Effective Reaction Rate Research Articles

Understanding the impact of nuclear-data covariances on various integral responses using adjustment

The EUCLID (Experiments Underpinned by Computational Learning for Improvements in Nuclear Data) project created a library of sensitivities for nine different integral responses with respect to nuclear data. These integral responses were obtained from measurements at LLNL (Lawrence Livermore National Laboratory) pulsed spheres, critical and sub-critical assemblies. At the same time, covariances for ENDF/B-VIII.0 were processed at LANL (Los Alamos National Laboratory). The combination of these data allow us to study the impact of nuclear-data covariances on various integral responses, either by forward-propagating covariances via sensitivities, or by using nuclear data, integral responses, and sensitivities for adjustment. Here, we will present: the impact of 1H, 9Be, 12C, 27Al, 56Fe, 235,238U, and 239,240Pu ENDF/B-VIII.0 covariances on simulated bounds of the following integral responses: LLNL pulsed-spheres neutron-leakage spectra, the effective neutron multiplication factor, reaction rates, and reactivity coefficients of ICSBEP critical assemblies. Also, adjustment results with the same nuclear-data covariances and responses will be discussed. LA-UR-22-31309

Effect of formic acid on O2 + OH˙CHOH → HCOOH + HO2 reaction under tropospheric condition: kinetics of cis and trans isomers.

Formic acid (HCOOH) is one of the highly abundant acids in the troposphere. It is important in the formation of atmospheric aerosols and impacts the acidity of rainwater. In the present scenario, the model chemistry of HCOOH(FA) sources and sinks is poorly understood. In this work, we apply quantum chemical methods coupled with advanced statistical rate theories to understand the production of FA and its catalytic behavior under tropospheric conditions. The potential energy surfaces (PES) for O2 + OH˙CHOH and O2 + OH˙CHOH(+FA) reactions were constructed using the CCSD(T)/6-311++G(3df,3pd)//M06-2X/6-311++G(3df,3pd) level and rate constants for the production of FA were predicted using Rice-Ramsperger-Kassel-Marcus (RRKM)/master equation (ME) simulation with Eckart tunnelling and canonical variational transition state theory (CVT) with small curvature tunnelling (SCT) between the temperature range of 200-320 K and pressure range of 0.001 to 10 bar. The reaction follows the formation of cis and trans intermediates followed by spontaneous decomposition via concerted HO2 elimination to form stable post intermediates, which then leads to the straight formation of cis and trans formic acid. The current study also helps understand the role of cis and trans contribution to the total rate constants. The results show that O2 + OH˙CHOH is dominated by both cis and trans isomers; however, the trans isomer plays a more important role in the catalytic reaction. This result is due to the formation of a strong hydrogen-bonded complex in the trans isomer, which is dominated by the enthalpy factor rather than the entropy factor. The results predict that the catalytic effect of FA on the O2 + OH˙CHOH reaction is important when the concentration of FA is not included in the calculations; however, it has no effect under tropospheric conditions, when the FA concentration is included in the calculation. As a result, the total effective reaction rate constants are smaller. This work provides experimental/theoretical confirmation of Franco et al. who predicted that methanediol is the precursor for the FA formation, resolving an open problem in the kinetics of the gas phase reaction. O2 + OH˙CHOH and O2 + OH˙CHOH(+FA) probably explain other diol systems, which can help explain the formation of other atmospheric acids that affect aerosol formation and cloud evolution.

ANALISIS NEUTRONIK KEKRITISAN TERAS REAKTOR NUSCALE BERBAHAN BAKAR DENGAN MENGGUNAKAN SOFTWARE OPENMC

[Title: Neutronic Analysis of the criticality level of the nuscale reactor core with fuel using the openMC software] This study analyzed the design of the NuScale reactor, which aims to determine the level of criticality by modeling the shape of the cell pin, assembly, and core with nuclear fuel in the form of uranium dioxide, which will be varied by changing the percentage of uranium-235 content as much as 0% to 7% by using monte carlo methods in OpenMC program code. This study was conducted to obtain the design of nuclear reactors as well as the calculation of the effective multiplication factor, fission reaction rate, and neutron flux distribution for two years of the combustion process (Burn-up). The result of the calculation for the effective multiplication factor and reaction rate states that the greater the percentage of enrichment in uranium-235, the greater the value of the resulting in both parameters. While the distribution of neutron flux produces the most significant value in the middle region or center of the fuel and is seen from the average value produced, and the smallest value is at the edge of the cell. The analysis of this NuScale reactor can later be used as a reference in preparing a safe and efficient reactor core.

Effects of Adding Different Proportions of H2 to the Simulated Hydrogen‐Rich Blast Furnace

AbstractThe volume‐fraction changes of CO2 and H2O after adding different proportions of H2 to the hydrogen‐rich blast furnace were simulated by thermodynamic calculations to evaluate the effects of H2 on coke gasification in a blast furnace. Thermodynamic calculations indicated that the H2O content in the mixed gas gradually increased with higher H2 content. The coke gasification kinetics effective diffusion coefficient De and interfacial reaction rate constant k+ of the coke gasification reaction improved with higher H2 content. In addition, the reactivity of cokes enhanced and the coke strength after reaction decreased with higher H2 content. Mercury porosimeter experiments demonstrated that the coke gasification reaction mainly occurred on the surface.

Clinical Study of Ligustrazine Magnetic Nanoparticles Combined with Moxibustion in the Treatment of Migraine

The purpose of this article is to explore the clinical application of ligustrazine magnetic nanoparticles combined with moxibustion in the treatment of migraine. In this study 60 patients diagnosed with migraine were enrolled and divided into three groups of ligustrazine magnetic nanoparticles group, moxibustion treatment group and ligustrazine magnetic nanoparticles combined moxibustion group. Patients in ligustrazine magnetic nanoparticles treatment group were injected with quantitative ligustrazine magnetic nanoparticles, moxibustion treatment group used self-adhesive small. Acupuncture moxibustion in patients with moxibustion patients, ligustrazine magnetic nanoparticles combined with moxibustion treatment group using the combination of the above two treatments, after the treatment period, the treatment of patients in each group is effective, prognosis recurrence rate and adverse reaction rate perform statistics and analysis. The research results show that the treatment efficiency of the ligustrazine magnetic nanoparticles combined with moxibustion treatment group is as high as 97.2%, which is higher than that of the other two groups. The prognosis recurrence rate is only 4.76%, which is lower than that of the other two groups, and the adverse reaction rate is 3.85%, which is lower than the other two groups. It can be seen that the treatment of ligustrazine magnetic nanoparticles combined with moxibustion is an effective way to treat migraine.

Comparative kinetics study of the catalytic oxidation of benzene and its mono-halogenated derivatives over V 2 O 5 –WO 3 /TiO 2 catalyst

The SCR-DeNOx commercial catalysts are reported as possible candidates to remove aromatic VOCs and NO x simultaneously. In this paper, we present the kinetic studies of the oxidation of benzene and its mono-halogenated derivatives over V 2 O 5 –WO 3 /TiO 2 catalyst as typical high-dust SCR-DeNOx system. The kinetic investigation follows the influence of temperature on the conversion of aromatic VOCs to establish the apparent energy activation and dependence on between temperature and the effective constant rate of the catalytic oxidation reaction. The data shows that the catalytic oxidation process takes place after a combined kinetic mechanism, mass transport through pores—chemical transformation.

Impact of Physical Heterogeneity and Transport Conditions on Effective Reaction Rates in Dissolution

A continuous-time random walk (CTRW) reactive transport model is used to study the impact of physical heterogeneity on the effective reaction rates in porous media in a sample of length 15 cm over timescales up to 10^8 s (3 years). The model has previously been validated using nuclear magnetic resonance (NMR) measurements during dissolution of a limestone. The model assumes first-order reaction. We construct three domains with increasing physical heterogeneity and study dissolution at four Péclet numbers, Pe = 0.0542, 0.542, 5.42 and 54.2. We characterize signatures of physical heterogeneity in the three porous media using velocity distributions and show how these imprint on the signatures of particle displacement, namely particle propagator distributions. In addition, we demonstrate the ability of our CTRW model to capture the impact of physical heterogeneity on the longitudinal dispersion coefficient over several orders of magnitude in space and time. Reactive transport simulations show that the effective reaction rates depend on (i) initial physical heterogeneity and (ii) transport conditions. For all heterogeneities and Pe, the late-time reaction rate exhibits a time dependence t^{-a} with a ne 0.5 that indicates the persistence of incomplete mixing. We show that the higher the initial heterogeneity, the lower the late-time reaction rate. A decrease in Pe promotes mixing by diffusion over advection, resulting in higher reaction rates. The post-dissolution propagators indicate an increase in the degree of non-Fickian transport. Overall, we establish a framework to demonstrate and quantify the impact of physical heterogeneity on transport and effective reaction rates in porous media.

Supercapacitor and oxygen evolution reaction performances based on rGO and Mn2V2O7 nanomaterials

Manganese vanadate Mn2V2O7 (MVO), and reduced graphene oxide (rGO) have been synthesized for supercapacitors and electrocatalytic applications. The structure and electrochemical characterization studies were performed by several techniques, including XRD, SEM, TEM, XPS, BET, cyclic voltammetry (CV), Linear sweep voltammetry (LSV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). The characterization tools of the investigated samples showed an amorphous structure for rGO and a monoclinic structure for MVO. The single electrodes of the investigated samples showed a specific capacitance of 120, 235, and 330 F/g for rGO, MVO, and rGO@MVO, respectively, in an electrolyte of 1M of LiClO4 in propylene carbonate solution. The electrochemical behavior of an asymmetric supercapacitor (ASC) of rGO@MVO//AC was studied under a potential window of 0–2 V, providing a high energy density of 66.6 Wh kg−1 at a power density of 19478 W kg−1. The ASC cell showed a specific capacitance of 112 F/g at a current density of 10 A/g and cycling stability with 86.6% capacitance retention over 8000 cycles. For oxygen evolution reaction, the rGO@Mn2V2O7 electrode showed a lower overpotential of 225 mV at a current density of 10 mA cm−2, with a Tafel slope of 54 mV dec−1, displaying a fast and effective reaction rate. These outcomes indicate that rGO@Mn2V2O7 can be used as hopeful electrode material for supercapacitor and water splitting applications.

Steam Methane Reforming with Chemical-Looping Combustion: Scaling of Fluidized-Bed-Heated Reformer Tubes

The combination of chemical-looping combustion (CLC) and steam methane reforming (SMR) bears the potential for quantitative and energy-efficient CO2 capture along with hydrogen production from natural gas. A 2-dimensional axisymmetric model of a SMR tube was used to estimate the possibility to adapt the tube dimensions to better fit into fluidized-bed heat exchangers. A constant surrounding fluidized-bed temperature was set as the boundary condition. There are two phenomena that affect the reactor performance: the effective heat-transfer rate from the fluidized bed to and through the tube wall and onward to and into the catalyst bed on the one hand and the effective reaction rates of the governing chemical reactions on the other hand. Literature models were used for the heat-transfer description assuming a state-of-the-art reforming catalyst and classical SMR kinetics were formulated. The simulation results show a temperature decrease toward the tube center in steady state operation. The gas phase composition at the tube outlet reflects the radial temperature distribution as the chemical equilibrium is approached well. Simulations with smaller tube diameters indicate that the necessary tube length for equivalent gas conversion is significantly reduced. In a 1/2-scale setting with 63 mm inner diameter (ID) of the tube instead of 126 mm ID in full scale, the necessary tube length is only 6.0 m instead of 12.5 m, and in a 1/4-scale setting with 31.5 mm ID, the necessary tube length is only 3.3 m. A temperature increase of the fluidized bed from 900 to 950 and 1000 °C may reduce the necessary tube length in the 1/4 scale from 3.3 to 2.6 and 2.2 m, respectively. These indications are promising with respect to the possibilities for fluidized-bed immersed reformer tube dimensioning and arrangement. More detailed reactor design studies will be necessary to judge the industrial feasibility of the CLC-SMR combination.

Comparison of flow dynamics and reactor performance in gas-solids circulating turbulent fluidized bed with other fluidized beds across regimes

The hydrodynamics and the reactor performance in the recently proposed gas-solids circulating turbulent fluidized bed (CTFB) were compared with that in the low-velocity conventional fluidized beds and the high-density circulating fluidized bed (HDCFB) riser. The average solids holdup distributions, fluctuations, and probability density distributions of the instantaneous solids holdup signals indicate that the CTFB either more resembles a TFB if the Gs/Ug ratio is large or more resembles an HDCFB if the Gs/Ug ratio is small. The distributions of the bubble occurrence, equivalent bubble size, and bubble phase fraction were extracted from the optical fiber signals of the local solids holdup using the wavelet analysis method. The CTFB was found to have a greater number of smaller bubbles than the bubbling and turbulent fluidized beds and relatively fewer and larger bubbles than that in an HDCFB. The effect of flow dynamics and bubble behaviors on the reaction performance in different types of fluidized beds are compared by analytical calculation based on the K-L reactor model. A superior reactor performance can be achieved using the CTFB reactor for a higher effective reaction rate, higher mass transfer rates, and a lower degree of solids backmixing.

Chemical transformation of <i>α</i>-pinene-derived organosulfate via heterogeneous OH oxidation: implications for sources and environmental fates of atmospheric organosulfates

Abstract. Organosulfur compounds are found to be ubiquitous in atmospheric aerosols – a majority of which are expected to be organosulfates (OSs). Given the atmospheric abundance of OSs, and their potential to form a variety of reaction products upon aging, it is imperative to study the transformation kinetics and chemistry of OSs to better elucidate their atmospheric fates and impacts. In this work, we investigated the chemical transformation of an α-pinene-derived organosulfate (C10H17O5SNa, αpOS-249) through heterogeneous OH oxidation at a relative humidity of 50 % in an oxidation flow reactor (OFR). The aerosol-phase reaction products were characterized using high-performance liquid chromatography–electrospray ionization–high-resolution mass spectrometry and ion chromatography. By monitoring the decay rates of αpOS-249, the effective heterogeneous OH reaction rate was measured to be (6.72±0.55)×10-13 cm3 molecule−1 s−1. This infers an atmospheric lifetime of about 2 weeks at an average OH concentration of 1.5×106 molecules cm−3. Product analysis shows that OH oxidation of αpOS-249 can yield more oxygenated OSs with a nominal mass-to-charge ratio (m/z) at 247 (C10H15O5S−), 263 (C10H15O6S−), 265 (C10H17O6S−), 277 (C10H13O7S−), 279 (C10H15O7S−), and 281 (C10H17O7S−). The formation of fragmentation products, including both small OSs (C <10) and inorganic sulfates, is found to be insignificant. These observations suggest that functionalization reactions are likely the dominant processes and that multigenerational oxidation possibly leads to formation of products with one or two hydroxyl and carbonyl functional groups adding to αpOS-249. Furthermore, all product ions except m/z=277 have been detected in laboratory-generated α-pinene-derived secondary organic aerosols as well as in atmospheric aerosols. Our results reveal that OSs freshly formed from the photochemical oxidation of α-pinene could react further to form OSs commonly detected in atmospheric aerosols through heterogeneous OH oxidation. Overall, this study provides more insights into the sources, transformation, and fate of atmospheric OSs.

Machine learning to predict effective reaction rates in 3D porous media from pore structural features

Large discrepancies between well-mixed reaction rates and effective reactions rates estimated under fluid flow conditions have been a major issue for predicting reactive transport in porous media systems. In this study, we introduce a framework that accurately predicts effective reaction rates directly from pore structural features by combining 3D pore-scale numerical simulations with machine learning (ML). We first perform pore-scale reactive transport simulations with fluid–solid reactions in hundreds of porous media and calculate effective reaction rates from pore-scale concentration fields. We then train a Random Forests model with 11 pore structural features and effective reaction rates to quantify the importance of structural features in determining effective reaction rates. Based on the importance information, we train artificial neural networks with varying number of features and demonstrate that effective reaction rates can be accurately predicted with only three pore structural features, which are specific surface, pore sphericity, and coordination number. Finally, global sensitivity analyses using the ML model elucidates how the three structural features affect effective reaction rates. The proposed framework enables accurate predictions of effective reaction rates directly from a few measurable pore structural features, and the framework is readily applicable to a wide range of applications involving porous media flows.

Effect of Water and Formic Acid on ·OH + CH4 Reaction: An Ab Initio/DFT Study

In this work, we used ab initio/DFT method coupled with statistical rate theory to answer the question of whether or not formic acid (HCOOH) and water molecules can catalyze the most important atmospheric and combustion prototype reaction, i.e., ·OH (OH radical) + CH4. The potential energy surface for ·OH + CH4 and ·OH + CH4 (+X) (X = HCOOH, H2O) reactions were calculated using the combination of hybrid-density functional theory and coupled-cluster theory with Pople basis set [(CCSD(T)/ 6-311++G(3df,3pd)//M06-2X/6-311++G(3df,3pd)]. The results of this study show that the catalytic effect of HCOOH (FA) and water molecules on the ·OH + CH4 reaction has a major impact when the concentration of FA and H2O is not included. In this situation the rate constants for the CH4 + HO···HCOOH (3 × 10−9 cm3 molecule−1 s−1) reaction is ~105 times and for CH4 + H2O···HO reaction (3 × 10−14 cm3 molecule−1 s−1 at 300 K) is ~20 times higher than ·OH + CH4 (~6 × 10−15 cm3 molecule−1 s−1). However, the total effective rate constants, which include the concentration of both species in the kinetic calculation has no effect under atmospheric condition. As a result, the total effective reaction rate constants are smaller. The rate constants when taking the account of the FA and water for CH4 + HO···HCOOH (4.1 × 10−22 cm3 molecule−1 s−1) is at least seven orders magnitude and for the CH4 + H2O···HO (7.6 × 10−17 cm3 molecule−1 s−1) is two orders magnitude smaller than ·OH + CH4 reaction. These results are also consistent with previous experimental and theoretical studies on similar reaction systems. This study helps to understand how FA and water molecules change the reaction kinetic under atmospheric conditions for ·OH + CH4 reaction.

Improvement of acid treatment with the sintanol preparation after hydro-sand blasting of wells in the conditions of ANK «Bashneft»

A sandblasting hammer is lowered into the well, setting against the selected processing interval, and hydraulic clamps are necessary for the rig to be held firmly. The displacement of the latter eliminates the possibility of selective processing. After the usual sandblasting and flushing the well from sand, without changing the position of the perforator, an acid solution is pumped into the pipes, which, entering the channel formed, is filtered through its walls into the treated section of the formation. The part of the acid that, after the end of the treatment, has accumulated in the wellbore, is forced into the reservoir by the squeezing fluid through the annular space. Increase the acid depletion time, i.e. slow down the reaction rate by adding special reagents to the solution. So, a syntanol DS-10 TU 2483-016-71150986-2012 (a non-ionic surfactant and is intended for use as an effective surfactant) is a very effective reaction rate reducer. Adding it in an amount of 0.5% (by weight of the volume of the solution) can reduce the reaction rate by 2.7 times. Keywords: speed; reaction; syntanol; processing; pressure.

Effect Of Butylphthalide Combined with Ozagrel Sodium on Cerebral Perfusion and Oxidative Stress Indexes in Patients with Transient Ischemic Attack

Background The pathogenesis of transient ischemic attack is not clear. Microthrombosis theory is a theory with high clinical recognition. Microthrombosis of carotid artery and vertebral basilar artery wall occurs shedding and vasospasm, resulting in transient cerebral insufficiency. Microembolic decomposition or distal movement, cerebrovascular dilatation, local collateral circulation after the establishment of symptoms relieved or disappeared. Most patients can be relieved in a short time, but recurrent attacks can gradually damage the structure and function of brain tissue, and increase the risk of acute cerebral infarction. The clinical treatment of this disease is mainly based on the comprehensive control of risk factors, anti thrombosis, and anti-platelet aggregation. Objective To observe the effect of butylphthalide combined with ozagrel sodium on cerebral perfusion and oxidative stress indexes in patients with transient ischemic attack. Methods A total of 116 patients diagnosed as transient ischemic attack in our hospital (February 2018 - February 2020) were selected and divided into two groups according to the treatment methods. 58 cases in the control group were treated with ozagrel sodium, 58 cases in the observation group were treated with butylphthalide combined with ozagrel sodium. The CT perfusion imaging parameters, oxidative stress indexes, plaque area, and the levels of platelet activating factor ( PAF ), α-granule membrane protein-140 ( GMP-140 ), fibrinogen ( FIB ), platelet aggregation rate (PAgT), neuron-specific enolase (NSE), oxygend-inducible factor-1α (HIF-1α), and matrix metalloproteinases 9 (MMP-9) in the two groups were recorded, and the total effective rate and adverse reaction rate were counted. Results The total effective rate of the observation group was higher than that of the control group, and the difference was statistically significant (χ2=4.640, P = 0.031). Compared with before treatment, the average time (MTT) required for the two groups of contrast agents to pass through the local brain tissue and the time (TTP) required to start the injection of contrast agents to reach the peak concentration decreased compared with before treatment. After treatment, the MTT and TTP of the observation group were shorter than those of the control group (P < 0.05). Compared with before treatment, superoxide dismutase ( SOD ) in the two groups was higher than that in the control group, PAF, GMP-140, FIB, PAgT, NSE, HIF-la, MMP-9, malondialdehyde (MDA) and plaque area decreased. After treatment, the levels of related factors in the observation group were better than those in the control group, and the plaque area was less than that in the control group (P < 0.05). There was no significant difference in the adverse reaction rate between the observation group and the control group (χ2 = 0.438, P=0.508). Conclusion Butylphthalide combined with ozagrel sodium in the treatment of transient ischemic attack can improve cerebral perfusion, reduce oxidative stress injury, reduce plaque and improve curative effect.

The effect of alkali and alkaline earth metals oxides addition on oxygen uncoupling rate of copper-based oxygen carrier: A kinetic and experimental investigations

• Oxygen uncouples ability of CuO at low temperatures tested by adding AAEMs oxides. • 5% wt of Na 2 O, K 2 O, MgO, and CaO added to CuO. • An isothermal test was done; MgO, CaO enhanced the process and Na 2 O, K 2 O declined. • Kinetic analysis has been conducted for a more in-depth investigation. • Kinetic results was matched with the experimental, in both MgO was the best. Oxygen uncoupling is one of the most valued properties of oxygen carriers in chemical looping field. It allows to combust the fuel without gasification step and significantly enhances reactivity in all chemical looping fuel oxidation technologies (combustion, gasification, and reforming). Furthermore, it progressed recently to produce pure oxygen (Chemical looping air separation). However, few materials have this merit, among which CuO has the highest reactivity and oxygen transport (uncoupling) capacity. However, it needs a high temperature (about 950 °C) for a high effective reaction rate; in contrast, it suffers high attrition rate and sintering about this temperature. This work aimed to test the ability to enhance the uncoupling at lower temperatures by adding a small amount of common alkali and alkaline earth metals (AAEMs) oxides. CuO was prepared with 5%wt of Na 2 O, K 2 O, MgO, and CaO. An isothermal test was conducted in TGA at (850, 890, and 930 °C) to investigate the effect of additions. For deeper investigation, kinetic analysis has been conducted based on isothermal results. The model of reaction inferred was A 2 α of Avrami-Erofeev ( g α = - l n 1 - α 1 / 2 ) for pure CuO and with all additions, and then the activation energies and pre-exponential factors were calculated. Accordingly, CaO addition showed little increase in the reaction rates while the effect of MgO was significant. In contrast, Na 2 O and K 2 O addition declined the uncoupling rate.

A Loser-Take-All DNA Circuit.

DNA-based neural networks are a type of DNA circuit capable of molecular pattern recognition tasks. Winner-take-all DNA networks have been developed to scale up the complexity of molecular pattern recognition with a simple molecular implementation. This simplicity was achieved by replacing negative weights in individual neurons with lateral inhibition and competition across neurons, eliminating the need for dual-rail representation. Here we introduce a new type of DNA circuit that is called loser-take-all: an output signal is ON if and only if the corresponding input has the smallest analog value among all inputs. We develop a DNA strand-displacement implementation of loser-take-all circuits that is cascadable without dual-rail representation, maintaining the simplicity desired for scalability. We characterize the impact of effective signal concentrations and reaction rates on the circuit performance, and derive solutions for compensating undesired signal loss and rate differences. Using these approaches, we successfully demonstrate a three-input loser-take-all circuit with nine unique input combinations. Complementary to winner-take-all, loser-take-all DNA circuits could be used for recognition of molecular patterns based on their least similarities to a set of memories, allowing classification decisions for patterns that are extremely noisy. Moreover, the design principle of loser-take-all could be more generally applied in other DNA circuit implementations including k-winner-take-all.

The chemical continuous time random walk framework for upscaling transport limitations in fluid–solid reactions

Fluid-solid reactions play a key role in a large range of biogeochemical processes. Transport limitations at the pore scale limit the amount of solute available for reaction, so that reaction rates measured under well-mixed conditions tend to strongly overestimate rates occurring in natural and engineered systems. Although different models have been proposed to capture this phenomenon, linking pore-scale structure, flow heterogeneity, and local reaction kinetics to upscaled effective kinetics remains a challenging problem. We present a new theoretical framework to quantify these dynamics based on the chemical continuous time random walk framework. We study a fluid–solid reaction with the fluid phase undergoing advective–diffusive transport. We consider a catalytic degradation reaction, AF+BS→BS, where AF is in fluid phase and BS is in solid phase and homogeneous over the fluid–solid interface, allowing us to focus on the role of transport limitations and medium structure. Our approach is based on the concept of inter-reaction times, which result from the times between contacts of transported reactants with the solid phase. We use this formulation to quantify the global kinetics of fluid-reactant mass and test our predictions against numerical simulations of advective–diffusive transport in stratified channel flow and Stokes flow through a beadpack. The theory captures the decrease of effective reaction rates compared to the well-mixed prediction with increasing Damköhler number due to transport limitations. Although we consider simple kinetics and media, these findings will contribute to the understanding and modeling of the effect of transport limitations in more complex reactive transport problems.

Effect of ammonia and water molecule on OH\u2009+\u2009CH3OH reaction under tropospheric condition

The rate coefficients for OH + CH3OH and OH + CH3OH (+ X) (X = NH3, H2O) reactions were calculated using microcanonical, and canonical variational transition state theory (CVT) between 200 and 400 K based on potential energy surface constructed using CCSD(T)//M06-2X/6-311++G(3df,3pd). The results show that OH + CH3OH is dominated by the hydrogen atoms abstraction from CH3 position in both free and ammonia/water catalyzed ones. This result is in consistent with previous experimental and theoretical studies. The calculated rate coefficient for the OH + CH3OH (8.8 × 10−13 cm3 molecule−1 s−1), for OH + CH3OH (+ NH3) [1.9 × 10−21 cm3 molecule−1 s−1] and for OH + CH3OH (+ H2O) [8.1 × 10−16 cm3 molecule−1 s−1] at 300 K. The rate coefficient is at least 8 order magnitude [for OH + CH3OH(+ NH3) reaction] and 3 orders magnitude [OH + CH3OH (+ H2O)] are smaller than free OH + CH3OH reaction. Our calculations predict that the catalytic effect of single ammonia and water molecule on OH + CH3OH reaction has no effect under tropospheric conditions because the dominated ammonia and water-assisted reaction depends on ammonia and water concentration, respectively. As a result, the total effective reaction rate coefficients are smaller. The current study provides a comprehensive example of how basic and neutral catalysts effect the most important atmospheric prototype alcohol reactions.

Phase Saturation Control on Mixing-Driven Reactions in 3D Porous Media.

Transported chemical reactions in unsaturated porous media are relevant to environmental and industrial applications. Continuum scale models are based on equivalent parameters derived from analogy with saturated conditions and cannot appropriately account for incomplete mixing. It is also unclear how the third dimension controls mixing and reactions. We obtain three-dimensional (3D) images by magnetic resonance imaging using an immiscible nonwetting liquid as a second phase and a fast irreversible bimolecular reaction. We study the impact of phase saturation on the dynamics of mixing and the reaction front. We quantify the temporally resolved effective reaction rate and describe it using the lamellar theory of mixing, which explains faster than Fickian (t0.5) rate of product formation by accounting for the deformation of the mixing interface between the two reacting fluids. For a given Péclet, although stretching and folding of the reactive front enhance as saturation decreases, enhancing the product formation, the product formation is larger as saturation increases. After breakthrough, the extinction of the reaction takes longer as saturation decreases because of the larger nonmixed volume behind the front. These results are the basis for a general model to better predict reactive transport in unsaturated porous media not achievable by the current continuum paradigm.