Том 43, № 8 (2024)

A thermogravimetric analysis of the thermal decomposition of polymethylmethacrylate (PMMA) in a carbon dioxide flow was carried out. The kinetic constants of the process were determined. The heating rate of the sample varied over a wide range and amounted to 2, 5, 8, 20, 35 and 50 K/min. The values of the kinetic constants of PMMA decomposition were determined using the isoconversional method. For the degree of conversion of the substance from 10 to 90%, the values of activation energy for the thermal decomposition of PMMA vary in the range from 213.5 to 194.3 kJ/mol, and the values of the pre-exponential coefficient change in the range from 1.62 ⋅ 10¹⁶ to 6.85 ⋅ 10¹² 1/s. The average activation energy for the thermal decomposition of PMMA in a carbon dioxide flow was 206 kJ/mol.

Small additions of hydrocarbons, such as propylene, which are widely studied as combustion and explosion inhibitors of hydrogen–air mixtures, are very specific objects. The known mechanism of the inhibitory effect of these additives is associated with the intensification of the termination of branching chains due to the addition of hydrogen atoms; but also such conditions exist in which these compounds, instead of inhibiting, have a neutral and even promoting effect. Such conditions, as well as the reasons leading to the fact that inhibition is practically absent, have not yet been studied. This article shows the results of numerical modeling, which make it possible to more fully outline the range of conditions where the addition of propylene practically does not inhibit hydrogen-air mixtures and outline possible reasons for this effect. Calculations were carried out with the detailed kinetic mechanism of chemical reactions NUIGMech 1.1 (2020). The objects of the study were three air mixtures containing hydrogen in amounts of 15, 29.6 and 50 vol. % (lean, stoichiometric and rich mixture, respectively) without additives and with 1% addition of propylene.

The influence of mechanical activation of the system 100−x(Ti+C)+x(Ti+2B) on the character of combustion of samples with different macrostructure: pressed compacts with relative density of 0.53-0.6 and bulk density granules of 0.6–1.6 mm size has been investigated. It was found that mechanical activation of powders leads to a gradual decrease in the combustion rate of pressed samples with increasing Ti+2B content in the mixtures (a descending dependence), and increasing Ti+2B content in compacts from nonactivated powders leads to an increase in the combustion rate (an ascending dependence). The obtained results contradict the theoretical ideas about the influence of mechanical activation on the combustion process, according to which the combustion rate should increase. One of the important factors influencing the change in the combustion rate is the release of impurity gases. For the first time the influence of mechanical activation on the character of combustion of granular mixtures was experimentally determined. It was found that the combustion rates of granular mixtures are higher than those of powder mixtures for all the compositions studied. It is shown that granulated mixtures from activated powder have a combustion rate on average 3 times higher compared to granules from nonactivated powder, and the dependence of the combustion rate on the mass content of Ti+2B has a local minimum, which is probably related to the peculiarities of the mechanical activation process.

A numerical model for the POX steam-oxygen conversion of methane to synthesis gas in a reversed flow non-premixed filtration combustion reactor with a reversed flow of steam-methane mixture and a continuous supply of oxygen to the reactor center is considered. The calculation was carried out for the oxygen/methane molar ratio 0.47 and steam/methane 0.5, i.e., in the parametric region close to the limit for the feasibility of the scheme. Various modes of initiation and control of flow reverse are considered, and dependences of the combustion temperature and the composition of products on the characteristics of the process are obtained. Comparison of the established cyclic mode of conversion with the predictions of the equilibrium model shows that kinetic constraints lead to a higher combustion temperature and incomplete conversion of methane. At high temperatures, the conversion proceeds via initial soot formation during the pyrolysis of methane and the subsequent reaction of soot with steam.

A new process has been proposed for pyrolysis of ammonia in a filtration combustion moving bed reactor to produce hydrogen. The process can be implemented in reactors with energy recovery with separate supply of reagents (including swiss-roll reactor, etc.). The mass-energy balance of the process was calculated. The analysis of pyrolysis products was carried out under the condition of thermodynamic equilibrium with varying temperature and pressure. The system pressure varied from 1 to 10 bar. The temperature range from 300 to 1100 K was considered. It has been shown that ammonia pyrolysis ends at a temperature of 620 K at atmospheric pressure. An increase in pressure in the system led to a slight increase in the temperature of ammonia pyrolysis. The portion of hydrogen that needs to be burned to cover the energy for heating and pyrolysis of the initial ammonia in the case of an adiabatic reactor was 0.13. From one mole of ammonia it is possible to obtain 1.31 moles of hydrogen.

The ignition of normal layer-by-layer burning and its transition to convective burning regime in mixtures of ammonium nitrate with bulk density aluminum are studied. The experiments in a constant-volume bomb with pressure registration were carried out. The porosity of the samples was 0.55–0.59, the particle size of the ammonium nitrate was varied from 20–40 to 250–630 µm, and the aluminum content varied from 8 to 47 wt %. Aluminum of two grades was used: ASD4 and PAP2. It is shown that mixtures are capable to be ignited at the igniter pressure close to or above the critical (minimum) value. The values of the critical pressure of the igniter, the pressure and time at which burning and convective burning occurs for mixtures with different particle sizes of ammonium nitrate and aluminum and different concentrations are measured. The replacement of aluminum ASD4 with PAP2 leads to a significant (by an order of magnitude or even more) decrease in the values of critical pressure and pressures at which the burning and convective burning begins.

The parameters of the plasma of a low-pressure glow discharge in neon with microparticles are determined numerically, at which regions with equal values of the ion confinement efficiency in the cloud of microparticles are realized. It is noted that such features are characteristic of dissipative synergetic systems controlled by feedback. Simulation of a complex glow discharge plasma in neon with microparticles showed that feedback in the plasma is realized through the source of the main losses of its energy a cloud of microparticles. Controlling the discharge parameters by changing the concentration of microparticles in the cloud makes it possible to control the concentration of ions in the plasma.

Replacing the English version of the title in the metadata on the p. 81:

Instead of “COLLISION EFFICIENCY IN AUTOIGNITION OF HYDROGEN–AIR MIXTURES” should be “THE ROLE OF THIRD-BODY COLLISION EFFICIENCY IN AUTOIGNITION OF HYDROGEN–AIR MIXTURES”.