Two-step Consecutive Reaction Research Articles

Investigating the Phase Transition Kinetics of 1-Octadecanol/Sorbitol Derivative/Expanded Graphite Composite Phase Change Material with Isoconversional and Multivariate Non-Linear Regression Methods.

Organic composite phase change materials (PCMs) have been extensively studied, and it is important to investigate the effect of added components on the phase change process of the organic matrix. Herein, the phase transition process of the composite PCM with 1-octadecanol (OD) as the matrix adsorbed by a network framework composed of 1,3:2,4-di-(3,4-dimethyl) benzylidene sorbitol (DMDBS) and expanded graphite (EG) was measured using differential scanning calorimetry (DSC) at several linear heating rates. Using isoconversional and multivariate non-linear regression methods, a two-step consecutive reaction model for the composite PCM was established, while the apparent activation energies and pre-exponential factors were determined. The reaction mechanism of the first step was altered compared to pure OD, while the activation energies significantly decreased at the initial stage of the phase transition process and increased at the later stage. Combined with microscopic morphology analysis, the main reasons were the size and nanoconfinement effect. The predictions of the composite PCM under various conditions suggested that the composite PCM had a wider available temperature range compared to pure OD. This research provided a new idea for the in-depth study of the phase transition process of organic composite PCMs, which was helpful for the evaluation of organic composite PCMs.

A study of pulsating behavior and stability parameter for one-dimensional non-ideal detonations

One-dimensional numerical simulations of non-ideal detonations were performed by using inviscid reactive Euler equations. Chemical reactions in the equations were described by two-step consecutive irreversible reactions A → B → C, which include an exothermic step (A → B) followed by an endothermic step (B → C). Non-ideal detonations are achieved when endothermicity exists in the system. The periodic oscillation behavior of peak pressure during the propagation of a one-dimensional detonation wave was studied with the different exothermicity/endothermicity and different degrees of overdrive. The results show that the increase in exothermicity, the reduction in endothermicity, and the enhanced degrees of overdrive can stabilize the propagation of detonation waves. The influence of the exothermic reaction plays a dominant role for the stability of the one-dimensional non-ideal detonations, which is further confirmed by a theoretical analysis. In addition, the stability parameter χ, proposed originally by Radulescu “The propagation and failure mechanism of gaseous detonations: experiments in porous-walled tubes,” Ph.D. thesis (McGill University, Montreal, Canada, (2003), was extended to predict the stability of non-ideal detonations, based on the Zel'dovich–Neumann–Döring structure of the non-ideal detonations. The results show that the extended stability parameter can well match the stability boundary for all of cases in the present study.

Consecutive Rate Model for Covid Infections and Deaths and Prediction of Level-Off Time.

Covid-19 infection and death rates are predicted based on a simple two-step consecutive reaction rate model. The infection rate is analogous to the first step of a consecutive reaction that results in an intermediate, and the death rate is analogous to the second step of the consecutive reaction in which a small fraction of the intermediate terminates in a product formation irreversibly. The model has been thoroughly tested, especially with infection data from different countries and two of the USA states California and New York, and predicts a linear infection-time relationship in the early stage of Covid infection. That is, the number of infections in 6 days is double the number of infections in 3 days, and infections in 9 days is 3 times the number of infections in 3 days, etc. In the later stage, the infection curve deviates from the linear relationship and follows a first-order constant "half-life" relationship. In the time interval of one half-life, the infection rises to 50% of the level-off value (maximum); during the second half-life, it rises by another 25% (50/2); and in the third half-life, it rises by another 12.5% (25/2), etc. That is, the infection curve reaches 50% (one "half-life"), 75% (two half-lives), 87.5% (three half-lives), etc. of the level off value after the time interval of one to three half-lives. Available data support our predictions.

Applying experiment and numerical simulation to evaluate the thermal hazards of Bis(1-(tert‑butylperoxy)-1-methylethyl)-benzene in the presence of metal ions or sulfuric acid

Bis(1-(tert‑butylperoxy)-1-methylethyl)-benzene (BIPB) is susceptible to thermal runaway or explosion when exposed to metal ions or acid during production. In this article, thermal decomposition of BIPB and its thermal sensitivity to metal ions and acid were firstly systematically studied by DSC and ARC. Experiments demonstrate that BIPB decomposes around 105–115 °C with ΔH¯ of 1483.78J·g−1. FeCl3 and H2SO4 have a more pronounced impact on the thermal decomposition characteristics of BIPB compared with other impurities. Furthermore, the effect became more pronounced with increasing H2SO4. The model-free and model-fitting methods were combined to determine BIPB's decomposition as a two-step consecutive n-order reaction (A→r1B→r2C), then to evaluate thermal hazard indicators. Ultimately, two sem-quantitative risk assessment methods were separately used to evaluate thermal risk of compounds and processes. It's shown that the MF of BIPB mixtures doped with FeCl3 is highest, 2, and the Borda index of the purification process in BIPB synthesis is 44 and risk rank is 2, which is an unacceptable risk.

Synthesis and in vitro synergistic antifungal activity of analogues of Panax stipulcanatus saponin against fluconazole-resistant Candida albicans

Oleanolic acid 3-O-β-d-glucopyranosyl-(1 → 3)-β-d-glucopyranoside (1) and oleanolic acid 3-O-β-d-glucopyranosyl-(1 → 3)-[α-l-arabinofuranosyl-(1 → 4)]-β-d-glucopyranoside (2), novel Panax stipulcanatus saponin analogues, were synthesized for the first time starting from commercially available oleanolic acid, d-glucose, and L-(+)-arabinose. Glycosyl N-phenyltrifluoroacetimidates as donors and two-step consecutive glycosylation reactions are crucial in the synthesis. In vitro antifungal activity results indicated that analogue 2 combined with fluconazole showed synergistic antifungal activity against fluconazole-resistant Candida albicans, with MIC50 values 31.80 μg/mL and FICI values 0.32. We also found that intermediate compounds 16 and 17 revealed synergistic antifungal activity against susceptible Candida albicans when combined with fluconazole, with MIC50 values 1.43 μg/mL and 1.59 μg/mL, FICI values 0.29 and 0.32, respectively.

Thermo-Acoustic Catalytic Effect on Oxidizing Woody Torrefaction

The torrefaction (mild pyrolysis) process modifies biomass chemical and physical properties and is applied as a thermochemical route to upgrade solid fuel. In this work, the catalytic effect of thermo-acoustic on oxidizing woody torrefaction is assessed. The combined effect of two acoustic frequencies (1411, 2696 Hz) and three temperatures (230, 250, and 290 °C) was evaluated through weight loss and its deviation curves, calculated torrefaction severity index (TSI), as well as proximate, calorific, and compression strength analysis of Eucalyptus grandis. A new index to account for the catalytic effects on torrefaction (TCEI) was introduced, providing the quantitative analysis of acoustic frequencies influence. A two-step consecutive reaction numerical model allowed the thermo-acoustic experiment evaluation. For instance, the thermogravimetric profiles revealed that the acoustic field has a catalytic effect on wood torrefaction and enhances the biomass oxidation process for severe treatments. The kinetic simulation of the acoustic coupling resulted in faster conversion rates for the solid pseudo-components showing the boosting effect of acoustic frequencies in anticipating hemicellulose decomposition and enhancing second step oxidizing reaction.

Kinetic modelling of waste wood devolatilization during pyrolysis based on thermogravimetric data and solar pyrolysis reactor performance

Within presented paper complex kinetic analysis of waste wood solar pyrolysis with fuel characterisation has been presented. Thermogravimetric (TGA) data were obtained for heating rates denoted in solar pyrolysis experiments: 5, 10, 15 and 20 K/min. Study presents alternative approach to lignocellulosic biomass kinetics using NETZSCH Kinetics Neo (v. 2.1.2.2) software. TGA data were enriched with the gas analyser indications and experiments results from solar pyrolysis examined on self-designed laboratory reactor. Presented methodology consisted of (1) isoconversional analysis: Friedman, Kissinger-Akahira-Sunose and Ozawa-Flynn-Wall analysis yielding apparent activation energies Eα, varying from 185.37 to 375.56 kJ/mol at reaction extent 0.1–0.9, (2) reaction model identification with generalised master plot method which showed that decomposition was driven by three-dimensional diffusion (D3) with transition to three-dimensional phase boundary (R3) and reaction order based models (F1,F2,Fn) at the end of conversion. Finally, (3) kinetic model construction was performed based on experiments observations, resulting in modelling of 3 main reactions of pyrolysis products formations. The most intensive condensable release was observed between 250 and 440 °C what correlated with CO2 release described by dominant two-step D3-F2 consecutive reaction with activation energies and logarithmic pre-exponential factors 159.92 kJ/mol, 10.44 log(1/s) and 256.78 kJ/mol, 19.05 log(1/s) for first and second step respectively. CO formation obeyed R3 reaction mechanism with activation energy 181 kJ/mol and pre-exponential factor 12.16 log(1/s). Last stage of pyrolysis, charring, was described by two-step consecutive reaction Fn(n = 3.463)-F2 resulting in formation of CH4 and H2 with activation energies and pre-exponential factors of 249.72 kJ/mol, 15.87 log(1/s) and 162 kJ/mol, 6.61 log(1/s) respectively. Kinetic models and isoconversional methods results were tested using Fisher-Snedecor test. Presented methodology was compared with traditional three pseudo-component wood pyrolysis model and discussed.

Kinetic study on pyrolysis of waste phenolic fibre-reinforced plastic

Pyrolysis is considered to be a promising method to recycle waste plastics for fuel or chemical feedstock. In order to provide guidance for reactor design and pyrolysis process management for recycling waste phenolic fibre-reinforced plastic (FRP), the pyrolysis behaviors of waste phenolic FRP is studied employing thermogravimetric analysis (TGA) over a wide heating rate range from 10 K/min to 70 K/min in nitrogen. A two-step consecutive reaction model is proposed to characterize the pyrolysis process. A global optimization algorithm called genetic algorithm (GA) coupled with the two-step consecutive reaction model is used to obtain all the kinetic parameters simultaneously based upon the experimental thermogravimetric data at heating rates of 10, 20 and 30 K/min. The predicted MLR and conversion curves using the optimized kinetic parameters and the two-step consecutive reaction model fit well with the experimental results not only at heating rates of 10, 20 and 30 K/min, but also at heating rates of 50, 60 and 70 K/min which are not used to obtain the kinetic parameters. The optimized kinetic parameters and the two-step consecutive reaction model may be applicable to the pyrolysis of waste phenolic FRP under more practical and complex thermal conditions that can be characterized by various heating rates.

Kinetic Modeling of Indian Rice Husk Pyrolysis

Abstract:To efficiently utilize agricultural biomass waste, kinetic modeling of the pyrolysis of rice husk, including both physical (mainly heat transfer) and chemical (reactions) terms, was conducted at different heating rates from (10 to 20 K min−1) to develop a transport model. For chemical kinetics, the parameters were estimated using different kinetic models, namely the single- or parallel-reaction kinetic model with higher orders and the two-step consecutive reaction model. The two-step model could adequately explain the pyrolysis reaction of multiple reactions with different reaction orders i. e., first step is of the first order (m = 1) with respect to the mass of biomass, and the second step is of the second order (n = 2) with respect to the mass of the intermediate to char. The intrinsic kinetics at different heating rates in the absence of oxygen was derived through thermogravimetric analysis. The kinetics of the evolution of non-condensable gases was studied in a self-designed reactor, and an appropriate kinetic model of rice husk biomass pyrolysis that showed excellent agreement with experimental data was established.

Polymerization of 1,4-dinitrosobenzene: Kinetics and Submicrocrystal Structure

In this study, the structure of the polycrystalline poly(l, 4-phenyleneazine N, N- dioxide) was investigated by Scanning Electron Microscopy and related with the previously calculated molecular structure. Kinetics of polymerization of 1, 4-dinitrosobenzene, prepared by both cryogenic UV photolysis and in vacuo deposition were measured by time-resolved FT-IR spectroscopy. Acquired data was analyzed by curve fitting with the standard Avrami- Erofeev and two-step consecutive reactions models. Activation parameters were calculated from Arrhenius and Eyring-Polanyi equations, for both models. The results obtained by using the two models, along with the goodness-of-fit parameters, were compared. It was shown that both bulk-based and reaction-based models can be used to adequately describe solid-state chemical reaction kinetics. Furthermore, a two- step consecutive reactions model is a suitable alternative to the most commonly used AvramiErofeev model.

Kinetic Modeling of Coal Thermal Decomposition under Air Atmosphere

The paper aims at establishing kinetic model to predict the thermal decomposition of coal in air. Three different rank coals, meager lean coal, fat coal, and gas coal, are investigated using thermogravimetry (TG) and differential scanning calorimetry (DSC). By analyzing the experimental TG curves with a model-fitting method, a two separate stages model is presented to describe the mass variation with temperature and the reaction mechanism. The two stages are found to abide by the first-order mechanism and the contracting-sphere mechanism, respectively. The two separate stages model is validated by comparing experimental and simulated conversion curves and TG curves. By analyzing experimental DSC results with an isoconversional method, a two-step consecutive reactions model is developed. Kinetic parameters of each step are ascertained with a multivariate nonlinear regression method. The two-step consecutive reaction model is validated by comparison of experimental and simulated DSC curves. The two separate...

Kinetics for the distribution of acrylamide in French fries, fried oil and vapour during frying of potatoes

Kinetic analysis for the formation of acrylamide in heated foods has been typically performed using only measured data of acrylamide in foods; however, its possible loss caused by release from heated foods into fried oil and air has seldom been considered. The results obtained from the monitoring of acrylamide by frying French fries indicated that acrylamide is distributed in three phases: French fries, frying oil, and air. From the evolved gas analysis of acrylamide and the measured concentration profile of the total acrylamide amount present in these phases, the kinetic behaviour for acrylamide formation does not obey the commonly used model of two-step consecutive reactions during frying, while a lumped kinetic model was proposed for the total acrylamide amount. Moreover, a high acrylamide level in air was observed, implying that, apart from consumers of French fries, fast-food restaurant workers are potentially subject to occupational hazards from acrylamide inhalation.

Kinetic studies of two-stage sulphuric acid hydrolysis of sugarcane bagasse

The present paper reports the two-stage hydrolysis of sugarcane bagasse to produce monomer sugars by using dilute and concentrated sulphuric acid. About 88% of the sugars present in bagasse could be recovered with a little formation of toxic compounds such as furfural/HMF. The sugar concentration in the first-stage of hydrolysis was obtained as xylose-rich solution of 49.7 g l−1 using 8% acid concentration at 100 °C and a solid to liquid ratio of 1:4, whereas, with the same solid to liquid ratio of 1:4, 73.4 g l−1 glucose-rich solution was obtained in the second-stage of hydrolysis by using 40% acid concentration at 80 °C. The acid hydrolysis of bagasse could be described by a first-order, two-step consecutive reaction model, where the polysaccharides first decompose into monomers through hydrolysis, and thereafter, decompose into various products in the second step. The proposed kinetic model correlates the experimental data satisfactorily.

Performance of bifunctional СuO–CeO2/γ-Al2O3 catalyst in dimethoxymethane steam reforming to hydrogen-rich gas for fuel cell feeding

Dimetoxymethane steam reforming (DMM SR) to hydrogen-rich gas over a bifunctional СuO–CeO2/γ-Al2O3 catalyst was studied. The performance of γ-Al2O3, CeO2/γ-Al2O3, and СuO/γ-Al2O3 under DMM SR conditions was studied as well to elucidate the role of each catalyst component. BET, TPR, FTIR spectroscopy, XRD, TEM, EDXA and HAADF-STEM techniques were used for catalyst characterization. Complete DMM conversion was observed over the СuO–CeO2/γ-Al2O3 catalyst under atmospheric pressure, T=300°C, GHSV=10,000h−1 and H2O/DMM=5mol/mol with hydrogen productivity of 15.5L H2/(gcat·h) and CO content in the hydrogen-rich gas below the equilibrium value. DMM SR proceeds via a consecutive two-step reaction mechanism including DMM hydration to methanol and formaldehyde on γ-Al2O3 acid sites and steam reforming of the formed methanol and formaldehyde to hydrogen-rich gas on alumina-supported mixed copper–cerium oxide species. The СuO–CeO2/γ-Al2O3 catalyst proved to be highly promising for multi-fuel processor approach: steam reforming of DMM, dimethyl ether and methanol on the same catalyst under similar reaction conditions to hydrogen-rich gas for fuel cell feeding.

Consecutive reactions in a countercurrent plug-flow reactor. Gas-liquid system

A mathematical model of a bimolecular two-step consecutive exothermic reaction in the liquid phase of a gas-step consecutive exothermic reaction in the liquid phase of a gas-flow reactor is proposed. Spatial profiles of the heatings and relative concentrations of the reactants in both phases for the steady state of the system are presented. The behavior of the reaction intermediate product is examined. The kinetic characteristics of the reaction are demonstrated to substantially influence the behavior of the system in the reactor.

Effect of Particle Size and Morphology on the Dehydration Mechanism of a Non-Stoichiometric Hydrate

A hydrated form of 7-methoxy-1-methyl-5-(4-(trifluoromethyl)phenyl)-[1,2,4]triazolo[4,3-a]quinolin-4-amine (designated Form B) exhibits moisture sorption behavior that is very strongly affected by particle size and morphology. When studied pre- and post-micronization, the simple rate of dehydration at ambient temperature is faster by >2 orders of magnitude after micronization. Complementary techniques were employed to understand this behavior including environmental X-ray powder diffractometry (XRPD), gravimetric vapor sorption (GVS), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), hot-stage microscopy (HSM), single-crystal X-ray diffractometry (SCXRD), and solid-state nuclear magnetic resonance (SSNMR). Solid-state kinetics analysis of thermal data revealed that dehydration of the nonmicronized material follows a two-step consecutive reaction with the first step being a diffusion limited reaction and the second step being a first order reaction, whereas the micronized material ...

Thermal analysis of hydrogen titanate nanotubes prepared by potassium dititanate with water vapour treatment

Hydrogen titanate nanotubes were prepared by K2Ti2O5 with water vapour treatment. TG/DTG techniques were used to investigate their water content and dehydration kinetics. It was shown that chemical formula for hydrogen titanate nanotubes is TiO2·0.58H2O which is close to H2Ti2O5. The activation energy of dehydration from hydrogen titanate nanotubes is about 60 kJ/mol according the calculation of Friedman and Flynn–Wall–Ozawa methods. With multivariate non-linear regression calculation, it was found that dehydration of hydrogen titanate nanotubes is a two-step consecutive reaction. The first step is a reaction of nth order with autocatalysis. The second step is a reaction of nth order.

Characterisation of the Degradation of Salvianolic Acid B Using an On‐line Spectroscopic Analysis System and Multivariate Curve Resolution

Chinese herbal medicines contain complex ingredients that are unstable during the manufacturing process. Current off-line methods are usually time-consuming and inaccurate. The aim of this study was to develop a continuous-flow-based on-line spectroscopic system for monitoring the degradation of unstable compounds in Chinese herbal medicines. An on-line spectroscopic analysis system in the evaluation of the degradation of unstable compounds was implemented, using salvianolic acid B from Danshen (Radix Salviae Miltiorrhizae) as a model compound. Resolution of the mixture spectra obtained during the reaction was performed with multivariate curve resolution (MCR), and the pure spectra and kinetic profiles of reactant species were reconstructed. The degradation process of salvianolic acid B is probably a consecutive two-step reaction of the form A → B → C, where A is salvianolic acid B, and B and C are the intermediate and final products, respectively. The intermediate and final products were suggested to be a mixture of lithospermic acid and danshensu [3-(3, 4-dihydroxyphenyl) lactic acid], and a mixture of danshensu and salvianolic acid A, respectively. The findings suggested that the combined use of on-line spectroscopic analysis and MCR might be a cheap, readily available, sensitive tool to monitor the transformation of unstable components of Chinese herbal medicines.

Ferryl Intermediates in Heme-Based Dioxygenases

In contrast to the wide spectrum of cytochrome P450 monooxygenases, there are only two heme-based dioxygenases in humans, tryptophan dioxygenase (hTDO) and indoleamine 2,3-dioxygenase (hIDO). hTDO and hIDO catalyze the same oxidative ring cleavage reaction of L-tryptophan (L-Trp) to N-formyl kynurenine (NFK), the initial and rate-limiting step of the kynurenine pathway. Despite immense interest, the mechanism by which the two enzymes execute the dioxygenase reaction remains elusive. Here, we report the first experimental evidence for a key ferryl intermediate of hIDO. It supports a new mechanism, in which the two atoms of dioxygen are inserted into the substrate via a consecutive two-step reaction. This finding introduces a paradigm shift in our understanding of the heme-based dioxygenase chemistry, which was previously believed to proceed via simultaneous incorporation of both atoms of dioxygen into the substrate. The ferryl intermediate is not observable during the hTDO reaction, highlighting the structural differences between the two dioxygenases, as well as the importance of stereoelectronic factors in modulating the reactions.

An exploratory analysis of the electron donor–acceptor complex formation between risperidone and iodine by principal component analysis, soft- and second-order hard-modelling approaches

An exploratory analysis of the electron donor–acceptor complex formation between risperidone and iodine has been done by a strategy equipped with rank augmentation, principal component analysis (PCA) and soft-modelling approach, orthogonal projection approach (OPA), followed by second-order hard-modelling in two non-aqueous solvents with different polarities. From the results of PCA and OPA, the correct number of chemical components and the reactions were identified. In all cases the collected data were found to be rank deficient. In the case of electron donor–acceptor complex formation in acetonitrile, a single second-order reaction and for the process in chloroform, a consecutive two-step reaction was identified. Iodine participates in the second-order rate determining steps in the two solvents. Rank deficiency of the processes was broken through second-order global analysis of the multiple processes with different initial concentrations. Second-order global hard-modelling of the non-linear parameters (rate constants) as well as linear parameters (absorptivities) based on the model derived resulted in well-defined parameters with small standard deviations. Well-resolution of the parameters and the profiles indicated that the models were properly selected.