Reaction Rate Equation Research Articles

Thermal Stability and Thermodynamics in the Process of Synthesising 1, 3-dimethylurea

The present work aims to study the thermal stability and thermodynamics in the process of synthesizing 1, 3-dimethylurea. The HPLC spectrograms were used to study the impacts of reaction time and temperature on the thermal behaviour of the ammonolysis reaction system. Rate equation of the ammonolysis reaction can be summed up as c(t) = 1016.24*e-(t/47.9403) +16.1935. Thermal stability curve also can be determined. Experimental results revealed that the process of synthesizing 1, 3-dimethylurea was of pseudo-first-order reaction kinetics and k value was 0.0163 min-1. Thermodynamics results indicated that enthalpy was -1.92 kJ/mol, Gibbs free energy was -8.51 J/mol, and entropy was 15.96 J/mol*K. The reaction was an exothermic, spontaneous and entropy increasing process. Based on thermal stability and thermodynamics study, synthesis of 1, 3-dimethylurea was unfavourable at higher temperature as well as long reaction time.

Phase behaviors and curcumin encapsulation performance of Gemini surfactant microemulsion

Protection of environment-sensitive bioactive component is an important issue in biological and pharmaceutical applications. The aim of this study is to provide an alternative for the solubility enhancement and the controlled release of curcumin by encapsulation with the microemulsion formed with Gemini surfactant. Pseudo-ternary phase diagrams for the surfactant/cosurfactant/oil/water (S/C/O/W) systems are obtained and the phase behaviors are systematically investigated. Less amount of water can be solubilized in the microemulsion containing alcohol with a longer carbon chain or surfactant with a longer spacer. A lower mass ratio of S/C or a higher temperature also leads to a smaller microemulsion area. As a representative, the oil-in-water microemulsion of the 14-4-14/1-propanol/n-heptane/water system is applied to encapsulate curcumin. High drug loading capacity and encapsulation efficiency are achieved higher than 7 mg·g−1 and 99%, respectively. Moreover, the in vitro release data are adequately described by the first-order reaction rate equation at both fast and mild release stages. A higher content of oil causes a slower release and a lower stable concentration for the packaged curcumin. The free radical scavenging activity is somewhat reduced when compared with that of free curcumin in ethanol due to gradual release.

Reversible Dehalogenation in On‐Surface Aryl–Aryl Coupling

AbstractIn the emerging field of on‐surface synthesis, dehalogenative aryl–aryl coupling is unarguably the most prominent tool for the fabrication of covalently bonded carbon‐based nanomaterials. Despite its importance, the reaction kinetics are still poorly understood. Here we present a comprehensive temperature‐programmed x‐ray photoelectron spectroscopy investigation of reaction kinetics and energetics in the prototypical on‐surface dehalogenative polymerization of 4,4′′‐dibromo‐p‐terphenyl into poly(para‐phenylene) on two coinage metal surfaces, Cu(111) and Au(111). We find clear evidence for reversible dehalogenation on Au(111), which is inhibited on Cu(111) owing to the formation of organometallic intermediates. The incorporation of reversible dehalogenation in the reaction rate equations leads to excellent agreement with experimental data and allows extracting the relevant energy barriers. Our findings deepen the mechanistic understanding and call for its reassessment for surface‐confined aryl–aryl coupling on the most frequently used metal substrates.

Kinetic Models of Ethylene Oxide Production on Ag Catalysts: A Review

Process modeling and design of the ethylene oxide production plant is mainly depended on the kinetics of the ethylene oxide production reactions. In this article, the kinetics equations for partial oxidation (epoxidation) of ethylene on silver catalyst were reviewed. There are three competitive reactions in this system: ethylene partial and total oxidation and ethylene oxide total oxidation. The reaction rate equations for these three reactions were compared and advantage and the disadvantage of kinetic models were discussed. Dichloroethane (DCE) is used in these reactions to increase the ethylene oxide selectivity. Therefore, the kinetics of the reactions considering the role of DCE is also reported. Most of the kinetics models have some weaknesses. However, one of the reviewed models was the complete model because of including all three reactions of partial and total oxidation of ethylene and total oxidation of ethylene oxide. Also, this model considered the concentration of selectivity promoter (DCE) and reverse reactions.

Hydrothermal corrosion behavior of CVD SiC in high temperature water

The hydrothermal corrosion of polished and as-cut high purity chemical vapor deposited (CVD) SiC was studied in a constantly refreshing water loop. Light water reactor (LWR) conditions were simulated at 288, 320, and 350 °C with dissolved gas concentrations between 0.15 and 3 ppm H2 or between 1 and 4 ppm O2. In hydrogenated water, the rate of material loss was low, calculated to be ∼1.3 μm of recession after 5 years of service in 320 °C water. Moreover, there was no observed localized attack at any temperature. In oxygenated conditions, the corrosion rate was higher, with a calculated material loss >10 μm after 5 years of service in 1 ppm O2, 320 °C water. Mass loss significantly increased when grain fallout became significant (as early as 200h with 4 ppm O2 at 350 °C or after 1000–2000h with 2 ppm O2 at 288 °C). Grain fallout more than doubled the corrosion rate and a steady state corrosion rate in the grain fallout regime was not observed but expected to eventually occur once large grains begin to be removed. Polished specimens had lower mass loss than unpolished coupons. A kinetic analysis of the data in this work suggests that the corrosion rates are controlled by a single activation step in both oxygenated and deoxygenated conditions, with the reaction order with respect to oxygen being 1. A resulting reaction rate equation to predict corrosion of SiC (in mg/cm2s) in high purity water from 288 to 350 °C and up to 4 ppm O2 was constructed: Rate=0.14581+SA T(1.09(1−10−3T)[O2]e−1.275x104T+7.91x10−6e−7.39x103T).

Uso didáctico de reactores agitados continuos para la determinación de cinéticas de reacción heterogénea

<p class="p1">Se describen la modelación, la construcción y el uso de un reactor continuo de tanque agitado para la obtención de datos experimentales de rapidez de reacción heterogénea. En primer lugar, mediante análisis de balances de materia se enfatiza cómo la capacidad de este tipo de reactor de operar en estado estacionario es ventajosa para el estudio de sistemas catalíticos heterogéneos. Consecuentemente, se propone una práctica experimental para determinar ecuaciones de rapidez globales a partir de ecuaciones intrínsecas obtenidas por el método de la etapa limitante. Se emplea un reactor continuo de tanque agitado cuya fabricación y operación son sencillos y se describen a detalle. La hidrólisis de sacarosa se implementa como reacción modelo a 60 °C y 1 atm, siendo de fácil monitoreo. La reacción se cataliza con una resina ácida (Amberlite 120 H, capacidad total de intercambio ≥ 1.80 eq/L). El experimento ilustra una aplicación del método de la etapa limitante para la obtención de ecuaciones de rapidez de reacción global y es una herramienta didáctica para reforzar el aprendizaje práctico en cursos de ingeniería de reacciones heterogéneas.</p>

Reversible Dehalogenation in On-Surface Aryl-Aryl Coupling.

In the emerging field of on-surface synthesis, dehalogenative aryl-aryl coupling is unarguably the most prominent tool for the fabrication of covalently bonded carbon-based nanomaterials. Despite its importance, the reaction kinetics are still poorly understood. Here we present a comprehensive temperature-programmed x-ray photoelectron spectroscopy investigation of reaction kinetics and energetics in the prototypical on-surface dehalogenative polymerization of 4,4''-dibromo-p-terphenyl into poly(para-phenylene) on two coinage metal surfaces, Cu(111) and Au(111). We find clear evidence for reversible dehalogenation on Au(111), which is inhibited on Cu(111) owing to the formation of organometallic intermediates. The incorporation of reversible dehalogenation in the reaction rate equations leads to excellent agreement with experimental data and allows extracting the relevant energy barriers. Our findings deepen the mechanistic understanding and call for its reassessment for surface-confined aryl-aryl coupling on the most frequently used metal substrates.

Effects of surfaces and macromolecular crowding on bimolecular reaction rates

Biological cells are complex environments that are densely packed with macromolecules and subdivided by membranes, both of which affect the rates of chemical reactions. It is well known that crowding reduces the volume available to reactants, which increases reaction rates, and also inhibits reactant diffusion, which decreases reaction rates. This work investigates these effects quantitatively using analytical theory and particle-based simulations. A reaction rate equation based on only these two processes turned out to be inconsistent with simulation results. However, accounting for diffusion inhibition by the surfaces of nearby obstacles, which affects access to reactants, it led to perfect agreement for reactions near impermeable planar membranes and improved agreement for reactions in crowded spaces. A separate model that quantified reactant occlusion by crowders, and extensions to a thermodynamic ‘cavity’ model proposed by Berezhkovskii and Szabo [], were comparably successful. These results help elucidate reaction dynamics in confined spaces and improve prediction of in vivo reaction rates from in vitro ones.

Rapid data-driven model reduction of nonlinear dynamical systems including chemical reaction networks using ℓ1-regularization.

Large-scale nonlinear dynamical systems, such as models of atmospheric hydrodynamics, chemical reaction networks, and electronic circuits, often involve thousands or more interacting components. In order to identify key components in the complex dynamical system as well as to accelerate simulations, model reduction is often desirable. In this work, we develop a new data-driven method utilizing ℓ1-regularization for model reduction of nonlinear dynamical systems, which involves minimal parameterization and has polynomial-time complexity, allowing it to easily handle large-scale systems with as many as thousands of components in a matter of minutes. A primary objective of our model reduction method is interpretability, that is to identify key components of the dynamical system that contribute to behaviors of interest, rather than just finding an efficient projection of the dynamical system onto lower dimensions. Our method produces a family of reduced models that exhibit a trade-off between model complexity and estimation error. We find empirically that our method chooses reduced models with good extrapolation properties, an important consideration in practical applications. The reduction and extrapolation performance of our method are illustrated by applications to the Lorenz model and chemical reaction rate equations, where performance is found to be competitive with or better than state-of-the-art approaches.

A Mathematical Model of the Synthesis of Pentaerythritol

Based on the results of a kinetic study of the condensation of acetaldehyde and formaldehyde in the presence of sodium hydroxide and taking into account well-known data, we compiled a reaction scheme of the process, in which pentaerythritol, dipentaerythritol, tripentaerythritol, bispentaerythritolformal, pentaerythritol methyl ether, and sodium 2,2-bis(hydroxymethyl)propanoate are formed. According to the reaction scheme, we developed a mathematical model of the process, which includes reaction rate equations and formulas for calculating the activity coefficients of ions and the degrees of ionization and equilibrium concentrations of intermediate substances. The effective kinetic parameters and activation energies of reactions were found. The adequacy of the mathematical model was statistically evaluated under the following conditions: an acetaldehyde–formaldehyde–sodium hydroxide molar ratio of 1 : 4–9 : 1.2, an initial acetaldehyde concentration of 0.4–0.9 mol/L, and a temperature of 13–47°C.

Macroscopic Kinetics of Simultaneous Desulfurization and Denitrification by MgO/NaClO2 Solution

Based on the early research results of reaction characteristics of the simultaneous desulfurization and denitrification by MgO/NaClO2 solution, the macroscopic reaction kinetics was investigated in a small-scale bubbling reactor. The effect of various factors on the reaction rate was investigated in the experiments, i.e. initial NaClO2 concentration, solution pH and reaction temperature. The reaction rate equations and the reaction order of NO, SO2 and NaClO2 were also obtained by experiments and analysis. The results showed that reaction orders of NO, SO2 and NaClO2 during simultaneous desulfurization and denitrification were all pseudo-first-order. And the reaction equations of NO, SO2 and NaClO2 were r=0.079C0.984 NO , r=0.066C0.989 SO 2 and r=0.066C0.998 SO 2 , respectively. The reaction rate of NO, SO2 and NaClO2 were proportional to the NaClO2 concentration and inversely proportional to the solution pH; the reaction rate of SO2 was less affected by the concentration and pH of NaClO2. When the reaction temperature was 50 °C, the reaction rate of NO and SO2 was the largest, and the reaction temperature had little effect on the reaction rate of NaClO2.

Determination of Minimum Effective Concentration of Cashew Nut Shell (CNS) Pyrolysis Products for Antibacterial Escherichia coli Using Kinetics Approach

Determination of minimum effective concentration of cashew nut shell (CNS) pyrolysis products as an antibacterial Escherichia coli using kinetics approach has been done. The purpose of this study is to determine minimum concentration of CNS pyrolysis products which are effective as antibacterial E. coli using chemical kinetics and determine reaction order (n) and rate constant (k), equipped with the rate of reaction equation. And it also determine the relation of initial concentration [A]o, concentration in time [A]t and time variable (t). The results showed that the CNS pyrolysis products consist of two groups: phenolic compounds and alkane compounds. GCMS results also showed that main constituent of the compound is m-octyl-phenol (13.86%). Inhibitory zone on variation in concentration of 100%, 75%, 50%, 25% and 12.5% was 1.47; 1.20; 1.19; 0.87; and 0.75 cm respectively. Reaction order (n) = 0.3 and rate constants (k) = 3.3 so reaction rate equations is r = 3.3 [A]0.3. Relations of initial concentration [A]o and concentration in time [A]t and time variable (t) obtained [A]t = [A]o-0.05t. Minimum concentration making the CNS pyrolysis products effective as an antibacterial E. coli is 24.06%.

Optimization of LiNO3–Mg(OH)2 composites as thermo-chemical energy storage materials

To reduce the emission of greenhouse gases, the substitution of fossil fuel by renewable energy sources is increasingly important. Matching energy supply and demand is however required, even more so if intermittent renewable energy sources are employed. Thermal energy storage then offers significant advantages. Thermo-chemical energy storage systems, using reversible reactions, have a high reaction enthalpy that exceeds the storage capacities of sensible and latent heat modes.Magnesium hydroxide is a candidate TCES material for such a system at temperature around 300 °C, and adaptable when doping Mg(OH)2 with metal salts. Both pure Mg(OH)2 and its composites with 1, 3, 6 and 10 wt% LiNO3 are studied. The present work validates this TCES process and develops reaction rate equations needed for its design. The LiNO3-doping significantly reduces the onset temperature of dehydration. For pure Mg(OH)2, the temperature is 325 °C. It is reduced to 289 °C when 1 wt% LiNO3 is present, and further reduced to 269 °C at a dosage of 10 wt% LiNO3. Whereas the dehydration of pure Mg(OH)2 is slow, with a rate constant k of 1.72 10−5 s−1 at 300 °C, adding increasing amounts of LiNO3 progressively increases the reaction rate constant to ~10−2 s−1 at 300 °C when 10 wt% LiNO3 is present. The kinetic expressions enable to predict the conversion yield and amount of heat stored or released for any desired temperature and selected duration of the heat-induced dehydration. LiNO3- doped Mg(OH)2 have a high potential in TCES applications when the heat source is available at temperatures between 250 and 400 °C, since the equilibrium temperature and the extent of de-hydration Mg(OH)2 can be tuned to the required temperature range by adding different wt% of LiNO3.

Steady detonation propagation in thin channels with strong confinement

We examine asymptotically the dynamics of two-dimensional, steady detonation wave propagation and failure for a strongly confined high explosive (HE), in which the width of the explosive is small relative to the reaction zone length. An energy balance equation is derived, which shows how the longitudinal acceleration of subsonic flow behind the detonation shock is influenced both by chemical reaction and by the effects of HE boundary streamline deflection, specifically via the induced rate of change of mass flux through the detonation wave. The latter serves to either counteract or reinforce the acceleration of longitudinal flow, depending on the sign of the gradient of the boundary streamline deflection at the detonation shock. The analysis is valid for general equations of state and chemical reaction rates in the HE. The asymptotically derived form of the energy equation represents an eigenvalue problem for the determination of the steady detonation propagation speed, solved via a shooting method. We explore specific results for ideal and stiffened equations of state, along with a pressure-dependent reaction rate for which changes in the pressure exponent and reaction order are also studied. We consider the influences of both straight and curved HE boundary streamline shapes. The asymptotic analysis reveals significant physical insights into how detonation propagation and failure are affected by strong confinement.

The chemical CO2 capture by carbonation-decarbonation cycles

The abatement of CO2 emitted from combustion is a hot research topic. Current CO2 capture techniques of adsorption, absorption, membrane separation and cryogenics involve high investment and operation costs. For moderate and high temperature exhaust gas, carbonation/decarbonation cycles offer an attractive alternative. An objective assessment method (screening index) was applied to select the most appropriate chemical reactions, with MgO and Mg(OH)2 being screened as having the highest potential. Macro-thermogravimetric experiments determined a CO2 capture yield between 60 and 70% for Mg(OH)2 at temperatures between 260 and 330 °C, and from 85 to 98% for MgO at temperatures of 400–440 °C. Reaction rates were measured for both MgO–CO2 and Mg(OH)2–CO2. The reaction kinetics are best fitted by the Jander 3D-diffusion approach. The Arrhenius equation is applied to the reaction rate constant, and both its activation energy and pre-exponential factor are determined. Integrating the Jander expression in the reaction rate equation enables to predict the CO2-capture conversion for any selected temperature and/or contact time.

Plasma-catalytic degradation of BTX over ternary perovskite-type La1-x(Co, Zn, Mg, Ba)xMnO3 nanocatalysts

Volatile organic compounds, as an emerging group of organic pollutants, have significant harmful effects on both human health and the environment. BTX, which consists of benzene, toluene and xylene, is the most important kind of these compounds, which is extensively produced in the oil and gas industry. To date, various treatment methods have been used to remove volatile organic compounds. Among them, the non-thermal plasma technology has attracted more attention as an efficient technology for the removal of VOC compounds due to its numerous advantages. perovskite-type metal oxides have recently been found to be effective catalysts for the total oxidation of VOCs. This research has been conducted in two steps. In the first step, a series of La0.8A0.2MnO3 (A: Co, Zn, Mg, Ba) nano-catalysts were synthesized by sol-gel method and then their catalytic activity for removal of BTX compounds were investigated in a non-thermal hybrid plasma system with the dielectric reactor, among which La0.8Zn0.2MnO3 was the most active catalyst. In the next step, further studies focused on zinc doped perovskite nanocatalysts. The catalytic activity of La1-xZnxMnO3 (x=0.1, 0.2, 0.3, 0.4, 0.5, 0.6) nanocatalysts was investigated where La0.8Zn0.2MnO3 catalyst showed highest removal efficiency by degradation 89.73% of benzene, 88.98% of toluene and 88.66% of xylene. It should be noted that product analysis was performed using GC analyzer. The effect of operating parameters such as plasma voltage, activation time, the amount of catalyst loading on optimal sample catalyst and air flow rate were further evaluated. The results exhibited that increasing plasma voltage, activation time and the amount of catalyst loading and PDC use will develop degradation percentage, reduce air flow rate and increase the process time. The physical and chemical properties of perovskite nanocatalysts were evaluated using XRD, SEM, EDX, FTIR, DRS, BET, TEM and SAED analyses. The XRD results suggested that all the samples demonstrated a typical pure perovskite phase. SEM analysis results confirm the formation of nanostructured catalysts and EDX analysis exhibited a good dispersion of elements in optimal photocatalyst. The FTIR results showed that all the characteristic absorption peaks of perovskite were present in synthesized samples. The EDX analysis exhibited a good dispersion of elements in optimal photocatalyst and the BET analysis also revealed that the optimal catalyst had higher specific surface area. Topography and morphology was determined by TEM analysis and the SAED results showed the catalyst structure. The reaction rate equations were also calculated.

Kinetics Study of Surface Reaction Between Acid and Sandstone Based on the Rotation Disk Instrument

The chemical reaction between acid and rock mineral during the acidizing process is the key point for the acidizing technique. In this study a rotating disk method is used to simulate strata conditions, such as high temperature, high pressure, and acid shear flow reaction. The work investigates the kinetics of the rock acidizing reaction and analyzes the factors effecting the reaction rate, including mineral composition, temperature, pressure, acid concentration, shear velocity, and common-ion effect. The kinetic parameters, such as velocity constant, reaction order, activation energy, and frequency factor, were successfully extracted by curve fitting and the linear regression method. In was shown that hydrochloric acid does not participate directly in the reaction between mud acid (which is a mixture of hydrochloric and hydrofluoric acids) and sandstone mineral but catalyzes the reaction between hydrofluoric acid and sandstone. In this work, the acid rock reaction rate equation has been established, and the impact of the hydrochloric acid catalytic effect has been considered.

Reduction Kinetics of Fe-based Oxygen Carriers Using Syngas in a Honeycomb Fixed-Bed Reactor for Chemical-Looping Combustion

Chemical-looping combustion (CLC) is considered to be a vital method for utilizing hydrocarbon fuel with low carbon emissions. A honeycomb fixed-bed reactor is a new kind of reactor for CLC. However, the further application of the reactor is limited by the inadequacy of the kinetic equations for CLC. In this paper, the experimental studies on the kinetic of Fe-based oxygen carriers were carried out by the CLC experiments using syngas which was obtained from one typical type of coal gasification products. The experimental results show that there were two individual stages for the kinetic characteristics during the fuel reaction process. Therefore, the CLC fuel reaction process could be described by a two-stage unreacted-core shrinking model and the reaction rate equations for each of the two phases were provided. In both stages, the dominant resistances were analyzed. The activation energy and the reaction order in both stages were calculated respectively as well. Comparing the experimental results of reaction rate with the calculated results of the obtained rate equations, it could be clearly seen that the reaction kinetics model was appropriate for the CLC in the honeycomb reactor. This work is expected to provide a guideline for the future development and industrial design of the honeycomb CLC reactors from the perspective of kinetics.

Kinetic Study on Thermal Decomposition Behavior of Hematite Ore Fines at High Temperature

The ironmaking processes that directly use iron ore fines as raw material are under development and receiving more and more attention. In a flash reduction process, both the thermal decomposition reaction and the reduction reaction of ore fines are extremely fast and cause loss of oxygen from iron oxides. However, it is difficult to distinguish between the thermal decomposition and reduction during the conversion from hematite to magnetite. In this work, the thermal decomposition behavior of hematite ore fines with different particle sizes is investigated by using a thermogravimetric analyzer (TGA). The kinetic parameters are calculated based on the Coats–Redfern method and then verified by the Satava–Sestak method. The F2 model is identified as the most probable mechanism function under the present experimental conditions. The average values of activation energy and the pre-exponential factor are 1256 kJ mol−1 and 1.94 × 1041 s−1, respectively. The internal morphology of the fine hematite particle with partial decomposition is observed to further investigate the reaction mechanism. Moreover, the relative contribution of the two kinds of chemical reactions (thermal decomposition and gaseous reduction) to the overall conversion process from hematite to magnetite is investigated by kinetic calculations based on the obtained reaction rate equations.

Surface improvement effect of silica nanoparticles on epoxy nanocomposites mechanical and physical properties, and curing kinetic

In this paper, surface modification was performed on silica nanoparticles using 3-aminopropyl trietoxylsilane (APTES) and surface changes of nanoparticles were investigated using TEM and FE-SEM imaging. Furthermore, its physical and mechanical properties were investigated by building three samples including pure epoxy, epoxy/unmodified nano silica, and epoxy/modified nano silica with weights of 1, 3 and 5% of the nanoparticles to the whole system (epoxy and hardener). The results show that the modified nanoparticles were well dispersed in an epoxy matrix, and elastic modulus has improved. For example in a sample with 5% weight percentage of nano silica, the tensile elastic modulus, yield stress, and failure strain are increased by 77%, 124%, and 32%, respectively. Since the epoxy curing process is an important factor that affects the performance of the cured epoxy, curing process samples were analyzed using DSC. Also, various methods of activation energy were measured at the appropriate kinetic model. The reaction rate equation was obtained for each sample. The modified particles reduce the activation energy of the process compared to the two epoxy and epoxy/unmodified nano silica.