Vol 60, No 1 (2019)

The effects of different n-butanol blending ratios (R_b) on the formation of propargyl radical (C₃H₃), an important benzene precursor, during the combustion of n-butanol/n-butane blends are studied. A detailed kinetic combustion model of n-butanol/n-butane is developed and the premixed n-butanol/n-butane flames are calculated at an equivalence ratio of 1.5, an initial pressure of 1.0 atm, and a temperature range from 800 to 2000 K in a perfectly stirred reactor (PSR), with R_b varying from 0 to 1.0. The results show that under the investigated conditions, the peak value of the mole fraction of C₃H₃ decreases non-linearly with the increase of R_b. Due to the interaction between combustion products of n-butane and n-butanol during the combustion process, the actual peak mole fraction of C₃H₃ is higher than the theoretical value. A rate of production (ROP) analysis reveals that the number of β-carbon atoms in the molecule of n-butane and n-butanol affects the efficiency of H-abstraction reactions in generating 2-butyl (sC₄H₉) and C₄H₈OH-3 (CH₃–*CH–CH₂–CH₂–OH), which are the two major original sources of C₃H₃. For both n-butane and n-butanol, the main pathway of forming C₃H₃ from propene (C₃H₆) is basically the same, which is C₃H₆ → C₃H₅-a (symmetric allyl radical) → C₃H₄-a (allene) → C₃H₄-p (propyne) → C₃H₃. When R_b ranges from 0.4 to 0.6, the deviation degrees of the peak mole fraction of the involved C₃ species reach a maximum, indicating that the interaction between the two fuels is the most significant. The non-linear decrease in the mole fraction of C₃H₃ can attribute to three reasons: (a) the increase of R_b promotes the increase of the conversion ratios of n-butane to sC₄H₉ and n-butanol to C₄H₈OH-3; (b) the contribution ratios of the reactions involved in the C₃H₅-a → C₃H₄-a → C₃H₄-p → C₃H₃ pathway decrease with increasing R_b; (c) C₃H₅-t (tertiary allyl radical) → C₃H₄-p → C₃H₃ is the secondary pathway for the formation of C₃H₃. With the increase of R_b, the dependence of C₃H₄-p on C₃H₅-t increases and the conversion ratio of C₃H₅-t to C₃H₄-p increases. This study investigates the non-linear decrease of the mole fraction of C₃H₃ by revealing the interactions between n-butanol and n-butane during the combustion, which can help better understand the effect of n-butanol on the formation of benzene.

Fourier-transform IR and NMR spectroscopy are used to show that, in the reaction with 2,2'‑diphenyl-1-picrylhydrazyl radical, the secondary products of natural phenol conversion are dimeric compounds formed by recombination of phenoxyl radicals. According to thermodynamic parameters of the reaction calculated by the DFT method the most stable structures in the studied system are CC dimers. The resulting dimeric phenols show a lowered antiradical activity compared to the original phenol, which ensures a prolonged effect of the original antioxidant and enhances its overall antioxidant activity in radical oxidation reactions.

Solvent effects in epoxidation of fatty acid methyl esters (FAMEs) by hydrogen peroxide on a TS-1 heterogeneous catalyst is studied for the first time. It is found that the catalytic activity of TS-1 (titanium silicalite) is significantly affected by the polarity of the solvent and its proton-donor–acceptor properties. The highest activity and selectivity is ensured by the use of solvents that are not donors of hydrogen bonds. The best results were achieved when acetonitrile was used as a solvent: the conversion of FAMEs after 6 h was 77%, and the selectivity to epoxide was 61%.

The effects of temperature (540–640°C), weight hour space velocity (1.0–7.0 h^–1), and steam : raw material ratios (0–2.5) on the yield of C₂–C₄ olefins, conversion, and octane characteristics in the cracking of a mixture of model hydrocarbons (cyclohexane and 1-hexene) were studied. The influence of the structure of zeolites in mono-, bi-, and tri-zeolite catalysts on the distribution of cracking products was examined. It was found that the combination of catalyst components in bi- and tri-zeolite systems makes it possible to increase the efficiency of the consecutive cracking of hydrocarbons (C₆–C₁₂ → C₄–C₈ → C₃–C₆ → C₂–C₄) according to the following reaction scheme: matrix → ZSM-5 → FER. The maximum total yield of C₂–C₄ olefins (50.2 wt % at a conversion of 75.5%) was achieved with the use of a bi-zeolite catalyst of ZSM-5 + FER.

The influence of modifying additives and synthesis conditions on the genesis of the phase composition of alumina–chromium catalysts was studied by differential dissolution (DD) and X-ray diffraction (XRD) analysis. The salts of potassium (KNO₃) and lithium (LiCl) were added as additives. It was found that the individual nature of the additives affected the formation of phases. Although potassium and lithium cations occur in the same group of the periodic system, they differently react with a phase of γ-Al₂O₃ in the support: lithium forms a Li_xAl₁ solid solution with the crystallized finely dispersed γ-Al₂O₃ species, whereas potassium mainly remains on the surface of the finely dispersed Al₂O₃ species and partially forms potassium aluminate. The interaction of lithium cations with the active component Cr(VI) of the catalyst leads to the formation of lithium chromate analogously to the reaction of the potassium cation with \({\text{CrO}}_{4}^{{2 - }}.\) However, a portion of lithium cations is introduced into the structure of the substitution solid solution of Cr(III) in γ‑Al₂O₃ to form addition solid solutions (Al₁Cr_{x1– x2}Li_{y1 –y2}).