Thermokinetic Data Research Articles

Predicting solvation energies of free radicals and their mixtures: A robust approach coupling the Peng-Robinson and COSMO-RS models

Detailed kinetic models are valuable tools for a clear understanding of the dynamics of complex reacting systems based on radical-chain mechanisms, such as combustion and oxidation. Gas-phase automatic kinetic generators, such as EXGAS, RMG, MAMOX, NetGen, REACTION, and GENESYS can be used to establish a detailed network of reaction pathways and the rates associated with each reaction. The range of applications of these gas-phase kinetic generators can be extended to liquids through diffusional and solvation corrections directly applied to the gas-phase thermo-kinetic data. In this work, a flexible framework is proposed for the calculation of the solvation correction involving closed-shell (i.e., non-free radical) and open-shell (i.e., free radicals) molecules. This novel model relies on the Peng-Robinson cubic equation of state (EoS) combined with a quantum-based continuum solvation model (COSMO-RS) through an advanced mixing rule. Unlike most predictive equations of state, the proposed model requires only pure compound inputs: critical temperature (Tc,i), critical pressure (Pc,i), acentric factor (ωi), and the screening charge distribution (σ-profile). These inputs were obtained for C/H/O free radicals using group corrections applied to the known values of the associated closed-shell molecules (parent molecules). The resulting EoS is able to provide fast predictions of solvation quantities of closed-shell molecules and C/H/O free radicals with a mean unsigned error of around 0.30 kcal/mol. The great advantage of this method is that it allows high-throughput computation of solvation quantities in pure solvents and mixtures at any temperature (including the supercritical domain), which could enable the simulation of complex oxidation kinetics in a wide range of applications.

Thermokinetic analyses of metal-sensitive reactions in a ceramic flow calorimeter

A ceramic flow calorimeter for metal-sensitive reactions is characterized and used to obtain thermokinetic data on highly exothermic reactions.

Microstructure modeling of nuclear structural materials: Recent progress and future directions

Modeling and simulation of microstructures are essential to understand the complex responses and behaviors of nuclear materials in extreme environments. The needs to assess the extended life operation as well as the growing interest in accelerating nuclear materials development and qualification have stimulated the use of high-fidelity multiscale models aided by empirical and ab initio data. This paper reviews the role of various models across different length and time scales in investigating irradiation effects on microstructure evolution and degradation, in particular the embrittlement caused by radiation induced or enhanced formation of nanoscale chemical heterogeneities. The strength and limitations of these models, including classical rate theories, cluster dynamics, phase-field methods, and atomistic models informed by ab initio energies, are discussed with seminal examples. Challenges regarding the lack of thermo-kinetic data and theoretical treatments considering chemical complexities and magnetic excitations, as well as the stabilizing effect by excess point defects in nuclear structural materials are presented, along with potential solutions based on ab initio informed surrogate energy models and statistical sampling by Monte Carlo simulations. The review then highlights the opportunities to leverage the advantages of different methods by establishing hybrid models by shared variables or coupled codes and applications. Finally, the review concludes with forward-looking remarks on how the use of physics-based models can aid the improvement of machine-learning models of property degradation and vice versa.

Thermal explosion energy evaluation on LCO and NCM Li-ion polymer batteries using thermal analysis methodology

An advanced lithium-ion polymer battery (LIPB) has higher energy density, long-life cycle, and flexible configuration that can be arbitrarily shaped. It is the mainstream candidate for electronics products as energy storage device. However, an energetic LIPB will generate an abnormal electrochemistry reaction and will even cause spontaneous ignition to the battery pack in case cells fail, such as a short circuit or thermal runaway. Two commercial 603450 LIPBs, whose cathodes include lithium cobalt oxide (LiCoO₂, LCO) and lithium nickel cobalt manganese oxide (LiNixCoyMnzO2, NCM), were examined for their thermophysical data. Enhanced calorimetry methods are modified to analyse an LIPB’s heat capacity and enthalpy. In case thermal runaway the heat capacity and enthalpy are 0.99 kJ g–1 K–1 and 11.76 kJ for an LCO cell and 0.96 kJ g–1 K–1 and 10.68 kJ for an NCM cell, respectively. Furthermore, TNT equivalency mass is 7.62 g for an LCO and 7.01 g for an NCM cell. An LIPB is examined to identify the fire-explosion behaviour and thermokinetic data for enhancing battery thermal management.

Reaction Calorimetry and Scale-Up Considerations of Bromo- and Chloro-Boron Subphthalocyanine

The formation mechanism of boron subphthalocyanines (BsubPcs) has thus far evaded researchers, making it nearly impossible to accurately estimate the overall reaction enthalpy─a critical metric for determining chemical process safety for scale-up. To address this gap, reaction calorimetry was used to collect thermokinetic data for a baseline Br-BsubPc reaction at three temperatures and two BBr3 reagent ratios and a proposed semibatch process for Cl-BsubPc. For the Br-BsubPc process, the magnitude of the enthalpy of reaction (ΔHr) increased with increasing reaction temperature, from −244.6 kJ/mol-BBr3 at 25 °C to −332.7 kJ/mol-BBr3 at 50 °C to −391.3 kJ/mol-BBr3 at 75 °C. However, this increase in the magnitude of ΔHr did not result in a noticeable increase in Br-BsubPc yield, achieving 50%, 49%, and 52% yields at 25 °C, 50 °C, and 75 °C, respectively. When the molar equivalence of BBr3 was increased by 1.5× at 25 °C, the magnitude of ΔHr increased slightly (−252.2 kJ/mol-BBr3), but the yield did not improve (47%). Therefore, further attempts were made to try and improve the yield of Br-BsubPc by increasing the molar equivalence of BBr3. It was found that BBr3 equivalencies greater than 0.48 resulted in significant reductions in Br-BsubPc yield. The ΔHr of the semibatch Cl-BsubPc process was −266.5 kJ/mol-BCl3 with a yield of 33%. These processes were assessed based on criticality criteria and were both found to be “Criticality Class 1”, which is relatively safe for scale-up. Based on the calorimetry measurements, preliminary estimates for process conditions and reactor design for scale-up are provided.

Automating the generation of detailed kinetic models for halocarbon combustion with the Reaction Mechanism Generator

Originally developed to predict the chemical kinetics of hydrocarbon combustion via automated generation of detailed reaction mechanisms, Reaction Mechanism Generator (RMG) contains extensive thermokinetic data for C,H,O chemisty, and has more recently been expanded to nitrogen and sulfur. In this work, we present the addition of halogen (fluorine, chlorine, and bromine) chemisty to RMG to enable automated generation of detailed kinetic models for halocarbon combustion. RMG’s existing reaction templates are updated to include halogens, and 11 new reactions families are created specific to halogen chemistry. Notably, kinetics for more than 1000 elementary reactions are calculated via ab inito methods and transition state theory, and these kinetic data are combined with kinetics from literature sources to train rate rule decision tree estimators. Additionally, halogen groups are added to RMG’s statistical mechanics database, enabling model generation with RMG’s pressure dependence module and automated computation of microcanonical rate constants for unimolecular networks. Halogen groups are also incorporated in RMG’s transport database to provide estimated parameters for the Lennard-Jones potential, important for transport-dependent simulations including laminar flame speeds. To demonstrate RMG’s capability for predicting halocarbon combustion, RMG is used to build a flame suppression model for 2-BTP (CH2=CBrCF3) in methane flames. The laminar flame speeds of RMG’s 2-BTP model show good agreement with a published model under a variety of reaction conditions. Automating the generation of detailed kinetic models for halocarbon combustion will facilitate the exploration of previously unexplored reaction pathways, thereby accelerating the development of greener refrigerants and suppressants, as well as advancing the field of automated mechanism generation.

Valorization of the biomass of Rhizoclonium hookeri through slow pyrolysis and its thermokinetic investigation for bioenergy potential

The macroalgae, Rhizoclonium hookeri has the ability to grow in fresh and wastewater rich in nutrients like phosphorus and nitrogen. Here we have performed the slow pyrolysis of dried R. hookeri at three different thermal rates of 5, 10 and 20 °C min−1 from 25 to 800 °C using the thermogravimetric technique to get the thermokinetics for its bioenergy value. Four different thermal degradation stages were considered to get the kinetic triplets from its pyrolysis. The activation energy was obtained for each stage of thermal decomposition utilizing four classical isoconversional methods (Friedman, Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, and Starink). The activation energies obtained through these isoconversional methods for the four valorization zones of R. hookeri were in the range of 151.15–192.62 kJ mol−1. The pre-exponential factor (A) showing the chemical nature of each reaction step was extracted from the kinetic compensation effect and has values in the range of 1.99 × 1020 to 2.63 × 1012 min−1. The thermodynamic parameters revealed the non-spontaneous, endothermic and complex nature of the pyrolysis process of Rhizoclonium biomass. The thermokinetic data showed that Rhizoclonium biomass has bioenergy potential like other macroalgae and is a suitable feedstock for the large-scale pyrolysis process. In conclusion, the outcomes from this study suggest the suitability of Rhizoclonium hookeri as a feedstock for producing bioenergy and is of great significance for designing large-scale equipment to pyrolyze this macroalgal specie.

Reactor performance estimation in microscale flow calorimeter for rapid characterization of exothermic reactions

Continuous flow calorimeters are a promising tool in process development and safety engineering, especially for flow chemistry applications to characterize the heat release and kinetic parameters of rapid chemical reactions. In this study, the digital accompaniment of an isoperibolic flow calorimeter for characterization of exothermic reactions is presented. To support experimental planning and evaluation, computational fluid dynamic simulations are carried out for single-phase flow in the microreactor. The residence time distribution is obtained and used for estimation of conversion and temperature profiles along the microreactor channel. This leads to an integration of CFD simulations into the calorimeter’s software-guided workflow reducing the experimental effort regarding the determination of thermokinetic data. The approach is tested for a highly exothermic test reaction, which provides further hints for future investigations.Article highlights• Estimation of conversion and temperature profiles within a microscale calorimeter• Combination of CFD simulations and reactor performance estimation• Approach was tested for highly oxidation of sodium thiosulfate• Estimated conversion and temperature profiles are in good agreement with experimental dataGraphical abstractComputational Fluid Dynamics simulations are combined with reactor performance estimation to support experimental design for the determination of thermokinetic data. Insights of the dynamic behavior are gained to assist the operator in the investigation of exothermic reactions.

Differential scanning calorimetry investigation of crystallization kinetics and glass-forming ability of sulfonamides

Robust determination of the parameters governing the stability of the amorphous drugs is one of the key tasks of modern pharmaceutics. The kinetic stability of such systems is of crucial importance, as it affects their practical applications. In the present work we have determined the critical cooling rates, and the kinetic parameters of the cold crystallization of four slowly crystallizing sulfonamides, i.e. sulfaguanidine, sulfapyridine, sulfalene, and sulfadimidine. The Nakamura crystallization model was shown to have a good prognostic ability, as it allows determination of the stability time profile of the drug systems prone to crystallization from the non-isothermal thermokinetic data.

Extracting the Oscillatory Component and Defining a Mean Amplitude of Thermokinetic Oscillations in the H/Pd System

Self-sustained oscillations may help in the research of catalytic reactions. But analysis of the resulting nonlinear time series may be complicated, not least due to the lack of a definite baseline. A mathematical method to transform such irregular time series into a more useful form that oscillates around the zero line has been proposed, which preserves both the frequency and the key topological aspects of the originals in the process. To this end, the mean value theorem for integrals has been applied in constructing a base curve for nonequilibrium, periodic thermokinetic oscillations, q(t), recorded microcalorimetrically in two experiments, respectively, with oscillatory sorptions of H2 and D2 in Pd. Once the mean values are so calculated for each period of q(t), they are subjected to cubic spline interpolation to form a new nonoscillatory curve, h(t). The latter can be used as an essential baseline for the oscillatory component of the original thermokinetic time series. Crucially, the areas under both q(t) and h(t) are supposed to be strictly identical. This being confirmed, the pointwise subtraction q(t) – h(t) yields another oscillatory time series g(t), considered to be the oscillatory component extracted from the original thermokinetic data. Subsequently, the method has been applied to a further group of nine microcalorimetric time series q(t) representing thermokinetic oscillations in the H/Pd system. Using the so-constructed g(t) curves (i.e., extracted oscillatory components), a new parameter, the mean amplitude, has been defined and used for correlating the observed gradation of intensities (i.e., amplitudes) of thermokinetic oscillations with a range of experimental conditions applied. The mean amplitude turns out to be a linear function of the first ionization potential of noble gases, admixed intentionally to H2 before its contacting Pd.

Thermochemical and kinetic studies of H-abstraction reaction of benzofurans and benzodioxins by H-atoms

The thermo-kinetic data of the H-abstraction of benzofurans (benzofuran and dibenzofuran) and benzodioxins (1,4-benzodioxin and dibenzo-p-dioxin) have been obtained by the CCSD(T)-F12/CBS//CAM-B3LYP/6–311++G(d,p) method. Based on the Bonding Dissociation Energies (BDE) we have observed a stabilization effect exerted by the O-atom on the H-atoms located in β-position of it, thereby increasing their BDEs. In line with these BDEs, we have classified the H-atoms into four groups: group 1, H-atoms in the benzene ring unaffected by the stabilization effect of the oxygen atom; group 2, H-atoms in the benzene ring under the influence of the stabilization effect of the oxygen atom; group 3, H-atoms positioned in the dioxin ring and group 4, H-atoms located in the furan ring. We have calculated and evaluated the kinetic constants for the H-abstraction reactions for each of these H-atoms thereby deducing the average values for each type of the H-abstracted.

Software-guided microscale flow calorimeter for efficient acquisition of thermokinetic data

Fast chemical process development is inevitably linked to an optimized determination of thermokinetic data of chemical reactions. A miniaturized flow calorimeter enables increased sensitivity when examining small amounts of reactants in a short time compared to traditional batch equipment. Therefore, a methodology to determine optimal reaction conditions for calorimetric measurement experiments was developed and is presented in this contribution. Within the methodology, short-cut calculations are supplemented by computational fluid dynamics (CFD) simulations for a better representation of the hydrodynamics within the microreactor. This approach leads to the effective design of experiments. Unfavourable experimental conditions for kinetics experiments are determined in advance and therefore, need not to be considered during design of experiments. The methodology is tested for an instantaneous acid-base reaction. Good agreement of simulations was obtained with experimental data. Thus, the prediction of the hydrodynamics is enabled and the first steps towards a digital twin of the calorimeter are performed. The flow rates proposed by the methodology are tested for the determination of reaction enthalpy and showed that reasonable experimental settings resulted.Graphical abstractA methodology is suggested to evaluate optimal reaction conditions for efficientacquisition of kinetic data. The experimental design space is limited by thestepwise determination of important time scales based on specified input data.

Gas-Phase Ozone Reactions with a Structurally Diverse Set of Molecules: Barrier Heights and Reaction Energies Evaluated by Coupled Cluster and Density Functional Theory Calculations.

Reactions with ozone transform organic and inorganic molecules in water treatment systems as well as in atmospheric chemistry, either in the aqueous phase, at gas/particle interfaces, or in the gas phase. Computed thermokinetic data can be used to estimate the reactivities of molecules toward ozone in cases where no experimental data are available. Although the gas-phase reactivity of olefins with ozone has been characterized extensively in the literature, this is not the case for the richer chemistry of ozone with polar molecules, which occurs in the aqueous phase or in microhydrated environments. Here, we selected a number of model reactions with small molecules (ethene, ethyne, hydrogen cyanide, hydrogen chloride, ammonia, bromide, and trimethylamine) to study the accuracy of different quantum chemical methods for describing the reactivities of these molecules with ozone. We calculated benchmark electronic energies of gas-phase reactions of these systems with single-reference coupled cluster (CC) theory. These benchmark results for the binding energy in the van der Waals complex, the energy of the transition structure, and the reaction energy were estimated to be accurate within 1-2 kcal mol-1. Singlet oxygen (1O2) is a common product of ozone reactions. Coupled cluster calculations with up to perturbative quadruples (CCSDT( Q)) were needed to obtain reaction energies accurate within 1 kcal mol-1 when this species was involved. In (micro)hydrated environments or at interfaces, coupled cluster methods are prohibitively expensive in most cases. We tested the suitability of some contemporary density functional theory (DFT) methods to reproduce the benchmark electronic energy differences. Range-separated functionals were found to be promising candidates to estimate forward barrier heights, with LC-ωPBE rivaling the accuracy of CCSD( T). For energies of reaction, however, DFT methods exhibited large systematic errors, depending on their fraction of orbital exchange. This was found to worsen when 1O2 is a product, and no safe recommendation can be given for DFT reaction energies in such cases.

Effects of UV for Cycloaliphatic Epoxy Resin via Thermokinetic Models, Novel Calorimetric Technology, and Thermogravimetric Analysis

The cycloaliphatic epoxy resin selected for this study was 3,4-epoxycyclohexane methyl-3′4′-epoxycyclohexyl-carboxylate (EEC). Epoxy resin has numerous applications, such as varnishes, tires, and electronic materials. However, the extensive used of chlorofluorocarbon (CFC) compounds in the last century has resulted in the formation of a hole in the ozone layer. As a consequence, solar radiation is intensifying gradually; therefore, continuous irradiation by sunlight should be avoided. The results of solar radiation can exacerbate the deterioration and photolysis of compounds. Through thermogravimetry and differential scanning calorimetry, the apparent onset temperature of EEC and EEC was analyzed under UV radiation for different durations. Thermokinetic data were used to determine the parameters of thermal decomposition characteristics through simulation to assess the reaction of EEC and EEC under UV radiation for different durations. The goal of the study was to establish the parameters of thermal decomposition characteristics for the effects of UV on EEC, as well as the probability of severity of thermal catastrophe.

Reaction kinetics to infer the effect of dopants on ion transport - A case study for Mo+6 doped lithium titanates (Li2TiO3-δ and Li4Ti5O12-δ)

In this paper, a unique approach to correlate influence of doping on ionic mobility, through thermo-kinetic analysis, is reported. Formation kinetics of Li2TiO3 and Li4Ti5O12, with Mo+6 doping, were successfully analyzed in ultra-pure Ar atmosphere using differential scanning calorimetry. The results were compared with formation kinetics of pure Li2TiO3 and Li4Ti5O12 under identical conditions. Field emission scanning electron microscopy (FE-SEM) with electron diffraction spectroscopy (EDS), X-ray diffraction and Raman spectroscopy were employed for the characterization of resulting phases and presence of oxygen vacancy. The results indicate that for doped samples, oxygen vacancy concentration was reduced due to the charge compensation mechanism of the doped ion. The activation energy (Eα) of the different reactions with and without Mo+6 doping was determined by Kissinger-Akahira-Sunose method. The most probable reaction mechanism was predicted through Master plot approach. The reaction rate controlling step shifted from three-dimensional diffusion (D3) for undoped Li2TiO3 to a chemical reaction (Fn) for doped Li2TiO3. For Li4Ti5O12 the reaction mechanism (or rate controlling step) was a chemical reaction (Fn) for undoped and nucleation (An) for doped material. The results show that diffusion of ions becomes faster in the Mo+6 doped materials by reducing the charge transfer resistance. Finally, the thermodynamic functions of the transition complex were calculated from kinetic triplets and correlated with thermo-kinetic data.

Reaction Calorimetry for Exothermic Reactions in Plate‐Type Microreactors Using Seebeck Elements

AbstractA flexible reactor and measurement setup to safely obtain thermokinetic data for exothermic chemical reactions in plate‐type microreactors is presented. Precise heat flux measurement is realized by means of Seebeck elements and allows for direct as well as space‐ and time‐resolved heat flux determination across the reactor. The microreactor used in this work is manufactured from poly(vinylidene fluoride) foils and consists of 11 SZ‐shaped mixing channel elements. The Seebeck elements are calibrated by the Joule effect, while its performance is demonstrated in heat transfer and neutralization reaction experiments. Furthermore, the local resolution enables an estimation of mixing time scale for rapid reactions. A comparison of obtained results indicates good accordance with literature data and is the base of further investigations using the calorimeter.

Assessment of thermal explosion for an industrial recovery reactor by GC/MS product analysis combined with calorimetric techniques

The reaction of propylene with adsorbents such as BASF selexsorb CD and UOP of various sizes was studied. Adiabatic runaway tests were conducted on propylene mixed with various adsorbents to obtain knowledge on the thermal profile of each. Thermokinetic data were obtained from non-isothermal calorimetric study from the oligomerized reaction between propylene and various adsorbents. A detailed distribution of sorbent product from the adsorber has been analyzed for carbon product greater than 6 ( >C6) using gas chromatography/mass spectrometry results. The test revealed oligomerization and carbonaceous deposit formation of the adsorbent products. The reason for over-temperature of the reactor wall can be anticipated from the agglomeration of carbonaceous deposit disrupting the normal flow of propylene stream causing channeling and lowering the carry-away of heat-accumulated. This approach of real conditions, along with the simulation of process design and operation using computational fluid dynamics (CFD) studies, can render safer process information for avoiding the occurrence of similar runaway explosion induced industrial disaster.

Isothermal and non-isothermal calorimetric techniques combined with a simulation approach for studying the decomposition characteristics of di(2,4-dichlorobenzoyl) peroxide

Disasters caused by organic peroxides, such as di(2,4-dichlorobenzoyl) peroxide (DCBP), are mainly attributed to the presence of unstable oxygen atom bonds. In this study, DCBP was investigated through differential scanning calorimetry and thermal activity monitor III, which yielded thermokinetic data to delve into the pure decomposition characteristics of DCBP undergoing chemical reactions. In addition, the thermokinetic data were used to determine the thermal safety parameters through simulation using a best-fit approach based on an appropriately chosen kinetic model and thermal safety software. We found that DCBP decomposes more satisfactorily by an autocatalytic reaction at low temperatures. The apparent activation energy determined through various approaches, such as Kissinger and Ozawa methods, and thermal safety software simulation were studied. Although DCBP decomposition deposits with dioxins, which require major decontamination measures, DCBP is used to produce silicone products globally. The present study establishes threshold thermokinetic parameters for packing and handling thermally sensitive organic peroxides; these thresholds help predict unwarranted runaway reactions, which entail enormous pressure rise and release of toxic by-products to the environment.

Production of Poly (3-Hydroxybutyric Acid) by Ralstonia eutropha in a Biocalorimeter and its Thermokinetic Studies.

Bioplastic production from microbial sources is an emerging area which provides opportunities even to convert the wastes into bioplastics. Poly (3-hydroxybutyric acid), commonly called as PHB, is a bioplastic, which is stored as intracellular cytoplasmic inclusions in microorganisms. The objectives of this study are to calorimetrically monitor the PHB production and evaluate the thermokinetic data in a bioreaction calorimeter (BioRC1e). Thus, a well-known PHB-producing bacteria Ralstonia eutropha was selected for batch process in a bioreaction calorimeter. The metabolic heat generated was found to be correlated with the biomass, substrate consumption, oxygen uptake rate (OUR), carbon dioxide evolution rate (CER) and PHB production. The OUR pattern explained the oxidative metabolism of the strain R. eutropha. The heat yields due to biomass and glucose consumption during PHB production were found to be 12.56 and 13.56kJ/g, respectively. The oxycalorific value obtained for the PHB production was 443.80kJ/mol of O2. The concentration of PHB obtained in BioRC1e was 4.33g/L with a production rate of 0.09g/L/h. The chemical structure of the extracted PHB by R. eutropha was confirmed using fourier transform infrared spectroscopy (FT-IR) and (1)H and (13)C nuclear magnetic resonance (NMR) analysis.

Study of kinetics of α ⇔ β phase transformation in Ti–4.4 mass% Ta–1.9 mass% Nb alloy using differential scanning calorimetry

The kinetics of α ⇔ β phase transformations in a Ti–4.4 mass% Ta–1.9 mass% Nb alloy has been studied as a function of heating and cooling rates in the range of 3–99 °C min−1 using isochronal differential scanning calorimetry. The transformation start (Ts), peak (Tp) and finish (Tf) temperatures show a systematic variation with heating and cooling rates resulting in a kinetic widening of the α + β phase field. The α ⇔ β phase transformation kinetics is modeled using standard non-isothermal Kolmogorov–Johnson–Mehl–Avrami (KJMA) model for diffusional phase transformation in order to evaluate the effective activation energy and transformation exponent, based on which the mechanism of α → β transformation is identified as diffusion controlled, while the reverse transformation is interface controlled. Based on the thermo-kinetic parameters determined, continuous heating (CHT) and cooling (CCT) diagrams for this alloy have been generated. Being a developmental alloy, the thermo-kinetic data provide useful inputs for the selection of process parameters during manufacturing and heat treatments.