Initial Reactant Concentrations Research Articles

Homogeneous continuous flow nitration of O-methylisouronium sulfate and its optimization by kinetic modeling.

Nitration of O-methylisouronium sulfate under mixed acid conditions gives O-methyl-N-nitroisourea, a key intermediate of neonicotinoid insecticides with high application value. The reaction is a fast and highly exothermic process with a high mass transfer resistance, making its control difficult and risky. In this paper, a homogeneous continuous flow microreactor system was developed for the nitration of O-methylisouronium sulfate under high concentrations of mixed acids, with a homemade static mixer eliminating the mass transfer resistance. In addition, the kinetic modeling of this reaction was performed based on the theory of NO2 + attack, with the activation energy and pre-exponential factor determined. Finally, based on the response surface generated by the kinetic model, the reaction was optimized with a conversion of 87.4% under a sulfuric acid mass fraction of 94%, initial reactant concentration of 0.5 mol/L, reaction temperature of 40 °C, molar ratio of reactants at 4.4:1, and a residence time of 12.36 minutes.

UV/Advanced Oxidation Process for Removing Humic Acid from Natural Water: Comparison of Different Methods and Effect of External Factors

Humic acid (HA) is an organic compound naturally present in aquatic environments. It has been found to have detrimental effects on water color, the transport of heavy metals, and the elimination of disinfection by-products (DBPs), thereby exerting an impact on human health. This study introduced four synergistic ultraviolet/advanced oxidation processes (UV/AOPs) systems aimed at eliminating HA from water. The research explored the effect of solution pH, duration of illumination, initial reactant concentration, and oxidant concentration on the degradation of HA. The results indicated that the mineralization rate achieved by individual UV or oxidant systems was less than 15%, which is significantly lower compared to UV/AOPs systems. Among these methods, the UV/peroxymonosulfate (UV/PMS) process demonstrated the highest effectiveness, achieving a mineralization rate of 94.15%. UV/peroxydisulfate (UV/PDS) and UV/sodium percarbonate (SPC) were subsequently implemented, with UV/sulfite (S(IV)) demonstrating the lowest effectiveness at 19.8%. Optimal degradation efficiency was achieved when the initial concentration of HA was 10 mg/L, the concentration of PMS was 3 mmol/L, and the initial pH was set at 5, with an illumination time of 180 min. This experimental setup resulted in high degradation efficiencies for chemical oxygen demand (COD), UV254, and HA, reaching 96.32%, 97.34%, and 92.09%, respectively. The energy efficiency of this process (EE/O) was measured at 0.0149 (kWh)/m3, indicating the capability of the UV/PMS system to efficiently degrade and mineralize HA in water. This offers theoretical guidance for the engineered implementation of a UV/PAM process in the treatment of HA.

Analysis of discharge performance and thermo-electric conversion efficiency in thermally regenerative ammonia-based flow battery with foam copper electrode

This paper established a numerical model of mass transport and electrochemical reaction coupling in porous media of thermally regenerative ammonia-based flow battery with foam copper electrode (TRAFB-FCE) for the first time. The effects of the structural parameters of the foam copper electrode on the power density, energy density, discharge capacity, and active species distribution of the battery were comprehensively studied based on the coupled numerical model. Special attention was paid to the selection strategy of the initial reactant concentration for the battery under different discharge conditions. The results suggest that increasing the porosity or thickness of the foam copper electrode causes the voltage and power density of the battery to first increase and then decrease, while the discharge capacity and energy density monotonically increase. Moreover, the battery should avoid discharging at current densities exceeding 720 A·m−2. When the discharge current density is less than 200 A·m−2, it is preferable to set the initial concentration of Cu2+ to 0.4 mol/L, while the discharge current density is in the range of 200–720 A·m−2, the initial concentration of Cu2+ is preferable to be 0.3 mol/L. When it discharges at about 5 % of its maximum power density, the Carnot-relative efficiency of this battery is comparable to the highest value currently reported in the field of liquid-based thermo-electric conversion achieved by the Thermal Regenerative Electrochemical Cycle (TREC) technology, and the power density of the former is 8.87 times that of the latter.

Catalytic hydrogenation reaction micro-kinetic model for dibenzyltoluene as liquid organic hydrogen carrier

The implementation of the liquid organic hydrogen carrier (LOHC) technology for efficient energy storage requires the development of a reliable kinetic model for both hydrogenation and dehydrogenation processes. In this research study, the catalytic hydrocarbon saturation for a dibenzyltoluene (DBT) mixture solution, containing dibenzylbenzene (DBB), dibenzylethylbenzene (DBEB) and impurities has been performed in the presence of Ru/Al2O3 particles. The influence of different reaction conditions, such as temperature, pressure, initial reactant concentration, catalyst amount and stirring speed has been examined. A measurement-based system micro-kinetics, based on the Langmuir–Hinshelwood mechanism with dissociative H2 surface adsorption, has been derived. H2 thermodynamic solubility equilibrium was defined through Henry's law. The adsorbing, desorption and reactivity of inert solvent molecules was not considered to be relevant. The mass transfer resistance over 1000 rpm stirring speed was negligible. Relative- and mean squared error of representation were 40.9% and 1.00×10−4, respectively. Expressions gave an excellent data prediction for the profile period trends with a relatively accurate estimation of H2 intermediates' rate selectivity, H2-covered area approximation and pathway rate-determining steps. Due to the lack of commercially available standard chemical compounds for quantitative analysis techniques, a novel experiment-based numerical calibration method was developed. Mean field (micro)kinetics represent an advancement in the mesoscale mechanistic understanding of physical interface phenomena. This also enables catalysis structure–activity relationships, unlocking the methodology for new LOHC reaching beyond traditional, such as ammonia, methanol and formate, which do not release H2 alone. Integrated multiscale simulations could include fluidics later on.

On photokinetics under polychromatic light.

Since the dawn of photochemistry 150 years ago, photoreactions have been conducted under polychromatic light. However, despite the pivotal role that photokinetics should naturally play for such reactive photosystems, the literature lacks a comprehensive description of that area. Indeed, one fails to identify explicit model integrated rate laws for these reactions, a characteristic type for their kinetic behavior, or their kinetic order. In addition, there is no consensus in the community on standardized investigative tools to evaluate the reactivity of these photosystems, nor are there venues for the discussion of such photokinetic issues. The present work is a contribution addressing some of these knowledge gaps. It proposes an unprecedented general formula capable of mapping out the kinetic traces of photoreactions under polychromatic light irradiation. This article quantitatively discusses several reaction situations, including the effects of initial reactant concentration and the presence of spectator molecules. It also develops a methodology for standardizing actinometers and defines and describes both the spectral range of highest reactivity and the photonic yield. The validity of the model equation has been proven by comparing its results to both theoretical counterparts and those generated by fourth-order Runge-Kutta numerical calculations. For the first time, a confirmation of the -order character of the kinetics under polychromatic light was established.

Deep learning for kinetics parameters identification: A novel approach for multi-variate optimization

This work presents an innovative deep-learning approach for multi-variate optimization, focusing on the identification of Mg(OH)2 precipitation kinetics parameters. The study employs three distinct experimental datasets, one for the Population Balance Model (PBM) fitting and two for validation. These datasets explore the impact on Particle Size Distributions (PSDs) of (i) increasing the initial reactant concentrations from 0.125 to 1 M and (ii) decreasing the flow rate from 12 to 4 m/s, both in a T-mixer, (iii) increasing the initial reactant concentration over a wider concentration range from 0.01 to 1 M in a more complex Y-mixer system. Leveraging PBM, we create a dataset to train a Neural Network (NN), referred to as the ‘mirror model,’ which predicts kinetics parameters based on experimental sizes. Notably, the PBM, fitted with dataset (i), excels at describing changes in flow rate (dataset (ii)) and substantial reductions in reactant concentrations in the Y-mixer (dataset (iii)), even though these conditions were not encountered during the fitting step. Key Performance Indicators (KPIs) reveal that the mirror model consistently outperforms two widely used algorithms, Conjugate Gradient (CG) and Particle Swarm Optimization (PSO), highlighting its remarkable potential for practical applications.

Modeling of reaction–desorption process by core–shell particles dispersed in continuously stirred tank reactor (CSTR)

Abstract Transient responses of reaction–desorption process were predicted from mathematical solutions of modeling equations for CSTR (continuously stirred tank reactor) containing core–shell adsorbent particles. Analytical solutions on the core–shell particles were derived for core–shell spherical, cylindrical, and slab-type morphologies, assuming inert-cores. Unlike continuous adsorber, CSTRs for reaction–desorption process containing spherical particles exhibited the slowest reduction rate of concentration of adsorbate, because the amount of adsorbed component on the particles is the largest among three kinds of particle shapes. Factors affecting the transient concentration in bulk medium of reaction–desorption process were investigated by adjusting inert-core thickness, inlet flow rate, initial concentration of reactant in inflow stream, amount of adsorbent, and Thiele modulus. Concentration profile inside the particles as well as average intra-particle concentration could be also predicted for comparison with bulk concentration of CSTR. For non-linear isotherm and non-linear reaction kinetics, concentration of active component could be predicted by solving non-linear coupled differential equation using finite element method. For connected CSTRs in series, systems of reaction-diffusion equations were solved by finite element method to study the effect of number of connected reactors. When the number of reactors was sufficiently large, the reactor system could be approximated to fixed bed reactor for reaction–desorption process.

On photokinetics under monochromatic light.

The properties of photokinetics under monochromatic light have not yet been fully described in the literature. In addition, for the last 120years or so, explicit, handy model equations that can map out the kinetic behaviour of photoreactions have been lacking. These gaps in the knowledge are addressed in the present paper. Several general features of such photokinetics were investigated, including the effects of initial reactant concentration, the presence of spectator molecules, and radiation intensity. A unique equation, standing for a pseudo-integrated rate law, capable of outlining the kinetic behaviour of any photoreaction is proposed. In addition, a method that solves for quantum yields and absorption coefficients of all species of a given photoreaction is detailed. A metric (the initial velocity) has been adopted, and its reliability for the quantification of several effects was proven by theoretical derivation, Runge-Kutta numerical integration calculations and through the model equation proposed. Overall, this study shows that, under monochromatic light, photoreaction kinetics is well described by -order kinetics, which is embodied by a unifying model equation. This paper is aimed at contributing to rationalising photokinetics via reliable, easy-to-use mathematical tools.

Parameter estimation and estimability analysis in pharmaceutical models with uncertain inputs

AbstractA methodology is proposed to aid parameter estimation in fundamental models of pharmaceutical processes. This methodology addresses situations with insufficient data to reliably estimate all parameters, when the estimation is complicated by uncertain independent variables. The proposed method uses an augmented sensitivity matrix to rank the combined set of parameters and uncertain inputs from most estimable to least estimable. An updated mean‐squared‐error criterion is then used to determine the appropriate parameters and inputs that should be estimated, based on the ranked list. A model for one step in a batch pharmaceutical production process with an uncertain initial reactant concentration is used to illustrate the method, revealing that the initial reactant concentration in each batch should be estimated along with three out of six model parameters. Non‐estimable parameters are fixed at their initial values to prevent overfitting. The method will aid error‐in‐variables parameter estimation in many situations involving limited data.

Effect of variable solubility on reactive dissolution in partially miscible systems.

When two partially miscible systems are put in contact, one phase, A, can dissolve into the other one with a given solubility. Chemical reactions in the host phase can impact this dissolution by consuming A and by generating products that impact the solubility of A. Here, we study theoretically the optimal conditions for transfer of a reactant A in a host phase containing a species B when a bimolecular A +B →C reaction generates a product C that linearly decreases the solubility of A. We have quantified numerically the influence of this variable solubility on the reaction-diffusion (RD) concentration profiles of all species in the host phase, on the temporal evolution of the position of the reaction front, and on the flux of A through the interface. We have also computed the analytical asymptotic concentration profiles, solutions at long times of the RD governing equations. For a fixed negative effect of C on the solubility of A, an increase in the initial concentration of reactant B or an increase in the diffusion rate of species B and C results in a larger flux of A and hence a larger amount of A dissolved in the host solution at a given time. However, when the influence of C on the solubility increases, the mass transfer decreases. Our results help understand to what extent a chemical reaction can optimize the reactive transfer of a solute to a host phase with application to, among other things, the geological sequestration of carbon dioxide in an aquifer.

A Comprehensive Monte Carlo Model of the Grafting of Maleic Anhydride onto Polypropylene with Experimental Validation

AbstractA Monte Carlo model is employed to investigate the grafting of maleic anhydride onto polypropylene using a peroxide initiator. The study aimed to develop a comprehensive model that considered a very detailed kinetic mechanism, including chain transfer to polymer, homopolymerization as well as several copolymer reactions. The relative importance of these reactions is evaluated using a sensitivity analysis, which identified homopolymerization, β‐scission, chain grafting, and termination by disproportionation as the most influential reactions. The kinetic constants of these reactions are tuned to fit reported experimental data using the Surface Response Method. The model considers a pseudo‐homogeneous reaction medium and predicts average molecular weights, degree of grafting, molecular weight distribution, and grafting distribution. Furthermore, model simulations provided useful information about the impact of initial concentrations of reactants and reaction time on the molecular properties of the grafted polymer.

Unsymmetrical design and operation in counter-flow microfluidic fuel cell: A prospective study

Performance of counter-flow microfluidic fuel cell is severely limited by the uneven current density distribution within the electrodes. In this work, in-depth numerical investigations are performed to examine the prospects of unsymmetrical design and operation in an all-vanadium counter-flow microfluidic fuel cell with flow-through electrodes to better utilize the electrode effective zone considering the anode-cathode mismatch on the mass transfer and electrochemical kinetics. Results indicate that size and position of the electrode effective zone vary under different operation conditions. Longer electrodes are required when the electrolyte flow rate or reactant concentration decreases. Optimized cathode length is smaller than its anode counterpart due to the faster diffusion rate of the oxidant and improved electrochemical reaction rate at the cathode. Concentration-related activation loss is found to play a key role in the performance of counter-flow microfluidic fuel cells and consequently, unequal initial flow rates are preferred in the cell operation to unequal initial reactant concentrations. Catholyte flow rate could be safely reduced to half of that in the anode with 95% retention of the output current, bringing a reduction of 50% in the catholyte consumption. The present findings could provide useful guidance for the future development of counter-flow microfluidic fuel cells.

Modeling of slurry-type photocatalytic reactors containing core-shell particles for predicting transient behaviours based on Langmuir-Hinshelwood kinetics

Governing equations were derived for photocatalytic batch reactors and CSTR (Continuously Stirred Tank Reactor) containing photocatalytic pellets to obtain numerical solutions of the concentration in bulk medium and intra-particle concentration based on Langmuir-Hinshelwood kinetics. Numerical solutions could be obtained by finite element method under proper initial and boundary conditions to solve coupled reaction-diffusion equations using partial and ordinary differential equations. Effects of Thiele modulus, Biot number, Langmuir—Hinshelwood parameter and photocatalyst loading were investigated by predicting the performance of batch reactor. Effects of residence time and initial reactant concentration were studied for CSTR. In addition to conventional morphologies of pellets such as sphere, cylinder and slab, mathematical modeling of core-shell particles was also conducted to study the effect of thickness of inert core. Although the performance of spherical pellets was the best, cylindrical pellets also showed good activity for removing reactant by photocatalytic decomposition. In core-shell spherical pellets, there was little effect of thickness of inert core on the reduction rate of reactant concentration and steady-state concentration in batch and CSTR, respectively, compared to core-shell cylindrical and slab-type particles. The cascade connection of photocatalytic CSTRs and fixed bed reactors with back mixing could be also analysed by finite element method. Experimental data about the removal of methylene blue using silica-titania core-shell particles in batch photocatalytic reactor were compared with numerical solutions to estimate reaction parameters.

One-Pot Synthesis of Fatty Amines: Rh-Catalyzed Hydroaminomethylation of 1-Decene in an Aqueous Microemulsion System—Influence of Reaction Conditions on the Reaction Performance

The hydroaminomethylation of the long-chain olefin 1-decene and diethylamine with a homogeneous Rh(acac)(cod)/SulfoXantphos catalyst complex as a one-pot synthesis was investigated. The influence of reaction conditions such as temperature and synthesis gas pressure was determined, as well as the effects of the initial concentrations of catalyst precursor, ligand, and reactants on the yield of fatty amine. Hydroaminomethylation was successfully carried out in an aqueous microemulsion system using a non-ionic surfactant with a reaction time of 2 h. A maximum yield of 34%, high regioselectivities >97%, and chemoselectivities >85% were achieved.

Preparation and performance of hydroxyapatite-graphene oxide composite microspheres

Drug-loaded microspheres have been widely studied and applied in biomedical materials, but there are still some open problems such as low drug loading and sudden release. In order to solve such problems, hydroxyapatite-graphene oxide (HA-GO) composite microspheres were prepared by using hydroxyapatite (HA) and graphene oxide (GO). Firstly, spherical calcium carbonate-graphene oxide (CaCO₃-GO) composites were synthesized by hard template method. Then, spherical hollow HA-GO composite microspheres were successfully prepared by a method of hydrothermal-assisted ion exchange. The effect of different synthesis conditions on the prepared HA-GO composites was studied. Through a series of measurements, such as X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman infrared spectroscopy, field emission scanning electron microscope (FESEM), ultraviolet visible spectrophotometer (UV-VIS), etc., the prepared samples were analyzed and characterized. The drug-loading performance of the microspheres was tested by using curcumin as the drug-loading model, and the drug-loading performance was evaluated by two indicators of encapsulation efficiency and drug-loading capacity. At the same time, the cytotoxicity test of the microsphere sample materials was also performed. The research results show that the reactant concentration of the system and the hydrothermal reaction time greatly affect the forming effect of the composite microspheres. When the initial reactant concentration is 0.3 mol/L and the hydrothermal reaction time is 6 h, hollow HA-GO composite microspheres with good morphology can be prepared, with a particle size from 5.1 μm to 7.7 μm and a pore size of about 40 nm. At the same time, it was found that the spherical structure can improve the drug loading, the drug encapsulation efficiency was (20.90 ± 0.31)%, and the drug loading was (2.95 ± 0.19)%. This shows that HA-GO composite microspheres have good medical application value.

Modeling Temperature and Species Concentration Profiles on a Continuous-Flow Reactor Applied to Aldol Condensation

This paper presents the modeling of a continuous-flow reactor used for the synthesis of organic products. The finite element method software, COMSOL Multiphysics, was used to model transport phenomena and reaction kinetics. The temperature is one of the most important kinetic factors that may modify the reaction. A rise in temperature can generate a positive reaction but also secondary side reactions. The design of our system and of many other continuous systems makes it impossible, however, to measure the temperature throughout the reactor. In this paper, we modeled the temperature profile within the reactors as a function of the flow rate, temperature set point, and type of reactor material. The results demonstrated that although it is not a good thermal conductor, polytetrafluoroethylene can be used like other materials. The desired temperature was not reached for any of the reactor material likely to affect the product yield. The model gave the residence time required to reach the stabilized temperature. The comparison of calculated and experimental values of outlet temperature showed good agreement, with a maximum relative difference of only 5%. Knowledge of the temperature profile made it possible to control the concentration distribution of the chemical species in the reactor. The aldol condensation was chosen to determine the kinetic parameters of this reaction as the products of this reaction are found in many natural molecules and drugs. To integrate the chemical model, the kinetic parameters were determined by using experimental data. An equilibrium concentration of 0.2 mol/L was found with initial reactant concentrations of 0.45 mol/L. The chemical modeling gave the species concentrations throughout the reactor. Calculated concentrations were in good agreement with experimental data, with a maximum relative difference of less than 9%. By modeling this reaction, the reaction yield as a function of reactant concentration, temperature, and residence times was estimated.

Spatial and Temporal Oscillations of Surface Tension Induced by an A + B → C Traveling Front

This work describes a new mechanism for the emergence of oscillatory dynamics driven by the interaction of hydrodynamic flows and reaction-diffusion processes with no autocatalytic feedback nor prescribed hydrodynamic instability involved. To do so, we study the dynamics of an A+ B → C reaction-diffusion front in the presence of chemically-driven Marangoni flows for arbitrary initial concentrations of reactants and diffusion coefficients of all species. All the species are assumed to affect the solution surface tension thereby inducing Marangoni flows at the air-liquid interface. The system dynamics is studied by numerically integrating the incompressible Navier-Stokes equations coupled to reaction-diffusion-convection equations for the three chemical species. We report spatial and temporal oscillations of surface tension triggered by differential diffusion effects of surfactant species coupled to the chemically-induced Marangoni effect. Such oscillations are related to the discontinuous traveling of the front along the surface leading to the progressive formation of local extrema in the surface tension profiles as time evolves.

Novel Simulator for Design and Analysis of Wax Removal Treatment from Well Flowlines Using Thermochemical Fluids

Summary Treatment of well flowlines with thermochemical/exothermic fluid has shown good results for wax removal compared with conventional hot oil, hot water, or solvent treatments. However, the technique has not gained widespread use because of the lack of sufficient scientific publications that can give more insights into its use and help in designing a safe and effective treatment. This paper presents a novel transient mathematical model for the design and analysis of thermochemical treatment for well flowlines by accounting for the chemical kinetics, heat transfer, fusion of wax, and associated two-phase flow. The governing equations have been solved using the finite-volume method. The resulting simulator can be used to prepare an optimum thermochemical plan by analyzing the effects of important factors including wax details, deposition profile, heat loss, formulation composition, and injection strategy. Simulation results obtained with the developed model indicate that the entire filling of flowline with thermochemical fluid is not necessary for complete wax removal. Injection of a small thermochemical spacer (TCS) in the flowline followed by its displacement with crude oil can be sufficient in the case of short flowlines of onshore fields. Selection of initial reactant concentration and pH has to be done judiciously based on the maximum allowed temperature in the flowline and the desired extent of chemical utilization. A sensitivity analysis has shown the existence of an optimum range of injection rate below which wax removal efficiency is compromised by excessive heat loss and above which it is reduced by insufficient residence time. The major limitation of this technique is encountered for large flowlines where a possibility of resolidification of removed wax deposits exists because of excessive heat loss. Flowlines of length less than 5 km are found to be ideal candidates as in that case, sufficiently high temperatures can be maintained throughout the journey of TCS in the flowline, which will prevent resolidification.

Production of Battery Grade Lithium Hydroxide Monohydrate Using Barium Hydroxide Causticizing Agent

Lithium hydroxide monohydrate (LiOH⋅H2O) is a crucial precursor for the production of lithium-ion battery cathode material. In this work, a process for LiOH⋅H2O production using barium hydroxide (Ba(OH)2) from lithium sulfate (Li2SO4) (leachate of lithium mineral ores) solution is developed. The effect of operating parameters including reagent type, initial reactant concentration and reaction temperature are investigated. Under the best conditions, more than 90% of the lithium in the initial concentrated Li2SO4 solution is converted to solid LiOH⋅H2O with 99.6% purity in a one-step sonication assisted process. Additional lithium recovery and purification steps are proposed to improve this process. The by-product of the process is barium sulfate (BaSO4), which can be directly sold or used to reproduce the initial Ba(OH)2 reagent and is proved to be feasible in this study. Technoeconomic analysis of the process indicates that it is economically viable. It is expected this study would help the lithium industry improve the production of high quality LiOH⋅H2O from lithium resources in a sustainable and efficient manner.

Experimental Assessment of Perhydro-Dibenzyltoluene Dehydrogenation Reaction Kinetics in a Continuous Flow System for Stable Hydrogen Supply.

The development of alternate clean energy resources is among the most pressing issues in the energy sector in order to preserve the global natural environment. One of the ideal candidates is the utilization of hydrogen as a primary fuel in lieu of fossil fuels. It can be safely stored in liquid organic hydrogen carrier (LOHC) materials and recovered on demand. A uniform supply of hydrogen is essential for power production systems for their smooth operation. This study was conducted to determine the operating conditions of the dehydrogenation of perhydro-dibenzyltoluene (H18-DBT) to ensure that hydrogen supply in a continuous flow reactor remains stable over a wide range of temperatures. The hydrogen flow rate from the dehydrogenation reaction was measured and correlated with the degree of dehydrogenation (DoD) evaluated from the refractive index of reactant liquid samples at various temperatures, WHSV and the initial reactant concentrations. Moreover, a kinetic model is presented holding validity up to a WHSV of 67 h−1. The results acquired present a range for an order of reaction from 2.3 to 2.4 with the required activation energy of 171 kJ/mol.