Film Mass Transfer Coefficient Research Articles

Novel Bubble Column Design Constructed for Catalytic Ozonation – Effectiveness Assessment by Hydrodynamics and Kinetic Regime Determination

ABSTRACT This article introduces an innovative design for a bubble column tailored for catalytic ozonation. A semi-batch reactor was employed with strategically positioned baffles to accommodate catalysts throughout the column. These baffles, constructed with a specially designed mesh-type material, not only served as catalyst supports but also provided an additional active surface for efficient mass transfer on both macro and micro scales. This groundbreaking approach has advanced heterogeneous catalysis by utilizing a multi-structured scaffold enriched with chemically active species. The dual role of the baffles was envisioned to enhance the physical absorption of ozone gas into the liquid and catalytic action in the production of reactive oxygen species (ROS) through ozone decomposition. However, it is crucial to note that any alteration in the column’s geometry can influence the mass transfer resistance. The primary objective of this study was to assess the efficiency of the newly constructed bubble column by determining hydrodynamic parameters. For the column without mesh, the volumetric mass transfer coefficient (kLa) ranged between 0.007 and 0.009 1/s. Upon the incorporation of the mesh, kLa increased to values between 0.007 and 0.01 1/s. Simultaneously, the overall interphase surface rose from 42.16 ± 6.2 1/m to 53.29 ± 7.9 1/m, and the film mass transfer coefficient (kL) improved from (1.68 ± 0.1) × 10−4 to (2.13 ± 0.2) × 10−4 m/s after the mesh installation. This novel column design was specifically engineered for the treatment of textile wastewater. Dye degradation experiments demonstrated a higher rate of color removal when the mesh was inserted, surpassing traditional ozonation methods. Furthermore, the Hatta number increased from 3 to 5 with mesh usage, and the enhancement factor (E) shifted from 2.6 to 4. These enhanced Hatta values and improvement factors suggest that the new column construction successfully transitioned the operating regime from moderate to high speed.

Phase separation behavior and CO2 absorption kinetic analysis of DETA/DEA/DMAC biphasic absorbent

Lower regeneration energy and superior cyclic capacity have enabled biphasic absorbents great potential in the area of flue gas CO2capture. The liquid film mass transfer coefficient(kL) is a vital parameter in the development of absorbents with efficient CO2 absorption mass transfer performance, while the phase separation behavior of biphasic solutions could be an essential factor for the absorption mass transfer and the stability of absorber. However, systemic kinetic research towards biphasic absorbents, especially the impact of phase separation behavior, is limited. In this study, a typical amide-based biphasic absorbent diethylenetriamine(DETA)/diethanolamine(DEA)/N, N-dimethylacetamide(DMAC) which has achieved great reduction in regeneration energy, was selected as the subject of kinetic investigation in a wetted wall column. The CO2 overall mass transfer coefficient(KG) of DETA/DEA/DMAC exceeded other biphasic solvents, blended amine solution, and 40% K2CO3 solution, with 3 times that of 40% K2CO3 solution. Moreover, various operational conditions including absorption temperature, gas flow rate, and water content of solution were taken into account to build a multiple-condition kinetic mechanism to offer guidance for biphasic absorbents. Furthermore, phase separation behavior was revealed as the main blame for the deterioration in the liquid film chemical mass transfer process of biphasic solvents in the CO2 absorption process, resulting in the kL of DETA/DEA/DMAC before phase separation decreased by 75.3% at the phase separation stage. Therefore, it is crucial to ensure that the CO2 loading of the solution entering absorber is lower than the phase separation point in applications. After phase separation, DETA/DEA/DMAC split into the organic and aqueous phases, the kL of the aqueous phase gradually exceeded that of the organic phase as CO2 loading increased for its higher chemical enhancement factor(E).

Experimental study for the effect of changing flow on absorption in wetted wall column

Gas absorption is the unit operation in which one or more soluble components of gas mixture are dissolved in a liquid. The absorption may be a purely physical phenomenon or may involve chemical reaction with one or more constituents in the liquid solution. In order to obtain the highest rate of absorption, gas and liquid streams flow in opposite directions in counter-current flow. The unit in this work has been designed to help grasp the basic principles of the chemical and physical aspects involved in absorption. This study unit is made of borosilicate transparent glass in order to show the water spread in the column and get the visual distribution of fluids behavior which helps to fully understand the phenomenon. In this work, the wetted wall column is used to determine gas/liquid mass transfer coefficients, which is essential to design absorption towers. This study investigates the absorption of oxygen from air into deoxygenated water (prepared by nitrogen sparing) in liquid film controlled absorption experiment. The liquid film mass transfer coefficients calculated at various mass flow rates of water and air. This work also studies the effect of water flow(expressed by Sherwood number) and air flow (expressed by Reynolds number)on oxygen concentration in the oxygenation and de-oxygenation process so affect on absorption process. From results, found that relation between Reynolds and Sherwood in wetted wall column been proportional this mean when we increase flow rate of water from 4 to 12 L/hr or air from 60 to 180 L/hr in wetted wall; concentration of oxygen in water out increase which mean absorption is better. Also, the final equation shows linear relation between Reynolds and Sherwood in wetted wall column. All these result help in understanding absorption process and factors influence in efficiency of towers used in real plant and helpful in design absorption tower.

Desulfurization of Zawia Refinery Diesel Using Adsorption Fixed Bed Process

The study focuses on the dynamic modeling of a fixed-bed adsorber for the adsorption of sulfur compounds in diesel fuel. The model considers non-ideal plug flow behavior and velocity variation along the column, providing a more realistic representation of the adsorption process. Additionally, internal mass-transfer resistances due to pore diffusion mechanisms are incorporated into the model. The study investigates adsorption performance by examining different flow rates (5 cc/min, 10 cc/min, 15 cc/min, and 20 cc/min) and inlet concentrations ranging from 586 to 100 ppm. The bed height is constant at 30 cm. The behavior of various parameters, such as bed utilization, breakpoint time, film mass transfer coefficient, and height of the adsorption zone, is analyzed. The results indicate that a sharp front of the breakthrough curve is observed, followed by the broadening of the tail of the breakthrough curve. The breakthrough curve represents the adsorbate concentration in the effluent stream over time. The investigation reveals that a high flow rate of 20 cc/min and a high inlet concentration yield better overall bed capacity utilization for the adsorption system. This means that the bed is more effectively utilized at higher flow rates and higher inlet concentrations, leading to improved adsorption performance. In conclusion, high flow rates and high inlet concentrations are favorable for enhancing the adsorption system's performance in terms of bed utilization. These results provide valuable insights for optimizing the design and operation of fixed-bed adsorbers that remove sulfur compounds from diesel fuel.

Effects of Temperature and DC Electric Fields on Perfluorooctanoic Acid Sorption Kinetics to Activated Carbon.

Sorption to activated carbon is a common approach to reducing environmental risks of waterborne perfluorooctanoic acid (PFOA), while effective and flexible approaches to PFOA sorption are needed. Variations in temperature or the use of electrokinetic phenomena (electroosmosis and electromigration) in the presence of external DC electric fields have been shown to alter the contaminant sorption of contaminants. Their role in PFOA sorption, however, remains unclear. Here, we investigated the joint effects of DC electric fields and the temperature on the sorption of PFOA on activated carbon. Temperature-dependent batch and column sorption experiments were performed in the presence and absence of DC fields, and the results were evaluated by using different kinetic sorption models. We found an emerging interplay of DC and temperature on PFOA sorption, which was linked via the liquid viscosity (η) of the electrolyte. For instance, the combined presence of a DC field and low temperature increased the PFOA loading up to 38% in 48 h relative to DC-free controls. We further developed a model that allowed us to predict temperature- and DC field strength-dependent electrokinetic benefits on the drivers of PFOA sorption kinetics (i.e., intraparticle diffusivity and the film mass transfer coefficient). Our insights may give rise to future DC- and temperature-driven applications for PFOA sorption, for instance, in response to fluctuating PFOA concentrations in contaminated water streams.

Determining flux-limiting mechanism of hydrogen permeation through palladium membrane by n value

Pd film has been endowed with the hydrogen selective permeation capability and widely used for hydrogen separation via a series of complex processes. Clarifying the exact relationship between permeating mechanism and hydrogen pressure exponent (n) is of great significance to optimize the purification performance, adequate exploration toward which is nevertheless insufficient. In this work, Pd membrane-based hydrogen permeation was divided into seven steps according to the “dissociation-diffusion” principle. The effect of each step on permeation flux with and without considering external mass transfer process was quantified by mathematical and physical models, in which the relationship between n value and the flux-limiting mechanism was deeply analyzed. The calculation suggested that desorption-limiting mechanism acting as leading role would result in n value to be 0, while external mass transfer dominating the permeation would make n value to be 1. When n value was between 0 and 0.5, desorption and diffusion processes would impose combined impact on the permeation (ignoring external mass transfer) and desorption might have more weight as n approaching to 0. On the other hand, taking external mass transfer into account, desorption-limiting and external mass transfer-limiting mechanism would work together as 0 < n < 1. The closer n approaching to 1, the more significant of external mass transfer mechanism. In addition, the influences of Pd film thickness, ΔP variation and mass transfer coefficient on n value were also elucidated systematically.

Machine learning-based ethylene and carbon monoxide estimation, real-time optimization, and multivariable feedback control of an experimental electrochemical reactor

Electrochemical reduction of CO2 gas is a novel CO2 utilization technique that has the potential to mitigate the global climate crisis caused by anthropogenic CO2 emissions, and enable the large-scale storage of energy generated from renewable sources in the form of carbon-based chemicals and fuels. However, due to the complexity of the electrochemical reactions, the explicit first-principles models for CO2 reduction are not available yet, and there has been a limited effort to develop process modeling, optimization and control of CO2 electrochemical reactors. To this end, a rotating cylinder electrode (RCE) reactor has been constructed at UCLA to understand the mass transfer and reaction kinetics effects separately on the productivity. In the RCE reactor, the applied potential strongly influences the reaction energetics and the electrode rotation speed affects the hydrodynamic boundary layer and modifies the film mass transfer coefficient, which involves convective and diffusive transport. The present work aims to develop a multi-input multi-output (MIMO) control scheme for the RCE reactor that integrates techniques from artificial and recurrent neural network modeling, nonlinear optimization, and process controller design. Specifically, production rates of two products from the experimental reactor, ethylene and carbon monoxide, are controlled by manipulating two inputs, applied potential and catalyst rotation speed. Process dynamics and controllability are analyzed, a feedback control strategy is designed and the controllers are tuned accordingly. The experimental electrochemical cell is employed to gather data for process modeling and implement the multivariable control system. Finally, the experimental results are presented which demonstrate excellent closed-loop performance by the control system and regulation of the outputs at three different set-points including an economically-optimal set-point.

Different efficiency toward the biomimetic aerobic oxidation of benzyl alcohol in microchannel and bubble column reactors: Hydrodynamic characteristics and gas–liquid mass transfer

The selective aerobic oxidation of benzyl alcohol to benzaldehyde has attracted considerable attention because benzaldehyde is a high value-added product. The rate of this typical gas–liquid reaction is significantly affected by mass transfer. In this study, CoTPP-mediated (CoTPP: cobalt (II) meso-tetraphenylporphyrin) selective benzyl alcohol oxidation with oxygen was conducted in a membrane microchannel (MMC) reactor and a bubble column (BC) reactor, respectively. We observed that 83% benzyl alcohol was converted within 6.5 min in the MMC reactor, but only less than 10% benzyl alcohol was converted in the BC reactor. Hydrodynamic characteristics and gas–liquid mass transfer performances were compared for the MMC and BC reactors. The MMC reactor was assumed to be a plug flow reactor, and the dimensionless variance was 0.29. Compared to the BC reactor, the gas–liquid mass transfer was intensified significantly in MMC reactor. It could be ascribed to the high gas holdup (2.9 times higher than that of BC reactor), liquid film mass transfer coefficient (8.2 times higher than that of BC reactor), and mass transfer coefficient per unit interfacial area (3.8 times higher than that of BC reactor). Moreover, the Hatta number for the MMC reactor reached up to 0.61, which was about 15 times higher than that of the BC reactor. The computational fluid dynamics calculations for mass fractions in both liquid and gas phases were consistent with the experimental data.

Experimental Study for The Effect of Changing Flow on Absorption in Wetted Wall Column.

Gas absorption is the unit operation in which one or more soluble components of gas mixture are dissolved in a liquid. The absorption may be a purely physical phenomenon or may involve chemical reaction with one or more constituents in the liquid solution. In order to obtain the highest rate of absorption, gas and liquid streams flow in opposite directions in counter-current flow. The unit in this work has been designed to help grasp the basic principles of the chemical and physical aspects involved in absorption. This study unit is made of borosilicate transparent glass in order to show the water spread in the column and get the visual distribution of fluids behavior which helps to fully understand the phenomenon. In this work, the wetted wall column is used to determine gas/liquid mass transfer coefficients, which is essential to design absorption towers. This study investigates the absorption of oxygen from air into deoxygenated water (prepared by nitrogen sparing) in liquid film controlled absorption experiment. The liquid film mass transfer coefficient is calculated at various mass flow rates of water and air. This work also studies the effect of water flow and air flow on oxygen concentration in the oxygenation and de-oxygenation process so affect on absorption process .

Experimental Study for The Effect of Changing Flow on Absorption in Wetted Wall Column.

Gas absorption is the unit operation in which one or more soluble components of gas mixture are dissolved in a liquid. The absorption may be a purely physical phenomenon or may involve chemical reaction with one or more constituents in the liquid solution. In order to obtain the highest rate of absorption, gas and liquid streams flow in opposite directions in counter-current flow. The unit in this work has been designed to help grasp the basic principles of the chemical and physical aspects involved in absorption. This study unit is made of borosilicate transparent glass in order to show the water spread in the column and get the visual distribution of fluids behavior which helps to fully understand the phenomenon. In this work, the wetted wall column is used to determine gas/liquid mass transfer coefficients, which is essential to design absorption towers. This study investigates the absorption of oxygen from air into deoxygenated water (prepared by nitrogen sparing) in liquid film controlled absorption experiment. The liquid film mass transfer coefficient is calculated at various mass flow rates of water and air. This work also studies the effect of water flow and air flow on oxygen concentration in the oxygenation and de-oxygenation process so affect on absorption process .

Strontium adsorption characteristics of natural Zeolites for permeable reactive barrier in Fukushima Daiichi nuclear power station

ABSTRACT Laboratory experiments and model estimates were carried out to evaluate the effectiveness of sorbent for construction of the Permeable Reactive Barrier (PRB) at downstream of H4 tank area in Fukushima-Daiichi Nuclear Power Station in September 2014. Measurement of cation exchange capacity and X-ray diffraction analyses of crystal structures were carried out for natural zeolites. The Sr adsorption isotherms were measured for these zeolites contacted with water containing Sr or the simulated groundwater containing Na, K, Ma, Ca, and Sr. According to these equilibrium characteristics, Akita-Futastui zeolite was selected as candidate. The zeolite was served for the column tests to obtain Sr breakthrough curves with different conditions such as particle size of zeolite, Darcy Flux, Sr concentration in the simulated groundwater, and mixed bed with gravel. From the breakthrough curves, kinetic properties such as the film mass transfer coefficient and the effective intraparticle diffusivity were derived by fitting with adsorption model. Based on these kinetic properties, Sr breakthrough curves were estimated for the simulated groundwater containing 0.3 ppm Sr passed at 10 cm∙day-1 through 1.5 m thick PRB with zeolite and gravel. The breakthrough points for the PRB with 33 wt.% zeolite was evaluated as more than 70 years.

Electrochemically modified adsorbents for treatment of aqueous arsenic: Pore diffusion in modified biomass vs. biochar

Canola straw-based biomass and biochar adsorbents were electrochemically modified and used to remove arsenate (As(V)) from water. Studying the effects of the modification parameters on the As(V) adsorption capacity of the modified materials showed that the materials treated at lower pH (3) and drying temperatures (60 °C) had higher As(V) uptake. The modification conditions were optimized to obtain optimum modified biomass (OBM) and biochar (OBC) with the highest As(V) adsorption capacity. Characterization of the OBM and OBC indicated that the deposited iron oxide on the surface of the adsorbents was goethite. The adsorption isotherms and kinetic data suggested that a hybrid adsorption mechanism took place under the experimental conditions with a higher probability of heterogeneous multilayer chemisorption. Solid-phase speciation of the sorbed As(V) indicated a negligible reduction (2.5%) of As(V) to arsenite (As(III)) on OBM, while no reduction occurred on OBC. The liquid film mass transfer coefficient (kf) and effective pore diffusion coefficient (Dp) were estimated using a shrinking core model combined with a genetic algorithm. A higher tortuosity factor of 3.75 for the OBM was obtained as compared to 2.93 for the OBC. Overall, the applied electrochemical modification successfully enhanced the As(V) sorption capacity of both the biomass and biochar from 8 to 766 and 25 to 922 µg/g, respectively, indicating promising potential of this method for preparation of high performance adsorbents.

Modeling of Fixed‐Bed Rapid Temperature Swing Adsorber for Butanol Dehydration

AbstractA fixed‐bed system of rapid temperature swing adsorption (RTSA), which uses a solid absorbent for dehydration of butanol, was studied. The packed bed was simulated using proper partial and algebraic equations which were solved by the central difference method in MATLAB software. The equilibrium relationship and fixed‐bed breakthrough curves were determined experimentally. The value of unknown parameters such as equilibrium constants, liquid film mass transfer coefficient, intraparticle diffusion coefficient, and axial diffusivity were estimated by appropriate equations. The model fitted well to experimental breakthrough data. The results proved that it would be possible to operate a complete RSTA cycle in just a few hours to allow a large quantity of organic solvent dehydrated with reasonable concentration.

Simultaneous removal of carbon dioxide, sulfur dioxide and nitric oxide in a biofilter system: Optimization operating conditions, removal efficiency and bacterial community

Anthropogenic NOx, SO2 and CO2 emission from the fossil-fuel-fired power plants has aroused growing attention. This study investigated the removal performance of CO2, SO2 and NOx in flue gas as well as conversion efficiency of nitric- and sulfur-compounds in liquid phase in a biofilter. In order to develop the potential of the biofilter, simulative industry wastewater was employed as the spray solution. The satisfactory flue gas removal performance (75.23% CO2, 100% SO2 and 82.81% NO) were achieved under the optimal operating conditions of biofilter: initial solution pH of 9 and liquid-gas ratio (L/G) of 3. The gas film mass transfer coefficients (kGa) results showed that the resistance of gas mass transfer was decreased with increasing the pH value and L/G ratio, respectively. The final transformation product of NO was mostly N2 while about 78% SO2 was converted to elemental sulfur. The microbial community analysis results showed that the relative abundance of bacteria with denitrification capacity was increased by 3.05% which might have contributed to the conversion of NO intermediates products in present study. Collectively, this biofilter system achieve a better flue gas removal performance via the proper operation system, which provides an economic feasible strategy of flue gas purification and increases potential for industrial application.

Numerical approximation of a two-dimensional non-equilibrium model of non-isothermal liquid chromatography considering core-shell particles

A nonlinear and non-isothermal two-dimensional lumped kinetic model (2D LKM) is solved numerically to simulate the transport of multi-component mixtures in fixed-bed liquid chromatographic columns of cylindrical geometry packed with core-shell particles. The model considers axial and radial dispersions, interfacial mass, and heat transfers, nonlinear adsorption, and rectangular pulse injections. It is formed by a nonlinear system of partial differential equations coupled with differential and algebraic equations. A semi-discrete high-resolution finite volume scheme (HR-FVS) is extended and applied to approximate the model equations. A few case studies related to single and multi-component elution are considered to illustrate the effects of important parameters, such as core radius fraction, enthalpy of adsorption, radial and axial-dispersion coefficients, equilibrium constant, as well as film mass and heat transfer coefficients. A typical performance criterion is adopted to quantify the influence of thermal effects on the process performance and to evaluate the optimum value of inert core radius. The results obtained in various case studies are useful for understanding and upgrading liquid chromatographic processes considering non-isothermal conditions and core-shell particles.

Radial Variations in Axial Velocity Affect Supercritical CO2 Extraction of Lipids from Pre-pressed Oilseeds

Packed beds of spherical particles in a cylindrical vessel have a high porosity region next to the vessel wall that allows preferential fluid flow. Consequently, there are radial variations in porosity (e) and superficial fluid velocity (U) that depend on the vessel-to-particle diameter ratio (D/dp) and the flow regime of the fluid. This work ascertained if these radial variations affected SuperCritical (SC) CO2 extraction curves of oil from pre-pressed seeds at 40 °C and 28 MPa, as compared with the commonly adopted plug flow condition. It focused specifically on comparing extraction curves as a function of the controlling mass transfer mechanism (characterized by the dimensionless Biot number, Bi) and D/dp ratio. A predictive model was adopted to describe the SC-CO2 extraction of oil from sheared seeds comparing plug flow with radial variations in superficial CO2 velocity, U(r), from literature correlations. Selected independent variables included the initial oil content of the substrate (132.7 ≤ Co ≤ 397.2 g/kg), dp (1 or 2 mm), U (1–4 mm/s), and vessel volume (0.038–495 L). Co markedly affected the effective diffusivity of the oil (0.780 ≤ De ≤ 6.24 × 10−10 m2/s), whereas dp and U moderately affected the film mass transfer coefficient (2.44 ≤ kf ≤ 7.40 × 10−5 m/s). Radial variations in superficial CO2 velocity decreased extraction rates, with differences between extraction curves when considering plug flow or adopting U(r) diminishing as Bi increased for D/dp = 20, or as D/dp increased for Bi = 18. Bi increased by increasing U and kf, or decreasing Co and De, whereas D/dp increased by increasing vessel volume. The radial variations in porosity in a packed bed and associated changes in superficial CO2 velocity may have a more pronounced negative impact in laboratory or pilot plant extraction vessels (small D) than industrial vessels (large D), mainly when extracting small particles and applying large superficial CO2 velocities. A proxy for the SC-CO2 extraction of oil from pre-pressed seeds in an industrial extraction vessel (495-L capacity, D/dp = 270) would be plug flow using the porosity, and superficial CO2 velocity predicted for the axis of the extraction vessel (eo and Uo, respectively). Literature correlations predict a value of eo slightly less than e, and value of Uo slightly less than U. The remainder of the CO2 bypassing the vessel along a high porosity region near the vessel wall, containing a small fraction of the loaded substrate.

Capillary microbioreactors for VOC vapor treatment: Impacts of operating conditions

Micro-capillary bioreactors (1 mm ID, 10 cm long) were investigated for the biodegradation of toluene vapors as a model volatile organic compound (VOC). The intended application is the removal of VOCs from indoor air, when such microbioreactor is coupled with a microconcentrator that intermittently delivers high concentrations of VOCs to the bioreactor for effective treatment. The effects of key operating conditions were investigated. Specifically, gas film and liquid film mass transfer coefficients were determined for different gas and liquid velocities. Both mass transfer coefficients increased with gas or liquid velocity, respectively, and the overall gas-liquid mass transfer was dominated by the liquid-side resistance. Experiments with the microbioreactors focused on the effects of gas velocity, liquid velocity and mineral medium renewal rate on the treatment of toluene vapors at different inlet concentrations. The best performance in terms of toluene removal and mineralization to CO2 was obtained when the gas and liquid velocity ratio was close to one and achieving Taylor or slug flow pattern. Sustained treatment over extended periods of time with toluene elimination capacities ranging from 4000 to over 9000 g m−3 h−1 were obtained, which is orders of magnitude greater than conventional biofilters and biotrickling filters. Biological limitations generally played a more important role than mass transfer limitation. Continuous mineral medium supply at a high rate (10 h liquid retention time) enabled pH control and provided ample nutrient supply and therefore resulted in better toluene elimination and mineralization. Overall, these studies helped select the most suitable conditions for high performance and sustained operation.

Removal of V(V) From Solution Using a Silica-Supported Primary Amine Resin: Batch Studies, Experimental Analysis, and Mathematical Modeling.

Every year, a large quantity of vanadium-containing wastewater is discharged from industrial factories, resulting in severe environmental problems. In particular, V(V) is recognized as a potentially hazardous contaminant due to its high mobility and toxicity, and it has received considerable attention. In this study, a silica-supported primary amine resin (SiPAR) was prepared by in-situ polymerization, and the V(V) adsorption from the solution was examined. The as-prepared resin exhibited fast adsorption kinetics, and it could attain an equilibrium within 90 min for the V(V) solution concentration of 100 mg/L at an optimum pH of 4, whereas the commercial D302 resin required a treatment time of more than 3 h under the same conditions. Furthermore, the maximum adsorption capacity of the resin under optimum conditions for V(V) was calculated to be 70.57 mg/g. In addition, the kinetics and isotherm data were satisfactorily elucidated with the pseudo-second-order kinetics and Redlich–Peterson models, respectively. The silica-based resin exhibited an excellent selectivity for V(V), and the removal efficiency exceeded 97% in the presence of competitive anions at 100 mmol/L concentrations. The film mass-transfer coefficient (kf) and V(V) pore diffusivity (Dp) onto the resins were estimated by mathematical modeling. In summary, this study provided a potential adsorbent for the efficient removal of V(V) from wastewater.

Kinetic Modelling of Electroless Nickel-Phosphorus Plating under High Pressure.

In electroless nickel–phosphorus plating (ENPP), growth of the plated layer under high pressure was found to be faster than under ambient pressure. To quantitatively elucidate the effect of high pressure on the mechanism of the ENPP reaction, we propose a kinetic model that takes into account both mass transfer and reaction of the chemical species present in the plating solution. We solved the mass balance equations between the chemical species to calculate the transient changes in the thickness of the plated layer as well as the concentrations of the chemical species in the plating solution. By fitting the calculated results to the experimentally acquired results based on the nonlinear least square method, we determined such parameters as the film mass transfer coefficient, the adsorption constants, and the reaction rate constants of the chemical species in the model. As a result, we found that the film mass transfer coefficient under high pressure was greater than that under ambient pressure and revealed the dependence of the coefficient on pressure. The transient changes in the concentrations of the chemical species in the plating solution that we calculated based on the kinetic model employing our estimated parameters closely modeled the experimental results with the determination coefficients being mostly over 99%.

Determination of Mass Transfer Coefficients for Adsorption of Pb and Cd Onto Coir Pith and Statistical Analysis

Adsorption of Pb and Cd ions onto coir pith from single solute aqueous solutions was studied. Experimental data on variation of solute concentration in the solution with time were fitted to exponential kinetic model and model parameters were determined. New parameter, concentration decay constant, was introduced to comprehend the adsorption rate. Novel method was introduced to determine the liquid film mass transfer coefficient (kL) accurately using the exponential kinetic model equation. Liquid film mass transfer coefficient and Overall liquid phase mass transfer coefficient were calculated and the proposed method overcomes the errors due to approximation of initial rate of change of solute concentration and assumption of linear isotherm parameters. Statistical analysis of mass transfer coefficients showed that for all the parameters tested the variation of the parameters are significant with initial solution concentration for Pb.