Tian-Calvet Calorimeter Research Articles

Revisiting the thermodynamic properties of the ZrCr2 Laves phases by combined approach using experimental and simulation methods

A comprehensive study of ZrCr2 Laves phases is important for both fundamental research and technological applications. The ZrCr2 compound is a typical precipitate observed in Zr-based alloys including the newly developed Cr-coated Zr cladding known as Accident Tolerant Fuel cladding. The brittle behavior of the Laves phases and the low melting point at the interface zone between the precipitates and the Zr matrix are considered as governing the thermomechanical behaviors of these newly developed nuclear fuel claddings for normal operating conditions but more dramatically in case of Loss Of Coolant Accident (LOCA) conditions. The aim of the present study is to investigate the various ZrCr2 Laves polymorphs and their thermodynamic features particularly where conflicts exist in the literature. Based on diffraction experiments of annealed samples, it has been established that the transformation from the C14 high-temperature form to the C15 low-temperature form is of displacive nature without the C36 polymorph forming as an intermediate phase. The stable and metastable domains of C14 and C15 and their thermodynamic properties have been determined. The specific heat of both C14 and C15 types was measured over a wide range of temperatures from 2 to 1063 K by coupling relaxation calorimetry and DSC. The experimental data were fitted using a modified Einstein model. The room temperature entropies of the C14 and C15 phases were evaluated. The enthalpy of formation was measured for the first time using drop solution calorimetry in liquid Al at 1173 K in a Tian–Calvet calorimeter. The experimental value is in good agreement with Density Functional Theory (DFT) calculations. Finally, all these new results are discussed regarding the abundant literature on the ZrCr2 Laves phases.

Exploring the reactivity of Na3V2(PO4)3/C and hard carbon electrodes in sodium-ion batteries at various charge states

The interest in post-lithium batteries as an alternative to lithium-ion batteries boosted recently due to their substantial abundance, low cost, inherent safety, and sustainability. In recent years, the crucial need for the improvement of battery safety has been emphasized and safety remains a critical barrier for post-lithium technology. Therefore, the thermal stability and reaction enthalpies of electrochemically de-sodiated sodium vanadium phosphate (Na3V2(PO4)3/C) positive electrode and commercial coconut-shell derived hard carbon (HC) at various states of charge (SOCs) were systematically investigated. This study employed the 3D Tian-Calvet calorimeter (C80) and thermogravimetric analysis coupled with mass spectrometry (TGA-MS), to gain comprehensive insights into the thermodynamic aspects of these materials. Thermal stability of electrode materials at distinct sodiation / de-sodiation states draws great attention in cell design and is one of the reasons for the strong state of charge (SOC) dependence of the thermal runaway phenomenon, which represents the most critical safety issue for batteries. This combined experimental approach provides a comprehensive understanding of thermal stability and associated reactions in both, sodium vanadium phosphate (NVP) and hard carbon (HC) electrodes. NVP/C reacts with the electrolyte between 150 and 300 °C, releasing ∼400 J/g heat, although it thermally decomposed beyond 150 °C. The sodiated HC initiates decomposition at 100 °C, releasing ∼750 J/g heat in two steps in a reaction to the electrolyte. These data can facilitate optimizing the design of thermal management systems according to the cell's thermal performance.

Heat generation and degradation mechanisms studied on Na3V2(PO4)3/C positive electrode material in full pouch / coin cell assembly

Na3V2(PO4)3/C cathode and commercial hard carbon anode materials are coated with a roll-to-roll coater on an aluminum current collector. Sodium-ion pouch and coin cells are assembled. The degradation mechanism, cycle stability, morphology of cycle-aged material, and aging influence on the heat generation during cycling are thoroughly investigated. Electrochemical impedance spectroscopy permits resistance assignment to the specific electrodes by using the distribution of relaxation times. Comparison of pristine and cycle-aged cells allows separating the degradation contributions of the particular electrodes. The generated heat during charging and discharging is determined by means of an advanced highly sensitive MS80 3D Tian-Calvet calorimeter under isothermal conditions at 25 °C and the heat generation mechanisms are elucidated. It is observed that less heat is generated during charging than discharging process. Furthermore, the cell balancing reveals a pronounced effect (approximately 50% in charging and 20% in discharging) on the amount of generated heat, which is valuable feedback for the material developers and cell designers. These analyses represent a fingerprint for the underlying electrochemical processes at the electrodes and are very essential for state of health, aging prediction as well as the subsequent tackling of safety-related issues in sodium-ion batteries.

Combined Thermal Runaway Investigation of Coin Cells with an Accelerating Rate Calorimeter and a Tian-Calvet Calorimeter

Commercial coin cells with LiNi0.6Mn0.2Co0.2O2 positive electrode material were investigated using an accelerating rate calorimeter and a Tian-Calvet calorimeter. After cycling and charging to the selected states of charge (SOCs), the cells were studied under thermal abuse conditions using the heat-wait-seek (HWS) method with the heating step of 5 K and a threshold for self-heating detection of 0.02 K/min. The onset temperature and the rate of the temperature rise, i.e., the self-heating rate for thermal runaway events, were determined. The morphology of the positive electrode, negative electrode and the separator of fresh and tested cells were compared and investigated with scanning electron microscopy (SEM). Furthermore, the microstructure and the chemical compositions of the individual components were investigated by X-ray diffraction (XRD) and inductively coupled plasma with optical emission spectrometry (ICP-OES), respectively. In the Tian-Calvet calorimeter, the coin cells with the selected SOCs and the individual components (positive electrode, negative electrode and separator) were heated up with a constant heating rate of 0.1 °C/min (ramp heating mode). Simultaneously, the heat flow signals were recorded to analyze the heat generation. The combination of the three different methods—the HWS method using the ES-ARC, ramp heating mode on both cells and the individual components using the Tian-Calvet calorimeter—together with a post-mortem analysis, give us a complete picture of the processes leading to thermal runaway.

Phase behaviour and heat capacities of 1-butyl-1-methylpyrrolidinium-based ionic liquids with fluoro-sulfonate anions

Pyrrolidinium-based ionic liquids belong to the relatively common classes of these compounds; however, there are serious gaps in the knowledge and interpretation flaws of their physico-chemical properties, except for those containing the archetypal bistriflimide [NTf2] anion. Compounds combining the 1-butyl-1-methylpyrrolidinium cation [C4C1Pyrr] with various fluorinated sulfonate anions exhibit vast polymorphism, rendering the thermodynamic description even more complicated. Four 1-butyl-1-methylpyrrolidinium ionic liquids, available commercially in high purities, were subjugated to a combined calorimetric and crystallographic study with a special emphasis on establishing a complete interpretation of their phase behaviour.The samples were dried by vacuum heating and their purity was verified using the Karl Fischer titration and van't Hoff analysis of the melting peaks. Polymorphism was readily detected for all four compounds, but a complete description of their phase behaviour required an intensive and careful labour. Despite our experimental efforts, some of the polymorphs were found to be too elusive for a complete characterization by any of the used techniques. The obtained phase-transition temperatures and enthalpies were critically compared to the available literature with a variable agreement. While the existing thermodynamic data for [C4C1Pyrr][NTf2] were found complete and sensible, literature data for the other compounds were incomplete or ambiguous. Heat capacities of the four compounds were determined using a Tian-Calvet calorimeter, the results of which were in a good agreement with the existing adiabatic-calorimetric data for [C4C1Pyrr][NTf2]. Several crystal structures were newly resolved within the phase behaviour study and they are reported in the paper.

Heat Generation in NMC622 Coin Cells during Electrochemical Cycling: Separation of Reversible and Irreversible Heat Effects

The thermal behavior of a commercial lithium-ion cell with the cathode material LiNi0.6Mn0.2Co0.2O2 (NMC622) was investigated during the cycling process using a Tian-Calvet calorimeter (C80, SETARAM Instrumentation, France). Various current flows of 42.5, 85, and 170 mA corresponding to charging rates of 0.5, 1, and 2 C, respectively, were applied in the measurements. The corresponding heat flow rates were measured by the C80 calorimeter at 30 °C. The reversible heat effect due to the reversible electrochemical reaction was quantified by the entropy change measurement. The irreversible heat effect due to internal resistances was determined by the electrochemical impedance spectroscopy (EIS) and the galvanostatic intermittent titration technique (GITT). The results were compared with the direct measurement of the heat effect by calorimetry during electrochemical cycling.

Standard enthalpies of formation determination of lanthanum fluorbritholites

Lanthanum–enclosing silicate–fluorapatites or britholites Ca10-xLax (PO4)6-x (SiO4)x F2 with 1 ≤ x ≤ 6, were obtained by solid state reaction at high temperature and characterized by X-ray diffraction and IR spectroscopy. The enthalpies of solution were measured in nitric acidic solution at 298.15 K using a swinging differential Tian-Calvet calorimeter. The determination of the formation enthalpies from the elements, were performed handling a thermochemical cycle and complementary experiments. In the studied solid solution the stability decreases with the rate of substitution.

Evolution of Specific Heat Capacity with Temperature for Typical Supports Used for Heterogeneous Catalysts

Heterogeneous catalysts are widely used in the chemical industry. Compared with homogeneous catalysts, they can be easily separated from the reaction mixture. To design and optimize an efficient and safe chemical process one needs to calculate the energy balance, implying the need for knowledge of the catalyst’s specific heat capacity. Such values are typically not reported in the literature, especially not the temperature dependence. To fill this gap in knowledge, the specific heat capacities of commonly utilized heterogeneous catalytic supports were measured at different temperatures in a Tian–Calvet calorimeter. The following materials were tested: activated carbon, aluminum oxide, amberlite IR120 (H-form), H-Beta-25, H-Beta-38, H-Y-60, H-ZSM-5-23, H-ZSM-5-280, silicon dioxide, titanium dioxide, and zeolite 13X. Polynomial expressions were successfully fitted to the experimental data.

Mixing enthalpies of alloys with dynamical instability: bcc Ti-V system

Enthalpy of mixing is among the key materials parameters to determine phase stability and phase transformations in solid solutions. The possibility to predict it from first principles in the framework of the density functional theory is one of the corner stones of the modern materials modeling and the future data-driven materials design. Here we have considered body-centered cubic (bcc) Ti-V alloys, a system with high potential for aerospace, automotive biomedical and energy applications, which is known to exhibit the dynamical instability of the crystal lattice for Ti-rich alloys at low temperature. We have calculated the mixing enthalpies ΔH of bcc Ti-V alloys in the whole interval of concentration at high temperature using ab initio molecular dynamics (AIMD) simulations. A comparison with state-of-the-art static calculations at temperature 0 K shows drastic difference between the two methods: while AIMD predicts positive values of ΔH in the whole range of concentrations, the static zero-temperature simulations result in negative values of ΔH for Ti-rich alloys. We have measured the mixing enthalpy of bcc Ti-V alloys experimentally at 1073 K using an isoperibol high temperature Tian-Calvet calorimeter and found that the enthalpies are positive, in agreement with our finite temperature AIMD calculations. We attribute the failure of the standard static calculations of ΔH to lattice distortions associated with the dynamical instability of bcc Ti-V alloys at zero temperature and argue that the effect should be generally important in theoretical predictions of thermodynamic properties, especially for systems with dynamical instability.

Calorimetric and FTIR study of selected aliphatic octanols

Isobaric heat capacities of ten selected aliphatic octanols (3-octanol, CAS RN: 589-98-0; 2,2,4-trimethyl-3-pentanol, CAS RN: 5162-48-1; 2,2-dimethyl-3-hexanol, CAS RN: 4209-90-9; 2,3-dimethyl-3-hexanol, CAS RN: 4166-46-5; 2,4-dimethyl-3-hexanol, CAS RN: 13432-25-2; 2,5-dimethyl-3-hexanol, CAS RN: 19550-07-3; 3,5-dimethyl-3-hexanol, CAS RN: 4209-91-0; 4-ethyl-3-hexanol, CAS RN: 19780-44-0; 3-methyl-4-heptanol, CAS RN: 1838-73-9; 4-methyl-4-heptanol, CAS RN: 598-01-6) were measured with a Tian–Calvet calorimeter in the temperature range from 257 to 358 K; this temperature range was extended up to 423 K with a heat-flux DSC. For all studied compounds, a maximum on temperature dependence of heat capacity was observed; this feature was corroborated by FTIR spectroscopy performed from 303 K to a maximum of 463 K. Such maxima are related to disintegration of oligomers kept together by hydrogen bonds. The role of steric hindrance on hydrogen bonding is discussed. It is apparent that temperature of maxima is very sensitive to steric hindrance; however, further effort is required for full understanding of hydrogen bonding in aliphatic octanols.

Aminolysis of cyclic-carbonate vegetable oils as a non-isocyanate route for the synthesis of polyurethane: A kinetic and thermal study

Production of polyurethane is increasing since the recent years. Nevertheless, this production uses hazardous chemicals, which is isocyanate. Academy has put a lot of effort to develop some non-isocyanate polyurethane routes. One of the most promising is the aminolysis of cyclic-carbonate by diamine. To industrialize this way of production, kinetic and thermodynamic data are needed. The first steps were to optimize the production of methyl oleate, epoxidized methyl oleate and carbonated methyl oleate. Then, a kinetic model was built for a model reaction which is the aminolysis of carbonated methyl oleate by n-butylamine by taking into account the side reaction of amidation. The model fits correctly the experimental data. A Tian-Calvet calorimeter was used to determine the different reaction enthalpies. It was found that the reactions of aminolysis and amidation were low exothermic reactions.

The aid of calorimetry for kinetic and thermal study

Phosphoric acid, a non-renewable chemical, is used in different industries. Production of this chemical from natural phosphate can be done by two routes: wet process and thermal process. The nature of the natural phosphate, i.e., its chemical composition, plays an important role in the kinetics and thermodynamics of phosphoric acid production. Thus, the establishment of a kinetic model, based on reaction mechanism, for the dissolution of natural phosphate is cumbersome due to the presence of impurities. Besides, one should use an online analytical method because the dissolution reaction is fast. The dissolution of two natural phosphates with different percentages of phosphorus pentoxide (P2O5), phosphate samples (28 mass% of P2O5) from Gafsa region (Tunisia) and phosphate samples (18 mass% of P2O5) from Cheketma-Kasserine region (Tunisia), was studied from a kinetic and thermal aspect. Experiments were performed by using a Tian—Calvet calorimeter. Two acid solutions were used for the dissolution: one with phosphoric acid (S1) and the other a mixture of phosphoric and sulfuric acid (S2). For both natural phosphates, it was found that in case of using S1 solution the heat released due to the dissolution was lower than in case of using solution S2. This difference was explained by the precipitation of monohydrate sulfate calcium to its dihydrate form. By using a granulometry distribution lower than 500 μm, heat released during the dissolution of both phosphates by S1 was similar, i.e., − 230 J g−1, and the same observation was done by using S2 solution, i.e., between − 300 and − 350 J g−1. We have demonstrated that granulometry distribution plays an important role, and by using a granulometry lower than 120 μm for Cheketma-Kasserine region phosphate, the heat released during the dissolution was higher, i.e., − 400 J g−1 with solution S2. Avrami model was found to describe the precipitation of calcium sulfate, and three distinguished domains were obtained by using Gafsa region phosphate compared to two domains with Cheketma-Kasserine region phosphate.

Complexation equilibria studies of alkyl formate hydrolysis in the presence of 1-butylimidazole

Formic acid production by ethyl or methyl formate hydrolysis was improved using 1-butylimidazole as a complexing agent. The chemical process involved both hydrolysis and complexation steps. The complexation equilibria were investigated by deriving theoretical equations using the equilibrium constant of the hydrolysis step, the apparent formation constant of the complexation process and the initial concentration of the complexing agent. The treatment of the experimental results within the experimental domain indicated that an equimolar amount of the acid and the base did not lead to the complex formation. Experimental observation suggested that the derived equation could be simplified by assuming that the stoichiometric coefficient of the complexing agent was 0.5. The apparent reaction enthalpy obtained from this equation was compared to the experimental one using a Tian-Calvet calorimeter and a good agreement was found between them. FTIR spectroscopy was used to confirm the existence of the complex between formic acid and 1-butylimidazole.

Adsorption Microcalorimetry of CO2 in Confined Aminopolymers.

Aminopolymers confined within mesoporous supports have shown promise as materials for direct capture of CO2 from ambient air. In spite of this, relatively little is known about the energetics of CO2 binding in these materials, and the limited calorimetric studies published to date have focused on materials made using molecular aminosilanes rather than amine polymers. In this work, poly(ethylenimine) (PEI) is impregnated within mesoporous SBA-15, and the heats of CO2 adsorption at 30 °C are investigated using a Tian-Calvet calorimeter with emphasis on the role of PEI loading and CO2 pressure in the compositional region relevant to direct capture of CO2 from ambient air. In parallel, CO2 uptakes of these materials are measured using multiple complementary approaches, including both volumetric and gravimetric methods, and distinct changes in uptake as a function of CO2 pressure and amine loading are observed. The CO2 sorption behavior is directly linked to textural data describing the porosity and PEI distribution in the materials.

Optimization of a sensor for a Tian–Calvet calorimeter with LTCC-based sensor discs

Abstract. In this work, it is shown how a finite element method (FEM) model of a Tian–Calvet calorimeter is used to find improvements in the sensor design to increase the sensitivity of the calorimeter. By changing the layout of the basic part of the sensor, which is a low temperature co-fired ceramics (LTCC) based sensor disc, an improvement by a factor of 3 was achieved. The model was validated and the sensors were calibrated with a set of measurements that were later used to determine the melting enthalpies and melting temperatures of indium and tin samples. Melting temperatures showed a maximum deviation of 0.2 K while the enthalpy was measured with a precision better than 1 % for most samples. The values for tin deviate by less than 2 % from literature data.

First steps to develop a sensor for a Tian–Calvet calorimeter with increased sensitivity

Abstract. Initial steps to apply a ceramic multi-layer technique to build a new sensor for a Tian–Calvet calorimeter are presented in this contribution. The new sensor has a stacked design of ceramic sensor discs and insulating rings. The development was finite-element method (FEM) supported to design the sensor disc. In the next step, the function of the sensor disc was proven up to a temperature of 600 °C. Finally, the entire stack was tested at room temperature, delivering a resolution of 5 µW and a maximum sensitivity of 8.5 µV mW−1. The time constant is strongly dependent on the mass of the cuvette. We show that the time constant of the sensor can be more exactly characterized when using a novel low temperature co-fired ceramic (LTCC) cuvette with a low mass and an integrated heater. Then, the time constant can be reduced to T1∕e = 118 s. The new sensor shows similar specifications as commercial devices and presents a good starting point for future high temperature applications.

Enthalpies of Formation of Layered LiNixMnxCo1-2xO2 Compounds As Promising Li-Ion Battery Cathode Materials

Layer structured lithium mixed transition metal oxides with the general formula of LiNixMnyCozO2 (x+y+z=1) and theoretical capacity of approximately 280 mAh/g are considered as promising intercalation type positive electrode materials for Lithium-ion batteries. Owing to their lower costs and higher capacities, LiNixMnyCozO2 (NMCs) are extensively investigated for electric vehicles and grid storage applications as suitable substitutes for LiCoO2, the most widely used cathode material for Li-ion batteries. Several studies have been devoted to investigating the structure and electrochemical behavior of different compositions in the LiNixMnxCo1-2xO2 (0≤x≤0.5) solid solution series. However, there are very limited thermochemical data reported on these compounds. The enthalpies of formation of LiNi1−xCoxO2 compounds were determined by Wang et al. [1] using high temperature oxide solution calorimetry and the enthalpy of formation of LiNi1/3Mn1/3Co1/3O2 and its delithiated phases were measured by Idemoto et al. [2] using acid solution calorimetry. The aim of this work is therefore to determine the enthalpy of formation of selected compositions in LiNixMnxCo1-2xO2(0≤x≤0.5) series by calorimetric measurements in order to study the relative thermodynamic stabilities of these phases and further clarify structure–property relationships in these compounds. In this study, single phase LiNixMnxCo1-2xO2 for x=1/6, 1/3, 0.4, 0.5 were synthesized according to the sol-gel method using metal acetates and adipic acid as a chelating agent. The chemical compositions of the samples after the final heat treatment were measured by inductively coupled optical emission spectroscopy (ICP-OES). In addition, powder X-ray diffraction (XRD) was performed to determine phase impurities and lattice parameters of the respective compounds. Subsequently, the standard enthalpies of formation of the compounds were measured by employing high temperature oxide melt drop solution calorimetry using a Setaram AlexSys-1000 Tian–Calvet calorimeter (Setaram Instrumentation, Caluire-et-Cuire, France) with a sodium molybdate (3Na2O.4MoO3) solvent maintained at approximately 700°C. The powder-XRD results show that all compositions were single phase adopting the α-NaFeO2 type structure (space group: , No. 166). As x in LiNixMnxCo1-2xO2 increases, the a and c lattice parameters increase whereas the c/a ratio decreases. This can be explained by the difference in ionic radii between Ni2+ and Co3+ and the fact that Co3+ which is situated on the transition metal layer is continuously substituted by equal amounts of Mn4+ and Ni2+. The results of our high temperature oxide melt solution calorimetry measurements show that the standard enthalpies of formation of the LiNixMnxCo1-2xO2 compounds from the elements become more exothermic with increasing x. Therefore, contrary to the work of Idemoto et at. [2], we show that the investigated NMC compounds are energetically more stable than LiCoO2. The increasing thermodynamic stability is caused by the substitution of Co3+ with equal amounts of Mn4+ and Ni2+cations on the transition metal layer (3b sites). Keyword: Lithium nickel manganese cobalt oxide, Layered structure, Oxide solution calorimetry, Enthalpy of formation, Lithium-ion battery References Wang, M. & Navrotsky, A. Enthalpy of formation of LiNiO2, LiCoO2 and their solid solution, LiNi1-xCoxO2. Solid State Ionics 166 (2004), 167-173.Idemoto, Y., & Matsui, T. Thermodynamic stability, crystal structure, and cathodic performance of Lix(Mn1/3Co1/3Ni1/3)O2 depend on the synthetic process and Li content. Solid State Ionics 179 (2008), 625-635.

Calorimetric and FTIR study of selected aliphatic heptanols

Isobaric liquid phase heat capacities of nine selected aliphatic heptanols (1-heptanol, CAS RN: 111-70-6; 3-heptanol, CAS RN: 589-82-2; 4-heptanol, CAS RN: 589-55-9; 2-methyl-2-hexanol, CAS RN: 625-23-0; 5-methyl-2-hexanol, CAS RN: 627-59-8; 2-methyl-3-hexanol, CAS RN: 617-29-8; 3-ethyl-3-pentanol, CAS RN: 597-49-9; 2,2-dimethyl-3-pentanol, CAS RN: 3970-62-5; 2,4-dimethyl-3-pentanol, CAS RN: 600-36-2) were measured with a highly sensitive Tian-Calvet calorimeter in the temperature range from 261 K to 382 K. Experimental heat capacity data were correlated as a function of temperature. For eight compounds, a maximum on temperature dependence of heat capacity was observed. The phase behavior was investigated with a differential scanning calorimeter. Calorimetric measurements were complemented by FTIR spectroscopy from room temperature to a maximum of 428 K. The main aim of this work was to fill the gap in reliable heat capacity data for these compounds and to extend the knowledge base required for a better understanding of alcohols self-association.

Probing Intramolecular versus Intermolecular CO2 Adsorption on Amine-Grafted SBA-15.

A mesoporous silica SBA-15 is modified with an array of amine-containing organosilanes including (i) propylamine, SiCH2CH2CH2NH2 (MONO), (ii) propylethylenediamine, SiCH2CH2CH2NHCH2CH2NH2 (DI), (iii) propyldiethylenetriamine, SiCH2CH2CH2NHCH2CH2NHCH2CH2NH2 (TRI), and (iv) propyltriethylenetetramine, SiCH2CH2CH2NHCH2CH2N(CH2CH2NH2)2 (TREN) and the low loading silane adsorbents (∼0.45 mmol silane/g) are evaluated for their CO2 adsorption properties, with a focus on gaining insight into the propensity for intramolecular vs intermolecular CO2 adsorption. Adsorption isotherms at low CO2 coverages are measured while simultaneously recording the heat evolved via a Tian-Calvet calorimeter. The results are compared on a silane molecule efficiency basis (mol CO2 adsorbed/mol silane) to assess the potential for intramolecular CO2 adsorption, employing two amine groups in a single silane molecule. As the number of amines in the silane molecule increases (MONO < DI < TREN ∼ TRI), the silane molecule efficiency is enhanced owing to the ability to intramolecularly capture CO2. Analysis of the CO2 uptake for samples with the surface silanols removed by capping demonstrates that cooperative uptake due to amine-CO2-silanol interactions is also possible over these adsorbents and is the primary mode of sorption for the MONO material at the studied low silane loading. As the propensity for intramolecular CO2 capture increases due to the presence of multiple amines in a single silane molecule (MONO < DI < TREN ∼ TRI), the measured heat of adsorption also increases. This study of various amine-containing silanes at low coverage is the first to provide significant, direct evidence for intramolecular CO2 capture in a single silane molecule. Furthermore, it provides evidence for the relative heats of adsorption for physisorption on a silanol laden surface (ca. 37 kJ/mol), a silanol-capped surface (ca. 25 kJ/mol), via amine-CO2-silanol interactions (ca. 46 kJ/mol), and via amine-CO2-amine interactions at low surface coverages (ca. 65 kJ/mol).

Kinetic modeling strategy for an exothermic multiphase reactor system: Application to vegetable oils epoxidation using Prileschajew method

Epoxidation of cottonseed oil by peroxyformic acid (PFA) was studied in a semibatch calorimeter. This liquid–liquid reaction system is composed of different exothermic steps. Thus, a kinetic modeling strategy to diminish the number of parameters to estimate was developed by investigating each reaction system: PFA synthesis and decomposition, ring‐opening and epoxidation. A thermal study was conducted by determining heat capacity of the different organic species, and by analyzing the evolution of global heat‐transfer coefficient with the reaction extent. The epoxidation reaction was performed in a semibatch reactor under isoperibolic mode within an initial temperature range of 50–70°C, an organic phase of 30–34 wt %, a formic acid molar flow rate of 0.02–0.05 mol/min and an addition time of 25–50 min. The interfacial mass transfer was supposed to be faster than the intrinsic reaction kinetics suppressing the use of mass transfer correlation. Nonlinear regression was used to estimate the kinetic and thermal parameters. The kinetic parameters of epoxidation of the three different fatty acids, namely oleic, linoleic, and its intermediate were estimated. The reaction enthalpy of epoxidation was estimated to −230 ± 3.8 kJ/mol, and the reaction enthalpy of ring‐opening was measured to be −90 kJ/mol by Tian–Calvet calorimeter. © 2015 American Institute of Chemical Engineers AIChE J, 62: 726–741, 2016