Thermodynamics and Kinetics Research of the Fluorination Process of the Concentrate Rutile

The growth in the production of titanium metal and its compounds leads to an increase in the amount of toxic waste. As a result, at the legislative level, emissions of such wastes are limited, which leads to a drop in the production of titanium-containing products and a shortage of titanium in the international market. This paper presents the results of the process of fluorination of rutile concentrate from the Tarsky deposit (Russia, Omsk region) with elemental fluorine using a laboratory setup of a special design. For fluorination, samples of rutile concentrate weighing 0.1–1.0 g were used. The particle size distribution of particles varied from 2 × 10−6 to 2 × 10−5 m. To determine the possibility of carrying out the process, the calculation of the change in the logarithm of the equilibrium constant versus temperature was performed. The influence of the following operating parameters on the fluorination process has been studied: various concentrations of F2 in a fluorinating mixture of fluorine with nitrogen; process time from 0 to 9 min; different ratios of the initial solid phase to fluorine (10 and 50% excess of fluorine and 10 and 50% of its deficiency); fluorination temperature in the range of 300–1800 K. A kinetic equation is selected that most accurately describes the fluorination process. The values of the activation energy and the preexponential factor in the kinetic equation are determined. The obtained results show that with an increase in the fluorine content in the fluorinating gas mixture and the temperature of the process, the fluorination rate increases. Optimal conditions for fluorination: temperature—680 K; time—5 min excess fluorine in the fluorinating mixture—20–25%. The obtained results allow to propose and consider the conditions of process execution on industrial equipment.

SULFONYL CHLORIDES - NOVEL SOURCE OF FREE RADICALS

Novel free radicals source based on sulfonyl chlorides is discovered. The radical mechanism is confirmed by 2,3-dimethyl-2,3-diphenylbutane formation under chlorosulfonated polyethylene heating in the isopropylbenzene solution. Concerted homolytic C-S and S-Cl bond scission of chlorosulfonated polyethylene thermal degradation mechanism proved by kinetic analysis. The proof of the two bonds simultaneous breaking is provided by the threefold activation energy reduction (83 kJ/mol) in comparison to the C-S and C-Cl bond dissociation energy (280 and 286 kJ/mol respectively), the 6 orders lower preexponential factor (2,46 ∙ 10 s) in Arrhenius equation in comparison to one bond cleavage (≈10-10 s) as well as the strongly negative activation entropy value (-134 J/mol∙K).

Determining Preexponential Factor in Model-Free Kinetic Methods: How and Why?

The kinetics of thermally stimulated processes in the condensed phase is commonly analyzed by model-free techniques such as isoconversional methods. Oftentimes, this type of analysis is unjustifiably limited to probing the activation energy alone, whereas the preexponential factor remains unexplored. This article calls attention to the importance of determining the preexponential factor as an integral part of model-free kinetic analysis. The use of the compensation effect provides an efficient way of evaluating the preexponential factor for both single- and multi-step kinetics. Many effects observed experimentally as the reaction temperature shifts usually involve changes in both activation energy and preexponential factor and, thus, are better understood by combining both parameters into the rate constant. A technique for establishing the temperature dependence of the rate constant by utilizing the isoconversional values of the activation energy and preexponential factor is explained. It is stressed that that the experimental effects that involve changes in the preexponential factor can be traced to the activation entropy changes that may help in obtaining deeper insights into the process kinetics. The arguments are illustrated by experimental examples.

The Nature of CVC Nonlinearity in Low-Voltage Scanning Tunneling Spectroscopy of Semiconductors

A new model of field emission in a scanning tunnelling microscope was developed. The model describes the tunnelling current from a surface of semiconductor (semimetal) and allows estimating the preexponential factor in the expression for the tunneling probability. It is shown that this factor is directly related to the degree of localization of the electron density and determines the shape of the local tunnel current-voltage characteristics (LTCVCs) at low voltages. The model allows separating the contributions of surface electronic states of different symmetry (dimension) of the tunnelling current. The practical application of the model is demonstrated by the example of mathematical processing of the LTCVCs of HOPG surface containing different structural defects.

Kinetics of low-temperature aluminothermic reduction of iron tantalate

The kinetics of low-temperature (900 – 1180 °C) reduction of iron tantalate (98.2 wt % FeTa2O6, 1.8 wt % Ta2O5, particle size < 0.1 mm) by excess aluminum (particle size < 0.14 mm) at the molar ratio Al:FeTa2O6 = 6 was studied. According to differential scanning calorimetry and X-ray powder diffraction, reduction is almost completed at 1180 °C, the metal products are TaFeAl, TaAl3, and Ta17Al12. Based on the results of thermokinetic calculations (Ozawa – Flynn – Wall and nonlinear regression methods), the formal mechanism of the process is represented by the Bna → CnC model, which includes two consecutive steps controlled by autocatalytically activated reactions. Kinetic parameters of the steps are: 1) Е1 = 429 kJ·mol–1, A1 = 1015.3 s–1; 2) Е2 = 176 kJ·mol–1, A2 = 103.9 s–1 (Ej is the activation energy, Aj is the preexponential factor). Prediction in the Bna → CnC model frames indicates the possibility of obtaining a reaction mixture containing ≥ 98 mol. % the final formal reduction product, with isothermal exposure in the temperature range of 1040 – 1120 °C during 1.5 – 5 minutes. The proposed model can be used to develop scientific foundations and substantiate technological modes for obtaining tantalum alloys from mineral and technogenic raw materials.

Determinación de los parámetros cinéticos de la pirolisis de la biomasa lignocelulosica

Over the past decades, interest in renewable energy and the environment has grown considerably, with a significant effort being made in the field of energy efficiency, the creation of sustainable technologies and the reduction of the carbon footprint. Therefore, the use of biomass in an economical and efficient way is of interest, and its study and analysis becomes necessary. In this work, kinetic parameters such as activation energy (Ea) and preexponential factor (A) were determined for apple residues using the non-isothermal thermogravimetric method and treating the data obtained under the models mathematicians of the differential method and the maximum speed method, and additionally performing the activation energy distribution. The calculation of the activation energy helped to see the way in which thermal decomposition takes place (if there are one or more processes and in what range of conversions they occur), through the characteristic kinetic constants provided by the kinetic models, allowed to identify the gaseous species emitted by the material, and thus study the processes through which such decomposition occurs

Water vapor transmission properties of acrylic organic coatings

In this work, we evaluate the water vapor transmission rate (WVTR), the permeability (P), solubility (S), and diffusion (D) coefficients of Paraloid B44, Paraloid B72, and Incralac coatings in the temperature range of 5–35°C. The Arrhenius function—diffusion activation energy and preexponential factor—has also been determined from the data: $$D_{B44} = 35.2\;{\text{cm}}^{2} \;{\text{s}}^{ - 1} \exp \left( { - 25\;{\text{kJ mol}}^{ - 1} /{\text{RT}}} \right)$$ D B 44 = 35.2 cm 2 s - 1 exp - 25 kJ mol - 1 / RT ; $$D_{B72} = 9.5\;{\text{cm}}^{2} \;{\text{s}}^{ - 1} \exp \left( { - 23\;{\text{kJ mol}}^{ - 1} /{\text{RT}}} \right)$$ D B 72 = 9.5 cm 2 s - 1 exp - 23 kJ mol - 1 / RT ; $$D_{\text{Incralac}} = 622.8\;{\text{cm}}^{2} \;{\text{s}}^{ - 1} { \exp }\left( { - 28\;{\text{kJ mol}}^{ - 1} /{\text{RT}}} \right)$$ D Incralac = 622.8 cm 2 s - 1 exp - 28 kJ mol - 1 / RT . These resins are important coating materials, for example, for conservators to protect metallic artifacts, such as statues, against corrosion. Despite Paraloid B44 and B72 resins being considered as reference materials in conservation practice, that is, new coating materials (either water vapor retarders or transmitters) are often compared to them, there are no comprehensive data for the quantities describing the vapor permeability (P, S, D) of these materials. The measurements are based on the ISO cup-method using substrate/coating composite samples. The strength of this technique is that it can also be used when the coating is non-self-supporting; nevertheless, P, S, and D can be deduced for the coating layer itself, and it seems to be a standardizable procedure for comparative performance testing of coating materials. Paraloid B72 layers exhibited higher WVTRs—from 39 to 315 g m−2 day−1 as the temperature increased from 5 to 35°C—compared to Paraloid B44 and Incralac coatings—from 17 to 190 g m−2 day−1, respectively. The transmission rate parameters were also compared to the results of corrosion tests. Incralac was the most effective corrosion inhibitor, and the performance of the B44 was better than the B72, which is in good agreement with the transmission rate tests.

Kinetic analysis of CO2 gasification of biochar and anthracite based on integral isoconversional nonlinear method

The nonisothermal thermogravimetric analysis was implemented for gasification of sawdust char (SD-char), wheat straw char (WS-char), rice husk char (RH-char), bamboo char (BB-char) and anthracite coal (AC) in the presence of CO2. The dependence of activation energy upon conversion for different biochars and AC was obtained by the integral isoconversional nonlinear (NL-INT) method which is a model-free method. Based on the activation energy values from the NL-INT method, a model-fitting method called random pore model (RPM) was used to estimate the kinetic parameters including the preexponential factor and pore structure parameter from the experimental data. The results are shown that the gasification reactivity of different samples from high to low can be sorted as that of WS-char, SD-char, BB-char, RH-char and AC. In the early stage of gasification, the activation energy values of biochars increase generally with an increase in the conversion degree, whereas the value of AC decreases. Thereafter, the activation energy values remain almost unchanged when the conversion is up to some extent. When the conversion degree varies between about 0.3 and 0.9, these carbon materials can be sorted in the order of average activation energy from low to high as WS-char, SD-char, AC, RH-char and BB-char, respectively, 134.3, 143.8, 168.5, 184.8 and 193.0 kJ/mol. It is shown that a complex multistep mechanism occurs in the initial stage of gasification, while a single-step gasification mechanism exists in the rest of the gasification process. The RPM is suitable for describing the gasification of biomass chars and AC except the initial gasification. Additionally, it is found that the kinetic compensation effect (KCE) still exists in the gasification reactions of biochars and AC. However, the AC deviates markedly from the KCE curve. This may be caused by the similarity of carbonaceous structure of biochars and the difference in reactivity between biochars and AC.

Study of Nitrobenzene Kinetic Particularities over Ni-containing Hypercrosslinked Polystyrene

This paper presents a study of the kinetics of catalytic hydrogenation of nitrobenzene to aniline in the presence of Ni-containing catalysts based on super-crosslinked polystyrene. Aniline hydrogenation is a complex multi-stage process accompanied by the formation of a large number of both intermediate and by-products, including azobenzene, azoxybenzene, nitrosobenzene, phenylhydroxylamine and other substances. Therefor the study of the process kinetics is an important scientific and technical task necessary to increase the yield of the target product — aniline. The hydrogenation reaction of nitrobenzene was carried out in a six-cell high-pressure reactor Parr instruments, Series 5000. The products were analyzed by chromatography using a gas chromatograph Kristallux-4000M (Russia, Meta–Chrom). The effect of temperature, pressure, and concentration of the catalyst was studied; optimal reaction conditions were selected that ensure the maximum yield of aniline. Investigation of the effect of the nitrobenzene initial concentration on the rate of its transformation shows that increase of catalyst to nitrobenzene ratio from 0.2 to 0.6 kg (Cat)/kg (NB) leads to a linear increase in the rate of transformation of nitrobenzene from 0.0002 kg (NB) / (kg (Cat)*s ) to 0.0028 kg(NB)/(kg(Cat)*s), a further increase in the ratio of catalyst concentration to nitrobenzene concentration to 1.2 kg (Cat)/kg(NB) leads to stabilization of the nitrobenzene transformation rate at the level of 0.003 kg(NB)/(kg(Cat)*s). An increase in the temperature of the reaction from 90 to 160 °C contributes to a significant increase in the nitrobenzene transformation rate. The constructed dependences made it possible to calculate the apparent activation energy of the process, which amounted to be 50.4 kJ/mol and the preexponential factor, which amounted to be 15821.1 1/s. The applicability of the Langmuir–Henschelwood model to describe the basic kinetic laws of the reaction of catalytic nitrobenzene hydrogenation with the formation of aniline is studied. Numerical methods in the Matlab software allows to determine the values of preexponential factors and activation energies of the nitrobenzene hydrogenation processes, adsorption of nitrobenzene and adsorption of hydrogen, which made it possible to establish the optimal area of nitrobenzene hydrogenation process of hydrogenation of Pн2 = 15–18 atm, C(NB) = 1.2 kg(NB)/kg(Cat), t =115–120 °C providing maximum speed.

Calculation of Kinetic Parameters of Thermal Decomposition of Forest Waste using the Monte Carlo Technique

This paper deals with the pyrolysis of forest waste in the presence of an inert atmosphere. Experiments are carried out at different heating rates (5 °C, 10 °C and 15 °C) to determine derivative thermogravimetric behaviour of the material. Unlike the conventional scheme, the Monte Carlo technique is implemented to solve the distributed activation energy model (DAEM). DAEM is transformed into the inverse pyrolysis problem to determine the kinetic parameters of thermal degradation of forest waste. Activation energy, the preexponential factor and the distribution parameters are estimated by introducing the Monte Carlo Technique in the thermal conversion process.