Mass Transport Parameters Research Articles

Glucose oxidation on gold in alkaline solution: A DEMS and microkinetic modelling study

The mechanism and kinetics of the electrochemical oxidation of glucose on gold surfaces in 0.1 M NaOH solution are investigated by rotating disc electrode and differential electrochemical mass spectrometry coupled to microkinetic modelling. For this purpose, the glucose mass-transport parameters (solution viscosity and density, glucose diffusion coefficient) were determined in the relevant conditions. Koutecký-Levich analysis of rotating disc electrode current-potential curves revealed that the glucose oxidation reaction (GOR) follows a one-electron mechanism at 0.6 V vs RHE, while H2 production could be evidenced by DEMS in this potential range. This suggests that the glucose oxidation selectively produces gluconate at 0.6 V vs RHE through an electrochemical oxidative dehydrogenation (EOD) mechanism. A microkinetic model of the current-potential curves was developed, taking into account the hydrogen electrode reactions kinetics, the dissociative adsorption/desorption of glucose, and the glucose electrooxidation on gold surfaces. The dissociative adsorption of glucose was found to be the rate-determining step of the reaction. It is also revealed that the release of anodic H2 through the Tafel step is triggered by the consumption of the adsorbed reaction intermediates. The gluconate electrooxidation into further products has to be considered for potential above 0.7 V vs RHE.

Probing the Depths of Electrocatalysis Systems: X-Ray Absorption Spectroscopy Reveals Catalyst Behavior

X-ray absorption spectroscopy (XAS) is a powerful experimental technique used to study the electronic structure and local environment of atoms in a material. It provides valuable insights into the chemical bonding, oxidation states, and coordination geometry of elements. XAS has been widely applied in various fields of electrochemistry, including popular topics like the hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), and CO2 reduction reaction (CO2RR).Despite the growing recognition of the practical importance of XAS techniques, correlating experimental spectroscopy with the working mechanisms and deciphering the structure of the electrochemical interface under reaction conditions remains challenging. In the case of CO2RR, we utilized operando XAS to investigate multiple Cu-based catalysts in different cell configurations. Our findings revealed that altering the reaction environment can induce an alternative pathway for catalyst structural changes. Moreover, operando XAS demonstrated that the reduction of Cu oxide catalysts is not solely governed by applied potentials but is also influenced by mass transport and other parameters. For ORR, in situ XAS not only provides information about the local environment changes of Pt-based catalysts but also unveils surface properties through △μ-X-ray adsorption near-edge spectroscopy (△μ-XANES). This further aids in the discovery of degradation mechanisms in proton exchange membrane fuel cells (PEMFCs). In the case of HER, in situ XAS enables characterization beyond catalysts and extends to the electrochemical interface.Overall, XAS techniques play a crucial role in understanding the electronic structure and local environment of atoms in electrochemical systems, shedding light on reaction mechanisms and catalyst performance under realistic conditions Acknowledgement The authors thank the funding source from Liquid Sunlight Alliance under the U.S. DOE, Office of Science, Office of Basic Energy Sciences, Fuels Award Number DE-SC0021266 and the Laboratory Directed Research and Development Program of the Lawrence Berkeley National Laboratory under the U.S. DOE Contract No. DE-AC02-05CH11231.

Discovering Electrochemistry with an Electrochemistry‐Informed Neural Network (ECINN)

AbstractMachine learning is increasingly integrated into chemistry research by guiding experimental procedures, correlating structure and function, interpreting large experimental datasets, to distill scientific insights that might be challenging with traditional methods. Such applications, however, largely focus on gaining insights via big data and/or big computation, while neglecting the valuable chemical prior knowledge dwelling in chemists’ minds. In this paper, we introduce an Electrochemistry‐Informed Neural Network (ECINN) by explicitly embedding electrochemistry priors including the Butler–Volmer (BV), Nernst and diffusion equations on the backbone of neural networks for multi‐task discovery of electrochemistry parameters. We applied the ECINN to voltammetry experiments of and redox couples to discover electrode kinetics and mass transport parameters. Notably, ECINN seamlessly integrated mass transport with BV to analyze the entire voltammogram to infer transfer coefficients directly, so offering a new approach to Tafel analysis by outdating various mass transport correction methods. In addition, ECINN can help discover the nature of electron transfer and is shown to refute incorrect physics if imposed. This work encourages chemists to embed their domain knowledge into machine learning models to start a new paradigm of chemistry‐informed machine learning for better accountability, interpretability, and generalization.

Discovering Electrochemistry with an Electrochemistry-Informed Neural Network (ECINN).

Machine learning is increasingly integrated into chemistry research by guiding experimental procedures, correlating structure and function, interpreting large experimental datasets, to distill scientific insights that might be challenging with traditional methods. Such applications, however, largely focus on gaining insights via big data and/or big computation, while neglecting the valuable chemical prior knowledge dwelling in chemists' minds. In this paper, we introduce an Electrochemistry-Informed Neural Network (ECINN) by explicitly embedding electrochemistry priors including the Butler-Volmer (BV), Nernst and diffusion equations on the backbone of neural networks for multi-task discovery of electrochemistry parameters. We applied the ECINN to voltammetry experiments of and redox couples to discover electrode kinetics and mass transport parameters. Notably, ECINN seamlessly integrated mass transport with BV to analyze the entire voltammogram to infer transfer coefficients directly, so offering a new approach to Tafel analysis by outdating various mass transport correction methods. In addition, ECINN can help discover the nature of electron transfer and is shown to refute incorrect physics if imposed. This work encourages chemists to embed their domain knowledge into machine learning models to start a new paradigm of chemistry-informed machine learning for better accountability, interpretability, and generalization.

Rational downstream development for adeno-associated virus full/empty capsid separation – A streamlined methodology based on high-throughput screening and mechanistic modeling

Recombinant adeno-associated virus (AAV) has emerged as one of the most promising systems for therapeutic gene delivery and has demonstrated clinical success in a wide range of genetic disorders. However, manufacturing of high-quality AAV in large amounts still remains a challenge. A significant difficulty for downstream processing is the need to remove empty capsids that are generated in all currently utilized expression systems and that represent product-related impurities that adversely affect safety and efficacy of AAV vectors. Empty and full capsids exhibit only subtle differences in surface charge and size, making chromatography-based separations highly challenging. Here, we present a rapid methodology for the systematic process development of the crucial AAV full/empty capsid separation on ion-exchange media based on high-throughput screening and mechanistic modeling. Two of the most commonly employed serotypes, AAV8 and AAV9, are used as case studies. First, high-throughput studies in filter-plate format are performed that allow the rapid and comprehensive study of binding and elution behavior of AAV on different resins, using different buffer systems, pH, salt conditions, and solution additives. Small amounts of separated empty and full AAV capsids are generated by iodixanol gradient centrifugation that allow studying the binding and elution behavior of the two vector species separately in miniaturized format. Process conditions that result in maximum differences in elution behavior between empty and full capsids are then transferred to benchtop chromatography systems that are used to generate calibration data for the estimation of steric mass-action isotherm and mass transport parameters for process simulation. The resulting column models are employed for in-silico process development that serves to enhance understanding of separation constraints and to identify optimized conditions for the removal of empty particles. Finally, optimized separation conditions are verified experimentally. The methodology presented in this work provides a systematic framework that affords mechanistic understanding of the crucial empty/full capsid separation and accelerates the development of a scalable AAV downstream process.

Quantification Method of Mass Transfer Resistance in Cathode Catalyst Layer in PEFC

IntroductionTo spread PEFCs, it is important to optimize the cathode catalyst layer (CCL) because the oxygen reduction reaction (ORR) in CCL is sluggish. Our previous study proposed that the mass transfer resistance in the through-plane direction in CCL can be quantified by measuring ORR rate dependency on oxygen partial pressure, effective oxygen diffusion coefficient, ORR rate constant, or CCL thickness[1]. In this study, dependency of the polarization curve on the oxygen partial pressure was measured with commercial supported-platinum catalysts at fixed RH and temperature. The objective of this study is to establish the quantification methods of mass transfer resistances in CCL.TheoryIn our previous study[2, 3], the current density, i is expressed as i = 4F δ (C) k vcm p Oc F e [A/m2], (1)where δ (C) is the cathode catalyst layer (CCL) thickness, k vc is the reaction rate constant per unit volume of CCL [mol/(Pa·m3·s)] which does not include through-plane mass transport resistance. p O is the oxygen partial pressure [Pa]. The subscripts m and c denote PEM–CCL boundary and CCL–gas diffusion layer boundary, respectively. F e is the effectiveness factor, a function of the following 4 dimensionless moduli, M Om , M pm , P Om , and y Oc . F e is defined as the ratio of the observed reaction rate to the reaction rate which does not have the influence of through-plane mass transfer resistance. M Om denotes the ratio of O2 diffusion resistance to the reaction resistance. M pm denotes the ratio of proton transfer resistance to the reaction resistance. P Om is defined as the ratio of O2 diffusion resistance to the convection resistance. y Oc denotes the oxygen mole fraction. Definitions of the dimensionless four moduli are expressed as M Om =δ (C) (k vcm RT/D eO)0.5, (2) M pm = δ (C) (4F k vcm RT/(σ ep b c))0.5, (3) P Om = δ (C) N gm /(C g D eO), (4) y Oc = p Oc /P, (5)where R, T, σ ep, N gm and P denotes the gas constant [J/(mol K)], cell temperature [K], effective proton conductivity [S/m], total gas flux [mol/(m2 s)] and total pressure [Pa], respectively. When the cathode emf at the PEM–CCL boundary, E cm , T, and relative humidity (RH) are fixed, M Om is fixed. F e and M pm are proportional to i/p Oc and p Oc 0.5, respectively. The relationship between F e and M pm shown in Fig. 1 corresponds to that between i/p Oc and p Oc 0.5. Thus, F e and M pm can be determined just by fitting experimental data of i/p Oc plotted against p Oc 0.5 to the theoretical curves.Results and DiscussionPolarization curves shown in Fig. 2 were measured at 80 °C and 0.77 of inlet RH at varied p Oc . As expected from Eq. (1), current densities at a fixed E cm increases when p Oc increases. The current densities at the fixed E cm are plotted against p Oc as shown in Fig. 3. The current density is sublinear against p Oc . This is because M pm expressed in Eq. (3) increased when p Oc is higher. The ORR rate is lower than the value expected from the Tafel equation when mass transfer resistance increases.The dimensionless moduli were determined by fitting the theoretical relationship to the measured i/p Oc vs. p Oc 0.5 graph. From the determined dimensionless moduli, the ORR rate and mass transport parameters, k vc⊕, D eO and σ ep were also obtained and these values are shown in Table 1 with values in literature[4, 5].Effective proton conductivity, σ ep is relatively low compared with values in literature. This resulted from an experimental error in the current density at p Oc of 16 kPa. Lowering the current density at high p Oc leads to decrease in σ ep because M pm increases when p Oc is raised. By extensively measuring the polarization curves dependency on p Oc , the ORR rate parameters and mass transport parameters can be determined more accurately. Recalculated results using the obtained mass transport parameters are shown in Figs. 3 and 4. The recalculated results appropriately reproduced the ORR rate dependency on E cm and p Oc .ConclusionsThe through-plane mass transfer resistance in CCL was quantified by measuring the ORR rate dependency on the oxygen partial pressure. From the determined dimensionless moduli, mass transport parameters were obtained. Recalculated results appropriately reproduced the ORR rate dependency on cathode emf and oxygen partial pressure.AcknowledgementThis work was supported by the FC-Platform Program: Development of design-for-purpose numerical simulators for attaining long life and high performance project (FY 2020–2023) conducted by the New Energy and Industrial Technology Development Organization (NEDO), Japan. Figure 1

Heat and mass transfer of a novel CO2 desorption process integrated with highly turbulent catalytic heat exchanger

This was the first work that pioneered the development a novel catalytic CO2 desorption process using an agitated jacket vessel with a coil heat exchanger (JVC) into a bench-scale pilot plant for post-combustion carbon capture technology. The key parameters of heat and mass transport e.g., overall heat transfer coefficient, overall volumetric liquid-side mass transfer coefficient and the enhancement factor for catalyst effect, were experimentally investigated by varying the operating conditions, including temperature, stirring speed, and heating methods. The proposed investigations revealed that the utilization of the JVC was a promising technology for improving heat transfer and mass transfer performance in the desorption process due to the high turbulence flow and more favorable thermal distributions achieved by the JVC. In comparison to the conventional process with a fixed catalyst bed, the JVC demonstrated a remarkable approximately 30 % catalytic enhancement and a substantial 50 % reduction in catalyst demand. Additionally, other potential benefits and challenges of further practical operations were discussed in this paper. This research carried significant potential to contribute to the advancement of knowledge and offer valuable insights into the practicability of the catalytic desorption process for further commercial application in carbon capture. The integration of catalyst and JVC could potentially motivate the utilization of catalyst towards commercial-scale applications.

On the equivocal nature of the mass absorption curves

The idea behind the research presented is based upon apparently contradictory experimental results obtained here by means of photoacoustics modalities for the same drug donor/acceptor membrane system, serving as a surrogate for a transdermal delivery system. The first modality allowed for the monitoring of the total amount of mass uptake (m(t)-type data), while the second technique allowed for the quantification of time-dependent concentration distribution within the acceptor membrane (c(x,t)-type data). Despite of a very good agreement between the mt data and the 1st-order uptake fitting model (standard Fickian diffusion with constant source boundary condition), the standard approach failed during the c(x,t) data analysis. The results led to the analysis of the interfacial transfer contribution to the overall mass transfer efficiency, which eventually allowed to question reliability of the mt data analysis for the determination and quantification of the mass transport parameters. A more detailed analysis of the c(x,t) by means of the newly introduced transport rate number parameter revealed, that the mass uptake by the acceptor is almost equally influenced by interfacial and bulk transport processes. The analyses performed were translated into a model-free characteristic times, i.e. parameters independent of the model scheme used.

Bio-Resorption Control of Magnesium Alloy AZ31 Coated with High and Low Molecular Weight Polyethylene Oxide (PEO) Hydrogels.

Magnesium AZ31 alloy has been chosen as bio-resorbable temporary prosthetic implants to investigate the degradation processes in a simulating body fluid (SBF) of the bare metal and the ones coated with low and high-molecular-weight PEO hydrogels. Hydrogel coatings are proposed to control the bioresorption rate of AZ31 alloy. The alloy was preliminary hydrothermally treated to form a magnesium hydroxide layer. 2 mm discs were used in bioresorption tests. Scanning electron microscopy was used to characterize the surface morphology of the hydrothermally treated and PEO-coated magnesium alloy surfaces. The variation of pH and the mass of Mg2+ ions present in the SBF corroding medium have been monitored for 15 days. Corrosion current densities (Icorr) and corrosion potentials (Ecorr) were evaluated from potentiodynamic polarisation tests on the samples exposed to the SBF solution. Kinetics of cumulative Mg ions mass released in the corroding solution have been evaluated regarding cations diffusion and mass transport parameters. The initial corrosion rates for the H- and L-Mw PEO-coated specimens were similar (0.95 ± 0.12 and 1.82 ± 0.52 mg/cm2day, respectively) and almost 4 to 5 times slower than that of the uncoated system (6.08 mg/cm2day). Results showed that the highly swollen PEO hydrogel coatings may extend into the bulk solution, protecting the coated metal and efficiently controlling the degradation rate of magnesium alloys. These findings focus more research effort on investigating such systems as tunable bioresorbable prosthetic materials providing idoneous environments to support cells and bone tissue repair.

Mathematical modeling of breakthrough curves for 8-hydroxyquinoline removal from fundamental equilibrium and adsorption rate studies

The mathematical modeling of the dynamic adsorption of 8-Hydroxyquinoline on activated carbon (AC) in batch and fixed-bed adsorbers is outlined in this study. The model is centered on the mass transport phenomena occurring in the solution and inside the adsorbent and considers the axial dispersion, convective transport, intraparticle diffusion mechanisms, and adsorption on the active site. Moreover, this work proposes a methodology to solve the model based on basic studies of adsorption equilibrium and rate; therefore, the prediction of the breakthrough curves by fitting the mass transport parameters is not considered, which is a significant advance in the design of fixed-bed columns. The equilibrium results demonstrated that 8-HQ adsorbs on AC by dispersive π-π and hydrophobic interactions with a mass 8-HQ adsorbed of 454 mg g−1. The kinetic study revealed that the time to achieve equilibrium diminished by up to 200 min upon establishing a turbulent stirring regime. In addition, it was found that intraparticle transport is governed by surface diffusion. Finally, using the information obtained in the batch regime, it was possible to interpret and predict the packed bed behavior in a broad range of operational conditions with an error of 10.6 % in the prediction of the breakthrough point.

Changes in transmural mass transport correlate with ascending thoracic aortic aneurysm diameter in a fibulin-4 E57K knockin mouse model.

Thoracic aortic aneurysm is characterized by dilation of the aortic diameter by greater than 50%, which can lead to dissection or rupture. Common histopathology includes extracellular matrix remodeling that may affect transmural mass transport, defined as the movement of fluids and solutes across the wall. We measured in vitro ascending thoracic aorta mass transport in a mouse model with partial aneurysm phenotype penetration due to a mutation in the extracellular matrix protein fibulin-4 [Fbln4E57K/E57K, referred to as MU-A (aneurysm) or MU-NA (no aneurysm)]. To push the aneurysm phenotype, we also included MU mice with reduced levels of lysyl oxidase [Fbln4E57K/E57K;Lox+/-, referred to as MU-XA (extreme aneurysm)] and compared all groups to wild-type (WT) littermates. The phenotype variation allows investigation of how aneurysm severity correlates with mass transport parameters and extracellular matrix organization. We found that MU-NA ascending thoracic aortae have similar hydraulic conductance (Lp) to WT, but 397% higher solute permeability (ω) for 4 kDa FITC-dextran. In contrast, MU-A and MU-XA ascending thoracic aortae have 44-68% lower Lp and similar ω to WT. The results suggest that ascending thoracic aortic aneurysm progression involves an initial increase in ω, followed by a decrease in Lp after the aneurysm has formed. All MU ascending thoracic aortae are longer and have increased elastic fiber fragmentation in the extracellular matrix. There is a negative correlation between diameter and Lp or ω in MU ascending thoracic aortae. Changes in mass transport due to elastic fiber fragmentation could contribute to aneurysm progression or be leveraged for treatment.NEW & NOTEWORTHY Transmural mass transport is quantified in the ascending thoracic aorta of mice with a mutation in fibulin-4 that is associated with thoracic aortic aneurysms. Fluid and solute transport depend on aneurysm severity, correlate with elastic fiber fragmentation, and may be affected by proteoglycan deposition. Transport properties of the ascending thoracic aorta are provided and can be used in computational models. The changes in mass transport may contribute to aneurysm progression or be leveraged for aneurysm treatment.

New Mass Transport Correlation for Vanadium Redox-Flow Batteries Based on a Model-Assisted Parameter Estimation

In this work, a two-dimensional mathematical model is applied to develop a new mass transport correlation for an SGL GFD4.6A carbon felt applied in a 100 cm2 single cell vanadium redox-flow battery under realistic flow conditions. Already published mass transport equations for carbon felt electrodes show a large variation for the resulting Sherwood numbers and are summarized in this work to narrow the probable range of mass transport parameters. A detailed investigation of electrolyte properties, impedance spectroscopic characterization for evaluation of kinetic properties, and the use of potential probe signals to identify the overpotential of positive and negative electrodes are carried out before mass transport parameter estimation by a comparison of model and experimental data. The model validation yields a good agreement between predicted and experimental data with the following new and reliable mass transport equation: Sh = 0.07 Re0.66Sc0.45 (0.0018 < Re < 0.11). The characteristic length applied for the Sherwood and Reynolds number is the diameter of the carbon felt fibers.

Interactions between Sodium Hyaluronate and β-Cyclodextrin as Seen by Transport Properties.

Knowledge of mass transport parameters, diffusion, and viscosity of hyaluronic acid (HA) in the presence of cyclodextrins is of considerable importance for areas such as food packaging and drug delivery, among others. Despite a number of studies investigating the functionalization of HA or the corresponding sodium salt by cyclodextrins, only a few studies have reported the effect of cyclodextrins on the mass transport of HA in the presence of these oligosaccharides. Here, we report the tracer binary and ternary interdiffusion coefficients of sodium hyaluronate (NaHy) in water and aqueous β-cyclodextrin solutions. The diffusion behavior of sodium hyaluronate was dependent on the reduced viscosity of NaHy, which, in turn, presented a concave dependence on concentration, with a minimum at approximately 2.5 g dm-3. The significant decrease in the limiting diffusion coefficient of NaHy (at most 45%) at NaHy concentrations below 1 g dm-3 in the presence of β-cyclodextrin, taking water as the reference, allowed us to conclude that NaHy strongly interacted with the cyclodextrin.

A model of changing of charge carriers mobility value in an implanted-junction rectifier under influence of mismatch-induced stress

PurposeThe purpose of this paper is (1) to analyze the dependence of charge carriers mobility in an implanted-junction heterorectifier on mismatch-induced stress and (2) to elaborate an analytical approach for analysis of mass transfer with the possibility to take into account changing of parameters of mass transport in space and time at one time as well as nonlinearity of the considered transfer.Design/methodology/approachIn this paper, the author analyzed charge carriers mobility changing in an implanted-junction heterorectifier under the influence of mismatch-induced stress. The author introduced a model to describe the considered changing of carriers mobility. Based on the analysis of the model, the author formulated conditions (1) to decrease and to increase of the mobility under influence of the stress; and (2) the author analyzed the possibility to control of mismatch-induced stress by radiation processing of materials of the considered multilayer structure. The author also introduced an analytical approach for analysis of mass transfer. The approach gives a possibility to take into account changing of parameters of mass transport in space and time at one time as well as nonlinearity of the considered transfer.FindingsFindings dependence of charge carriers mobility in an implanted-junction heterorectifier on mismatch-induced stress. Also the author finds an analytical approach for analysis of mass transfer. The approach gives a possibility to take into account changing of parameters of mass transport in space and time at one time as well as nonlinearity of the considered transfer.Originality/valueAll results of this paper are original.

Fluoride electrosorption in the presence of competing anions of environmental relevance by two activated carbons modified with La(III)

Here it is reported the electrosorption of fluoride in the presence of competing anions of environmental relevance (chloride, nitrate, sulfate, phosphate and arsenate) by two activated carbon electrodes impregnated with La(III), La-0.5% and La-1.5% (w/w %). The electrosorption kinetics were evaluated using equimolar initial concentrations (0.263 mM of each studied anion) in both binary solutions (F− vs. anion) and in a complex mixture comprising all anions simultaneously. For La-0.5%, the presence of nitrate and chloride did not significantly modify its fluoride removal (q = ∼19.25 µmol g−1), while these same anions decreased the fluoride removal of La-1.5% from 32.85 to 17.2 and 13.95 µmol g−1, for nitrate and chloride, respectively. In general, the divalent anions competed the most during the kinetics, decreasing the fluoride removal in both carbons; the lowest capacity values were 5.75 and 4 µmol g−1 for La-0.5% and La-1.5%, respectively. The increases in the pH of the solution corroborated that all anions anchored to the modified surface by a ligand-exchange mechanism involving the exposed hydroxyls from the La(III) clusters. The discussion of the results was not centered on the charge and the hydrated radius of the anions, but it was also expanded to other thermodynamic parameters that also denote selectivity, such as the hydration energies and mass-transport parameters. Electrochemical impedance spectroscopy was performed as a characterization technique in two electrolytes: 0.1 M NaF and the working solution, 0.263 mM NaF (5 ppm F− solution). The information obtained from the latter correlated the most with the electrosorption performance of the electrodes.

An accelerated approach for mechanistic model based prediction of linear gradient elution ion-exchange chromatography of proteins

With growing demands for therapeutic monoclonal antibodies, in silico downstream process development based on mechanistic modeling of chromatography separation process is being increasingly used for process optimization and process characterization. Application of mechanistic modeling in biopharmaceutical industry has been sparse due to the significant investment of time and resources that are required for performing model calibration. Mechanistic modeling of the chromatography process involves a large number of mass transport and binding parameters and their initial input values are required for simulations. These input values of column parameters can be easily obtained either from experiments or from empirical correlations available in literature. On the other hand, obtaining the model input valves for binding kinetic parameters is usually a cumbersome process as it involves performing batch experiments which are not only tedious but also require significant quantities of purely isolated main product and its related impurities, which is challenging as the product related impurities are typically present in smaller quantities and hence are difficult to obtain as pure species. In the present work, a mechanistic model that is based on the general rate model coupled with extended Langmuir binding model has been used for prediction of linear gradient elution peaks of monoclonal antibody on cation exchanger chromatography. The present work describes an accelerated approach for obtaining the input values for binding kinetic parameters in the extended Langmuir binding model from the two Yamamoto coefficient A and B values obtained by Yamamoto method directly from the model calibration linear gradient elution runs of different gradient slopes and at low to moderate protein loadings. The equations that can relate the two coefficients to the extended Langmuir model equation binding kinetic parameters were derived. Therefore, once A and B are determined, the binding kinetic parameter values were determined straightforward, thereby avoiding the problem of multiple solutions for the model parameters. The estimated binding parameters were successfully validated from isocratic elution experiments performed at low loading. What we demonstrate is that the proposed approach allows us to estimate binding kinetic parameters in a significantly more efficient and accelerated manner than presently used approaches, thereby accelerating development and implementation of mechanistic modeling for process chromatography.

Prospect of modeling industrial scale flow batteries – From experimental data to accurate overpotential identification

A vast literature exists on modelling of small-scale single-cell experiments for flow batteries, but very few reports have been published on large stacks, consisting of tens of cells, each with an active area of hundred square centimeters. In this report, a large set of measurements taken on a kW-class vanadium test facility is used to develop an accurate ad-hoc physical model. Experimental data consist of polarization curves at a broad range of states of charge and electrolyte flow rates, as well as electrochemical impedance spectra. The model is capable to decouple three sources of voltage losses: activation, ohmic, and concentration overpotentials. In addition, a new numerical approach for identifying the main parameters of electrochemical kinetics and mass-transport has been proposed. To the best of our knowledge, this is the first time when a model for voltage losses analyses was developed and fitted to a data from large-scale flow battery, being validated with a sensitivity analysis study. Investigations showed that activation losses have a sophisticated nature in combination with mass-transport limitations and play an important role in a wide range of loading current densities. As a result, they must be included in a reliable model able to reflect a non-linear voltage behavior of large stacks. This work also highlights that, in the investigated case, activation losses are likely to be attributed to the positive electrode rather than to the negative one. The obtained results could facilitate the development of advanced simulation and design of large-scale flow battery stacks.

Study of Pressure Retarded Osmosis Process in Hollow Fiber Membrane: Cylindrical Model for Description of Energy Production

A new mathematical model was developed to predict the cylindrical effect of the membrane performance in the pressure retarded osmosis process. The cylindrical membrane transport layers (the draw side boundary and the porous membrane) were divided into very thin sublayers with constant mass transport parameters, among others with a constant radius in every sublayer. The obtained second-order differential mass balance equations were solved analytically, with constant parameters written for every sublayer. The algebraic equation system involving 2N equations was then solved for the determinant solution. It was shown that the membrane properties, water permeability (A), salt permeability (B), structural parameter (S) and the operating conditions (inlet draw side solute concentration and draw side mass transfer coefficient) affect the water flux strongly, and thus the membrane performance, due to the cylindrical effect caused by the variable surface and volume of the sublayers. This effect significantly depends on the lumen radius. The lower radius means a larger change in the internal surface/volume of sublayers with ΔR thickness. The predicted results correspond to that of the flat-sheet membrane layer at ro = 10,000 μm. At the end of this manuscript, the calculated mass transfer rates were compared to those measured. It was stated that the curvature effect in using a capillary membrane must not be left out of consideration when applying hollow fiber membrane modules due to their relatively low lumen radius. The presented model provides more precise prediction of the performance in the case of hollow fiber membranes.

Estimation of the mass transport parameters of aquifers according to data from field tests with a pulse or a continuous source and an arbitrary location of the observation well

An identification method for determining the aquifer’s mass transport parameters is proposed, based on data from field tracer tests with a pulse or a continuous source and an arbitrary position of the observation well in respect to the tracer entry point. The method is also applicable in the presence of a representative set of data on changes in the concentration of pollutants at different points in the aquifer around a short-term (instantaneous) or a continuous surface or underground source. The identification procedure is based on the automated comparison of the observations data with a series of theoretical curves by varying the required parameters in order to achieve maximum compliance. The tracer transport is represented by analytical solutions of the partial differential equation for mass transfer in a homogeneous and isotropic two-dimensional porous media. The developed computer programs include numerical optimization using the Levenberg-Marquardt algorithm. Results from tests performed in order to assess reliability and errors of detection and identification are presented. Using the programs, the mass transport parameters: active porosity n0, effective (sorption) porosity nS, longitudinal dispersivity αL, transverse dispersivity αT and rate constant γ can be determined.

Probing mass transport processes in Li-ion batteries using electrochemical impedance spectroscopy

Electrochemical techniques, such as electrochemical impedance spectroscopy (EIS), are widely applied to probe dynamic processes across a range of systems including lithium-ion batteries (LIBs). Key questions remain on how different degradation phenomena effect the processes that allow LIB to function. One of the key processes that determines the response of batteries is the mass transport, particularly the transport of Lithium within the constituent electrode materials. This study considers mass transport within LIBs, and the extent to which electrochemical techniques, particularly EIS, can be used to meaningfully probe mass transport in LIBs with the aim to serve as a guide for future studies that wish to track changes in mass transport as batteries age and degrade. Herein, the benefits of using EIS compared to the Galvanostatic Intermittent Titration Technique (GITT) are demonstrated using well defined finite element method (FEM) simulations as the basis. Distribution of Relaxation Times was then applied to assign and map battery electrochemical processes to the EIS spectra based on their time constants. Effects such as electrode geometry, mass transport heterogeneities and the overlap between mass transport and other processes are considered and discussed with particular focus on how they affect the extraction of solid Lithium diffusion coefficients. • Directly map impedance spectrum to battery processes. • Provide new analysis of impedance spectrum based on modelling results. • Estimation of mass transport parameters in lithium-ion battery from impedance. • Link finite element modelling, circuit fitting models and Distribution of Relaxation Times. • Compare EIS to the Galvanostatic Intermittent Titration Technique method.