The prospects of implementing the mechanochemical activation method of volcanic silicate and aluminosilicate rocks - perlites, tuffs, pumice, etc. are being considered for the production of a wide range of building materials using energy-conserving technologies. The thermodynamic and kinetic parameters of interaction in the systems of aluminosilicate – NaOH have been presented, indicating low-temperature sintering of volcanic rocks with sodium hydroxide. According to the degree of activity, the rocks have the following order: perlites, tuffs, obsidian, microcline. Kinetic parameters are presented: concentration, temperature, conversion degree, reaction rate constant, time of complete reaction and product layer thickness.
In the context of sustainable use of resources, hydrothermal conversion of biomass has received increased consideration. As well, the hydrochar (the solid C-rich phase that occurs after the process) has caused great interest. In this work, spruce bark (Picea abies) wastes were considered as feedstock and the influence of hydrothermal process parameters (temperature, reaction time, and biomass to water ratio) on the conversion degree has been studied. Using the response surface methodology and MiniTab software, the process parameters were set up and showed that temperature was the significant factor influencing the conversion, while residence time and the solid-to-liquid ratio had a low influence. Furthermore, the chemical (proximate and ultimate analysis), structural (Fourier-transform infrared spectroscopy, scanning electron microscopy) and thermal properties (thermogravimetric analysis) of feedstock and hydrochar were analyzed. Hydrochar obtained at 280 °C, 1 h processing time, and 1/5 solid-to-liquid ratio presented a hydrophobic character, numerous functional groups, a lower O and H content, and an improved C matter, as well as a good thermal stability. Alongside the structural features, these characteristics endorsed this waste-based product for applications other than those already known as a heat source.
Microporous chitosan nanofibers functionalized with different amounts of an antimicrobial agent via imine linkage were prepared by a three-step procedure including the electrospinning of a chitosan/PEO blend, PEO removal and acid condensation reaction in a heterogeneous system with 2-formylphenylboronic acid. The fibers’ characterization was undertaken keeping in mind their application to wound healing. Thus, by FTIR and 1H-NMR spectroscopy, it was confirmed the successful imination of the fibers and the conversion degree of the amine groups of chitosan into imine units. The fiber morphology in terms of fiber diameter, crystallinity, inter- and intra-fiber porosity and strength of intermolecular forces was investigated using scanning electron microscopy, polarized light microscopy, water vapor sorption and thermogravimetric analysis. The swelling ability was estimated in water and phosphate buffer by calculating the mass equilibrium swelling. The fiber biodegradation was explored in five media of different pH, corresponding to different stages of wound healing and the antimicrobial activity against the opportunistic pathogens inflicting wound infection was investigated according to standard tests. The biocompatibility and bioadhesivity were studied on normal human dermal fibroblast cells by direct contact procedure. The dynamic character of the imine linkage of the functionalized fibers was monitored by UV-vis spectroscopy. The results showed that the functionalization of the chitosan microporous nanofibers with antimicrobial agents via imine linkage is a great route towards bio-absorbable wound dressings with “on demand” antimicrobial properties and biodegradation rate matching the healing stages.
Oscillations, including chaotic ones, can spontaneously appear in chemical reactors or lean premixed combustors. Such behavior of the system is undesirable and should be identified at the stage of its modeling. This article analyzes the behavior of reverse-flow tubular chemical reactor with longitudinal dispersion in terms of chaotic oscillations. The purpose of using reverse flow is to increase the conversion degree. For the analysis of the reactor, among others, spectral analysis, entropy, and bifurcation analysis were used. The obtained results show the chaotic behavior of the reactor in a wide range of changes in the parameter’s values.
The aim of the study is to assess the influence of the atmosphere during pyrolysis on the course of CO2 gasification of a tire waste char. Two approaches were used: the pyrolysis step was carried out in an inert atmosphere of argon (I) or in an atmosphere of carbon dioxide (II). The examinations were carried out in non-isothermal conditions using a Rubotherm DynTherm thermobalance in the temperature range of 20–1100 °C and three heating rates: 5, 10 and 15 K/min. Based on the results of the gasification examinations, the TG (Thermogravimetry) and DTG (Derivative Thermogravimetry) curves were developed and the kinetic parameters were calculated using the KAS (Kissinger-Akahira-Sunose) and FWO (Flynn-Wall-Ozawa) methods. Additionally, the CO2 gasification of tire chars reaction order (n), was evaluated, and the kinetic parameters were calculated with the use of Coats and Redfern method. Tire waste char obtained in an argon atmosphere was characterized by lower reactivity, which was reflected in shift of conversion and DTG curves to higher temperatures and higher mean values of activation energy. A variability of activation energy values with the progress of the reaction was observed. For char obtained in an argon atmosphere, the activation energy varied in the range of 191.1–277.2 kJ/mol and, for a char obtained in an atmosphere of CO2, in the range of 148.0–284.8 kJ/mol. The highest activation energy values were observed at the beginning of the gasification process and the lowest for the conversion degree 0.5–0.7.
The torrefaction process upgrades biomass characteristics and produces solid biofuels that are coal-like in their properties. Kinetics analysis is important for the determination of the appropriate torrefaction condition to obtain the best utilization possible. In this study, the kinetics (Friedman (FR) and Kissinger–Akahira–Sunose (KAS) isoconversional methods of two final products of lignocellulosic feedstocks, miscanthus (Miscanthus x giganteus) and hops waste (Humulus Lupulus), were studied under different heating rates (10, 15, and 20 °C/min) using thermogravimetry (TGA) under air atmosphere as the main method to investigate. The results of proximate and ultimate analysis showed an increase in HHV values, carbon content, and fixed carbon content, followed by a decrease in the VM and O/C ratios for both torrefied biomasses, respectively. FTIR spectra confirmed the chemical changes during the torrefaction process, and they corresponded to the TGA results. The average Eα for torrefied miscanthus increased with the conversion degree for both models (25–254 kJ/mol for FR and 47–239 kJ/mol for the KAS model). The same trend was noticed for the torrefied hops waste samples; the values were within the range of 14–224 kJ/mol and 60–221 kJ/mol for the FR and KAS models, respectively. Overall, the Ea values for the torrefied biomass were much higher than for raw biomass, which was due to the different compositions of the torrefied material. Therefore, it can be concluded that both torrefied products can be used as a potential biofuel source.
The specific objectives of the presented study were related to the optimization of the production process of N-alkyl-, N,N-dialkyl-, and N-cycloalkyl-O-isobutyl thiocarbamate; trial industrial production of N-ethyl-O-isobutyl thiocarbamate; and the evaluation of flotation efficiency of N-ethyl-O-isobutyl thiocarbamate using a real ore sample. The optimization of thiocarbamate syntheses were performed by varying the molar ratio of isobutyl alcohol, carbon disulfide, potassium hydroxide, reaction time, and reaction temperature. In the first step, one-pot reaction took place to produce alkyl xanthate and was followed with chlorination to give alkyl chloroformate (O-alkyl carbonochloridothioate); finally, thiocarbamates were obtained by the reaction with corresponding amines. N-alkyl-O-ethyl thiocarbamate was synthesized as a comparative flotation agent. The structure of the synthesized compounds was confirmed by IR, 1H and 13C NMR, and MS instrumental methods, and the purity was determined by gas chromatographic method and elemental analysis. The optimized methods gave high-purity products in a significant yield that was also confirmed by semi-industrial production of N-ethyl-O-isobutyl thiocarbamate. The optimized thiocarbamate synthesis, without isolation of intermediates, is of great importance from the aspect of green technologies. Flotation efficiency test results, using real copper and zinc ores, showed the highest activity of N-ethyl-O-isobutyl thiocarbamate. The optimal one-pot thiocarbamate synthesis provides a simple procedure with a high conversion degree, and, thus, offers valuable technology applicable at the industrial scale.
This article is devoted to the analysis of the results of the investigation of the process of forming mixtures of linear polymers formed simultaneously in situ according to different mechanisms. The first mechanism is polyaddition, the second mechanism is radical polymerization. This is one of the possible ways to obtain multicomponent polymer systems. The kinetics of chemical reactions of the formation of components and the phase separation which accompanies these reactions were studied for mixtures of poly(methyl methacrylate) (PMMA) with two polyurethanes (PU) of different chemical nature of both flexible and rigid blocks. PU-1 was synthesized from macrodiisocyanate based on oligo(tetramethylene glycol) with molecular mass 1000 g·mol–1 and hexamethylene diisocyanate taken in the molar ratio 1 : 2 using diethylene glycol as a chain extender. PU-2 was synthesized from macrodiisocyanate based on olygo(propylene glycol) with molecular mass 1000 g·mol–1 and toluylene diisocyanate taken in the molar ratio 1 : 2 using butanediol as a chain extender. The mixture of polystyrene (PS) with PU-2 was studied too. It is established that regardless of the chemical nature of the components, the process of in situ mixture formation is subject to general laws. In particular, the change in the chemical nature of the component formed by the mechanism of polyaddition (mixtures PMMA/PU-1 and PMMA/PU-2) or of the component formed by radical polymerization (mixtures PMMA/PU-2 and PS/PU-2) does not affect the nature of the dependence of the conversion degree of components and the fraction of formed polymers at the beginning of the phase separation on the composition of the initial reaction mixtures. Only the absolute values of these parameters change due to different reactivity and different thermodynamic compatibility of the mixed components.
In this work, molecular dynamics (MD) simulations are conducted to study the thermo-mechanical properties of a family of thermosetting epoxy-amine. The crosslinked epoxy resin EPON862 with a series of cross-linkers are built and simulated under the polymer consistent force-field (PCFF). Three types of curing-agents (rigidity1,3-phenylenediamine (1,3-P), 4,4-diaminodiphenylmethane (DDM), and phenol-formaldehyde-ethylenediamine (PFE)) with different number of active sites are selected in the simulations. We focus on the effects of the cross-linkers on thermo-mechanical properties such as density, glass transition temperature (T
g), elastic constants, and strength. Our simulations show a significant increase in T
g, Young’s modulus and yield stress with the increase of conversion degree. The simulation results revealed that the mechanical properties of thermosetting polymers are strongly dependent on the molecular structures of cross-linker and network topological properties, such as end-to-end distance, crosslinking density and conversion degree.
Pyrolysis, one of the key thermochemical conversion technologies, is very promising to obtain char, oil and combustible gases from solid fuels. Kinetic modeling is a crucial method for the prediction of the solid conversion rate and analysis of the pyrolysis process. We recently developed a new statistical model for the universal description of solid fuel decomposition, which shows great potential in studying solid fuel pyrolysis. This paper demonstrates three essential applications of this new model in the analysis of Artemisia apiacea pyrolysis, i.e., identification of the conversion rate peak position, determination of the reaction mechanism, and evaluation of the kinetics. The results of the first application show a very good agreement with the experimental data. From the second application, the 3D diffusion-Jander reaction model is considered as the most suitable reaction mechanism for the description of Artemisia stem pyrolysis. The third application evaluates the kinetics of Artemisia stem pyrolysis. The evaluated kinetics vary with the conversion degree and heating rates, in which the activation energies and pre-exponential factors (i.e., lnA vs. Ea) show a linear relationship, regardless of the conversion and heating rates. Moreover, the prediction of the conversion rate using the obtained kinetics shows an excellent fit with the experimental data.