Higher-order Reactions Research Articles

Numerical analysis of higher order chemical reaction on electrically MHD nanofluid under influence of viscous dissipation

In this paper, the groundwork of some thermophysical properties of higher-order chemical processing and dissipation of viscous on nanofluid along with a continuously stretching porous sheet is taken. The porous medium is considered with two space coordinates, laminar, time-invariant, MHD incompressible Newtonian nanofluid. The equations are framed to govern the fluid flow as coupled equations involving nonlinear partial derivatives. The impacts of electric and magnetic fields on nanofluid with viscous dissipation in the presence of higher-order chemical reaction, analyzing conservation of momentum and energy, is the novelty of the problem. The level of raising thermal conductivity and the output of transferring the heat on nanofluid is observed. Finally, the governing equations involving partial derivatives have complied with nonlinear ordinary differential equations. The transformations are subjected to the similarity variable used to solve these equations. Approximate solutions are obtained using a numerical method of the Runge-Kutta-Felburg method with shooting technique. The effects of emerging parameters Kr,Er,λ,Nt,δ,Nb are porous, electric, mixed convection, thermophoresis, chemical process and, Brownian motion, and non-dimensional numbers such as Hartmann, Prandtl, Schmidt, and Eckert are extensively explained. The electrically conducting nanofluid flow for velocity fluid, temperature fluid and, nanoparticles concentration volume fraction fluid with transferring heat, Nusselt, and transferring mass, Sherwood number are examined with graphical representation. The Lorentz resistive force due to the applied strength of electric develops the thickness of boundary layers of momentum and thermal regions. This helps to cool the electronic systems and radiators. The dimensionless Nusselt number diminishes with various values of thermophoresis and Brownian motion parameters as a dependent function of Hartmann, electric number, and homogeneous chemical reaction parameter.

On 3D Prandtl nanofluid flow with higher-order chemical reaction

In this paper, the boundary layer analysis of three-dimensional Prandtl nanofluid flow over a convectively heated sheet in a porous material is addressed. Nonlinear radiation and high-order chemical reaction analysis are featured in this work. Nonlinear differential equations representing flow expressions are numerically solved by shooting technique. Features of Brownian motion and thermophoresis accounting for nanoparticle diffusion are taken into account. Then, a complete discussion of the influences of the flow regime on several thermofluidic parameters is presented. The outcome of the present study is that velocity field lines are grown due to the strengthening of Prandtl fluid numbers [Formula: see text] and [Formula: see text] while a reverse trend takes place for temperature profile. Furthermore, it is shown that when the magnetic strength is improved, the skin friction coefficient and heat transfer rate triggers considerable evolution. The obtained results of this model closely match with those available in the literature as a limiting situation.

Effects of cellulose, hemicellulose and lignin on biomass pyrolysis kinetics

In order to investigate interactions among biomass components on pyrolysis kinetics, pyrolysis experiments of individual components, synthetic biomass (designed by Design-Export software) and natural biomass (rice husk and corn straw) were conducted on a thermogravimetric analyzer (TGA). The results revealed that the pyrolysis behavior of cellulose is sharp, which is with low pyrolysis reaction order (1.38), high activation energy (168.61 kJ/mol) and high pre-exponential factor (3.50E+12/s). The pyrolysis behavior of hemicellulose and lignin is slower but more complicated, both with high pyrolysis reaction order (2.30, 1.51), low activation energy (126.31, 87.21 kJ/mol), and low pre-exponential factor (9.67E+09, 2.59E+05 /s). Comparison of the experimental and calculated kinetics of synthetic samples confirmed that interactive effects on pyrolysis kinetics exist in the co-pyrolysis process. In particular, the presence of lignin inhibited the pyrolysis reaction rate of synthetic biomass, and cellulose played the dominant role in the activation energy and frequency factor. The pyrolysis reaction order was strongly influenced by hemicellulose owing to its abundant and complex branched chains. The predicted model was also established for calculating kinetic parameters of natural biomass with known proportions of three components. The predicted results were consistent with the experimental ones, validating the effectiveness of the prediction model.

3-D electromagnetic radiative non-Newtonian nanofluid flow with Joule heating and higher-order reactions in porous materials

The aim of this work is to discuss the effect of mth-order reactions on the magnetic flow of hyperbolic tangent nanofluid through extending surface in a porous material with thermal radiation, several slips, Joule heating, and viscous dissipation. In order to convert non-linear partial differential governing equations into ordinary ones, a technique of similarity transformations has been implemented and then solved using the OHAM (optimal homotopy analytical method). The outcomes of novel effective parameters on the non-dimensional interesting physical quantities are established utilizing the tabular and pictorial outlines. After a comparison with previous literature studies, the results were finely compliant. The study explores that the reduced Nusselt number is diminished for the escalating values of radiation, porosity, and source (sink) parameters. It is found that the order of the chemical reaction m = 2 is dominant in concentration as well as mass transfer in both destructive and generative reactions. When m reinforces for a destructive reaction, mass transfer is reduced with 34.7% and is stabled after η = 3. In the being of the destructive reaction and Joule heating, the nanofluid's temperature is enhanced.

Interpretation of photocurrent transients at semiconductor electrodes: Effects of band-edge unpinning

The transient photocurrent response of semiconductor electrodes to chopped illumination often shows spikes and overshoots that are usually interpreted as evidence that surface recombination is occurring. In the case of the high intensities used for light-driven water splitting, the interpretation is less straightforward since the electron transfer reactions are so slow that the minority carrier concentration at or near the surface increases to high values that modify the potential drop across the Helmholtz layer in the electrolyte, leading to ‘band edge unpinning’. In addition, changes in chemical composition of the surface or local changes in pH may also alter the potential distribution across the semiconductor/electrolyte junction. A quantitative theory of band edge unpinning due to minority carrier build up is presented, and numerical calculations of transient photocurrent responses are compared with experimental examples for n-type Fe2O3 and p-type lithium-doped CuO electrodes. It is shown that the apparently high reaction orders (up to third order) with respect to hole concentration reported for hematite photoanodes can be explained as arising from an acceleration of hole transfer by the increased voltage drop across the Helmholtz layer associated with band edge unpinning. The limitations of the band edge unpinning model are discussed considering additional effects associated with modification of the potential distribution brought about by light-induced changes in surface composition, surface dipoles and surface ionic charge.

Velocity fluctuations of stochastic reaction fronts propagating into an unstable state: Strongly pushed fronts.

The empirical velocity of a reaction-diffusion front, propagating into an unstable state, fluctuates because of the shot noises of the reactions and diffusion. Under certain conditions these fluctuations can be described as a diffusion process in the reference frame moving with the average velocity of the front. Here we address pushed fronts, where the front velocity in the deterministic limit is affected by higher-order reactions and is therefore larger than the linear spread velocity. For a subclass of these fronts-strongly pushed fronts-the effective diffusion constant D_{f}∼1/N of the front can be calculated, in the leading order, via a perturbation theory in 1/N≪1, where N≫1 is the typical number of particles in the transition region. This perturbation theory, however, overestimates the contribution of a few fast particles in the leading edge of the front. We suggest a more consistent calculation by introducing a spatial integration cutoff at a distance beyond which the average number of particles is of order 1. This leads to a nonperturbative correction to D_{f} which even becomes dominant close to the transition point between the strongly and weakly pushed fronts. At the transition point we obtain a logarithmic correction to the 1/N scaling of D_{f}. We also uncover another, and quite surprising, effect of the fast particles in the leading edge of the front. Because of these particles, the position fluctuations of the front can be described as a diffusion process only on very long time intervals with a duration Δt≫τ_{N}, where τ_{N} scales as N. At intermediate times the position fluctuations of the front are anomalously large and nondiffusive. Our extensive Monte Carlo simulations of a particular reacting lattice gas model support these conclusions.

Asymmetric Cross [10+2] Cycloadditions of 2-Alkylidene-1-indanones and Activated Alkenes under Phase-Transfer Catalysis.

Isobenzofulvene species are versatile synthons in organic chemistry, which have been employed in diverse challenging higher-order cycloaddition reactions. Here, the first chemoselective and asymmetric cross [10+2] cycloaddition reaction between activated 2-alkylidene-1-indanones and a variety of electron-deficient alkenes has been developed, relying on the in situ generation of dearomative 1-hydroxyl isobenzofulvene anion intermediates under the catalysis of a newly designed bulky cinchona-derived phase-transfer compound. An array of fused frameworks with multifunctionalities were generally furnished in excellent diastereo- and enantioselectivity, even at 1 mol % catalyst loadings.

Многокомпонентные реакции высшего порядка - эффективный путь к молекулярной сложности

Многокомпонентные реакции высшего порядка - эффективный путь к молекулярной сложности

Efficient upgrading of CO to C3 fuel using asymmetric C-C coupling active sites

The electroreduction of C1 feedgas to high-energy-density fuels provides an attractive avenue to the storage of renewable electricity. Much progress has been made to improve selectivity to C1 and C2 products, however, the selectivity to desirable high-energy-density C3 products remains relatively low. We reason that C3 electrosynthesis relies on a higher-order reaction pathway that requires the formation of multiple carbon-carbon (C-C) bonds, and thus pursue a strategy explicitly designed to couple C2 with C1 intermediates. We develop an approach wherein neighboring copper atoms having distinct electronic structures interact with two adsorbates to catalyze an asymmetric reaction. We achieve a record n-propanol Faradaic efficiency (FE) of (33 ± 1)% with a conversion rate of (4.5 ± 0.1) mA cm−2, and a record n-propanol cathodic energy conversion efficiency (EEcathodic half-cell) of 21%. The FE and EEcathodic half-cell represent a 1.3× improvement relative to previously-published CO-to-n-propanol electroreduction reports.

8+3]-Cycloaddition of Tropones with Azaoxyallyl Cations.

Although azaoxyallyl cations are widely used as 1,3-dipoles for various cycloaddition reactions leading to nitrogen-containing heterocycles, their application in higher-order cycloaddition reaction remains scarce. Herein, we present the [8+3]-cycloaddition reaction of tropones with in situ generated azaoxyallyl cations allowing the one-step construction of cycloheptatriene-fused 1,4-oxazinones in moderate to good yields. This base-promoted new carbon-oxygen and carbon-nitrogen bond-forming reaction takes place under mild conditions in the absence of transition metal catalysts.

Front transition in higher order diffusion equations with a general reaction nonlinearity

In this paper, we investigate the wave front solutions of a class of higher order reaction diffusion equations with a general reaction nonlinearity. Linear stability analysis with a modulated travelling wave perturbation is used to prove the existence of wave front solutions. We proved that the studied equation supports both monotonic translating front and patterned front solutions. Also, a minimal front speed and the condition for a transition between these front types (monotonic and patterned) are determined. Two numerical examples are discussed (the extended Fisher-Kolmogorov equation with two different reaction nonlinearities) to support the obtained results.

Higher-order cycloaddition reactions: A computational perspective

Higher-order cycloaddition reactions are more common in the chemical literature now than ever before. With this class of reactions, we see a prime example of experimental and computational science working together to drive innovation. Here, we present a brief overview of some of the computational developments with a focus on how this work has driven experiment and vice versa.

Stability criterion for the intensification of batch processes with model predictive control

Thermal runaways in batch processes can lead to significant issues for safety and performance during normal operation in industry. This is usually circumvented by running such processes at lower temperatures than necessary, hence losing the opportunity to intensify production and therefore reduce reaction time. The detection of the thermal stability of batch systems can potentially be embedded in an advanced control scheme, therefore improving the performance by being able to intensify the process, achieving higher yields while keeping a stable operation.The derivation of stability criterion K for high-order reactions is presented in this work, resulting in better control when embedded in Model Predictive Control (MPC) schemes than standard nonlinear MPC schemes, based on the work in Kähm and Vassiliadis (2018). The non-trivial extension of stability criterion K for multi-component reactions with application to MPC systems is discussed in detail. The logic and verification of the form of the resultant Damköhler number in particular is discussed and demonstrated with case studies. A comparison of various MPC schemes is presented, showcasing that the implementation using criterion K results in intensified processes kept stable at all times, whilst reducing computational cost with regard to standard nonlinear MPC schemes. Furthermore, reaction times are reduced by at least twofold with respect to processes run at constant temperatures.

Rates of Ammonia Absorption and Release in Calcium Chloride

After synthesis, ammonia can be selectively absorbed by calcium chloride; nitrogen and hydrogen are not absorbed. The kinetics of release seem to be diffusion controlled. The kinetics of absorption are consistent with a first-order reaction after an initial period of a higher-order reaction, which may indicate a nucleation event. At 225 °C, both absorption and release show half-lives of around 10 min if the ammonia partial pressure is swung from 2 to 1 bar, which allows design of an absorber for the periodic separation of ammonia. When this absorber replaces the ammonia condenser in a conventional ammonia synthesis, the ammonia production at low pressure can have the same rate as the conventional process operating at higher pressure.

Construction Method of Broadband High-order Reaction Force Observer for the Reproduction of the Expert Skills

Construction Method of Broadband High-order Reaction Force Observer for the Reproduction of the Expert Skills

Protein a resin lifetime study: Evaluation of protein a resin performance with a model-based approach in continuous capture

ABSTRACTA modified shrinking core model (MSCM) has been used to describe the mechanism for the degradation of Protein A resin particles taking place under continuous chromatographic operation. The model is based on the hypothetical shrinkage of the boundary layer of the resin particles, which house the active Protein A ligands within their pores. The caustic during the sanitization phase of chromatography has been determined to cause the Protein A ligand degradation. Protein A resins provided by manufacturers possess unique caustic stability, which has been used in MSCM to appraise the ligand degradation. The kinetic model utilized semiempirical parameters including diffusion constant, rate constant, stoichiometric factor, and reaction order. The parameters were estimated from column breakthrough experiments to simulate continuous Protein A chromatography for three distinct resins. The reaction order has been identified as the key parameter for predicting the degradation kinetics. The recorded reaction orders vary for three different resins with the resin B showing the highest reaction order of 4 and lowest being 1.65 for the resin C. The model can predict the effects of caustic on resin performance and displayed that minimal degradation of the resins A and B occurred, when exposed to 0.1 N and 0.2N NaOH, retaining up to 96% binding capacity after 240 cycles. The adsorption study conducted for the resin B demonstrated the dynamic physical and chemical changes transpiring through the life cycle of the resin, further supported the degradation model. The performance data demonstrate that the resin B exhibits the desirable performance, with higher reaction order indicating slower resin degradation, higher binding capacities, and increased sustenance of this binding capacity for extended duration. The degradation model can be extended to build effective cleaning strategies for continuous downstream processing.

Catalytic Asymmetric [8+2] Annulation Reactions Promoted by a Recyclable Immobilized Isothiourea.

Higher-order cycloaddition reactions constitute an efficient approach towards the construction of medium to large ring systems. However, enantioselective versions of these transformations remain scarce, which hampers their deployment in medicinal chemistry, or any other discipline in which homochirality is deemed crucial. Herein, we report a novel method for the production of enantiomerically enriched cycloheptatrienes fused to a pyrrolidone ring on the basis of an isothiourea-catalyzed periselective [8+2] cycloaddition reaction between chiral ammonium enolates (generated in situ from carboxylic acids) and azaheptafulvenes. The resulting bicyclic compounds can be hydrogenated, but, most remarkably, they can also undergo completely regioselective [4+2] cycloaddition with active dienophiles to give architecturally complex polycyclic compounds in a straightforward manner.

Cover Picture: Cycloaddition Reactions: Why Is It So Challenging To Move from Six to Ten Electrons? (Angew. Chem. Int. Ed. 34/2017)

Celebrating cycloaddition reactions with numbers and orbitals: The orbital interaction diagrams for [4+2], [6+4], and [8+2] cycloaddition reactions in the paintings on the wall look simple. However, in reality, it is challenging to move from six to ten electrons for cycloaddition reactions as is discussed by K. A. Jørgensen et al. in their Essay on page 10033 ff. Being successful with [6+4] and [8+2] higher-order cycloaddition reactions deserves a toast and celebrations—as Angewandte Chemie celebrates the 80th birthday of Roald Hoffmann—as illustrated by the flowers with a very special shape and several contributions in this issue. Celebrating cycloaddition reactions with numbers and orbitals: The orbital interaction diagrams for [4+2], [6+4], and [8+2] cycloaddition reactions in the paintings on the wall look simple. However, in reality, it is challenging to move from six to ten electrons for cycloaddition reactions as is discussed by K. A. Jørgensen et al. in their Essay on page 10033 ff. Being successful with [6+4] and [8+2] higher-order cycloaddition reactions deserves a toast and celebrations—as Angewandte Chemie celebrates the 80th birthday of Roald Hoffmann—as illustrated by the flowers with a very special shape and several contributions in this issue. Porphyrin Tautomerism Ge4Se3Te Structure Methane Activation

Thermal decomposition of rape straw: Pyrolysis modeling and kinetic study via particle swarm optimization

The aim of this work is to implement an efficient and robust optimization approach for parameter estimation of pyrolysis kinetic model to study the pyrolysis of a typical agricultural residue. Thermogravimetric profiles of rape straw were obtained at a wide heating range of 10, 20, 30 and 40°C/min in an inert atmosphere of nitrogen and the thermal decomposition process was studied in detail. First, three different kinetic methods (Friedman, KAS and OFW) were applied for activation energy determination. The activation energies ranged from 191.16kJ/mol to 264.31kJ/mol. Then, the reaction mechanism and pre-exponential factor were analyzed by using the generalized master-plots method. It is found that at conversion level higher than 0.4 the rape straw decomposition was governed by 3-D diffusion model and it tended to high order reaction model at lower conversion. Finally, a multi-component parallel reactions scheme incorporated into the Particle Swarm Optimization (PSO) technique was presented to determine kinetic parameters. The kinetic triplets and other stoichiometric parameters were optimized against profiles for heating rates of 20 and 30°C/min. The optimized activation energy value is 156.41kJ/mol, 211.26kJ/mol and 57.84kJ/mol for hemicellulose, cellulose and lignin, respectively. These results are in conformity with results reported in previous literatures. Meanwhile, the obtained pre-exponential factors values also lie in the reasonable range of lnAi=25.32–39.14ln/s according to intrinsic transition-state theory. Furthermore, cross-validated results show that the optimized parameters can be applied not only to conditions where they were obtained, but also to conditions beyond (10 and 40°C/min), indicating that the derived results are appropriate to simulate and predict rape straw pyrolysis under various heating rates, which will be useful for further design and sizing of biomass thermochemical process reactors.

Uncatalyzed C−H Amination of Aromatic Compounds under Unusually Mild Conditions with Negative Enthalpies of Activation

AbstractAromatic amines have been synthesized by the simple treatment of carboximides with concentrated azetidine in a fast reaction at room temperature. Strongly negative energies of activation and high reaction order for azetidine were found, which violated Arrhenius′ theory for a simple activated complex. The application of this reaction to perylenes allowed the synthesis of bathochromically absorbing functional dyes.