Non-reactive Systems Research Articles

Prebiotic chemical reactivity in solution with quantum accuracy and microsecond sampling using neural network potentials

While RNA appears as a good candidate for the first autocatalytic systems preceding the emergence of modern life, the synthesis of RNA oligonucleotides without enzymes remains challenging. Because the uncatalyzed reaction is extremely slow, experimental studies bring limited and indirect information on the reaction mechanism, the nature of which remains debated. Here, we develop neural network potentials (NNPs) to study the phosphoester bond formation in water. While NNPs are becoming routinely applied to nonreactive systems or simple reactions, we demonstrate how they can systematically be trained to explore the reaction phase space for complex reactions involving several proton transfers and exchanges of heavy atoms. We then propagate at moderate computational cost hundreds of nanoseconds of a variety of enhanced sampling simulations with quantum accuracy in explicit solvent conditions. The thermodynamically preferred reaction pathway is a concerted, dissociative mechanism, with the transient formation of a metaphosphate transition state and direct participation of water solvent molecules that facilitate the exchange of protons through the nonbridging phosphate oxygens. Associative-dissociative pathways, characterized by a much tighter pentacoordinated phosphate, are higher in free energy. Our simulations also suggest that diprotonated phosphate, whose reactivity is never directly assessed in the experiments, is significantly less reactive than the monoprotonated species, suggesting that it is probably never the reactive species in normal pH conditions. These observations rationalize unexplained experimental results and the temperature dependence of the reaction rate, and they pave the way for the design of more efficient abiotic catalysts and activating groups.

Method for determining estimates of random variable models for describing phase equilibrium in rectification processes

The phase equilibrium modeling for multi-component systems is essential in process systems engineering. In particular, phase stability analysis, Gibbs free energy minimization and estimation of parameters in thermodynamic models are challenging global optimization problems involved in phase equilibrium calculations and modeling for both reactive and non-reactive systems. To date, many significant works have been performed in the area of global optimization, and several algorithms and computational contributions of global optimization have been used for solving these problems; global optimization methods used include both deterministic and stochastic algorithms. To the best of our knowledge, there is no review in the literature that focuses on the global optimization methods and their applications to phase equilibrium modeling and calculations. In this paper, we briefly describe the deterministic and stochastic optimization algorithms selected for our rectification process, and then consider their use for phase stability analysis, Gibbs free energy minimization, and parameter estimation in phase equilibrium models. In short, we present an overview of global optimization for modeling and computing the phase behavior of systems with and without chemical reactions, including the prediction of azeotropes and critical points.

Temperature Distribution Assessment in Gas–Solid Reactive and Nonreactive Systems Heated by Microwaves

Research studies have shown that selective heating of different phases in gas–solid systems exposed to microwave (MW) irradiation leads to a temperature gradient between gas and MW absorber solids. This can suppress undesired secondary gas-phase reactions and yield apparent kinetic improvements and energy savings. However, the effects of reaction exothermicity/endothermicity, gas velocity, temperature probe location at the microscale, and MW penetration depth in fixed beds on the temperature difference between solid and gas phases exposed to MWs and temperature distribution in the fixed beds are poorly understood. Highlighting these effects was targeted in this study and accomplished with the help of multiphysics simulations by COMSOL Multiphysics (5.6). The corresponding COMSOL model was initially verified and validated by data collected from literature studies and those obtained experimentally by the authors in this study. Simulation results from the verified and validated model indicated that the temperature gradient between the gas and the MW absorber solid increases by increasing the gas velocity or switching from an endothermic reaction to no reaction and/or an exothermic reaction. In addition, the collected results show nonuniform temperature distribution in a fixed-bed reactor made of MW absorber particles irradiated by MWs due to the limited penetration depth of MWs and hotspot formation. This operational deficiency makes the large-scale design of this type of reactor very challenging for MW heating-assisted reactions.

Impact of the sizing reactivity of glass fibers on composites hydrothermal aging

Epoxy composites were prepared with reactive and non-reactive sizings deposited on glass fibers. The resulting interphase properties have been studied during hydrothermal aging. The purpose here is to evaluate at nano and macroscale the dependence of aging, interfacial strength, and mechanical properties of model composites on the glass sizing reactivity. SEM/AFM, DMA and 3 points bending experiments have been done before and after water immersion at 70 °C for several weeks. Water diffusion kinetics have been found to be related only to the presence of sized glass fibers but not to the sizing reactivity. The SEM observations demonstrated a cohesive fracture at matrix/fiber in the case of composite elaborated with reactive sizing and an adhesive one in the case of non-reactive sizing, and this remains true with aging. Depending on the sizing nature and on the aging time, the evolution of interphase zones around fibers has been identified by a specific α-relaxation (Tan δ) and confirmed by AFM nanomechanical measurements. The results showed that the interphase thickness was almost the same at initial state (around 200 nm) for both composites, then it progresses with aging time to reach 400 nm and 500 nm (at 42 days) for reactive and non-reactive systems respectively. It suggests that water molecules diffusion is related to the hydrophilic character of the sizing and to the degree of cross-linking/or plasticization of the interphase during hydrothermal aging.

Phase stability analysis and phase equilibrium calculations in reactive and nonreactive systems using new hybrids of Pelican and Gorilla troops algorithms

Phase stability and equilibrium calculations are very significant in the process industries, ranging from process simulation, equipment design, operation and design. These problems involve several systems of complex and nonlinear equations, which are mathematically challenging. An alternative solution is formulating the problems into a global optimisation problem. A robust and reliable optimisation technique is required to solve these global optimisation problems. In this study, two recently developed stochastic global optimisation algorithms, POA and GTO were applied to phase stability and equilibrium problems. The need to enhance their performance necessitated the development of two modified algorithms, PGOA1 and PGOA2, which are the hybridisation of POA and GTO. All the algorithms' abilities were explored for solving computationally challenging and multidimensional phase stability and equilibrium problems, and their performances were compared. The implementation of POA and GTO was good in solving most problems, though GTO slightly outperformed POA. The hybridisation of both to develop PGOA1 and PGOA2 was worthwhile as both outperformed the POA and GTO. PGOA2 is more robust and reliable in solving phase stability and equilibrium, and its performance superseded the performances of the other algorithms.

Stability of a layered reactive channel flow

We analyse the linear stability of a reactive plane Poiseuille flow, where a reactant fluid A overlies another reactant B in a layered fashion within a two-dimensional channel. Both reactants are miscible and have the same viscosity, while upon reaction, they produce either a less or more-viscous product fluid C . The reaction kinetics is of simple A + B → C type, and the production of C occurs across the initial contact line of reactants A and B in a mixed zone of small and finite width. All three fluids have the same density. We demonstrate the effects of various controlling parameters such as the log-mobility ratio, Damköhler number, Schmidt number, Reynolds number, position and thicknesses of the reactive zone on the stability characteristics. We show that a tiny viscosity stratification by the reaction destabilizes the flow at a moderate (10–1000) and even at low Reynolds numbers (0.01–1). The maximum growth occurs for shorter waves than for the Tollmien–Schlichting eigenmode, and the ranges of unstable wavenumbers are wider than that known for non-reactive channel flow systems. In most cases, the instability occurs due to the overlap of the critical layer with the viscosity-stratified layer. Surprisingly for some parameters, it is observed that the reaction can make σ M decrease with increasing Reynolds number.

Reactive Spreading Dynamics of Molten Polymer Liquids

Despite the key to the adhesion between polymers and a plethora of materials, our understanding of reactive wetting is still rudimentary. In the present work, we report the reactive wetting dynamics of molten maleic anhydride-grafted polypropylene (MA-g-PP) liquids modeled by molecular-kinetic theory (MKT). The dependencies of the contact line friction (ζ) and viscosity (η) were compared for reactive and nonreactive wetting polymer systems. Compared with linear dependencies of ζ and η for the nonreactive wetting systems, the reactive wetting system presented a nonlinear relationship. In the capillary regime, the chemistry-affected regime is followed by a regime that is nearly not affected by chemical reactions, which is identified by the linear MKT. The formation of a new interface and the resulting entanglements of polymer chains in the chemistry-affected regime contribute to the dependence of ζ on η in the capillary regime.

Learning the Quantum Centroid Force Correction in Molecular Systems: A Localized Approach.

Molecular mechanics (MM) is a powerful tool to study the properties of molecular systems in the fields of biology and materials science. With the development of ab initio force field and the application of ab initio potential energy surface, the nuclear quantum effect (NQE) is becoming increasingly important for the robustness of the simulation. However, the state-of-the-art path-integral molecular dynamics simulation, which incorporates NQE in MM, is still too expensive to conduct for most biological and material systems. In this work, we analyze the locality of NQE, using both analytical and numerical approaches, and conclude that NQE is an extremely localized phenomenon in nonreactive molecular systems. Therefore, we can use localized machine learning (ML) models to predict quantum force corrections both accurately and efficiently. Using liquid water as example, we show that the ML facilitated centroid MD can reproduce the NQEs in both the thermodynamical and the dynamical properties, with a minimal increase in computational time compared to classical molecular dynamics. This simple approach thus largely decreases the computational cost of quantum simulations, making it really accessible to the studies of large-scale molecular systems.

Attaching Onto or Inserting Into an Intramolecular Hydrogen Bond: Exploring and Controlling a Chirality-Dependent Dilemma for Alcohols

Prereactive complexes in noncovalent organocatalysis are sensitive to the relative chirality of the binding partners and to hydrogen bond isomerism. Both effects are present when a transiently chiral alcohol docks on a chiral α-hydroxy ester, turning such 1:1 complexes into elementary, non-reactive model systems for chirality induction in the gas phase. With the help of linear infrared and Raman spectroscopy in supersonic jet expansions, conformational preferences are investigated for benzyl alcohol in combination with methyl lactate, also exploring p-chlorination of the alcohol and the achiral homolog methyl glycolate to identify potential London dispersion and chirality effects on the energy sequence. Three of the four combinations prefer barrierless complexation via the hydroxy group of the ester (association). In contrast, the lightest complex predominantly shows insertion into the intramolecular hydrogen bond, such as the analogous lactate and glycolate complexes of methanol. The experimental findings are rationalized with computations, and a uniform helicality induction in the alcohol by the lactate is predicted, independent of insertion into or association with the internal lactate hydrogen bond. p-chlorination of benzyl alcohol has a stabilizing effect on association because the insertion motif prevents a close contact between the chlorine and the hydroxy ester. After simple anharmonicity and substitution corrections, the B3LYP-D3 approach offers a fairly systematic description of the known spectroscopic data on alcohol complexes with α-hydroxy esters.

Observational comparative study in Kühni and ORC agitated columns for the mechanism and performance of molybdenum extraction under various hydrodynamic conditions

The present work is expressed to interpret the hydrodynamic parameters of rotation extraction columns in the reactive and non-reactive systems. The solvent extraction technique has been utilized for optimizing the transportation of molybdenum ions to the organic phase in two agitated columns (ORC and Kühni columns). Dispersed phase volume fraction, average droplet diameter, slip velocity, size distribution, and ions permeability of the aqueous phase have been investigated in terms of changing the operational variables including the agitation rate, flow rate of the inlet dispersed and continuous phases, column geometry, and reaction conditions. By considering the reactive and non-reactive conditions, the responses investigated indicated that the alteration in the agitation rate and reaction systems on the hydrodynamic parameters is considerable in comparison with the column geometry as well as both phase flow rates. Previous experimental research works for anticipating the drop behavior, holdup values, and slip velocity of droplets in different rotary columns have been reviewed and several new models have been derived by considering the geometric parameters and reactive or physical systems. The solvent extraction findings showed that the rotary extraction columns could be utilized as a suitable mass transfer device for chemical reaction systems.

A new model combining Helmholtz energy equations of state with excess Gibbs energy models to describe reactive mixtures

A new model is presented, which consistently combines equations of state in terms of the Helmholtz energy with excess Gibbs-energy models. It enables the description of reactive mixtures by solving the phase and chemical equilibrium based on Helmholtz-energy equations of state, that are commonly used to describe non-reactive systems. The consistent calculation of all thermodynamic properties in the complete fluid region, including gas, liquid, and supercritical states as well as phase equilibria, is possible. The fundamental property is the Helmholtz energy with the independent variables temperature, density, and composition. The new model reproduces well experimental vapor–liquid equilibrium, homogeneous density, and speciation data of the binary system of monoethanolamine + carbon dioxide as well as of the ternary system of water + monoethanolamine + carbon dioxide.

Residence time distribution in reactive and non-reactive flow systems in micro and millidevices

The present research evaluated the Residence Time Distribution (RTD) of three microdevice designs (Traditional T-shape, MTB and G1) in two flow conditions: non-reactive flow and reactive flow (biodiesel synthesis). Also, the scale-up effects on RTD were explored for the space time (τ) range between 2 and 60 s. In general, the deviation between mean residence time and ideal space time decreased with increasing τ. The axial dispersion analysis showed larger deviations from plug flow for oil streams, while ethanol streams exhibited plug flow behavior for longer space times (τ ≥ 30 s). Despite this, high oil conversions (>90%) and relatively high biodiesel throughputs (≈19 g/h, about 63 greater than T-shape microchannels) were observed for MTB millidevices and G1 devices. Despite the observed deviations from plug flow, the proposed micromixer designs provided good performance for biodiesel synthesis.

Numerical simulation of ultrasonic enhancement by acoustic streaming and thermal effect on mass transfer through a new computation model

Mass transfer coefficient is an important parameter in the process of mass transfer to reflect the degree of enhancement of mass transfer process in liquid–solid reaction and in non-reactive systems. In the present paper, a new computational model including both acoustic streaming and ultrasonic thermal effect is established to quantitatively calculate the ultrasonic enhancement on mass transfer coefficient in liquid–solid reaction. A nonlinear Helmholtz equation containing the cavitation effect is used in the model to calculate the acoustic pressure distribution in the reactor, and a fluid-thermal coupling CFD involving mass transfer process for KOH solution is conducted to obtain the distribution and time-dependence of the mass transfer coefficient in silicon–KOH reaction. Mass transfer coefficient on silicon surface with a transducer at frequencies of 100 kHz has been numerically simulated, indicating that the mass transfer coefficient has the maximum value near the center of the silicon wafer, and increases with reaction time. The mass transfer coefficient in the center of the silicon wafer is increased by 14.3% from 6.043 × 10−5 m/s to 6.908 × 10−5 m/s under ultrasound power of 50W during reaction time from 0.1 hour to 1 hour (the mass transfer coefficient without ultrasound changes from 2.525 × 10−6 m/s to 7.615 × 10−7 m/s). A set of control simulations shows that the enhancement of mass transfer coefficient comparing to the situation without ultrasound is mainly resulted from the acoustic streaming, while the increasing of mass transfer coefficient with time is due to the thermal effect of ultrasound. The mass transfer coefficients under transducer power of 10W and 30W are also calculated, indicating that the mass transfer coefficient is positively correlated with the ultrasonic power.

State function‐based flash specifications for open systems in the absence or presence of chemical reactions

AbstractDiverse engineering fields require flash calculations like isothermal flash, isenthalpic flash, and isentropic flash. They can be cast as minimization of a thermodynamic state function and solved by Michelsen's Q‐function approach. Flash calculations for open systems, that is, systems where chemical potentials are specified instead of the mole numbers for some components, also belong to this scope. By analyzing the construction of Q‐functions through Legendre transforms, we extend this approach to the flash for open systems in the absence or presence of chemical reactions, resulting in general formulations for various specifications. For systems without reactions, the classical framework using mole numbers as independent variables is employed; for those with reactions, the modified‐RAND framework is employed. We present examples for open systems at constant temperature and pressure. Using the Q‐function minimization, we can solve multicomponent nonreactive or reactive systems at a specified chemical potential with quadratic convergence over a wide range of conditions.

Computational Modeling of Bubbles Growth Using the Coupled Level Set-Volume of Fluid Method.

Understanding the generation, growth, and dynamics of bubbles as they absorb or release dissolved gas in reactive flows is crucial for optimizing the efficiency of electrochemically gas-evolving systems like alkaline water electrolysis or hydrogen production. To better model these bubbly flow systems, we use a coupled level set and volume of fluid approach integrated with a one-fluid transport of species model to study the dynamics of stationary and rising bubbles in reactive two-phase flows. To accomplish this, source terms are incorporated into the continuity and phase conservation equations to allow the bubble to grow or shrink as the species moves through the interface. Verification of the hydrodynamics of the solver for non-reactive systems demonstrates the requisite high fidelity interface capturing and mass conservation necessary to incorporate transport of species. In reactive systems where the species impacts the bubble volume, the model reproduces the theoretically predicted and experimentally measured diffusion-controlled growth rate (i.e., R(t) ∝ t0.5). The model is then applied to rising bubbles to demonstrate the impact of transport of species on both the bubble velocity and shape as well as the concentration field in its wake. This improved model enables the incorporation of electric fields and chemical reactions that are essential for studying the physicochemical hydrodynamics in multiphysics systems.

Wetting Transition in a Molten Metal and Solid Substrate System in High Magnetic Fields

Wetting transitions between molten metals and different solid substrates were investigated using the sessile drop method to evaluate the possibilities of regulating wettability by high magnetic fields (HMFs) during wetting. For most wetting counterparts, the molten-metal droplet outline showed an apparent change because of the influence of HMFs. Contact angles that were measured with HMFs decreased compared with contact angles that were measured without HMFs. The temperature and magnetic-flux density had an evident but more complicated effect on the wetting transition. For reactive wetting systems, the effect of HMFs on changes of element distributions at the metal/substrate interface may lead to a variety of wetting transitions. For non-reactive wetting systems, solidified metal droplets can move from the solid substrates after wetting. No detailed and comprehensive explanations on HMF wetting-transition mechanisms exist, and further work is required. This study contributes to perfect wetting mechanisms and theories and provides a scientific approach to control wettability.

Chemo-Hydrodynamic Patterns and Instabilities

By modifying a physical property of a solution like its density or viscosity, chemical reactions can modify and even trigger convective flows. These flows in turn affect the spatiotemporal distribution of the chemical species. A nontrivial coupling between reactions and flows then occurs. We present simple model systems of this chemo-hydrodynamic coupling. In particular, we illustrate the possibility of chemical reactions controlling or triggering viscous fingering, Rayleigh–Taylor, double-diffusive, and convective dissolution instabilities. We discuss laboratory experiments performed to study these phenomena and compare the experimental results to theoretical predictions. In each case we contrast the chemo-hydrodynamic patterns and instabilities with those that develop in nonreactive systems and unify the different dynamics in terms of the common features of the related spatial mobility profiles.

A Practical Procedure for Measuring Contact Angles in Wettability Studies by the Sessile Drop Method

ABSTRACTAn old procedure used to carry out a graphical derivation of curves, which is based on the optical properties of plane mirrors, has been adapted for the measurement of the contact angle (θ) formed between a liquid drop and a flat solid substrate in wettability experiments carried out by the so-called “sessile drop” method. The method was tested for mercury on soda-lime glass at room temperature in air as well as for Cusil (Ag-28wt.%Cu) and Incusil-ABA (Ag-27wt.%Cu-12wt.%In-2wt.%Ti) brazing alloys on pressureless-sintered silicon carbide (PLS-SiC) at 850 °C, under a vacuum of 10-4/10-5 Torr. The proposed method is fast, simple and accurate enough from high (∼140°) to relatively low (∼10°) contact angles. Although the proposed method has been tested for metal-ceramic systems, it is of general application, so that it would be useful for any liquid-solid system. The method is applicable for any temperature, pressure and atmospheric experimental conditions employed, as well as for any chemical composition of liquid and solid. It is also useful for both low and high contact angles, as well as for reactive and non-reactive systems, as long as a photograph of a liquid drop resting on a flat solid surface is available for the studied system.

Reactive pressure infiltration of Cu-46at.pct. Si into carbon

We explore how reaction at the interface between a solid porous ceramic and an infiltrating molten metal influences wetting in pressure infiltration, wetting being characterized by a drainage curve that plots the metal saturation versus the applied metal pressure. Specifically, we infiltrate Cu-46at.pct. Si into graphite preforms at 1050 °C, 1100 °C, 1150 °C or 1200 °C. The Si in the copper alloy reacts with the graphite to form SiC, which is better wetted by the alloy compared to the initial graphite. We show that, unlike what is observed in non-reactive systems, at fixed applied pressure reaction prevents stabilization of the metal saturation and causes the metal to continuously flow into the preform. Interpreting the data under the assumption that the applied pressure influences the local rate of thermally activated triple line motion as does the applied stress the rate of thermally activated motion of dislocations, measured infiltration velocities can be exploited to deduce both an activation volume and an activation energy for the interfacial process that governs reaction-driven motion of the triple line in this system. The resulting activation volume is on the order of one to a few 100 nm3, leading to estimated activation energy values of a few times 100 kJmol. Both are realistic for a process that is limited by the rate of SiC growth along the metal/graphite interface.

A Gibbs energy-driving force method for the optimal design of non-reactive and reactive distillation columns

A simple Gibbs energy-driving force method for the design of non-reactive and reactive distillation columns has been developed. Based on the binary driving force concept and the equilibrium Gibbs energy computation, a systematic procedure for the design of non-reactive distillation columns (NRDC) and reactive distillation columns (RDC) is proposed. The design method exploits the connection between the driving force values and the equilibrium Gibbs energy to determine the number of stages, the optimal feed location, and the heat required at the top and bottom of the column and the minimum reflux ratio. The final design guarantees an optimal operation since maximum thermodynamic efficiency is achieved. The maximum thermodynamic efficiency criterion is equivalent to the minimum entropy condition required for a stable operation of the distillation columns. The method is applied for the design of two non-reactive systems: a) Benzene-Toluene ideal system and b) Ethanol-Water non-ideal system. A reactive distillation column considering the isomerization of n-butane in the presence of an inert compound is designed. The optimal thermal feed condition obtained through the maximum separation efficiency guarantees that the final designs obtained correspond to the minimum energy requirements for the design target of separation.