Bulk Reaction Rate Research Articles

Universal slow dynamics of chemical reaction networks.

Understanding the emergent behavior of chemical reaction networks (CRNs) is a fundamental aspect of biology and its origin from inanimate matter. A closed CRN monotonically tends to thermal equilibrium, but when it is opened to external reservoirs, a range of behaviors is possible, including transition to a new equilibrium state, a nonequilibrium state, or indefinite growth. This study shows that slowly driven CRNs are governed by the conserved quantities of the closed system, which are generally far fewer in number than the species. Considering both deterministic and stochastic dynamics, a universal slow-dynamics equationis derived with singular perturbation methods and is shown to be thermodynamically consistent. The slow dynamics is highly robust against microscopic details of the network, which may be unknown in practical situations. In particular, nonequilibrium states of realistic large CRNs can be sought without knowledge of bulk reaction rates. The framework is successfully tested against a suite of networks of increasing complexity and argued to be relevant in the treatment of open CRNs as chemical machines.

Assessment of Bulk Oxygen Capacity and Transient Redox Behavior of Foamed Lanthanum Strontium Manganese Perovskites

Abstract Synthesis of solar thermochemical hydrogen (STCH) production redox materials with engineered structures, for example, replica foams, can enable efficient heat and mass transport and are critical for scaled-up systems. Prior work has motivated the use of lanthanum strontium manganese (LSM)-type perovskites as foamed STCH materials, but the effect of their morphology on bulk and kinetic behavior has not been reported. In this work, replica and direct foamed samples of La0.65Sr0.35MnO3-δ (LSM35) were fabricated and compared to synthesized powders and dense monoliths, and similarly synthesized CeO2-δ (ceria) foams, regarding their specific reaction rates and bulk oxygen capacity/H2 yields. Changes in oxygen capacity (Δδ) and reaction rates were measured between 1200 °C and 1400 °C by using fixed ratios of steam and hydrogen during both reduction and oxidation steps, allowing for analysis under practical high conversion conditions. Results suggest bulk behavior and reaction rates of the foamed LSM materials are comparable to their powder analogues. Differences in reaction rates were observed only when replica foamed samples were subjected to rapid laser heating (emulating conditions expected in solar furnaces), which is expected but has not been demonstrated at such a small scale. Foamed samples were further subjected to 50 redox cycles at 1400 °C to evaluate their stability. Results show no statistically significant decrease in hydrogen production for any of the foamed samples, but the direct foamed samples became brittle with time. Together, these results demonstrate the viability of replica foamed LSM perovskites for integration in scaled-up STCH systems.

Multiphase Kinetic Multilayer Model Interfaces for Simulating Surface and Bulk Chemistry for Environmental and Atmospheric Chemistry Teaching

This paper presents MATLAB user interfaces for two multiphase kinetic models: the kinetic double-layer model of aerosol surface chemistry and gas–particle interactions (K2-SURF) and the kinetic multilayer model of aerosol surface and bulk chemistry (KM-SUB). Each interface has simple and user-friendly features that allow undergraduate and graduate students in physical, environmental, and atmospheric chemistry classes to learn about multiphase chemistry modeling without prior computer programming or modeling experience. It is easy to input parameters, and the simulation results are promptly displayed in the interface; thus, these model interfaces are particularly suitable for in-classroom and homework teaching applications. The model input parameters include surface and bulk reaction rate coefficients, surface accommodation coefficient, and gas and bulk diffusivities, while model outputs include gas uptake coefficient and surface and bulk concentrations. Students can use the K2-SURF interface to simulate surface processes and the KM-SUB interface to simulate surface and bulk processes. Example simulations were performed for each interface to present atmospherically relevant applications and to demonstrate its versatility for exploring model sensitivity on various kinetic parameters. The K2-SURF interface was used to show how the rate of ozone uptake by an organic surface and temporal evolution of surface concentrations are affected by the surface accommodation coefficient, desorption lifetime, and surface reaction rate coefficient. Additionally, the KM-SUB interface was applied to demonstrate how bulk diffusivities impact the degradation kinetics of oleic acid particles, so that students can learn how the phase state (liquid vs semisolid vs glassy solid) impacts multiphase chemical kinetics. The developed K2-SURF and KM-SUB interfaces are effective tools for modeling surface and bulk reactions in college-level educational settings, helping students to obtain a deeper understanding of the complex behaviors of heterogeneous and multiphase systems.

Reactive Flow and Homogenization in Anisotropic Media

AbstractThe evolution of heterogeneous and anisotropic media in the uniform dissolution regime (low Damköhler number) is studied here using a numerical network model. The uniform dissolution extensively homogenizes the medium and therefore the flow field. The homogenization is further enhanced when the surface reaction is transport controlled—when slow diffusion of dissolved ions away from the mineral surface leads to the reduction of the global dissolution rate. Under those conditions, diffusive transport is more effective in narrow channels, which selectively enlarge, leading to an initial steep rise of the permeability. However, as dissolution proceeds, the void space widens and the overall dissolution rate drops, and permeability enhancement slows down. Finally, we review the relevance of these results to various processes in geological systems ranging from diagenesis and karst evolution, to carbon geosequestration. These findings provide fundamental insights into reactive transport processes in fractured and porous media and evolution of permeability, tortuosity, anisotropy, and bulk reaction rates in geological systems.

Hot-spot initiated burn waves in heterogeneous-explosive detonation reaction zones: Mixed-mode reaction and the reactive-thermal wave model

Heterogeneous detonation reaction spreads from sufficiently supercritical hot spots as burn waves, the growth and coalescence of which controls the bulk reaction rate. The statistical hot spot model formally homogenizes these effects, giving a rate term that depends on the number density of supercritical hot spots, η, and the burn wave speed, V. In order to completely specify statistical-hot-spot-based reaction rate laws for use in reactive flow models, one must obtain realistic expressions for η and V. The focus of this paper is upon the burn-wave structure and its speed, V. Specifically, a physically-based, temperature-dependent reactive-thermal wave prescription is developed which, when suitably nondimensionalized, depends on a single parameter, α. Numerical simulations show that α characterizes the reaction morphology. Specifically, α controls important elements of the degree-of-heterogeneity in mixed-mode reaction—transitional behavior that may lie anywhere between homogeneous and heterogeneous limiting cases. The model also yields an analytic, physical-properties-based formula for V. This expression enables the development of a new class of Arrhenius-based, formally-homogenized, mixed-mode-reaction-aware reaction rate law.

Investigation of chlorine wall decay in an old, decommissioned metallic pipe using a pipe section reactor

Abstract The study investigates the kinetics of free chlorine depletion in tap water from the Sofia distribution network. The overall decay rates, the bulk reaction rate coefficient, the wall reaction rate coefficient and the influence of mass transfer have been determined in a laboratory pipe section reactor (PSR), testing an old decommissioned metallic pipe. In total, 23 series of experiments were performed under different initial free chlorine concentrations and different hydraulic conditions. The applicability of different chlorine decay mathematical models has been investigated. A new model was proposed, combining zero order bulk reactions and first order wall reactions, describing the laboratory results with Nash-Sutcliffe efficiency coefficients over 0.99. The obtained values for the wall reaction coefficient vary in the range 0.008–0.030 m/h, decreasing exponentially with increasing initial chlorine concentration.

Activity and stability of the catalytic hydrogel membrane reactor for treating oxidized contaminants

The catalytic hydrogel membrane reactor (CHMR) is an interfacial membrane process that uses nano-sized catalysts for the hydrogenation of oxidized contaminants in drinking water. In this study, the CHMR was operated as a continuous-flow reactor using nitrite (NO2−) as a model contaminant and palladium (Pd) as a model catalyst. Using the overall bulk reaction rate for NO2− reduction as a metric for catalytic activity, we evaluated the effect of the hydrogen gas (H2) delivery method to the CHMR, the initial H2 and NO2− concentrations, Pd density in the hydrogel, and the presence of Pd-deactivating species. The chemical stability of the catalytic hydrogel was evaluated in the presence of aqueous cations (H+, Na+, Ca2+) and a mixture of ions in a hard groundwater. Delivering H2 to the CHMR lumens using a vented operation mode, where the reactor is sealed and the lumens are periodically flushed to the atmosphere, allowed for a combination of a high H2 consumption efficiency and catalytic activity. The overall reaction rate of NO2− was dependent on relative concentrations of H2 and NO2− at catalytic sites, which was governed by both the chemical reaction and mass transport rates. The intrinsic catalytic reaction rate was combined with a counter-diffusional mass transport component in a 1-D computational model to describe the CHMR. Common Pd-deactivating species [sulfite, bisulfide, natural organic matter] hindered the reaction rate, but the hydrogel afforded some protection from deactivation compared to a batch suspension. No chemical degradation of the hydrogel structure was observed for a model water (pH > 4, Na+, Ca2+) and a hard groundwater after 21 days of exposure, attesting to its stability under natural water conditions.

Picoliter enzyme reactor on a nanofluidic device exceeding the bulk reaction rate.

Single-cell analyses have recently become important to understand cell heterogeneity, the mechanism of cell function, and diseases. In contrast to single-cell analyses that target nucleic acids, single-cell protein analyses still pose challenges. We have proposed a general concept of integration and extended this concept to the 10-1000 nm scale with femtoliter-picoliter volumes which are smaller than the volume of a single cell exploring ultimate analytical performances (e.g. single-cell target proteomics). However, single-cell shotgun proteomics, which is used to analyze even unknown proteins, is still challenging because there is no digestion column with picoliter volume. The issues were long reaction time (overnight) and much larger reaction volume (microliter) in the conventional bulk method. In this study, an ultra-fast picoliter enzyme reactor using a nanochannel was developed. A device with a channel depth of 300 nm and a volume of 32.4 pL was fabricated. To prevent the self-digestion of trypsin (enzyme), the picoliter enzyme reactor was prepared by immobilizing trypsinogen which was activated to trypsin by enterokinase. The enzyme density obtained by the trypsinogen immobilization process was 2.5 times higher than that obtained by the conventional trypsin immobilization process. Furthermore, the apparent enzyme concentration was 36 times higher due to an extremely high surface-to-volume ratio of the nanochannel, compared to the limit concentration in the bulk. Finally, the enzyme reaction in the picoliter enzyme reactor was accelerated 25 times compared to that in the bulk. Using the picoliter enzyme reactor, protein solution with picoliter volume will be digested without self-digestion and artificial modification, which will greatly contribute to single-cell shotgun proteomics.

Relationship between chlorine decay and temperature in the drinking water

The bulk chlorine decay rate in drinking water supply systems depend on many factors, including temperature. In this document, the method to determine the order of reaction of chlorine with water is reported, as well as the method to estimate Kb (Bulk reaction rate constant). Experiments were carried out to determine the bulk chlorine decay, for which a set of water samples to determine the free residual chlorine every hour were analyzed. Chlorine concentrations were graphed against time and adjusted appropriately to the developed model. The experimental results showed that the average value of the mass decomposition rate was 0.15 h−1. It was shown that temperature affects the variation of the reaction rate of chlorine with water, Kb increases as temperature increases. In this manuscript it is reported:•The method that allows determining the reaction kinetic order of chlorine with drinking water.•The method that can help residual chlorine modelers in the correct definition of the bulk reaction rate constant.•The effectiveness of the method for evaluating the decomposition of residual chlorine in drinking water distribution networks as a function of temperature.

A dynamic model for discharge research of zinc-nickel single flow battery

A two-dimensional transient model for the study of zinc-nickel single flow battery was developed. The model is based on a comprehensive description of mass, momentum and charge transport and conservation, combining with a global kinetic model for reactions involving ions and proton. The model is validated against the experimental date and is used to study the effects of variations in concentration, flow rate, and applied current density. The model results indicate that increasing the initial concentration of hydroxide ions can increase the discharge voltage of the battery without increasing the ions concentration polarization, and higher zinc ion concentration can slightly decrease the discharge voltage. An increase in flow rate leads to a more rapid generation or consumption of the reactant concentration, a faster mass transfer and a more uniform distribution of the ion concentration. However, the effect of flow rate on the discharge voltage of the battery is small and limited. Bulk reaction rate depends on the applied current density. As the applied current density increases by one or two time, ion concentration polarization in reaction zone and the transfer current density almost double or triple and the over-potential increased a fixed amount each time.

Quantifying hydraulic and water quality uncertainty to inform sampling of drinking water distribution systems.

Sampling of drinking water distribution systems is performed to ensure good water quality and protect public health. Sampling also satisfies regulatory requirements and is done to respond to customer complaints or emergency situations. Water distribution system modeling techniques can be used to plan and inform sampling strategies. However, a high degree of accuracy and confidence in the hydraulic and water quality models is required to support real-time response. One source of error in these models is related to uncertainty in model input parameters. Effective characterization of these uncertainties and their effect on contaminant transport during a contamination incident is critical for providing confidence estimates in model-based design and evaluation of different sampling strategies. In this paper, the effects of uncertainty in customer demand, isolation valve status, bulk reaction rate coefficient, contaminant injection location, start time, duration and rate on the size and location of the contaminant plume are quantified for two example water distribution systems. Results show that the most important parameter was the injection location. The size of the plume was also affected by the reaction rate coefficient, injection rate and the injection duration, while the the exact location of the plume was additionally affected by the isolation valve status. Uncertainty quantification provides a more complete picture of how contaminants move within a water distribution system and provides more information when using modeling results to select sampling locations.

Chemotactic and hydrodynamic effects on collective dynamics of self-diffusiophoretic Janus motors

Collective motion in nonequilibrium steady state suspensions of self-propelled Janus motors driven by chemical reactions can arise due to interactions coming from direct intermolecular forces, hydrodynamic flow effects, or chemotactic effects mediated by chemical gradients. The relative importance of these interactions depends on the reactive characteristics of the motors, the way in which the system is maintained in a steady state, and properties of the suspension, such as the volume fraction. From simulations of a microscopic hard collision model for the interaction of fluid particles with the Janus motor we show that dynamic cluster states exist and determine the interaction mechanisms that are responsible for their formation. The relative importance of chemotactic and hydrodynamic effects is identified by considering a microscopic model in which chemotactic effects are turned off while the full hydrodynamic interactions are retained. The system is maintained in a steady state by means of a bulk reaction in which product particles are reconverted into fuel particles. The influence of the bulk reaction rate on the collective dynamics is also studied.

Hetero-multivalent binding of cholera toxin subunit B with glycolipid mixtures

GM1 has generally been considered as the major receptor that binds to cholera toxin subunit B (CTB) due to its low dissociation constant. However, using a unique nanocube sensor technology, we have shown that CTB can also bind to other glycolipid receptors, fucosyl-GM1 and GD1b. Additionally, we have demonstrated that GM2 can contribute to CTB binding if present in a glycolipid mixture with a strongly binding receptor (GM1/fucosyl-GM1/GD1b). This hetero-multivalent binding result was unintuitive because the interaction between CTB and pure GM2 is negligible. We hypothesized that the reduced dimensionality of CTB-GM2 binding events is a major cause of the observed CTB binding enhancement. Once CTB has attached to a strong receptor, subsequent binding events are confined to a 2D membrane surface. Therefore, even a weak GM2 receptor could now participate in second or higher binding events because its surface reaction rate can be up to 104 times higher than the bulk reaction rate. To test this hypothesis, we altered the surface reaction rate by modulating the fluidity and heterogeneity of the model membrane. Decreasing membrane fluidity reduced the binding cooperativity between GM2 and a strong receptor. Our findings indicated a new protein-receptor binding assay, that can mimic complex cell membrane environment more accurately, is required to explore the inherent hetero-multivalency of the cell membrane. We have thus developed a new membrane perturbation protocol to efficiently screen receptor candidates involved in hetero-multivalent protein binding.

Control of serpentinisation rate by reaction-induced cracking

Serpentinisation of mantle rocks requires the generation and maintenance of transport pathways for water. The solid volume increase during serpentinisation can lead to stress build-up and trigger cracking, which ease fluid penetration into the rock. The quantitative effect of this reaction-induced cracking mechanism on reactive surface generation is poorly constrained, thus hampering our ability to predict serpentinisation rate in geological environments. Here we use a combined approach with numerical modelling and observations in natural samples to provide estimates of serpentinisation rate at mid-ocean ridges. We develop a micromechanical model to quantify the propagation of serpentinisation-induced cracks in olivine. The maximum crystallisation pressure deduced from thermodynamic calculations reaches several hundreds of megapascals but does not necessary lead to crack propagation if the olivine grain is subjected to high compressive stresses. The micromechanical model is then coupled to a simple geometrical model to predict reactive surface area formation during grain splitting, and thus bulk reaction rate. Our model reproduces quantitatively experimental kinetic data and the typical mesh texture formed during serpentinisation. We also compare the model results with olivine grain size distribution data obtained on natural serpentinised peridotites from the Marum ophiolite and the Papuan ultramafic belt (Papua New Guinea). The natural serpentinised peridotites show an increase of the number of olivine grains for a decrease of the mean grain size by one order of magnitude as reaction progresses from 5 to 40%. These results are in agreement with our model predictions, suggesting that reaction-induced cracking controls the serpentinisation rate. We use our model to estimate that, at mid-ocean ridges, serpentinisation occurs up to 12 km depth and reaction-induced cracking reduces the characteristic time of serpentinisation by one order of magnitude, down to values comprised between 10 and 1000 yr. The increase of effective pressure with depth also prevents cracking, which positions the peak in serpentinisation rate at shallower depths, 4 km above previous predictions.

Effects of Temperature, Oxygen Level, Ionic Strength, and pH on the Reaction of Benzene with Hydroxyl Radicals at the Air-Water Interface in Comparison to the Bulk Aqueous Phase.

Atmospheric aerosols (e.g., fog droplets) are complex, multiphase mediums. Depending on location, time of day, and/or air mass source, there can be considerable variability within these droplets, relating to temperature, pH, and ionic strength. Due to the droplets' inherently small size, the reactions that occur within these droplets are determined by bulk aqueous phase and air-water interfacial conditions. In this study, the reaction of benzene and hydroxyl radicals is examined kinetically in a thin-film flow-tube reactor. By varying the aqueous volume (e.g., film thickness) along the length of the reactor, both bulk and interfacial reaction rates are measured from a single system. Temperature, pH, and ionic strength are varied to model conditions typical of fog events. Oxygen-poor conditions are measured to study oxygen's overall effect on the reaction pathway. Initial rate activation energies and the bulk aqueous phase and interfacial contributions to the overall rate constant are also obtained.

Interfacial Mass Transport in Porous Media Augmented with Bulk Reactions: Analytical and Numerical Solutions

The focus of this work is on the rate of interfacial mass transfer at the interface between two immiscible fluids in porous media, subjected to variations in velocity and first-order consumption in the bulk medium. Numerical and analytical solutions are presented. We quantify the entrance length scale, which is the typical length in the flow direction over which the local and equilibrium Sherwood numbers (\(Sh\)) become identical, for Darcy–Brinkman flows in the presence of first-order bulk reactions (presented by Damkohler (\(Da\)) number). The study considers the effect of Schmidt number (\(Sc\)), viscosity ratios, permeability and bulk reaction coefficients. Results suggest a closed form solution for the entrance length scale. It is also observed that the assumption of equilibrium conditions prior to approaching this length may be violated for lower bulk reaction rates. Numerical and analytical results are in good agreement and suggest limited dependency of equilibrium \(Sh\) and \(Da\), as \(Da\) diminishes.

Calcite dissolution rates in texturally diverse calcareous rocks

Abstract The injection of reactive fluids into carbonate reservoirs during enhanced recovery operations can induce important changes in rock permeability. However, reliably predicting these changes requires accurate knowledge of calcite reaction rates. While numerous studies have examined calcium carbonate dissolution rates, most have focused on pure calcite crystals rather than actual rocks. In this study, two types of flow-through experiments were carried out to determine the calcite dissolution rates in texturally diverse calcareous rocks: the first type of experiment had a duration of 3 days, while the second type ran for 3 months. Our experiments show that rocks with differing textures and roughness (samples included coarse-grained oolitic limestone, fine-grained Solnhofen limestone, marble and calcite spar) do in fact dissolve by different mechanisms. However, despite these differences, bulk reaction rates were found to be remarkably similar (with a relative standard deviation of <20%) and consistent with previously reported reaction rates for calcite. Thus, our results suggest that textural differences between rock types are unlikely to have an important impact on overall reaction rates in fractured carbonate reservoirs.

Coupled Diffusion and Abiotic Reaction of Trichlorethene in Minimally Disturbed Rock Matrices

Laboratory experiments were performed using minimally disturbed sedimentary rocks to measure the coupled diffusion and abiotic reaction of trichloroethene (TCE) through rock core samples. Results showed that, for all rock types studied, TCE dechlorination occurred, as evidenced by generation of acetylene, ethene, and/or ethane daughter products. First-order bulk reaction rate constants for TCE degradation ranged from 8.3 × 10(-10) to 4.2 × 10(-8) s(-1). Observed reaction rate constants showed a general correlation to the available ferrous iron content of the rock, which was determined by evaluating the spatial distribution of ferrous iron relative to that of the rock porosity. For some rock types, exposure to TCE resulted in a decrease in the effective diffusivity. Scanning electron microscopy (SEM) indicated that the decrease in the effective diffusivity was due to a decrease in the porosity that occurred after exposure to TCE. Overall, these coupled diffusion and reaction results suggest that diffusion of TCE into rock matrices as well as the rate and extent of back-diffusion may be substantially mitigated in rocks that contain ferrous iron or other naturally occurring reactive metals, thereby lessening the impacts of matrix diffusion on sustaining dissolved contaminant plumes in bedrock aquifers.

Small‐scale permeability heterogeneity has negligible effects on nutrient cycling in streambeds

Aquatic sediment hosts coupled pore water flow and biogeochemical reactions that mediate water quality across the fluvial corridor including adjacent alluvial aquifers. However, the effect of small‐scale variations in sediment hydraulic properties on nutrient transformation occurring within the sediment is poorly understood. We show through numerical flow and transport simulations, for two realistic heterogeneous permeability cases typical of lowland rivers and two idealized homogeneous ones, that there is little difference in the reactive transport fields, the bulk reaction rates, and nutrient sink/source function despite stark differences in flow fields. This is because the reactions are ultimately controlled by characteristic or bulk residence times that are similar for the heterogeneous and homogeneous cases. This is a promising result for predictive models based solely on relative ratios of residence times and reactive time scales.

The effect of 15N to 14N ratio on nitrification, denitrification and dissimilatory nitrate reduction

Earlier experiments demonstrated that isotopic effects during nitrification, denitrification and dissimilatory nitrate reduction can be affected by high (15) N contents. These findings call into question whether the reaction parameters (rate constants and Michaelis-Menten concentrations) are function of δ(15) N values, and if these can also lead to significant effects on the bulk reaction rate. Five experiments at initial δ(15) N-NO(3) (-) values ranging from 0‰ to 1700‰ were carried out in a recent study using elemental analyser, gas chromatography, and mass spectrometry techniques coupled at various levels. These data were combined here with kinetic equations of isotopologue speciation and fractionation. Our approach specifically addressed the combinatorial nature of reactions involving labeled atoms and explicitly described substrate competition and time-dependent isotopic effects. With the method presented here, we determined with relatively high accuracy that the reaction rate constants increased linearly up to 270% and the Michaelis-Menten concentrations decreased linearly by about 30% over the tested δ(15) N-NO(3) (-) values. Because the parameters were found to depend on the (15) N enrichment level, we could determine that increasing δ(15) N-NO(3) (-) values caused a decrease in bulk nitrification, denitrification and dissimilatory nitrate reduction rates by 50% to 60%. We addressed a method that allowed us to quantify the effect of substrate isotopic enrichment on the reaction kinetics. Our results enable us to reject the assumption of constant reaction parameters. The implications of δ-dependent (variable) reaction parameters extend beyond the study-case analysed here to all instances in which high and variable isotopic enrichments occur.