Kinetic Model Research Articles

Synergistic adsorption of methylene blue using ternary composite of phosphoric acid geopolymer, calcium alginate, and sodium lauryl sulfate.

The removal of dyes from the aquatic ecosystem is necessary being a major threat to life. For enhanced remediation of methylene blue (MB) dye, a new ternary biopolymer-geopolymer-surfactant composite adsorbent is synthesized by combining phosphoric acid geopolymer (PAGP), calcium alginate (Alg), and sodium lauryl sulfate (SLS). During the synthesis of the composites, PAGP and SLS were mixed with the alginate matrix, producing porous hybrid beads. The PAGP-SLS-alginate (PSA) beads prepared were characterized using different analytical tools, i.e., scanning electron microscopy (SEM), Fourier transform infrared spectrophotometry (FTIR), X-ray diffractometry (XRD), surface area and porosimetery (SAP), and thermogravimetric analysis (TGA). To ascertain the ideal conditions for the adsorption process, a batch reactor procedure was used to investigate the effects of several parameters on MB adsorption, including pH (2, 4, 6, 8, 10), PSA adsorbent dosage (0.06-0.12 g), MB concentration (50-500 mg/L), contact time (15 to 300 min), and temperature (25, 35, and 45 °C). The SEM investigation indicated that ~ 1860 μm-sized PSA beads with 6-8 μm voids are generated. Based on XRD, FTIR, and SAP examinations, the material is amorphous, having numerous functional groups and an average pore size of 6.42 nm. Variation of pH has a little effect on the adsorption process, and the pH of 7.44 was found to be the pHpzc of the PSA beads. According to the findings of the batch study, equilibrium adsorption was obtained in 270-300 min, showing that the adsorption process was moderately slow-moving and effective. The dye adsorption linearly increased with initial dye concentration over concentration range of 50-500 mg/L and reciprocally decreased with rise in temperature. 0.06 g adsorbent dose, 25 °C, pH10, and 270 min were found to be the better conditions for adsorption experiments. Langmuir isotherm fitted well compared to Freundlich, Temkin, and Dubinin-Radushkevich (DR) isotherm models on the experimental data, and the maximum adsorption capacity(qmax) calculated was 1666.6 mg. g-1. Pseudo-second-order (PSO) kinetics model and multi steps (two) intra particle diffusion (IPD) model fitted well on the adsorption kinetics data. The system's entropy, Gibbs free energy, and change in enthalpy were measured and found to be -109.171 J. mol-1. K-1, - 8.198 to - 6.014 kJ. mol-1, and - 40.747 kJ. mol-1. Thermodynamics study revealed that adsorption process is exothermic, energetically favorable and resulting in the decrease in randomness. Chemisorption is found to be the dominant mechanism as confirmed by pH effect, Langmuir isotherm, PSO kinetics, IPD model, and thermodynamics parameters. PSA beads were successfully regenerated using ethanol in a course of 120 min and re-used for five times. To sum up, the PSA adsorbent's impressive adsorption capability of 1666.66 mg/g highlights its potential as a successful solution for methylene blue removal. The results of this study add to the expanding corpus of information on sophisticated adsorption materials and demonstrate PSA's potential for real-world uses in wastewater treatment and environmental clean-up.

Impregnation of Silica Gel with Choline Chloride-MEA as an eco-friendly adsorbent for CO2 capture

Deep eutectic solvents (DES) are a generation of ionic liquids that benefit from low cost, good stability, and environmental-friendly features. In this research, a porous silica gel was impregnated with a eutectic Choline Chloride-Monoethanolamine solvent (ChCl-MEA) to greatly improve its CO2 capture performance. In the impregnation, the weight percentages of ChCl-MEA were used in the range of 10–60 wt% at a temperature of 25 °C. The effect of ChCl-MEA loading on the structural properties of the DES-modified silica samples was studied by BET, FTIR, and TGA analyses. Investigation of the CO2 adsorption performance at different operational conditions showed that the modified silica gel with 50 wt% ChCl-MEA (Silica-CM50) presents the highest CO2 capture capacity of 89.32 mg/g. In the kinetic modeling, the fractional order model with a correlation coefficient of 0.998 resulted in the best fit with the experimental data. In addition, the isotherm data for Silica-CM50 were well-fitted with the Dual site Langmuir isotherm model with a correlation coefficient of 0.999, representing two distinct sites for the adsorption process. Moreover, the thermodynamic parameters including Enthalpy, Entropy, and Gibbs free energy at 25 °C were obtained to be − 2.770, − 0.005 and − 1.162, respectively. The results showed the exothermic, spontaneous and feasibility of the adsorption process.

Formulation and Evaluation of Bilastine Thermosensitive Mucoadhesive Ophthalmic in situ Gel

Background: Bilastine is a non-sedating, second-generation antihistamine used to treat urticaria and allergic conjunctivitis. Objective: to formulate and test bilastine as a mucoadhesive ophthalmic in situ gel in order to extend its presence at site for longer time and help treat conjunctivitis and allergic rhinitis. Methods: We prepared formulations using different concentrations of poloxamers (Poloxamer 407 (P407) and Poloxamer 188 (P188)) in combination with hydroxypropyl methyl cellulose (HPMC). The prepared formulas were evaluated for their physicochemical properties, sol-gel transition temperature, viscosity, mucoadhesive strength, drug release, and kinetic modeling. Results: The prepared in situ gels were clear and transparent, having a pH ranging from 7.4 to 7.5 and a gelation temperature between 29.5 and 34.7 °C. Increasing the concentrations of P-407 and HPMC increased viscosity, gel strength, and mucoadhesion force, but caused a decrease in gelation temperature and drug release. Formula (F 14) containing P 407/P 188/HPMC as 19/4/0.75% w/v, respectively, exhibited favorable characteristics, including optimal gelation temperature (33°C), drug content (93%), gel strength (40 sec), mucoadhesive force (6125 dyne/cm2), and 91.4% in vitro drug release over 5 hours. Conclusions: The bilastine mucoadhesive in situ gel formulation is presented as a promising ophthalmic formulation for the treatment of allergic conjunctivitis.

Evaluation of the optical and magnetic properties of novel Nd0.9Zn0.1FeO3 perovskite nanoparticles and their adsorption of Pb2+ ions from water

Nd0.9Zn0.1FeO3 was prepared in a single-phase with an average crystallite size of 25.82 nm using a citrate combustion technique. The energy dispersive X-ray assures the chemical formula of the sample. The elemental mapping of Zn-doped NdFeO3 illustrates the good homogeneous distribution of the elements in the sample. Nd0.9Zn0.1FeO3 has antiferromagnetic properties with weak ferromagnetic components and has good UV absorbance. The values of the band gap for the direct and indirect transitions are 1.473 eV and 1.250 eV, respectively. The adsorption of nickel(II), cobalt(II), chrome(VI), cadmium(II), and lead(II) ions has been studied at pH 7. The highest removal efficiency (η = 73.72%) was observed for the lead ions from water. The current study has examined the kinetics, recoveries, and mechanisms of utilizing Nd0.90Zn0.10FeO3 to remove Pb2+ ions from water. The optimum conditions for the absorbing Pb2+ are pH 7 and a contact time of 60 min. The Freundlich isotherm model is the best model for the absorption of Pb2+ ions. While, the pseudo-second-order kinetic model describes the kinetic adsorption data. The sample has a good efficiency for removing Pb2+ ions from water several times.

A Numerical Hydration Model to Predict the Macro and Micro Properties of Cement–Eggshell Powder Binary Blends

This study aims to propose a hydration kinetic model for the cement–eggshell powder binary system and predict the performance development of composite concrete through this model. The specific content and results of the model are as follows. First, based on the cumulative hydration heat of the cement and eggshell powder binary system in the first seven days, the parameters of the cement hydration model and the eggshell powder nucleation parameter are calibrated. These parameters remain constant regardless of the mix ratio. Secondly, the hydration heat of the cement–eggshell powder binary system over 28 days is calculated using the hydration model. The results show that at 28 days, for specimens with 0%, 7.5%, and 15% eggshell powder substitution, the cement hydration degrees are 0.832, 0.882, and 0.923, respectively. The hydration heat per gram of cement is 402.69, 426.88, and 446.73 J/g cement, respectively, while the hydration heat per gram of binder is 402.69, 394.86, and 379.72 J/g binder, respectively. Additionally, the hydration model is used to calculate the chemically bound water and calcium hydroxide content of the cement–eggshell powder binary system. At 28 days, for samples with 0%, 7.5%, and 15% eggshell powder, the chemically bound water content is 0.191, 0.188, and 0.180 g/g binder, respectively, and the calcium hydroxide content is 0.183, 0.179, and 0.173 g/g binder, respectively. Finally, a power function is used to regress the calculated hydration heat with experimentally measured compressive strength and surface electrical resistivity. The correlation coefficients for compressive strength and surface electrical resistivity are 0.8474 and 0.9714, respectively. This is because the strength weak point effect of eggshell powder has minimal impact on hydration heat and surface electrical resistivity experiments but significantly affects the strength experiment.

Removal of Ammonium and Manganese from Water by MnOx Media: Establishment of Film Growth Kinetic Model and Chemical Peeling Film Mechanism

Removal of Ammonium and Manganese from Water by MnOx Media: Establishment of Film Growth Kinetic Model and Chemical Peeling Film Mechanism

A novel biosorbent material from waste fish scales (Cyprinus carpio) for biosorption of toxic dyes in aquatic environments

AbstractPolluted water sources are a growing concern in our world today, with more and more of our precious freshwater sources becoming contaminated. Pollution can come from a variety of sources, such as industrial discharge, agricultural runoff, and even urban runoff. Several treatment technologies have been investigated, mainly for dye pollution from textile and industrial wastes. In this study, the biosorption of methylene blue dye from the water environment was examined utilizing a low-cost and biodegradable biomaterial. Waste fish scales modified with NaOH were used as biomaterial. The biosorption effect of methylene blue concentration and pH variables was optimized. SEM for the surface morphology of the biomaterial and FT-IR analyses for the detection of functional groups were performed. The characterization of methylene blue biosorption was conducted to fully understand its nature, including its kinetics, equilibrium, and thermodynamic works. It has been determined that the biosorption process conforms most closely to the pseudo-second-order kinetic model for its kinetic results and to the Langmuir isotherm for its equilibrium results. Based on the Langmuir isotherm data, the maximum capacity for biosorption (qmax) was found to be 344.82 mg g−1. The thermodynamic results showed that the process of biosorption of methylene blue on various surfaces is spontaneous and occurs via physisorption. Additionally, the experimental design method was utilized to determine the optimum conditions of the methylene blue biosorption process under various conditions. The maximum biosorption capacity was determined to be 102.367 mg g−1 at the optimal conditions. The potential of biosorbent derived from the waste fish scales is promising as a novel biosorbent material due to its unique surface morphology and high biosorption capacity.

Photochemically Driven Peptide Formation in Supersaturated Aerosol Droplets

The condensation of amino acids into peptides plays a crucial role in protein synthesis and is thus essential for understanding the origins of life. However, the spontaneous formation of peptides from amino acids in bulk aqueous media is energetically unfavorable, posing a challenge for elucidating plausible abiotic mechanisms. In this study, we investigate the formation of amide bonds between amino acids within highly supersaturated aerosol droplets containing dicyandiamide (DCD), a cyanide derivative potentially present on primordial Earth. Metastable states, i.e. supersaturation, within individual micron‐sized droplets are studied using both an optical trap and a linear quadrupole electrodynamic balance. When irradiated with intense visible light, amide bond formation is observed to occur and can be monitored using vibrational bands in Raman spectra. The reaction rate is found to be strongly influenced by droplet size and kinetic modelling suggests that it is driven by the photochemical product of a DCD self‐reaction. Our results highlight the potential of atmospheric aerosol particles as reaction environments for peptide synthesis and have potential implications for the prebiotic chemistry of early Earth.

Theoretical description of photoinduced electron transfer in donor-acceptor supramolecular complexes based on carbon buckybowls.

Herein, we explore, from a theoretical perspective, the nonradiative photoinduced processes (charge separation and energy transfer) within a family of donor-acceptor supramolecular complexes based on the electron-donor truxene-tetrathiafulvalene (truxTTF) derivative and a series of curved fullerene fragments (buckybowls) of different shapes and sizes (C30H12, C32H12, and C38H14) as electron acceptors that successfully combine with truxTTF via non-covalent interactions. The resulting supramolecular complexes (truxTTF·C30H12, truxTTF·C32H12, and truxTTF·C38H14) undergo charge-separation processes upon photoexcitation through charge-transfer states involving the donor and acceptor units. Despite the not so different size of the buckybowls, they present noticeable differences in the charge-separation efficiency owing to a complex decay post-photoexcitation mechanism involving several low-lying excited states of different natures (local and charge-transfer excitations), all closely spaced in energy. In this intricate scenario, we have adopted a theoretical approach combining electronic structure calculations at (time-dependent) density functional theory, a multistate multifragment diabatization method, the Marcus-Levitch-Jortner semiclassical rate expression, and a kinetic model to estimate the charge separation rate constants of the supramolecular heterodimers. Our outcomes highlight that the efficiency of the photoinduced charge-separation process increases with the extension of the buckybowl backbone. The supramolecular heterodimer with the largest buckybowl (truxTTF·C38H14) displays multiple and efficient electron-transfer pathways, providing a global photoinduced charge separation in the ultrafast time scale in line with the experimental findings. The study reported indicates that modifications in the shape and size of buckybowl systems can give rise to attractive novel acceptors for potential photovoltaic applications.

Environmental Behaviour of Synthesized and Commercial Agricultural Zinc Products: Leaching, Migration, and Availability in Soils

AbstractThe aim of this paper is to examine the environmental effect of different chemical characteristics of Zinc (Zn) sources, assessing the transport, leaching and accumulation in the environment in sand, acidic (AS) and calcareous (CS) soils. Comparative short- and long-term studies applying ZnO sources [bulk, laboratory-synthesized and commercial nanoparticles (NP)], ZnSO4, complexed Zn (Zn-lignosulfonate) and chelated Zn (Zn-diethylenetriamine-pentaacetate, Zn-hydroxy-ethylenediamine-tetraacetate and Zn-ethylenediamine-tetraacetate) were carried out. For all treatments and media, the medium- and long-term dissolution kinetic model was fitted to a logistic function. The applied Zn in the form of ZnO was mainly retained at the upper half (0–7.5 cm) of the columns and in very available form (ranging 40–61% of added Zn in AS and 29–31% in CS). Leached Zn reached values below 6% in AS and 3% in CS. The use of chelated Zn in both soils and complexed Zn, and ZnSO4 in AS resulted in excessive leaching of Zn (around 70%). The amount of Zn available at the upper half of the column was less than 5%. In the CS, these fertilizers showed a higher aging than ZnO sources, negatively affecting its availability as a nutrient for crops. ZnO NP showed short- and medium-term dissolution kinetics that allow gradual nutrient release and high availability at the medium-term. These products provide an effective solution for plant nutrition while mitigating the environmental problems observed with more traditional sources related to leaching. Graphical Abstract

Photochemically Driven Peptide Formation in Supersaturated Aerosol Droplets.

The condensation of amino acids into peptides plays a crucial role in protein synthesis and is thus essential for understanding the origins of life. However, the spontaneous formation of peptides from amino acids in bulk aqueous media is energetically unfavorable, posing a challenge for elucidating plausible abiotic mechanisms. In this study, we investigate the formation of amide bonds between amino acids within highly supersaturated aerosol droplets containing dicyandiamide (DCD), a cyanide derivative potentially present on primordial Earth. Metastable states, i.e. supersaturation, within individual micron-sized droplets are studied using both an optical trap and a linear quadrupole electrodynamic balance. When irradiated with intense visible light, amide bond formation is observed to occur and can be monitored using vibrational bands in Raman spectra. The reaction rate is found to be strongly influenced by droplet size and kinetic modelling suggests that it is driven by the photochemical product of a DCD self-reaction. Our results highlight the potential of atmospheric aerosol particles as reaction environments for peptide synthesis and have potential implications for the prebiotic chemistry of early Earth.

Study of combustion flow field in a scramjet engine under inflow oscillation variations based on OpenFOAM

In this study, a compressible supersonic numerical model was established based on the open-source computational fluid dynamics software OpenFOAM. The supersonic air inflow was set in sinusoidal variation and gas hydrogen was employed as fuel for the DLR engine numerical simulation. The SST k-ω model and a 9-species 27-reaction hydrogen/oxygen chemical reaction model was employed as the turbulence and reaction mechanical kinetics models respectively. The effect of continuous variable inflow on the combustion performance for the scramjet engine was analyzed and the results showed that the combustion flame inside the scramjet engine exhibited significant partitioning phenomena around the combustion stabilization zones under periodic continuous variable inflow conditions. It was found that intense combustion zones were formed at both upstream and downstream flow as the induction of intersecting shock waves. When the flame was stabilized in the engine, the initiation position of the intense combustion zone at the upstream was transferred to the distance of twice the strut length, while the initiation position of the intense combustion zone at the downstream was anchored at a distance of about five times the strut length.

Cellulose Acetate Microparticles Synthesized from Agave sisalana Perrine for Controlled Release of Simvastatin.

Simvastatin (SIM) is widely prescribed to treat hyperlipidemia, despite its limitations, such as a short half-life and low oral bioavailability. To overcome these drawbacks, the development of a controlled-release formulation is desirable. This study aims to develop a microparticulate system based on cellulose acetate (ACT) obtained from Agave sisalana Perrine to promote a controlled SIM release. SIM-loaded microparticles (SMP) were prepared using the solvent emulsification-evaporation method. Several parameters were evaluated, including particle size, surface charge, morphology, encapsulation efficiency, thermochemical characteristics, crystallinity, and in vitro release profile. ACT exhibited favorable flow properties after acetylation, with a degree of substitution values superior to 2.5, as confirmed by both the chemical route and H-NMR, indicating the formation of cellulose triacetate. The obtained SMP were spherical with an average size ranging from 1842 to 1857 nm, a zeta potential of -4.45 mV, and a high SIM incorporation efficiency (98%). Thermal and XRD analyses revealed that SIM was homogeneously dispersed into the polymeric matrix in its amorphous state. In vitro studies using dialysis bags revealed that the controlled SIM release from microparticles was higher under simulated intestinal conditions and followed the Higuchi kinetic model. Our results suggest that ACT-based microparticles are a promising system for SIM delivery, which can improve its bioavailability, and result in better patient compliance.

Formulation and Evaluation of Niosomal Loaded Transdermal Patches for the Treatment of Osteoarthritis

Introduction: Osteoarthritis (OA) is a degenerative joint disease resulting from the breakdown of joint cartilage and underlying bone. The most common symptoms of osteoarthritis are joint pain and stiffness. The major hurdle in its treatment is that the oral administration of NSAIDs (Lornoxicam) causes side effects like GI side effects, cardiovascular problems, liver issues, or renal problems. Thus, there is a need to develop a Transdermal drug delivery system for the transport of drugs, which reduces side effects and has several benefits over oral delivery, and a Novel drug delivery system to enhance the permeation of drugs and give relief from symptoms of OA. Objectives: This work deals with the formulation and evaluation of niosomal-loaded Transdermal Patches for the treatment of Osteoarthritis. Method: The Niosomes were prepared using the thin film hydration method, and Niosomalloaded Transdermal patches were prepared using the Solvent Casting method. The preliminary evaluation and characterization studies were conducted to find the optimized formulation. The invitro release and ex-vivo permeation studies were investigated. Stability studies were also assessed. Result: The prepared Niosomes suspension (F2) was found to have particle size 320.2 nm, Zeta potential 23.9 mV, and Drug entrapment 79 ± 0.32%. The in-vitro drug release studies of optimized formulation show 96.44 ± 0.34 % drug release for 24 hours. Then, the optimized Niosome formulation (F2) was loaded into the transdermal patches. The in-vitro permeation studies of Niosomal-loaded transdermal patch F1 (NLXTP) were performed, which showed a higher permeability than plain drug-loaded transdermal patch. F1 (NLXTP) followed Zero order release kinetic model, which shows a non-fickian controlled release diffusion mechanism. The ex-vivo drug release studies of optimized formulation F1 (NLXTP) show 2.79 ± 0.76 (µg/ml) drug permeated for 8 hours with a flux value of 0.35 ± 0.55, and the percentage of drug retention was found to be 5.67%. The stability studies showed that patches were stable over 90 days in different atmospheric conditions. Conclusion: The Lornoxicam-loaded Niosomal transdermal patch was found to be a promising nano-drug-delivery alternative that showed better entrapment and release with a permeation profile for the daily management of osteoarthritis.

Determination of Deamidation in Adjuvanted Vaccine Antigens through Isoaspartic Acid Quantification

Deamidation is a post-translational chemical modification that occurs within proteins and can be influenced by many factors, including temperature and pH. In vaccines, deamidation is considered undesirable as it may lead to changes in structure, function, stability, and immunogenicity. Detecting deamidation in vaccines, especially adjuvanted vaccines, can be challenging due to the lack of simple quantitative techniques. In this study, the quantification of isoaspartic acid (isoAsp) was used to assess deamidation in model antigens in the presence and absence of common vaccine adjuvants. This study shows that the detection of isoAsp was possible in the presence of various types of adjuvants with little to no interference. High levels of isoAsp were detected in thermally and pH-stressed adjuvanted vaccines, suggesting significant deamidation and highlighting the stability-indicating capabilities of the assay. The quantification of isoAsp in stability programs of a vaccine drug product could possibly find applications in product shelf-life determination, using thermal kinetic modeling to predict deamidation over time. The ability to detect deamidation early in vaccine development enhances process improvements and ultimately improves the vaccine’s stability. To summarize, this paper describes a rapid and simple method to determine deamidation in adjuvanted vaccines. This method could be applicable to formulation development, stability assessment, or shelf-life determination.

Unveiling the Mechanism and Kinetics of Pollutant Attenuation by Free Radicals Triggered from Goethite in Water Distribution Systems.

Investigating the fate of persistent organic pollutants in water distribution systems (WDSs) is of great significance for preventing human health risks. The role of iron corrosion scales in the migration and transformation of organics in such systems remains unclear. Herein, we determined that hydroxyl (•OH), chlorine, and chlorine oxide radicals are generated by Fenton-like reactions due to the coexistence of oxygen vacancy-related Fe(II) on goethite (a major constituent of iron corrosion scales) and hypochlorous acid (HClO, the main reactive chlorine species of residual chlorine at pH ∼ 7.0). •OH contributed mostly to the decomposition of atrazine (ATZ, model compound) more than other radicals, producing a series of relatively low-toxicity small molecular intermediates. A simplified kinetic model consisting of mass transfer of ATZ and HClO, •OH generation, and ATZ oxidation by •OH on the goethite surface was developed to simulate iron corrosion scale-triggered residual chlorine oxidation of organic compounds in a WDS. The model was validated by comparing the fitting results to the experimental data. Moreover, the model was comprehensively applicable to cases in which various inorganic ions (Ca2+, Na+, HCO3-, and SO42-) and natural organic matter were present. With further optimization, the model may be employed to predict the migration and accumulation of persistent organic pollutants under real environmental conditions in the WDSs.

Efficient removal of cadmium and lead in water by using nano-manganese oxide-loaded hydrochloric acid pretreated biochar

Cadmium (Cd) and lead (Pb) contaminated water pose a serious threat to the safety of aquatic organisms and human food, which is a hot topic in the world. To improve the removal efficiency of straw biochar (BC) on Cd and Pb pollution water, the modified biochar (BCHMn) was manufactured by loading nano-manganese oxide (nano-MnOx) on hydrochloric acid pretreated BC. The adsorptive properties of Cd2+ and Pb2+ for BCHMn were examined by isothermal, kinetic adsorption models, and cycle tests. The results indicated that the adsorption of Cd2+ and Pb2+ by BCHMn is suitable for Langmuir, Sips, Avrami, and pseudo-second-order kinetic model, suggesting monolayer and heterogeneous chemical adsorption. The maximum theoretical adsorptive amount of Cd2+ and Pb2+ on BCHMn are 108.21 mg/g and 312.16 mg/g, respectively. The adsorption mechanism of BCHMn is primarily mineral precipitation, π electron interaction, and ion exchange. Moreover, BCHMn contained the special birnessite (δ-MnO2) structures and MnOx, which can form stable complexes with Cd/Pb (such as Mn-O-Cd/Pb and Mn-R-O-Cd/Pb). These results indicate that BCHMn can efficiently remove Cd2+ and Pb2+ from water, and provide a reference for the comprehensive utilization of straw waste and water pollution control.

Plasma Catalysis Modeling: How Ideal Is Atomic Hydrogen for Eley-Rideal?

Plasma catalysis is an emerging technology, but a lot of questions about the underlying surface mechanisms remain unanswered. One of these questions is how important Eley-Rideal (ER) reactions are, next to Langmuir-Hinshelwood reactions. Most plasma catalysis kinetic models predict ER reactions to be important and sometimes even vital for the surface chemistry. In this work, we take a critical look at how ER reactions involving H radicals are incorporated in kinetic models describing CO2 hydrogenation and NH3 synthesis. To this end, we construct potential energy surface (PES) intersections, similar to elbow plots constructed for dissociative chemisorption. The results of the PES intersections are in agreement with ab initio molecular dynamics (AIMD) findings in literature while being computationally much cheaper. We find that, for the reactions studied here, adsorption is more probable than a reaction via the hot atom (HA) mechanism, which in turn is more probable than a reaction via the ER mechanism. We also conclude that kinetic models of plasma-catalytic systems tend to overestimate the importance of ER reactions. Furthermore, as opposed to what is often assumed in kinetic models, the choice of catalyst will influence the ER reaction probability. Overall, the description of ER reactions is too much "ideal" in models. Based on our findings, we make a number of recommendations on how to incorporate ER reactions in kinetic models to avoid overestimation of their importance.

Continuous-flow synthesis of di-(2-ethylhexyl) peroxydicarbonate in a packed-bed microreactor: Process optimization and kinetic modeling

Di-(2-ethylhexyl) peroxydicarbonate (EHP) is a low-temperature liquid organic peroxide commonly used as an initiator for polymerization of vinyl chloride and ethylene. The exothermic nature of peroxidation and the instability of this peroxide product pose safety challenges during synthesis. Therefore, batch reaction processes for synthesizing such products often prioritize safety over efficiency. In this work, an efficient and safe protocol was proposed for EHP production with the use of a packed-bed microreactor. Response surface methodology was applied to optimize critical process parameters, resulting in a remarkable yield of 95.48% in a residence time of 23.8 min. It proves that the efficiency was significantly improved by the packed-bed microreactor compared with batch reactors. Additionally, an operational window was established to guide the process development for synthesizing EHP in flow. Finally, a kinetic model was established, which was of crucial theoretical significance and practical value for better understanding peroxidation processes and parameter optimization.

Lifting relations for a generalized total-energy double-distribution-function kinetic model and their impact on compressible turbulence simulation

Recently, Qi et al. (2022) and Guo et al. (2023) proposed two alternative designs of an efficient mesoscopic method using the total-energy double-distribution-function (DDF) formulation, hereafter referred to as the Qi model and the Guo model. The two models share the same advantage of using only 40 discrete particle velocities to fully reproduce the Navier–Stokes-Fourier (NSF) system. However, the Guo model is based on a more rigorous kinetic consideration, while the Qi model relies on a more general design of the source term to allow for adjustable bulk-to-shear viscosity ratio. In this paper, we derive lifting relations for the Qi model based on two alternative approaches, namely, the Hermite expansion and the Chapman-Enskog expansion, which can be used to construct the boundary and initial conditions for the mesoscopic method. For three-dimensional compressible turbulence simulations, including compressible decaying homogeneous isotropic turbulence and Taylor–Green vortex flows, the derived two sets of lifting relations are applied to the initialization distribution function to study their impacts. Interestingly, for the Qi model, the two sets of lifting relations yield the same results without numerical artifacts, whereas for the Guo model, an appropriate lifting relation must be specified to avoid numerical artifacts resulting from the flow initialization (Qi et al., 2023).