Surface Reaction Model Research Articles

The charge regulation of surfactants on the rock surface in nanoconfinement: A reaction-coupling fluid density functional theory study

The surface charge density and ζ potential of rock play an essential role in chemical enhanced oil recovery (CEOR), but the electrochemical properties of rock surfaces are difficult to predict under different reservoir conditions. Therefore, a new method was proposed combining fluid density functional theory (fluid DFT) and the surface reaction model. The surface charge density and ζ potential of silica pores under different conditions were predicted, in which the effects of pH, pore size (d), surfactant chain length (N), surfactant type, and concentration on the charge regulation of silica pores were thoroughly investigated. The surface tends to be more negatively charged with increasing pH and surfactant concentration. Moreover, the pore size effect is not negligible in charge regulation, but there is a critical pore size (CPS) that decreases as the surfactant concentration and pH increase. The difference between anionic and cationic surfactants is also investigated, which display different behaviors under nanoconfinements. The anionic surfactants’ behavior is similar to that of the simple salt. Furthermore, the ζ potential of silica pores increased as the surfactant concentration increased due to electrostatic screening, which is consistent with the results of molecular dynamics (MD) simulations and experiments.

Rare metals recycling from spent NCM cathode materials and simultaneous dehydrofluorination of polyvinylidene fluoride (PVDF) in subcritical water

Several studies have examined the recovery of lithium (Li), nickel (Ni), cobalt (Co), and manganese (Mn) from used lithium-ion batteries (LIBs). However, the environmentally friendly and cost-effective leaching and efficient separation of rare metals from the active cathode material of LIBs remains a challenge. In this study, we present a novel route for the extraction of high-value metals from the NCM cathode material of spent LIBs using subcritical water-containing polyvinylidene fluoride (PVDF). The experimental parameters such as reaction temperature, time, liquid–solid and mass ratios, were carefully investigated. The raw cathode material and the solid residues before and after leaching were characterized using ICP-OES, XRD, FT-IR and SEM-EDS analyses. Results showed that the maximum extraction efficiencies of Li, Ni, Co, and Mn of (98.69, 98.24, 97.52, and 99.04) %, respectively, were achieved under the optimized conditions of 350 °C, 2 h, 1:3 mass ratio, and 60:1 mL/g liquid–solid ratio. Meanwhile, the experimental results of leaching kinetics revealed that the reaction in the system was controlled by the surface chemical reaction model with the linear fitting degree of (R2 = 0.97–0.99) and the calculated activation energies of 63.72 kJ/mol (for Li), 73.55 kJ/mol (for Ni), 74.99 kJ/mol (for Co), and 71.88 kJ/mol (for Mn). The overall findings of this research concluded that the PVDF-assisted subcritical water extraction process is a beneficial and a promising alternative to other existing methods.

Effective leaching of spent lithium-ion batteries using DL-lactic acid as lixiviant and selective separation of metals through precipitation and solvent extraction.

Recycling cathodic materials from spent lithium-ion batteries (LIBs) is crucial not just for the environmental aspects but also for the supply of precious raw materials such as cobalt and lithium. As a result, developing a leaching process with low acid consumption, cost-effectiveness, low environmental impact, and high metal recovery is essential. In this article, the sustainable hydrometallurgical route for recovery of Li and Co from spent LIBs using DL-lactic acid as lixiviant is proposed. The different leaching parameters were studied to optimize the leaching conditions. With increasing lactic acid concentration from 0.1mol/L to 1.0mol/L, the leaching efficiency of Li and Co increased from 23% to 41% and 2% to 14%, respectively. The reductant H2O2 has a major role which reduced Co3+ to Co2+ and increasing the leaching efficiency of Co from 15.2% (1% H2O2) to 73.4% (6% H2O2). The maximum leaching efficiency of Li (99.8%) and Co (99%) was attained with 1.0mol/L lactic acid, 6% H2O2, 60°C, S/L ratio of 10g/L, and 60min leaching duration. The R2 values for the surface chemical reaction model were greater than 0.98, indicating that the lactic acid leaching process was controlled by the surface chemical reaction model. With 1.0mol/L 70% saponified Cyanex 272, a solvent extraction study showed a higher separation factor (βCo/Li) of 35.7 compared to other saponified and nonsaponified organophosphorus extractants. Using the precipitation method, 99.9% of Co and 99% of Li were precipitated as [Formula: see text] and [Formula: see text] with a purity of 99.4% and 98.3%, respectively.

Photocatalytic ceramic membrane: Effect of the illumination intensity and distribution

The principles and application of heterogeneous photocatalytic processes have gained wide attention, especially to the effectiveness of the process. In this work a mono and a multi-LED lamp are used to study the impact of the UV light intensity and distribution on the semiconductor surface during the degradation of organic compounds in water. A well-defined scan of the electromagnetic radiation profile on the surface of the membrane was obtained and evaluated. Comparing two lamp configurations with a total photon flux of 210 W.m−2 and using a filtration rate of 9.7 L.m−2.h−1, resulted in 20 % more degradation for the most homogeneous light distribution. Furthermore, the reaction rate relation to the photon flux was also studied, with a surface reaction model that includes possible mass transfer limitations. The surface reaction constant increased linearly with the irradiation intensity for the complete studied range [50 to 550 W.m−2] for the most homogeneous illumination distribution. A less uniform distribution resulted in a less than proportional reaction rate constant with respect to the incident photon flux between 100 and 210 W.m−2. This work adds valuable information to the photocatalysis field to improve the light efficiency in a photoreactor to enhance the degradation of pollutants.

Sensitivity of flame structure and flame speed in numerical simulations of laminar aluminum dust counterflow flames

Aluminum dust counterflow flames are investigated numerically using a two-stage model including the effects of interphase heat transfer, phase change, heterogeneous surface reaction (HSR), oxide cap growth, homogeneous combustion and radiation. The numerical model is first validated by simulating the aluminum dust counterflow flames of McGill University [Julien et al., 2017]. The results show that the particle velocity profile is consistent with the experimental results, and the error in the gas phase velocity caused by the use of aluminum particles as tracers in the experiment is analyzed. Then, further validation is conducted by comparison of the flame speed, and the predicted results agree well with the measurements. The flame structure of the aluminum dust counterflow flame is analyzed, and intermediate product (AlO) is observed to present a discrete distribution in space due to the nature of heterogeneous combustion. Different terms in the particle energy equation are analyzed, and the results indicate that the HSR plays an important role in the late preheating stage, while the interphase heat transfer dominates the rest of the conversion process. Under the assumption of unity Lewis number, the interphase heat/mass transfer models are found to have a great impact on the flame for a particle size smaller than 10 µm. With increasing particle sizes, the flame speed decreases, and most particles with a diameter of 12 µm cannot be fully burnt in the flame under the studied conditions. The effect of the strain rate on the flames is investigated with different particle sizes and unstretched reference flame speeds are obtained by linear extrapolation of the predicted results. Finally, a sensitivity analysis of the parameters of the heterogeneous surface reaction model is conducted.

Gas Selectivity Enhancement Using Serpentine Microchannel Shaped with Optimum Dimensions in Microfluidic-Based Gas Sensor.

A microfluidic-based gas sensor was chosen as an alternative method to gas chromatography and mass spectroscopy systems because of its small size, high accuracy, low cost, etc. Generally, there are some parameters, such as microchannel geometry, that affect the gas response and selectivity of the microfluidic-based gas sensors. In this study, we simulated and compared 3D numerical models in both simple and serpentine forms using COMSOL Multiphysics 5.6 to investigate the effects of microchannel geometry on the performance of microfluidic-based gas sensors using multiphysics modeling of diffusion, surface adsorption/desorption and surface reactions. These investigations showed the simple channel has about 50% more response but less selectivity than the serpentine channel. In addition, we showed that increasing the length of the channel and decreasing its height improves the selectivity of the microfluidic-based gas sensor. According to the simulated models, a serpentine microchannel with the dimensions W = 3 mm, H = 80 µm and L = 22.5 mm is the optimal geometry with high selectivity and gas response. Further, for fabrication feasibility, a polydimethylsiloxane serpentine microfluidic channel was fabricated by a 3D printing mold and tested according to the simulation results.

Computational Modeling of Physical Surface Reactions of Precursors in Atomic Layer Deposition by Monte Carlo Simulations on a Home Desktop Computer

Computational Modeling of Physical Surface Reactions of Precursors in Atomic Layer Deposition by Monte Carlo Simulations on a Home Desktop Computer

Impact of turbine impeller blade inclination on the batch sorption process

Batch sorption is a practical process used to remove various species from the wastewater. It is affected by different parameters such as initial concentrations, temperature, pH, surface area, coexisting ions, and mixing that need to be known for batch reactor design. Although reaction mixture in batch processes needs to be well-mixed, and there are many papers regarding sorption, mixing parameters are rather neglected. Therefore, the aim of this work was to analyse the impact of the turbine impeller blades inclination and baffle presence on sorption kinetics in the uncovered batch reactor. This impact was studied using copper (II) ions sorption on zeolite NaX particles. The experiments were conducted in the baffled and unbaffled reactor equipped with the four-blade turbine placed close to the vessel base. To determine the influence of impeller blades inclination on hydrodynamics and sorption kinetics, the blades inclination varied from 30° to 90°. A transient multiphase computational fluid dynamics model was developed to gain valuable insight into complex flow kinetics. The Ritchie model, Mixed surface reaction and diffusion-controlled sorption kinetic model, and Weber-Morris model were used for the kinetic analysis of the experimental kinetic data. According to Ψ and AARD values, the reaction is kinetic controlled regardless of the impeller blades inclination. The process is the fastest if the impeller with a blades inclination of 90° is used and in the baffled reactor. Concurrently, the energy consumption is the lowest for this impeller, regardless of the presence of the baffles.

Modelling the formation, growth and coagulation of soot in a combustion system using a 2-D population balance model

A 2-D population balance model utilizing carbon mass and surface sites as internal variables was developed for soot formation during hydrocarbon decomposition reactions. The model provides particle properties such as composition and mean polyaromatic hydrocarbon size, enabling the incorporation of cyclization reactions, soot maturation, and a dynamic model of surface reactions. Accompanied by a reduced kinetic model for gas-phase species, this population balance model was then discretized using the fixed-pivot method, to provide predictions of the soot distribution as a function of position within a plug flow reactor. The model predictions of the particle size distribution functions resulting from high-temperature hydrocarbon pyrolysis within a PFTR system provide good comparison with experimental measurements under a variety of conditions. In addition to this, by tracking the changes in particle composition occurring through cyclization reactions, the point of carbon particle maturity could be determined, allowing subsequent predictions of the size distributions of the primary particles comprising soot aggregates. Through comparison with TEM and SEM imaging, these primary particle distributions were found to be accurate for the experimental conditions examined. While the implementation of the second internal variable describing particle composition was not found to provide substantial improvements to the prediction of the overall aggregate distribution from existing models, the additional computational cost that accompanies additional variables is justified in applications where morphological predictions of particle aggregates are of interest, in addition to their size distribution.

Flow field of a rotating detonation engine fueled by carbon

Solid–gas rotating detonation engines have been widely studied, but experimental limitations have prevented the full information of the flow field from being revealed. This paper describes a numerical investigation of the effect of the equivalence ratio on the two-phase flow field of a rotating detonation engine fueled by carbon and air. The discrete phase model and multiple surface reaction model are employed to determine the flow and combustion of carbon particles. The Reynolds-averaged Navier–Stokes equations are solved for the gas flow. The results show that a low-temperature air gap appears in place of deflagration in the two-phase flow field, and the gap extends into the products. Before the detonation wave, this air gap is the difference between the air and fuel layers. At higher equivalence ratios, two rotating detonation waves are formed by the contact between the high-temperature products and the fuel–air mixture.

Diffusion-mediated surface reactions and stochastic resetting

In this paper, we investigate the effects of stochastic resetting on diffusion in , where is a bounded obstacle with a partially absorbing surface . We begin by considering a Robin boundary condition with a constant reactivity κ 0, and show how previous results are recovered in the limits κ 0 → 0, ∞. We then generalize the Robin boundary condition to a more general probabilistic model of diffusion-mediated surface reactions using an encounter-based approach. The latter considers the joint probability density or generalized propagator P(x, ℓ, t|x 0) for the pair (X t , ℓ t ) in the case of a perfectly reflecting surface, where X t and ℓ t denote the particle position and local time, respectively. The local time determines the amount of time that a Brownian particle spends in a neighborhood of the boundary. The effects of surface reactions are then incorporated via an appropriate stopping condition for the boundary local time. We construct the boundary value problem satisfied by the propagator in the presence of position resetting, and use this to derive implicit equations for the marginal density of particle position and the survival probability. We highlight the fact that these equations are difficult to solve in the case of non-constant reactivities, since resetting is not governed by a renewal process. We then consider a simpler problem in which both the position and local time are reset. In this case, the survival probability with resetting can be expressed in terms of the survival probability without resetting, which considerably simplifies the analysis. We illustrate the theory using the example of a spherically symmetric surface. In particular, we show that the effects of a partially absorbing surface on the mean first passage time (MFPT) for total absorption differs significantly if local time resetting is included. That is, the MFPT for a totally absorbing surface is increased by a multiplicative factor when the local time is reset, whereas the MFPT is increased additively when only particle position is reset.

Transport and surface reaction model of a photocatalytic membrane during the radical filtration of methylene blue

• A photocatalytic membrane was fabricated for water purification and it was tested and described. • Synergy between photocatalytic degradation and membrane filtration is explored. • Simple 1D mass transport model describes the dead-end photocatalytic membrane process. • A methylene blue discoloration of 68–23% was reached with the lowest to the highest filtration rate. This study explores the synergy between photocatalytic oxidation and membrane filtration using a photocatalytic membrane. Titanium dioxide coated alumina membranes were fabricated and tested in a customized Photocatalytic Membrane Reactor (PMR) module. The discoloration of methylene blue (MB), 3.2 mg·L −1 in an aqueous solution, was evaluated in dead-end filtration mode. A simple 1D analytic transport and surface reaction model was used based on advection and diffusion, containing intrinsic retention by the membrane and reaction kinetics to predict the permeate concentration. The discoloration of MB by the photocatalytic membrane could be well described by a single retention and reaction rate constant (second Damköhler number) for fluxes from 1.6 to 16.2 L·m −2 ·h −1 . The model furthermore indicates the potential synergy between membrane retention, which leads to increased concentration, and accompanying photocatalytic conversion, at the membrane surface.

RADIv1: a non-steady-state early diagenetic model for ocean sediments in Julia and MATLAB/GNU Octave

Abstract. We introduce a time-dependent, one-dimensional model of early diagenesis that we term RADI, an acronym accounting for the main processes included in the model: chemical reactions, advection, molecular and bio-diffusion, and bio-irrigation. RADI is targeted for study of deep-sea sediments, in particular those containing calcium carbonates (CaCO3). RADI combines CaCO3 dissolution driven by organic matter degradation with a diffusive boundary layer and integrates state-of-the-art parameterizations of CaCO3 dissolution kinetics in seawater, thus serving as a link between mechanistic surface reaction modeling and global-scale biogeochemical models. RADI also includes CaCO3 precipitation, providing a continuum between CaCO3 dissolution and precipitation. RADI integrates components rather than individual chemical species for accessibility and is straightforward to compare against measurements. RADI is the first diagenetic model implemented in Julia, a high-performance programming language that is free and open source, and it is also available in MATLAB/GNU Octave. Here, we first describe the scientific background behind RADI and its implementations. Following this, we evaluate its performance in three selected locations and explore other potential applications, such as the influence of tides and seasonality on early diagenesis in the deep ocean. RADI is a powerful tool to study the time-transient and steady-state response of the sedimentary system to environmental perturbation, such as deep-sea mining, deoxygenation, or acidification events.

Optimization of process parameters for the selective leaching of copper, nickel and isolation of gold from obsolete mobile phone PCBs

The sequential separation of base and precious metals from the end-of-life mobile phone printed circuit boards (PCBs) is a significant challenge for the development of recycling process that exhibit material circularity. In this contribution, a simple, eco-friendly, and efficient leaching process is developed for the dissolution of copper and nickel from obsolete mobile phone PCBs to facilitate the isolation of a gold-rich residue. Chemical pre-treatment of downsized PCBs produced a metallic portion for which the leaching parameters for copper and nickel were optimised, including the type of leaching reagent, temperature, time, pulp density and agitation speed. It was found that quantitative dissolution of base metals occurred using 3.0 M nitric acid at 30 °C with a 50 g/L pulp density, 2 h residence time, and 500 rpm stirring speed; under these conditions, no gold was dissolved. Design of Experiment analysis using Response Surface Methodology was also undertaken to validate the process. Finally, the kinetics of the leaching process were studied and shown to conform to the chemically controlled surface reaction model, with activation energies of 39.7 and 18.4 kJ/mol for copper and nickel. Importantly, the leaching process optimised in this work avoids the need for high temperatures and reduces energy consumption and effluent generation, leading to the cleaner processing of obsolete mobile phone PCBs for the separation of gold from the dominant base metals.

Methanation of CO2 on bulk Co–Fe catalysts

The efficiency of CO2 methanation was estimated through gas chromatography in the presence of Co–Fe catalysts. Scanning electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy were applied for ex-situ analysis of the catalysts after their test in the methanation reaction. Thermal programmed desorption mass spectroscopy experiments were performed to identify gaseous species adsorbed at the catalyst surface. Based on the experimental results, surface reaction model of CO2 methanation on Co–Fe catalysts was proposed to specify active ensemble of metallic atoms at the catalyst surface, orientation of adsorbed CO2 molecule on the ensemble and detailed reaction mechanism of CO2→CH4 conversion. The reaction step when OH group in the FeOOH complex recombined with the H atom adsorbed at the active ensemble to form H2O molecule was considered as the rate-limiting step.

Investigation on effects of tritium release behavior in Li4SiO4 pebbles

For deuterium–tritium fusion reactor, the fuel of tritium is not available naturally. Tritium should be produced by the reaction of Li (n, ɑ) T. Li4SiO4 is one of promising candidates due to its high lithium density. In present work, effects of tritium release behavior from Li4SiO4 have been investigated and compared. The main release peak at lower temperature was attributed to tritium located on/near the grain surface and chemical adsorption on pore surface. The small peak at higher temperature was designated as tritium diffusion from grain including lattice and boundary. The tritium release behavior was simulated by diffusion model and surface reaction model. Tritium behavior is controlled by both diffusion and surface reaction for different stages. Based on the desorption theory, the kinetic parameters were obtained. The effects on tritium release behavior were studied. The porosity has significant effects on tritium release. Higher porosity has large specific surface providing more activation sites and fast channels for tritium release which results in lower temperature of tritium release. The main tritium release form was considered as tritium water. The release peak of deuterium moved towards lower temperature after adsorbing water vapor for 1800 h. It was demonstrated that adsorbing water was beneficial for tritium release due to isotope exchange. Compared the effects of porosity and water vapor, higher porosity has larger effects on tritium release in the present work. Based on the work, the tritium release is controlled by both diffusion and surface reaction at different stage and affected by comprehensive effects including porosity and adsorption water.

Growth of carbon nanotubes inside porous anodic alumina membranes: Simulation and experiment

Porous anodic alumina (PAA) membranes represent a widely used and extensively studied template for production of carbon nanotubes (CNT). The PAA–CNT membranes possess a number of unique properties, such as controllable nanotube geometry, size– and chemically–based selectivity as well as high water permeability. In this work, we first propose a combination of gas phase and surface reaction models to quantitatively describe the growth of carbon nanotubes in PAA membranes in a commercial CVD reactor. A complimentary experimental study of CNT formation from ethanol precursor with argon as a carrier gas is performed. A new method for characterizing carbon nanotubes geometry by SEM and TEM image processing of membrane cross–sections is proposed. The simulations show that the carbon growth rate (in nm/min) averaged over the membrane remains constant during the deposition process until the pore diameter becomes relatively small, and rapidly falls to zero after that. The carbon nanotube thickness near the membrane surface is slightly higher than that in the membrane center. The carbon growth rate increases with synthesis temperature and pressure, while it decreases with the argon flow rate. The dependence of carbon growth rate on the ethanol/water flow rate reaches maximum at some intermediate value. These results are supported by the experimental data obtained from SEM/TEM image processing. It is found that the SEM data provide overestimated values of nanotube diameter and thickness in comparison with the TEM data. The obtained results provide new insights into the CNT growth kinetics in nanoporous media, and develop quantitative guidelines for synthesis of CNT–PAA membranes with precisely controlled nanopore geometry. It also validates the combined homogenous / heterogeneous reaction model by comparison with carbon deposition kinetics on a nanometer scale.

A numerical performance study of a fixed-bed reactor for methanol synthesis by CO2 hydrogenation

Synthetic fuels are needed to replace their fossil counterparts for clean transport. Presently, their production is still inefficient and costly. To enhance the process of methanol production from CO2 and H2 and reduce its cost, a particle-resolved numerical simulation tool is presented. A global surface reaction model based on the Langmuir-Hinshelwood-Hougen-Watson kinetics is utilized. The approach is first validated against standard benchmark problems for non-reacting and reacting cases. Next, the method is applied to study the performance of methanol production in a 2D fixed-bed reactor under a range of parameters. It is found that methanol yield enhances with pressure, catalyst loading, reactant ratio, and packing density. The yield diminishes with temperature at adiabatic conditions, while it shows non-monotonic change for the studied isothermal cases. Overall, the staggered and the random catalyst configurations are found to outperform the in-line system.

Unravelling CO oxidation reaction kinetics on single Pd nanoparticles in nanoconfinement using a nanofluidic reactor and DSMC simulations

Steady state catalytic oxidation of CO in nanofluidic channels decorated with Pd nano particles was studied using the Direct Simulation Monte Carlo (DSMC) method. Diffusion, collision, adsorption, desorption and reaction processes are simulated simultaneously. The influence of various adsorption (sticking coefficient, saturation coverage), desorption (activation energy, pre-exponential factor) and reaction (activation barrier) parameters on the final CO2 turnover are determined. These effects are considered to tune DSMC surface reaction model with respect to the experimental results. With DSMC, it was possible to get insights on reactivity of the individual Pd particles and the resulting varying reaction conditions along the channel due to local conversion effects. From the local coverages, the limit of CO:O2 inlet ratio to get maximum CO2 turnover without poisoning the catalyst with CO were determined. The approach paves the way to accurately represent micro- and nanoscale flows at the same system size as that of experiments.

Incorporation-limiting mechanisms during nitrogenation of monolayer graphene films in nitrogen flowing afterglows.

Monolayer graphene films are exposed to the flowing afterglow of a low-pressure microwave nitrogen plasma, characterized by the absence of ion irradiation and significant populations of N atoms and N2(A) metastables. Hyperspectral Raman imaging of graphene domains reveals damage generation with a progressive rise of the D/G and D/2D band ratios following subsequent plasma treatments. Plasma-induced damage is mostly zero-dimensional and the graphene state remains in the pre-amorphous regime. Over the range of experimental conditions investigated, damage formation increases with the fluence of energy provided by heterogenous surface recombination of N atoms and deexcitation of N2(A) metastable species. In such conditions, X-ray photoelectron spectroscopy reveals that the nitrogen incorporation (either as pyridine, pyrrole, or quaternary moieties) does not simply increase with the fluence of plasma-generated N atoms but is also linked to the damage generation. Based on these findings, a surface reaction model for monolayer graphene nitrogenation is proposed. It is shown that the nitrogen incorporation is first limited by the plasma-induced formation of defect sites at low damage and then by the adsorption of nitrogen atoms at high damage.