstrates higher H* utilization efficiency compared to single Pd, regardless of the 2,4-DCP concentration or reaction mode (batch or continuous-flow). This enhanced H* utilization efficiency is attributed to two key factors: the urchin-like and yolk/shell structure of U-TiO 2 enhances the mass diffusion of 2,4-DCP, and the strong interactions between Pd and U-TiO 2 generate electron-rich Pd species that enhance the adsorption and activation of COPs. Overall, this work highlights the synergistic effects of strong metal-support interactions and mass diffusion in enhancing atomic H* utilization. This study lays a significant experimental and theoretical foundation for designing efficient electrocatalysts for the detoxification of chlorinated organic pollutants and various other halogenated organic pollutants. [ABSTRACT FROM AUTHOR]

• A new model is proposed based on the lanoline conservation equations in the fluid and in the liquid phase. • The model depends on two parameters: the lanoline solubility and the mass-transfer coefficient. • The two 1st-order partial differential equations are solved together with parameter optimisation. • Extraction yields depend on time, flow rate, temperature, pressure, and wool packing factor. • Extraction yields are predicted with an average error of 2.18%. A new mathematical model is presented for the supercritical fluid extraction of lanoline from wool using near-critical ethanol-modified CO 2 , using our previous experimental data. The model is intended to account for the extraction of lanoline at conditions well above its melting point (60–80 °C) and pressures up to 150 bar. The model parameters are a Henry-type fluid-to-liquid partition coefficient for lanoline, K = Cg/C L , and a fluid-side mass-transfer coefficient, k G. For Re ∼1, K is independent of velocity and wool packing density, but increases with pressure (K = 4 − 15 × 10−4). k G is found to be independent of temperature; it increases with velocity, decreases with pressure, and increases with wool packing density. The values found are k G = 5.66 × 10-6 m/s (70 bar) and k G = 1.51 × 10-6 m/s (150 bar). [ABSTRACT FROM AUTHOR]

• A model for NH 3 -SCR based on kinetics and computational fluid dynamics (CFD). • Model validation with SCR by monolithic Cu-ZSM-5. • Inhibition of effect of hydrocarbons in engine emission tests. A simple kinetic model for the standard NH 3 -SCR reaction by Cu-ZSM-5 catalysts has been developed by assuming three reaction steps: NH 3 adsorption (desorption), reactions of adsorbed NH 3 with O 2 (NH 3 oxidation) and NO (NH 3 -SCR). The model is based on Arrhenius parameters for NH 3 -SCR and NH 3 oxidation by a powder catalyst, combined with models for heat and mass transport and parameters of monolithic catalysts. The model is validated with the experimental results, not included in the estimation of the model, for NH 3 -SCR by monolithic catalysts with different parameters (catalyst loading and cell density). NOx removal from diesel exhaust, generated by engine bench, was also carried out by using monolithic Cu-ZSM-5 and Cu-AFX catalysts. The results suggest the poisoning effect of hydrocarbons in the exhaust emissions on NOx conversion is more significant for Cu-ZSM-5 than Cu-AFX. [ABSTRACT FROM AUTHOR]

• An open source algorithm was validated with theoretical and experimental results. • The analogy between mass and momentum transfer was successful. • RDE: the uniformity of mass-transfer is lost for turbulent conditions. • RCE: the interelectrode gap is the critical parameter on the mass-transfer conduct. Results of numerical calculations and their comparison with analytical expressions or experimental data under laminar and turbulent flow conditions are reported. It is predicted the transient and steady-state behaviour of mass-transfer coefficients and shear stresses in electrochemical reactors composed of rotating electrodes. Computational fluid dynamics (CFD) simulations were performed for both the rotating disc electrode (RDE) and the rotating cylinder electrode (RCE) considering the laminar or Reynolds-Averaged Navier-Stokes (RANS) equations. In this last case, it was assumed the Shear Stress Transport (SST) k-ω turbulence model sensitised by a correction term that accounts for streamline curvature and rotation. The hydrodynamics, coupled to the averaged diffusion-convection equation under transient conditions, was solved using the open source software OpenFOAM. A good agreement was attained between simulations and experimental or analytical results. In both rotating systems, a steady-state can be reached with an oscillatory behaviour that can be periodic in the case of laminar flow; depending on the Schmidt number, the interelectrode gap and the hydrodynamics. Also, the uniformity of the mass-transfer coefficient is lost under some circumstances. Finally, the full numerical code and a tutorial on how to use it, in order to perform simulations for the RDE or RCE, are supplied. [ABSTRACT FROM AUTHOR]

A standardised hydrocyclone is examined as an alternative reactor for the electrochemical processing of two-phase systems. Experimental measurements and computational predictions of residence time distributions demonstrate an appropriate hydrodynamics of the equipment. A main peak near the mean residence time was detected revealing that a fluid by-pass or dead regions are absent and the Peclet number, obtained by correlation of the experimental data, was higher than 9. Mass-transfer measurements made by using a segmented, or a grooved or a smooth cathode corroborate the good performance of the cylindrical body of the hydrocyclone. The presence of the gas phase has little influence on the residence time distribution as well as on the mass-transfer behaviour of this device. Sulphur dioxide reduction to colloidal sulphur was used as a test reaction to check the performance of the reactor. The best results were obtained at a cathodic potential of −0.5 V, against a saturated calomel electrode, where hydrogen evolution is not possible as a cathodic side reaction. Thus, a 56% current efficiency with a specific energy consumption of 20.4 kWh kg−1 and a space time yield of 10.4 kg m−3 h−1 were attained under a two-phase flow of 5% SO 2 in nitrogen. The sulphur particles obtained from the spigot present an average size of 6.7 μm being those carried by the overflow stream smaller, both of them of high purity. • The hydrocyclone has high mass-transfer conditions under single- or two-phase flow. • The reaction performance of the cylindrical part is better than in the conical section. • A modified hydrocyclone is suitable for electrochemical processing of two-phase systems. [ABSTRACT FROM AUTHOR]

Abstract Natural gas + water-in-diesel emulsion + AA systems with and without wax were used to investigate the influence of wax crystals and their heat- and mass-transfer effect on hydrate formation from macroscopic and microscopic aspect in a flow system. Hydrate nucleation and initial growth were found to be a partially occurred phenomenon. Wax was found to prolong the hydrate induction time through two significant effects: one was the macroscopic heat-transfer effect produced by wax deposition with insulating effect, and the other was the microscopic mass-transfer resistance originating from the wax crystals that were adsorbed at or adjacent to the oil-water interface. Hydrate induction time shortened and became less scattered with the increasing initial pressure. Based on the heat-transfer theory of a flow system and the hydrate nucleation theory, an improved model for hydrate induction time prediction was developed by coupling calculation of hydraulics and heat-transfer and by introducing mass-transfer effect of adsorption of wax crystals. The findings of this work are meaningful for providing essential information and supports for the ongoing deep-sea oil and gas production and the application of hydrate-management strategies in the presence of wax crystals in a flow system. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Near-critical extraction of lanolin is well explained with a novel mass transfer model. • The more soluble lanolin is extracted first, followed by the less soluble fraction. • The solid-fluid mass transfer coefficient decreases with extraction pressure. Abstract This study deals with the modeling of the extraction of solid lanoline from raw wool under near-critical conditions using 5% ethanol in CO 2 , using our previous experimental data. A mass-transfer model is developed to explain the extraction results at T = 30 °C, below the melting point of lanoline (36–42 °C). Two variables are studied, the extraction pressure and the solvent mass flowrate. Our model depends on three parameters: the solubilities of the two lanoline fractions and the lanoline mass transfer coefficient. The model is a set of first-order partial differential equations, that is solved by orthogonal collocation in combination of optimization of the parameters. The fluid-side mass-transfer coefficient decreases with extraction pressure and is about 5 × 10−6 m/s for Re < 1 (at 70–150 bar) and depends on fluid velocity. The solubilities of lanoline fractions, independent of flowrate, agree very well with those previously reported. [ABSTRACT FROM AUTHOR]

Mass transfer was studied at the external electrode of a cylindrical electrochemical reactor with decaying swirling flow using a single phase electrolyte and also a dispersion of a gas phase in the solution. The local mass-transfer coefficients were measured with a segmented cathode using the reduction of ferricyanide as test reaction. Two strategies were used to introduce the gas phase. In the first case the gas was fed by three holes symmetrically drilled at the bottom of the central anode tube and in the second one by means of a tee fitting at the reactor inlet. The best performance was obtained with the single phase electrolyte giving 0.78 as the exponent of the Reynolds number and the mass-transfer distribution along the reactor length is more uniform than that reported for a parallel plate electrochemical reactor under laminar flow conditions. The mass-transfer enhancement factor related to an annular duct with axial developing flow ranges from 8 to 11. This high value is the consequence of two factors: (i) the intensive forced convection produced by the swirling flow at the outer electrode and (ii) the sudden expansion of the flow at the entrance due to the small tangential inlet. The fed of a gas phase in the reactor has scarce influence on the mass-transfer performance. A comparison of mass-transfer results with previous studies is made. [ABSTRACT FROM AUTHOR]

Ultrasonic is well-known to be helpful for the improvement of chemical reactions due to its acoustic cavitation. This work reports for the first time the use of ultrasonic to enhance micromixing and mass-transfer in a rotating packed bed (RPB) reactor. The ultrasonic probes were installed as stators on the cover of the RPB reactor. Comparisons of micromixing efficiency, effective interfacial area, and volumetric liquid-side mass-transfer coefficient in the RPB reactor with and without ultrasonic were investigated systematically. A discussion for the micromixing and mass-transfer improvement in the RPB reactor was given. Feasibility studies indicated that the relative segregation index decreasing, the relative effective interfacial area increasing, and the relative volumetric liquid-side mass-transfer coefficient increasing are 13.8%, 3.7%, and 5.5%, respectively. [ABSTRACT FROM AUTHOR]

In order to develop an electrochemical technology with low-energy consumption for water treatment applications, we fabricated a novel reactive electrochemical membrane (REM) operated in cross-flow filtration mode. The REM with three-dimensional ordered macroporous PbO 2 (3DEM-PbO 2 ) film was synthesized via templated deposition that was based on a porous Ti substrate. Compared to conventional flat Ti/PbO 2 (F-Ti/PbO 2 ) electrode, the 3DEM-PbO 2 possessed larger specific surface area (38.89 m 2 g −1 ), higher oxygen evolution potential (OEP, 1.9 V), larger Voltammetric charge (238 mC cm −2 ) and smaller electron transfer resistance (1.43 Ω). Furthermore, advection-enhanced mass transfer was obtained when the 3DEM-PbO 2 REM is operated in an electrochemical filtration reactor (EFR), relative to a traditional batch reactor (BR). The electrochemical mineralization experiments with flutriafol (FTF) demonstrated that the 3DEM-PbO 2 REM operated in the EFR was active for FTF and TOC removal at a low current density of 5 mA cm −2 . The oxidation current efficiency of REM operated in a EFR was much higher than that of conventional electrochemical system, and the corresponding energy consumption was lower (0.0505 kWh g −1 FTF, at FTF removal of 75%). The hydroxyl radicals (·OH) production and its utilization rate of the REM was significantly improved, resulting from a combination of the strong catalytic activity of 3DEM-PbO 2 and the enhanced mass transfer by filtration mode. Furthermore, computational fluid dynamics (CFD) method was carried out to help explain the improvement of oxidation performance with 3DEM-PbO 2 REM in a EFR. Eventually, the electrocatalysis experiments of practical wastewater demonstrated the extreme promise of 3DEM-PbO 2 REM for tailwater advanced treatment applications. [ABSTRACT FROM AUTHOR]

This work presents a two-dimensional analytical solution of the governing differential equation for falling film vapour-absorption around a plain horizontal tube. The solution of the species transport equation gives the LiBr mass fraction distribution within the liquid absorptive film flowing along the tube surface and can be used to characterize the mass transfer performance of falling film absorbers or generators. By means of the inclusion of partial wetting effects at reduced solution mass flowrates, this study obtains an analytical expression of the mass transfer coefficient of these devices applicable over an extended range of operative conditions. The hypotheses of small penetration for physical absorption and constant heat flux condition are applied at the film interface to reach a closed-form solution. Fourier method is used to solve the problem and the eigenvalues obtained from the characteristic equation depend on Lewis number, Biot number and the dimensionless heat of absorption. Given the boundary condition at the wall, the two-dimensional mass fraction field of the laminar film can be expressed analytically as a function of Schmidt, Reynolds numbers, the tube dimensionless diameter and the ratio of the wetted area to the total exchange surface. Finally, mass transfer coefficient and absorbed mass flux are locally and globally investigated as functions of the influent dimensionless groups to clarify their effects on the physical process and screen the potentiality of the model. Results show notable qualitative and quantitative agreement with previous numerical solutions and experimental results from previous literature. This model constitutes a widely applicable and time-saving tool for actual system simulations, design and control. [ABSTRACT FROM AUTHOR]

Three volatile organic compounds (VOC) with no acidic or basic function (butanol, butyraldehyde, methylethylketone), encountered at low concentrations in odorous effluents, were absorbed in water in a compact wet scrubber. This gas-liquid contactor consisted of a wire mesh packing structure where the gas phase flows at high velocity (>12 m s −1 ). A very turbulent two-phase downward flow could be observed in the scrubber with dispersed fine droplets (around 10 μm). For compounds showing a good affinity for water, such as butanol, removal efficiencies up to 90% were measured for a short contactor length of 32 cm leading to a gas residence time of 20 ms. However, the removal efficiency of butyraldehyde, which is poorly soluble in water, ranged between 10 and 30%. Mass-transfer modeling was achieved and underlined that working with several small scrubbers in series, fed with an unloaded solution, is effective to improve the removal efficiency. The influences of the VOC/solvent affinity, the contactor length, and the mass-transfer and hydrodynamic parameters on the removal efficiency were evaluated through a sensitivity analysis. [ABSTRACT FROM AUTHOR]

Mass transfer of light non-aqueous phase liquids (LNAPLs) trapped in porous media is a complex phenomenon. Water table fluctuations have been identified as responsible for generating significant variations in the concentration of dissolved hydrocarbons. Based on field evidence, this work presents a conceptual model and a numerical solution for mass transfer from entrapped LNAPL to groundwater controlled by both LNAPL saturation and seasonal water table fluctuations within the LNAPL smear zone. The numerical approach is capable of reproducing aqueous BTEX concentration trends under three different scenarios – water table fluctuating within smear zone, above the smear zone and partially within smear zone, resulting in in-phase, out-of-phase and alternating in-phase and out-of-phase BTEX concentration trend with respect to water table oscillation, respectively. The results demonstrate the model's applicability under observed field conditions and its ability to predict source zone depletion. [ABSTRACT FROM AUTHOR]

[Display omitted] • Alternating flow-through regime allows hydrogen distribution to cathodic biofilm. • Alternating flow-through regime removes high local pH (6.8) at cathode. • CO 2 conversion to n -caproate within 45 days after start-up in single system. • Clostridium sensu stricto 12 and Peptococcaceae main chain elongaters. Microbial electrosynthesis is an uprising concept for the combined carbon dioxide reduction and electricity storage in the form of green chemical compounds. Although several proof of principle studies show great promise, mass-transfer limitations of substrates, protons and products remains one of the issues that needs to be addressed to bring the systems towards greater scale applications. A previously tested solution formed force flow-through catholyte recirculation, but this set-up encountered difficulties with gas accumulation during start-up at higher current densities (∼ −10 kA/m3), creating the need for a bypass to release gas. In this study, start-up at high current density was achieved without a bypass by using an alternating flow-through regime. This regime decreased the operating energy input from 221 to 136 kWh per kg of produced hydrogen and reached acetate production within 10 days after start-up at high current density and elongation to n -caproate after 45 days. Mass-transfer studies were included by microsensor measurements of local conditions (hydrogen concentration, pH) combined with thermodynamic calculations at the start and end of 60-days biotic experiments. The microorganisms on the cathode decreased pH gradients and consumed the formed hydrogen. The presence of Clostridium sensu stricto 12 and Peptococcaceae species were related to chain elongation activity, and the presence of Methanobrevibacter was linked to methanogenesis activity. By identifying the effects of different flow-through strategies on local concentrations and functional microbial groups, this work provides insights on the optimal conditions for microbial CO 2 conversion and highlight the application potential of microbial electrosynthesis. [ABSTRACT FROM AUTHOR]

• Mass-transfer in bubbly flows is simulated in OpenFOAM. • Absorption and desorption as well as co- and counter-current flows are considered. • Comparison is made with literature data including concentration measurements. • Constant bubble size and mass transfer coefficient are taken from the experiment. • A demonstration of a polydisperse simulation is given. Mass transfer in bubbly flows is important in many engineering applications. Simulation of such processes on technical scales is feasible by the Euler-Euler two-fluid model, which relies on suitable closure relations describing interfacial exchange processes. In comparison with the pure fluid dynamics of bubbly flows however, modeling and simulation of bubbly flows including mass transfer is significantly less developed. In particular, previous studies have focused entirely on absorption in upward vertical flows, whereas the present study considers a larger variety of conditions including desorption and counter-current (downward) flow. Suitable experimental data for comparison are available from the classic work of Deckwer et al. [Canadian Journal of Chemical Engineering 56 (1978) 43–55]. In line with previous studies on the co-current absorption cases from that work, a monodisperse approximation is made. In addition, a class method to treat bubble shrinkage and growth is implemented in the OpenFOAM code and tested by showing the crossover between two monodisperse cases. [ABSTRACT FROM AUTHOR]

The kinetic modeling of NH 3 -SCR with a Cu-ion-exchanged chabazite (Cu-CHA) catalyst in steady-state reactions was investigated by a combination of flow reactor experiments and kinetic modeling with an in-house computational code. Here H-CHA and Cu-CHA monolith cylindrical catalyst specimens were used to identify the reactions at both Brønsted (H+) acid sites and Cu sites. Based on the proposals in the literature for NH 3 -SCR mechanism, a scheme for SCR and side reactions incorporating 17 reactions is proposed, and some of the reactions were verified by the experimental results here for the adsorption/desorption of NH 3 , unsteady-state reactions of the adsorbed NH 3 with NO 2 over the Cu-CHA and H-CHA, and NH 3 oxidation over Cu-CHA. The Arrhenius parameters for Standard, Fast, and Slow SCR reactions, NH 3 oxidation, NO oxidation to NO 2 , NO 2 decomposition to NO, and NH 3 desorption were obtained by kinetic experiments. This report develops a quantitative simulation model for SCR and side reactions, and the model was validated by experimental data for adsorption/desorption of NH 3 and NO 2 , steady-state SCR reactions (Standard, Fast, and Slow SCR), and side reactions (NH 3 and NO oxidation). The simulation model developed in this study can predict the steady-state SCR data and adsorption/desorption of NH 3 and NO 2 under unsteady-state. [Display omitted] • Investigations of reactions over Brønsted and Lewis acid sites by Cu-CHA and H-CHA catalysts. • The identified 17 kinds of important reactions were suggested through experiments. • Ammonia nitrate (NH 4 NO 3) production in Fast and Slow SCR reactions. • The developments of a kinetic SCR model considering energy transport, mass transport, diffusion, and chemical reactions. [ABSTRACT FROM AUTHOR]

• available models for the mass transfer coefficient are assessed. • a rather complete set of measurements from the literature is used. • fluid dynamical properties are predicted quite well. • prediction of mass transfer still has some deficiencies. • pressure is found to have a significant effect which has not been highlighted before. Mass transfer in bubbly flows is a field of obvious technological importance. On industrially relevant scales it may be studied by simulations based on the Euler-Euler two-fluid model, which however requires closure models for the interfacial exchange processes. Despite recently increased efforts, modelling of the exchange of mass between the phases is still much less developed than the corresponding exchange of momentum. The present study compares several proposed models for the mass transfer coefficient using a previously established set of closure relations for the purely fluid dynamical part of the problem. A set of experimental data for the absorption of O 2 into water in a bubbly mixing layer from the literature is used to assess their relative merits. A model for the pertinent material properties of this system has been assembled from available measurements. A rather sensitive dependence of the amount of absorbed O 2 is found on the pressure, which varies with the hydrostatic head above the test section. [ABSTRACT FROM AUTHOR]

• New Swell-Cavity Ratio parameter was used to characterize transport channel changes. • A model was built about the Hansen solubility parameter and Swell-Cavity Ratio. • Membrane mass transfer mechanism greatly affects the trend of the Swell-Cavity Ratio. • The model can accurately calculate the membranes pore changes in organic solvents. • The model is instructive for the application agility of membrane in organic solvents. The relationship between swelling, the difference (Δδ) in theoretical Hansen solubility parameters (HSP) between the two substances, and the change of membrane mass-transfer channel has been controversial. In this work, a completely new parameter, Swell-Cavity Ratio (SCR), defined as the ratio of membrane molecular weight cut off (MWCO), was introduced to characterize the changes in mass transfer channels before and after membrane swelling. Models of the relationship between Δδ and SCR were successfully constructed for nanoporous glassy (SCR = 0.19 × Δδ0.40) and rubbery (SCR = 17.7 × Δδ-0.93) membranes, using the swelling as a bridge. Based on this contradiction in models, we speculate that SCR variation is strongly related to the separation mechanism of the membranes. The theoretical model accurately calculates the influence of the solvent on the membrane mass transfer channel, allowing for the selection of the best membrane material and pretreatment process to maximize treatment efficiency. [ABSTRACT FROM AUTHOR]

For practical applications the Euler-Euler two-fluid model relies on suitable closure relations describing interfacial exchange processes. Concerning pure fluid dynamics of dispersed gas-liquid multiphase flow, an ongoing effort has led to a validated set of closures that is applicable under a rather broad range of conditions. Similar results for the technologically even more important field of mass transfer remain to be achieved. Progress so far has been hampered by a lack of spatially resolved data including measurements of concentration, which are suitable for CFD model validation. In addition, correlations proposed to describe the mass transfer coefficient differ widely. Here, a preliminary study of axial concentration profiles in a bubble column is given, based on the available experimental data found in the literature. For this purpose the simplified assumption of a constant mass transfer coefficient throughout the column is made and experimentally determined values are used. New measurements will be needed to come to a final conclusion. [ABSTRACT FROM AUTHOR]

Models proposed to describe the liquid side mass transfer coefficient in absorption processes differ widely in such basic questions as on which of the local flow variables they are based. Comparison of different alternatives with experimental data taken from the literature suggests that there are two basic mechanisms, a laminar and a turbulent one, each of which dominates under suitable conditions. A dimensionless number that allows to identify the corresponding regimes is suggested together with a preliminary model encompassing both. New experiments will be needed to come to a final conclusion. [ABSTRACT FROM AUTHOR]

Open cell foams are regarded with interest for applications as catalytic substrates for combustion, reformers and after-treatment converters for the pollutant emissions control. In this context, CFD represents a reliable and convenient tool for investigating and understanding the physical phenomena occurring at the micro-scale, in order to design and optimize these substrates. A CFD model for the simulation of the catalytic reactions occurring over the surface of open-cell foams is implemented and validated. The approach is based on a coupled finite-volume/finite-area strategy capable to describe the fluid-dynamic and the chemical phenomena occurring in both the fluid phase and solid phases. The adsorption/desorption of the reactants on the active sites and the surface reaction is modeled on the basis of a Langmuir–Hinshelwood mechanism. The model is able to describe the reactants conversion under both kinetics and diffusion control, allowing to predict the light-off curve characterizing the catalyst-coated foam substrate. [ABSTRACT FROM AUTHOR]

A simple dynamic absorption procedure to assess the mass-transfer performances of a solvent toward a selected gaseous solute is presented. Absorption was operated semi-continuously at transient state until the equilibrium was reached without solvent recirculation. Four volatile organic compounds (VOC) more or less hydrophobic (toluene, acetone, dichloromethane, isopropanol) were absorbed in water and two heavy organic solvents (Bis(2-ethylhexyl) adipate DEHA and polydimethylsiloxane PDMS). A numerical resolution procedure was developed to simulate the gas–liquid mass-transfer and to deduce the VOC partition coefficients, expressed as the Henry’s law constants, as well as the overall liquid-phase mass-transfer coefficients. The overall liquid-phase mass-transfer coefficients were correlated to the diffusion coefficients using the Higbie penetration theory. The results confirm the high selectivity of water whereas the two organic solvents, especially DEHA, exhibit rather good affinity with all VOC even if the Henry’s law constants of the most soluble and the less soluble compounds for those solvents differ by 1 or 2 orders of magnitude. The liquid-film mass-transfer coefficients in the two organic solvents, even being more viscous, are larger than in water which confirms their good potential for hydrophobic VOC treatment. [ABSTRACT FROM AUTHOR]

In this work, the concept of “s” shape distillation column and its elliptical tray were proposed to break up the stagnation in research focusing on enhancing the development of distillation tower internals. On the basis of conventional distillation experience, the advantages and disadvantages of an “s” shape distillation column and its elliptical tray were analyzed respectively. To investigate the performance of the “s” shape distillation column, it is necessary to first understand the properties of its elliptical tray. Three 3D two phase flow models were developed respectively in the Eulerian–Eulerian framework to predict hydraulics, residence time distribution and mass-transfer performance of the elliptical sieve tray (EST) and the circular sieve tray (CST). In particular, with ingenious design, we for the first time successfully applied the up-step change method in CFD to investigate the residence time distribution on trays. The results show that EST has less channeling, recirculation and stagnant zones as well as longer average residence time than CST. Consequently, EST has better tray efficiency than CST at the same operating conditions. It indicates that the elliptical outline has a positive influence on the performance of trays. [ABSTRACT FROM AUTHOR]

Several approximate solutions are derived to predict the concentration polarization effect in a shell-and-tube Pd-membrane empty separator with permeate flow either in the tube or in the shell. The first two approximations (Nekhamkina and Sheintuch (2015) [22] ) are governed by ODEs describing the axial profiles of the average variables coupled with algebraic relations that describe the radial profiles of velocity components and species concentrations. The hydrogen membrane flux is approximated by a mass transfer coefficient k=D (∂ c H2 /∂ r ) w /(〈 c H2 〉− c H2 w ) expressed via the Sherwood number Sh = kd/D which is a geometry-dependent parameter ( D is hydrogen diffusivity, c H2 w = p H 2 , w r e t / RT is its membrane wall concentration and d a characteristic length). Here Sh is obtained by 2-D CFD simulations in a wide range of parameters and when plotted vs the separator length, it reaches an asymptotic value that matches the predicted values and is independent of operating conditions. The third approximation reduces the polarization effect to an algebraic equation by approximating the effectiveness factor η =[( p H 2 , w r e t ) 0.5 −( p H 2 p e r ) 0.5 ]/[〈( p H 2 r e t )〉 0.5 −( p H 2 p e r ) 0.5 ] which depends mainly on the ratio of the mass-transfer coefficient to the membrane permeance parameter Γ = Γ ( Sh ). This expression can be used for fast design of separators that avoids or accounts for polarization effects. The three approximations offer a trade-off between accuracy and ease of application. [ABSTRACT FROM AUTHOR]

Application of commercial electrochemical oxidation reactor for industry discharge water was limited by the inefficient mass transfer of molecule. For this case, a functional electrocatalytic reactor was designed to enhance the mass transfer of the electrochemical oxidation. The reactor is composed of a tubular porous Ti-RuO 2 electrode and a stainless steel tube. The electrode was fabricated by loading an electrocatalytic membrane of RuO 2 on a porous Ti tube. Characterization of the electrode was analyzed by FE-SEM, XRD, XPS and bubble point method. The results show that the electrode consisted of micropore structure which pore size and porosity were 0.98 μm and 27%, respectively. Further, the results of cyclic voltammetry method have proved that porous electrode has larger electrochemical surface area than plate electrode with the same geometrical area. In addition, the steady-state of chronoamperometry measurements by the reactor was as twice as that of plate electrode, indicating a significant enhancement of mass transfer. Electrochemical oxidation of tricyclazole was investigated with reactor and plate electrode under different initial concentration and current density. By the comparison with plate electrode, the reactor has higher removal rate and current efficiency. The high performance of electrocatalytic reactor based on the tubular porous Ti-RuO 2 electrode in the electrochemical oxidation is mainly attributed to mass transfer enhancement via the pump and larger electrochemical surface area due to porous structure. [ABSTRACT FROM AUTHOR]

A continuous-flow adsorption/desorption process for the recovery of phenolic compounds (PCs) from olive mill wastewaters (OMWs) was developed in a 0.53 m packed column, using a previously selected resin (Amberlite XAD16) and an actual OMW. The main goals of the study were (i) to evaluate the PC adsorption/desorption performances of XAD16 by means of adsorption isotherms and adsorption/desorption breakthrough tests, and (ii) to develop a reliable model of the process. A combination of centrifugation and microfiltration resulted necessary to attain a high suspended solid removal (98.5%) and thus avoid clogging of the packed bed. The quality of two packing procedures was evaluated by means of frontal analysis tests. XAD16 performed well in terms of both adsorption yield at 20% breakthrough (87–88%) and PC/COD selectivity (PC/COD adsorption constant = 7–9). The desorption solvent (acidified ethanol) was effectively regenerated by vacuum distillation. The adsorption breakthrough curves were successfully simulated with a 1-D convection/dispersion model with mass-transfer ( R 2 = 0.95–0.99; k L a = 0.8–2.5 · 10 −3 1/s), whereas an equilibrium adsorption model with dispersion failed to predict the experimental data. In the perspective of a process scale-up, the simulation of the best-performing operational condition was used to evaluate the process performances for different column lengths (0.5–10 m). A precise and automated HPLC method for total PC measurement was developed and compared to the traditional Folin–Ciocalteu methodology. Further research is needed to optimize the desorption step, to scale up the process and to evaluate the long-term resin performances. [ABSTRACT FROM AUTHOR]

Solvent impregnated resins are promising for the removal of polar organic compounds from aqueous streams, but have low mass-transfer rates. A thorough understanding of the phenomena occurring inside the pores of the solvent impregnated resin is therefore required. In this study a mathematical model was developed to describe the simultaneous diffusion and reaction. The diffusion was described using the Maxwell–Stefan approach towards multi-component diffusion and included the volume-expansion of the organic phase. The model was validated using experimental data from the literature on the extraction of phenol by Cyanex923 impregnated in macro-porous polypropylene. The model described the experimental data as function of temperature and initial concentration accurately with an R 2 >0.96 and a regressed reaction rate constant with a confidence interval of ±6%. Analysis of the model results revealed that multi-component effects as described by the Maxwell–Stefan model were of limited importance whereas the volume expansion was essential to accurately describe the experimental data. [ABSTRACT FROM AUTHOR]

Ion-exchange (IX) is the most feasible technology for perchlorate removal from drinking water. Reuse of resins present challenges, however. Selective resins are non-regenerable, and are incinerated after one time use, while non-selective resins, when regenerable, produce a waste stream that contains high concentration of perchlorate that must be disposed of. A process to bioregenerate spent resin containing perchlorate with perchlorate-reducing bacteria (PRB) has been recently developed. In this research, potential mechanisms for bioregeneration of resin-attached perchlorate (RAP) were investigated. Batch bioregeneration experiments were performed using gel-type and macroporous-type resins. Various initial chloride concentrations and various resin bead sizes were used. The results of the bioregeneration experiments suggested that chloride, i.e. the product of perchlorate biodegradation, is more likely the desorbing agent of RAP; and increasing the concentration of chloride enhances the bioregeneration process. Both film and pore diffusion were found to be relevant with respect to the rate of perchlorate mass-transfer to the bulk liquid. Bioregeneration was found to be more effective for macroporous than for gel-type resins, especially in the case of macroporous resins with relatively small bead size in the presence of higher chloride concentration. [ABSTRACT FROM AUTHOR]

Phthalic acid esters, along with their degradation byproduct phthalic acid (PhA), can enter surface water systems through water leaching and remain in the environment for protracted periods causing serious problems to aquatic and human lives. Thus, the aim of the present study was to assess the possible application of photo-assisted electrochemical technology (PAE) in the removal of PhA and total organic carbon (TOC) from aqueous solutions using a DSA ® electrode. Examination of system parameters, including type and concentration of supporting electrolyte, applied current density, pH and temperature, revealed that highest removals of PhA and TOC could be attained at 30 °C with an applied current density of 20 mA cm −2 using acidic electrolytes containing 50 mmol L −1 NaCl. Under these conditions, the photolysis of electrogenerated HOCl produced highly reactive oxidizing agents, including HO , which promoted the complete removal of PhA and 60% removal of TOC within 3 h; however, the system requires further optimization since the mineralization current efficiency was low (20%) and the energy consumption was high (100 kW h g −1 ). [ABSTRACT FROM AUTHOR]

Approximate models are proposed to simulate the transmembrane hydrogen flux in an empty membrane separator. The hydrodynamic field is constructed under the assumption of constant density with a single unknown parameter – the normal wall velocity ( v w ). The 2-D concentration profiles are derived using a known velocity distribution. The problem is closed by definition of v w via the transmembrane flux, which admits Sievert’s law. Such an approach allows to derive two approximate models that are governed by the set of ODE equations with respect to the average variables coupled with algebraic relations to describe the radial profiles. The first model accounts for analytical concentration profiles c i ( z , r ), the second one presents model reduction using the mass transfer coefficient ( k c ) expressed as Sherwood (Sh) number. An analytical expression for local Sh is derived (Sh = 6 in a tube). We identified a parameter Γ which represents the ratio of diffusive to permeating flux and suggest that for Γ > 6 the concentration polarization effect can be neglected. We address two axisymmetric geometries (i) a tube with transport at its wall, as is the case in a membrane of an integrated reactor; (ii) an annular cylinder with transport at an inner tube, as is the case in a separator. The proposed approximations are validated by comparison with experimental and CFD simulation data. [ABSTRACT FROM AUTHOR]

This paper refers on gas mass-transfer characteristics of several metal sheet Mellapak structured packings (M250Y, M350Y, M452Y, M500Y) under absorption conditions. These characteristics have been measured using standard absorption systems of SO2 chemisorption into the NaOH aqueous solution (kGa) and CO2 chemisorption into the NaOH aqueous solution (effective area a). Measurements were performed with four elements of the packing with diameter of 0.29 m and total height of 0.84 m. Gas-phase mass-transfer coefficients for all studied packings have been correlated by the dimensionless equation ShG = 0.409 · ReG0.622 · ReL0.0592. The experimental values of kG are in the most cases significantly under-predicted by fundamental mass-transfer models, wetted-wall column correlations and by the model packages developed for structured packing. The exponent 0.622 of gas Reynolds criteria is lower than expected by the models starting from the imagination of the flow through the channel and corresponding experiments with wetted-wall columns. The revealed value of the exponent agrees better with those found for flow around submerged objects like spheres or through the bed consisting of random packing, suggesting that the wetted wall column is not a suitable experimental simplification for the study of structured packings. [ABSTRACT FROM AUTHOR]

This study analyzed and compared unsaturated flow response and tracer breakthrough curves from a 10-m high constructed pile experiment (CPE) in the field (Antamina, Peru) and two 0.8 m high laboratory-based columns. Similar materials were used at both experimental scales, with the exception of a narrower grain size distribution range for the smaller column tests. Observed results indicate that flow and solute transport regimes between experimental scales were comparable and dominated by flow and solute migration through granular matrix materials. These results are supported by analogous breakthrough curves (normalized to cross-sectional area and flow path length) that suggest observation- or smaller-scale heterogeneities within the porous media have been homogenized or smoothed at the transport-scale, long breakthrough tails, and similar recovered tracer mass fractions (i.e., 0.72–0.80) at the end of the experiment. CPE breakthrough curves do indicate a portion of the fluid flow follows rapid flow paths (open void or film flow); however, this portion accounts for a minor (i.e., ~ 0.1%) component of the overall flow and transport regime. Flow-corrected temporal moment analysis was used to estimate flow and transport parameter values; however large temporal variations in flow indicate that this method is better suited for conceptualizing transport regimes. In addition, a dual-porosity mobile–immobile (MIM), rate-limited mass-transfer approach was able to simulate tracer breakthrough and the dominant transport regimes from both scales. Dispersivity values used in model simulations reflect a scale-dependency, whereby column values were approximately 2× smaller than those values applied in CPE simulations. The mass-transfer coefficient, for solute transport between mobile and immobile regions, was considered as a model calibration factor. Column experiments are characterized by a larger “mobile to immobile” porosity ratio and a shorter experimental duration and flow path, which supports larger mass-transfer coefficient values (relative to the CPE). These results demonstrate that laboratory-based experiments may be able to mimic flow regimes observed in the field; however, the requirement of scale-dependent dispersivities and mass-transfer coefficients indicates that these tests may be more limited in understanding larger-scale solute transport between regions of different mobility. Nevertheless, the results of this study suggest that the reasonably simplistic modeling approaches utilized in this study may be applied at other field sites to estimate parameters and conceptualize dominant transport processes through highly heterogeneous, unsaturated material. [ABSTRACT FROM AUTHOR]

Highlights: [•] AFM study of laser-induced surface deformation and craters (holes) formation in LC photochromic polymers was performed. [•] Focused laser beam irradiation results in the craters formation formed due to a mass-transfer outside center of beam. [•] The craters formation takes place only for thick (5–10μm) films, whereas these phenomena do not take place for the thin spin-coated films. [•] For the nonaligned LC-films no preferable direction of mass transport nearby photoinduced holes was found. [•] In the uniaxially aligned nematic polymer the mass-transport occurs only in direction along LC-director. [ABSTRACT FROM AUTHOR]

Abstract: The selective removal of pyridine derivatives by solvent impregnated resins has been studied. A solvent impregnated resin consists of a macro-porous particle that is impregnated with a solvent. This technology allows the use liquid–liquid extraction in fixed-bed operation, and prevents problems like entrainment and irreversible emulsification. 4-Cyanopyridine was chosen as model pyridine derivative, and 4-nonylphenol was used as solvent. The aim of this study was to select the most suitable resin for this application. While in the literature there are mainly two types of resins used, MPP and Amberlite XAD type, a comparative study has not yet been conducted. In this study, a series of resins were impregnated with the solvent and applied in sorption experiments to study on the effect of the resin properties on the capacity, selectivity and mass-transfer rates of the solvent impregnated resins. It was found that the capacity could be estimated accurately with the previously developed liquid–liquid extraction equilibrium model. Additionally, the selectivity was determined by the solvent properties, and hardly affected by the resin matrix. The mass-transfer rates were primarily determined the by particle diameter, whereas the effect of the porosity is small. On the basis of the results it was established that Amberlite XAD4 had the best combination of capacity, mass-transfer rate, mechanical strength, selectivity and pressure drop over a fixed-bed column and was therefore chosen for a more detailed study. The results showed that the breakthrough curve is broad due to mass-transfer limitations. The loading cycle of the column could be described with great accuracy using the mathematical model developed in this study. Regeneration of the column could be performed efficiently with a pH-swing using hydrochloric acid at a pH of 1. The fixed bed column was percolated with 7000bed volumes of aqueous solutions varying in composition. No reduction in the capacity was observed which demonstrated that the SIR consisting of Amberlite XAD4 and 4-nonylphenol is highly stable. [Copyright &y& Elsevier]

Abstract: This work examined the effect of the solid matrix on supercritical carbon dioxide (SC CO2) extraction of essentials oils from boldo leaves (Peumus boldus M.) subjected to rapid decompression of a CO2-impregnated sample, conventional milling, and low-temperature milling. Low-temperature conditioning prior to milling decreased heat-driven losses of volatile compounds during milling, as attested by a higher extract yield for low-temperature (10.8g extract/kg extract-free substrate) than conventionally (9.63g/kg) milled sample. Extract yield was even larger for the rapidly decompressed sample (11.4g/kg). Results of SC CO2 extraction experiments carried out at 40°C and 10MPa were adjusted to a diffusional model using the effective diffusivity of the extract in the solid matrix (D e) and a single partition of essential oils between solid substrate and SC CO2 as best-fitting parameters. A microstructural factor (F M), which was estimated as the ratio between the binary diffusion coefficient of the essential oil in SC-CO2 under extraction conditions and D e, was used to characterize the effect of sample pretreatment on extraction rates. Values of F M for rapidly decompressed (202) and low-temperature milled (1740) samples were smaller than value for conventionally milled samples (2200), which revealed that the two first treatments disrupted secretory cavities in boldo leaves more effectively than the third. This was confirmed by light microscopy observations. The work included also measurements using oregano bracts (Origanum vulgare L.) as the substrate to confirm literature reports on the SC CO2 extraction of pretreated bracts and to serve as a reference to our main results with boldo leaves. Trends with oregano coincided with those of boldo. [Copyright &y& Elsevier]

Abstract: The main objective of this article is to evaluate quantitatively the kinetic constants of a photocatalytic reaction in micro-channel reactors despite the presence of a radial concentration profile (mass-transfer limitation) and axial dispersion. Photocatalytic micro-channel reactors with immobilized titanium dioxide as photocatalyst have been fabricated using stereolithography process. The photocatalytic degradation of salicylic acid is investigated as a function of rectangular micro-channel size, contaminant concentration, flow rate and incident UV light intensity. All the micro-channel reactors exhibit the same tendency. Higher degradation is observed for high incident light intensities, low pollutant concentrations and flow rates. A simple equation for the determination of the kinetic constants during the photocatalytic degradation is reported. The equation includes the hydrodynamic properties and a surface reaction model for the photocatalytic reaction (monomolecular Langmuir–Hinshelwood kinetics). In the experimental system, we demonstrate that some external mass-transfer limitation and axial dispersion occur. They are included in the modeling with calculated values of the mass-transfer coefficient of salicylic acid from the solution to the catalyst surface and the axial dispersion coefficient. A single couple of values of the reaction rate constant k and the adsorption equilibrium constant K represent properly the experimental degradation ratios for all reactor dimensions, flow rates and pollutant concentrations. The major parameter that controls the values of the reaction rate constant is the incident light intensity. The dependence of the reaction rate on the incident light intensity is first order. [Copyright &y& Elsevier]

Abstract: Mass transfer was studied at a rotating cylinder electrode with different turbulence promoters using the reduction of ferricyanide as a test reaction. Four types of turbulence promoters were examined: expanded plastic meshes, Teflon structures, a plastic woven mesh and a plastic perforated net, which were rotated together with the electrode. The best performance was obtained for the Teflon structures at low rotation speeds and for the plastic woven mesh at high rotation speeds. The effect of both the length and the number of sheets of the turbulence promoters as well as the use of static promoters were also analysed. Comparisons of mass-transfer performance of turbulence promoters are made with other three-dimensional structures. The mass-transfer enhancement factor related to a smooth rotating cylinder electrode is twice as large. [Copyright &y& Elsevier]

Abstract: Influence of ultrasound (US) on various unit operations in leather processing has been studied with the aim to improve the process efficiency, quality, reduce process time and achieve near-zero discharge levels in effluent streams as a cleaner option. Effect of US on substrate (skin/leather) matrix as well as substances used in different unit operations have been studied and found to be useful in the processing. Absorption of US energy by leather in process vessel at different distances from US source has been measured and found to be significant. Effect of particle-size of different substances due to sonication indicates positive influence on the diffusion through the matrix. Our experimental results suggest that US effect is better realized for the cases with pronounced diffusion hindrance. Influence of US on bioprocessing of leather has been studied and found beneficial. Attempts have also been made to improve the US aided processing using external aids. Operating US in pulse mode operation could be useful in order to reduce the electrical energy consumption. Use of US has also been studied in the preparation of leather auxiliaries involving mass-transfer resistance. Preliminary cost analysis carried out for ultrasound-assisted leather-dyeing process indicates scale-up possibility. Therefore, US application provide improvement in process efficiency as well as making cleaner production methods feasible. Hence, overall results suggest that use of US in leather industry is imminent and potential viable option in near future. [Copyright &y& Elsevier]

Abstract: We have investigated the transesterification of rapeseed (RO) and waste sunflower (SO) oils with methanol in the presence of potassium hydroxide as a catalyst. The transesterification of tri-acylglycerols was first conducted in a batch reactor. The effect of the temperature on the reaction rates was studied at a constant molar ratio of the alcohol to tri-acylglycerols (6:1) and for a constant concentration of the catalyst (1.0wt%). Size-exclusion chromatography and 1H NMR spectroscopy were used to quantitatively monitor the transesterification reaction. The mass-transfer coefficients of the tri-acylglycerols during the initial transesterification stage were found to be 0.2–1.2×10−5 mmin−1, depending on the type of oil and the temperature. Calculated activation energies implied that at higher temperatures the formation of mono-acylglycerols and glycerole was favored for the SO (93kJ/mol for the forward and 48kJ/mol for the backward reaction) and the RO (47kJ/mol for the forward and 36kJ/mol for the backward reaction), respectively. For the continuous industrial reactor/separator setup, the optimum methanol recycle ratio was established as 0.0550. [Copyright &y& Elsevier]

Abstract: Rotating packed bed (RPB) has been widely used in absorption, desorption, distillation, oxidation, crystallization, precipitation, polymerization, and production of nanoparticles. RPB utilizes centrifugal acceleration to intensify the mixing and mass-transfer processes. Under high-gravity, molecule diffusions are much faster than under normal gravity. With the centrifugal force generated by rotation, RPBs have considerable high mass-transfer and micromixing performance. However, because of the complexity of fluid flow inside the RPB, the flow experiments do not easily lead to the deeper understanding on the fluid dynamics in an RPB. In this paper, computational fluid dynamics model and two-, three-dimensional physical models have been developed to describe the RPB. Numerical simulation of the fluid flow and pressure drop in dry bed in an RPB using commercial software, Fluent, as a computational platform has been carried out. Different fluid flow rates, rotator speeds and gas flow rates have been systematically investigated. The preliminary simulation results show that the models used to describe the RPB can give rise to better understanding of the flow in an RPB. [Copyright &y& Elsevier]

Abstract: A novel comprehensive numerical study is presented for a better understanding of mass transfer in channel flows with catalytically active walls at moderate temperatures and surface reaction rates. Altogether, 18 different numerical models are compared, which represent mass transfer in single channels of a honeycomb-type automotive catalytic converter operated under direct oxidation conditions. Three different channel geometries have been investigated: circular cross-section, square cross-section, and square cross-section with rounded corners (fillets). 1D plug-flow, 2D boundary-layer and Navier–Stokes, and 3D Navier–Stokes equations are applied to model the reactor geometry. The diffusion limitation within the porous washcoat has been modeled by a simplified zero-dimensional effectiveness factor model as well as multidimensional reaction–diffusion models. Furthermore, simulations are also carried out for cases with instantaneous diffusion within the washcoat. All numerical models account for the coupled interactions of mass-transfer and heterogeneous chemistry within the channels. The chemical conversion of the pollutants on the platinum catalyst is described by an elementary-step-like heterogeneous reaction mechanism consisting of 74 reactions among 11 gas-phase species and 22 adsorbed surface species. The results of numerical simulations are compared with experimental data. [Copyright &y& Elsevier]

Abstract: The thermal decomposition of urea has been studied under flow reactor conditions using a differential scanning calorimeter (DSC) and Fourier transformed infrared spectroscopy (FT-IR). Samples of urea were administered using either a cordierite monolith impregnated with a urea/water solution or a silica cup with a dry urea sample. The samples were heated between 25 and 700°C with heating rates of 10 and 20K/min and the thermal response of the sample and off gas concentrations of ammonia and isocyanic acid were recorded. Biuret and cyanuric acid were decomposed in a separate set of experiments to verify some of the features observed in gas phase data during urea decomposition. Results show that depending on the way the sample is administered, i.e. cup or monolith different behavior in the evolved gases are observed. This is due to different reactions taking place in the vessel induced by the different conditions under which the pyrolysis of urea is preformed. [Copyright &y& Elsevier]

Abstract: Induced-fit responsive dopamine (DA) imprinted polymer, poly (melamine-co-chloranil), was used as a suitable coating material for the modification of a hanging mercury drop electrode. The zwitterionic conformation of the imprinted polymer responded differential pulse, cathodic stripping voltammetric current, without any false-positive or false-negative contributions of non-specific sorptions, in aqueous environment of complex matrices. The limit of detection (3σ) of dopamine was found to be as low as 0.148ngmL−1, by the proposed sensor that could be considered a sensitive marker of dopamine depletion in Parkinson''s disease (PD). [Copyright &y& Elsevier]

• Ultrasonic irradiation can improve the gas-liquid mass transfer process. • Numerical simulation on ultrasonic-assisted gas-liquid mass transfer is limited. • Extensive computational resource is required to model high frequency ultrasound waves. • Acoustic theory modeling needs to be improved for modeling of acoustic fountain. Ultrasonic Irradiation (UI) is one of the technologies used to enhance the gas-liquid mass transfer (GLMT) process. Sonophysical effects such as acoustic streaming, jet flow, acoustic fountain, and atomization are the main factors that enhance the mass transfer coefficient. Numerical simulation can provide insight into the complex fluid behaviors under the influence of ultrasound waves such as fluid flow, mixing, cavitation, and mechanism of GLMT. Study on numerical simulation related to high frequency ultrasound waves, particularly on the formation of acoustic fountain and atomization is found to be limited. Recently developed numerical studies of the ultrasonic-assisted GLMT process are reviewed especially on hydrodynamics and mass transfer modeling for varied frequencies of the ultrasound wave. Challenges and future directions on current modeling approaches are analyzed to highlight the potential of numerical modeling of ultrasonic-assisted GLMT phenomena for process design, scale-up, and optimization. [ABSTRACT FROM AUTHOR]

Abstract: The optimisation of nitrogen sparging during fermentative hydrogen production was investigated. A N2 sparging rate of 12mL/min/L-liquid was observed to maximise the H2 yield at approximately 2mol H2/mol glucose converted, compared to an H2 yield of approximately 1mol H2/mol glucose converted without any sparging. There was no significant increase in H2 yield at sparging rates of 12–80mL/min/L-liquid. The optimum sparging rate was lower than N2 sparging rates examined in the past (>20mL/min/L-liquid). To facilitate improved scale-up, the overall volumetric mass-transfer coefficients (KLa) for H2 and CO2 were measured and the relationship between the dimensionless Sherwood and Froude numbers was determined. The optimal sparging rate occurred at a KLa value of 5.0h−1 for H2, corresponding to a Sherwood number of 4800. By holding the Sherwood number constant upon scale-up, the full-scale KLa can be determined and the appropriate sparging rate can be determined from the corresponding Froude number. The benefits of operating at the optimum sparging rate, including minimising product hydrogen gas dilution and energy use, can thus be achieved in larger-scale systems. [Copyright &y& Elsevier]

Abstract: Column outflow experiments operated at steady state flow conditions do not allow the identification of rate limited release processes. This requires an alternative experimental methodology. In this study, the aim was to apply such a methodology in order to identify and quantify effective release rates of heavy metals from granular wastes. Column experiments were conducted with demolition waste and municipal waste incineration (MSWI) bottom ash using different flow velocities and multiple flow interruptions. The effluent was analyzed for heavy metals, DOC, electrical conductivity and pH. The breakthrough-curves were inversely modeled with a numerical code based on the advection–dispersion equation with first order mass-transfer and nonlinear interaction terms. Chromium, Copper, Nickel and Arsenic are usually released under non-equilibrium conditions. DOC might play a role as carrier for those trace metals. By inverse simulations, generally good model fits are derived. Although some parameters are correlated and some model deficiencies can be revealed, we are able to deduce physically reasonable release-mass-transfer time scales. Applying forward simulations, the parameter space with equifinal parameter sets was delineated. The results demonstrate that the presented experimental design is capable of identifying and quantifying non-equilibrium conditions. They show also that the possibility of rate limited release must not be neglected in release and transport studies involving inorganic contaminants. [Copyright &y& Elsevier]

Abstract: The Formal Graph theory, a new language able to model graphically instead of algebraically most of basic equations used in physics and chemistry, is applied to mass-transfer occurring in electrochemical reactions. The integral admittance used in electrodynamics is generalized to all domains where energy is defined. Associated with the concept of energy coupling, this leads to very simple relationships between variables and operators describing processes in a system containing several energy varieties. The paradox of two different forms for the electric capacitance, linear in electrostatics and exponential in electrified materials, is treated and understood. The concept of energetic path brings physical meaning into mathematical models by attributing to each link a role in the conservation or dissipation of the energy. Normal transient diffusion, featured by an exponent 1/2, conserves half of energy, while anomalous diffusion, featured by an exponent p different from 1/2, conserves only 100 p%. The principle of every electrochemical measurement is represented in a simple and clear way by associating two Formal Graphs. The use of a mass-transfer operator generalizing all kinds of mass-transfer (diffusion, convection, thin layer, etc.) and for all geometric situations, allows the characterization of unknown process without previous knowledge of an algebraic model. [Copyright &y& Elsevier]

Abstract: Kinetic modeling, in combination with flow reactor experiments, was used in this study for simulating NH3 selective catalytic reduction (SCR) of NO x over Cu-ZSM-5. First the mass-transfer in the wash-coat was examined experimentally, by using two monoliths: one with 11wt.% wash-coat and the other sample with 23wt.% wash-coat. When the ratio between the total flow rate and the wash-coat amount was kept constant similar results for NO x conversion and NH3 slip were obtained, indicating no significant mass-transfer limitations in the wash-coat layer. A broad range of experimental conditions was used when developing the model: ammonia temperature programmed desorption (TPD), NH3 oxidation, NO oxidation, and NH3 SCR experiments with different NO-to-NO2 ratios. 5% water was used in all experiments, since water affects the amount of ammonia stored and also the activity of the catalyst. The kinetic model contains seven reaction steps including these for: ammonia adsorption and desorption, NH3 oxidation, NO oxidation, standard SCR (NO+O2 +NH3), rapid SCR (NO+NO2 +NH3), NO2 SCR (NO2 +NH3) and N2O formation. The model describes all experiments well. The kinetic parameters and 95% linearized confidence regions are given in the paper. The model was validated with six experiments not included in the kinetic parameter estimation. The ammonia concentration was varied from 200 up to 800ppm using NO only as a NO x source in the first experiment and 50% NO and 50% NO2 in the second experiment. The model was also validated with transient experiments at 175 and 350°C where the NO and NH3 concentrations were varied stepwise with a duration of 2min for each step. In addition, two short transient experiments were simulated where the NO2 and NO levels as well as NO2-to-NO x ratio were varied. The model could describe all validation experiments very well. [Copyright &y& Elsevier]

Abstract: The effect of anode gas composition on the overpotential in a 100cm2 class molten carbonate fuel cell is investigated. A total of five different gas compositions are used. They are applied to cross-check the effect of flow rate and composition, e.g., a given composition with different gas flow rates and a total flow rate with different gas compositions. The overpotential at the anode is analyzed via steady-state polarization, inert gas step addition and reactant gas addition methods. The analyses reveal that the anodic overpotential depends on the flow rate of the reactant species rather than the composition. Two identical gas compositions show less overpotential when a larger flow rate is applied. Compositions with large flow rates of CO2 and H2O also yield less overpotential due to the gas species. Overpotential analyses show that the three measurements have complementary relationships. [Copyright &y& Elsevier]