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Keywords: kinetics

Thermal decomposition of low-density polyethylene: kinetic study using TGA and DTG data

https://doi.org/10.58224/2619-0575-2025-8-1-1
Abstract
Pyrolysis of low-density polyethylene (LDPE) waste is considered as a highly efficient and promising recycling method. The aim of this work is to investigate the pyrolysis kinetics using three model-free methods (Friedman, Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS)) and two model-fitting methods (Arrhenius and Coates-Redfern). Thermogravimetric (TGA) and differential thermogravimetric (DTG) thermograms at 5, 10, 20 and 40 K min−1 showed a linear curve, which implies the first-order reactions. The kinetic parameter values (E_A and A) of LDPE were calculated at different conversions by three model-free methods, and the average values of activation energies obtained were in good agreement and ranged from 190.23 to 191.89 kJ/mol. These kinetic parameters were additionally calculated at different heating rates using the Arrhenius and Coates-Redfern methods.
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Kinetics of Cu(II) removal from aqueous solution with the use of Fe3O4/C nanocomposite

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 5-12 p.
Abstract
this work studied the sorption kinetics of the Fe3O4/C nanocomposite obtained by heating polyacrylonitrile (PAN) and FeCl2∙4H2O in air, the preparation procedure of which was described in the previous works [9, 10]. The main task was to calculate the sorption characteristics and check the practical application of this nanocomposite, that is the possibility of purification from heavy metals from water sources, verified on the example of modeling the sorption of copper ions from an aqueous solution of copper(II) acetate hexahydrate, hence the equations of diffusion (Morris-Weber model) and chemical kinetics (Lagergren's pseudo-first order, Ho and McKay's pseudo-second order), as well as the Elovich chemosorption model were applied. Analysis of the data illustrated that the diffusion of copper ions inside the pores of the nanocomposite and chemical interactions between copper ions and functional groups of the sorbent surface, such as hydroxyl, carboxyl, carbonyl, etc., which are typical of carbon sorbents, contribute to the total sorption rate. Experimentally, the capacity of this nanocomposite for copper sorption was 208.4 mg/g, however, modeling showed that this value could theoretically be higher by 37%.
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STUDY OF THE EFFECT OF ANIONS ON THE DISSOLUTION RATE OF CO2O3 AND CR(OH)3

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 95-100 p.
Abstract
Сhromium compounds are widely used in industry, therefore, studies related to the study of the process of dissolution of oxides in various environments, including aggressive ones, are relevant. Currently, a huge amount of experimental material has been accumulated on the dissolution of metal oxides and hydroxides. Despite this, the effect of anions on the dissolution rate of these compounds has not yet been sufficiently studied, models have not been developed and generalized dissolution mechanisms have not been found. This article presents experimental studies on the effect of nitrate and sulfate ions on the dissolution rate of chromium (III) oxide and hydroxide. It was found that chromium (III) oxide and hydroxide dissolve better in sulfuric acid in the presence of nitrate ions than sulfate ions. Moreover, chromium (III) hydroxide dissolves better in acids with the addition of anions than chromium (III) oxide. Based on the data obtained, using the equation of the chain mechanism (the Barton-Stransky model), we found the functional dependence of the specific rate of dissolution on the concentration of anions in an acidic medium. With the help of the mathematical computer program MathCad, models of the dissolution of chromium oxide phases were selected. A scheme of the mechanism of the heterogeneous process of dissolution of chromium oxide and hydroxide in acidic media was proposed.
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SULFURIC ACID MODIFIED SAWDUST OF ACACIA AURICULARIS (ACACIA AURICULIFORMIS) FOR THE PURIFICATION OF WASTEWATER FROM COPPER IONS (II)

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 12-23 p.
Abstract
Modified sorption materials based on acacia sawdust (Acacia Auriculiformis) were obtained by treating their surface with low-concentration sulfuric acid solutions with concentrations of 1%, 2% and 3%. According to IR spectra, diffractograms, micrographs and histograms of the distribution of surface roughness of native and sulfuric acid-modified acacia sawdust, it was found that surface treatment of the sawdust with acid solutions leads to a change in the structure of the sorption material, namely, leaching of low molecular weight components from the composition of acacia wood. The regularities of the processes of adsorption of Cu2+ ions by native and sulfuric acid modified acacia filings under static conditions were studied. Using the obtained values of the initial and equi-librium concentrations of copper (II) ions in solutions, the sorption capacities of the materials were calculated and the adsorption isotherms of Cu2+ ions were constructed using native and modified acacia filings. Processing acacia sawdust with sulfuric acid solutions leads to an increase in the sorption capacity for copper ions, while the greatest sorption capacity is observed in the case of acacia sawdust treated with a 3% sulfuric acid solution. By processing the obtained sorption isotherms in the framework of the monomolecular models of Langmuir, Freindlich, Dubinin-Radushkevich, Temkin, the regression equations and approximation coefficients are determined. It was revealed that the processes of adsorption of Cu2+ ions by native and modified acacia sawdust with a 3% sulfuric acid solu-tion are best described by the Langmuir model, and the processes of copper ion adsorption by acacia sawdust mod-ified by 1% and 2% sulfuric acid solutions are described by the Freindlich model. The thermodynamic constants of the adsorption processes are calculated, from the values of which it is determined that all the studied processes belong to the processes of physical adsorption. By processing the kinetic dependences of the processes within the framework of the diffusion adsorption model, we calculated the Bio coefficients for the sorption processes of Cu2+ ions by native and modified acacia filings, the values of which determined the limiting stages of the processes (mixed diffusion).
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