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Isothermal kinetics of the exchange of absorbed water in a silica hydrogel (SH) with ethanol was examined. The isothermal kinetic curves of absorbed water exchange with ethanol were measured at the temperatures: T = = 297, 306 and 316 K. The rate of the exchange was analysed as a function of time. The possibility of mathematical description of the kinetics of exchange by the Brouers and Sotolongo-Costa’s (BS) fractal’s kinetics model was examined. Parameter values (n, τ, β) of the model and their changes with temperature were calculated. By applying the method of Ozao, it was determined that the rate limiting step of the process of exchange was the rate of exchange of the absorbed water with ethanol. Values of the fractal dimension of the SH-ethanol interphase were calculated. The dependences of the effective time-dependent rate coefficient, activation energy and pre-exponential factor on time and degree of exchange were calculated and discussed. The proposed model of the mechanism of the exchange of absorbed water with ethanol was discussed.

Fluorapatite nanopowders with different amounts of fluoride ions were prepared using the surfactant-assisted microwave method under isothermal conditions. Microwave irradiation was applied for the rapid formation of crystals. A micellar solution of polyoxyethylene (23) lauryl ether was used as a regulator of nucleation and crystal growth. Characterization studies from X-ray diffraction, field-emission scaning electron microscopy and Fourier-transform infrared spectra showed that crystals have an apatite structure and particles of all samples are nano size, with an average length of 50 nm and about 15-25 nm in diameter. Antimicrobial studies have demonstrated that synthesized fluorapatite nanopowders exhibit activity against tested pathogens: Escherichia coli, Staphylococcus aureus and Candida albicans. Activity increased with the amount of fluoride ions. The synthesized fluorapatite nanomaterials are promising as materials in environmental protection and medicine for orthopedics and dental restorations. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. III 43009]

The isothermal kinetics of the exchange of absorbed water in calcium alginate hydrogels with ethanol was investigated. The isothermal kinetic curves were measured within the temperature range from 297 to 316 K. By the application of differential isoconversional methods, it was found that the process of exchange of water absorbed in calcium alginate hydrogel with ethanol has a unique rate determining step (a single step process). Using the model fitting method, it was determined that the kinetics of the exchange can be mathematically described with the kinetic model of the first-order chemical reaction. The values of the kinetic parameters of water exchange: the rate constants (km), energy of activation (Ea = 18.0 kJ∙mol–1), and the pre-exponential factor (ln[A/min–1] = 4.0) were calculated. By using Eyring's equation, the values of thermodynamics parameters: standard enthalpy of activation (ΔH*), standard entropy of activation (ΔS*), and Gibbs energy of activation (ΔG*) were calculated. It was found that the rate of rearrangements of the bound water around hydrophilic groups of a polymeric network has a dominant effect on the kinetics of the exchange of the absorbed water with ethanol. The mechanism of the exchange of adsorbed water with ethanol was suggested. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 172015]

The effect of operating parameters such as reaction mixture inlet pressure p1 (101.3–1013.2 kPa), methanol to oil molar ratio M1 (3–12), the concentration of catalyst Cc (0.0–1.0 wt%), temperature T (25–50 °C) and the number of passes of the reaction mixture through the venturi type hydrodynamic cavitation reactor n (1–12) on alkali-catalyzed transesterification of sunflower oil with methanol assisted by hydrodynamic cavitation (ACTC) on the value of the degree of triglyceride conversion (DTC) was investigated. ACTC was performed by the venturi-type hydrodynamic cavitation reactor (VCR) of our construction. It was found that the values of DTC increase with the increase in p1, M1, Cc, and n, and decrease with the increase in T. Cavitation yield (CY) values were calculated. The ACTC was proved to be the simplest, fastest, and most highly energy-efficient current technology for the production of biodiesel. [ABSTRACT FROM AUTHOR]

The kinetics of the desorption of ethanol previously absorbed onto carbon molecular sieves (CMS-3A) was studied using the non-isothermal thermogravimetric technique. The dependence of activation energy (Ea,α) for a particular degree of desorption (α) was established. It was confirmed that the non-isothermal desorption of ethanol was a kinetically complex process. A novel mathematical model for the kinetics of non-isothermal desorption for the absorbed ethanol is established. This model is based on the proposed dependence of the specific desorption rate on time/temperature. The correlation dependences of the model parameters β and η on heating rates were established. A general kinetic equation for the non-isothermal desorption of ethanol was developed. It was found that the specific desorption rate at every single heating rate increases, whereas Ea, decreases during the desorption process. [ABSTRACT FROM AUTHOR]

The isothermal kinetics of the titanium-oxo-alkoxy cluster(TOAC)growth obtained in the controlled hydrolysis–condensation reactionof Ti(OPri)4with H2O in n-propanol solution was investigated. Kineticcurves of the TOAC growth were measured at five different temperatures:298, 303, 308, 313, and 318 K. It was established that the kineticcurves of the TOAC growth could be mathematically modeled by the cumulativetwo-parameter Weibull probability distribution function of the growthtime (t) in a wide range of the degree of growth(0.05 ≤ DG ≤ 0.95). It was found that the dependenciesof the shape parameter (β) and scale parameter (η) ontemperature (T) can be described by polynomial functions.The activation energy of TOAC growth (Ea,DG), as well as the pre-exponential factor (ln ADG) for different degrees of growth, were calculated usingFriedman’s isoconversional method. On the basis of knowing Ea,DG(DG) dependence, the procedure for calculatingisothermal dependence of Eavs growthtime was described. The isothermal probability distribution densityfunctions of Eafor the TOAC growth processwere calculated. It was established that the conversion kinetic curvesof the TOAC growth process could be fully described by a model ofthe infinite number of parallel first-order growth reactions withtime-varying value of the pre-exponential factor and activation energieswhich are distributed in accordance with a specific function of Ea. [ABSTRACT FROM AUTHOR]