Wyniki wyszukiwania - Biblioteka Nauki

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Dynamics of Molecular Hydrogen Exchange in Hydrogen-Bonded Systems

100%

Bureiko S. , Denisov G. S.

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tom Vol. 76 / nr 9

1177-1190

EN

The kinetics of hydrogen exchange in molecular systems with H-bonds studied by kinetic IR spectroscopy and low-temperatureNMRspectroscopy methods is critically reviewed. The experimental rate constants and activation energies obtained so far for molecules capable of forming H-bonds as both proton donors and proton acceptors are collected and analyzed from the point of view of the influence of H-bond formation ability of the molecules- partners. The evidence available testifies to a molecular mechanism of the H-exchange reactions in inert solvents and in the gas phase via the formation of cyclic, mostly bimolecular, intermediates. The different mechanisms of the molecular H-exchange process in inert media are discussed and the possible paths of experimental elucidation of reaction mechanism are offered.

2

Rate constants of electron-beam PAHs decomposition

100%

Gerasimov G.

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tom Vol. 52, nr 3

105-108

EN

The generalized kinetic model of the electron-beam induced processes in industrial flue gases elaborated earlier is used for the estimation of rate constants of hydroxyl-radicals interaction with high-ringed aromatic compounds. These data are received by means of the fit of the calculated PAHs concentrations to the measured ones as applied to benzo(a)anthracene, benzo(e)pyrene, benzo(a)pyrene, perylene, and dibenzo(a,h)anthracene. It is shown that the concentrations of PAHs decrease by more than an order of magnitude at the absorbed dose D = 20 kGy for compounds with rate constant of their interaction with OH-radical more than 1013 cm3źmol 1źs 1.

3

Comparative study of the kinetic approach on the alcoholic fermentation procedure conducted in laboratory and scale-up systems by inverse gas chromatography

88%

Lainioti G. C. , Kapolos J. , Koliadima A. , Karaiskakis G.

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tom Vol. 26, no. 2

371--389

EN

The major objective of the present work was to compare the kinetic study of alcoholic fermentations conducted in the presence of wheat supported biocatalysts in laboratory scale and in a scale-up system of 80 L and to compare these results with those reported in literature. The kinetic study of fermentation processes was accomplished with the technique of reversed flow gas chromatography (RFGC), which is a version of inverse gas chromatography. The wine yeast species used was Saccharomyces cerevisiae AXAZ-1, and fermentations were conducted between 20 and 2°C. At low temperatures, maximal ethanol productivity and fermentation rate were reduced. The rate constants, determined through a mathematical model obtained from RFGC, were higher in the laboratory scale comparing to the scale-up system at the temperatures of 20 and 15°C. However, with the reduction of temperature, both systems presented almost similar values proving the great fermentative ability of immobilized cells even at extremely low temperatures. Activation energies of the alcoholic fermentations in the two systems presented their higher values at the second phase (stationary) compared to those observed at the other two phases (growth and decline).

4

Wpływ modelowych czynników fizycznych na dynamikę przemian oksydacyjnych olejów tłoczonych na zimno

63%

Kondratowicz-Pietruszka E. , Ostasz L.

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2017

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nr 7(967)

33-51

PL

Celem badań było określenie wpływu temperatury i naświetlania promieniami UV na dynamikę oksydacji wybranych olejów tłoczonych na zimno. Oznaczono skład kwasów tłuszczowych olejów oraz liczby charakterystyczne. Próbki olejów ogrzewano w temperaturach 80°C, 100°C i 110°C bez naświetlania promieniami UV oraz po naświetlaniu. Do określenia zmian oksydacyjnych oleju wykorzystano pomiar liczby nadtlenkowej w czasie ogrzewania. Wraz ze wzrostem temperatury ogrzewania olejów stwierdzono wzrost wartości tej liczby. Badane procesy zachodziły z różną dynamiką, co potwierdzają wartości stałych szybkości oraz stosunki tych stałych. Obliczono odchylenie wartości doświadczalnych od teoretycznych dla funkcji opisowych, a także okresy stabilności prób olejów ogrzewanych w podanych temperaturach i ogrzewanych po uprzednim naświetleniu promieniami UV. Stwierdzono, że zarówno wzrost temperatury, jak i naświetlenie powoduje znaczne skrócenie okresu stabilności badanych olejów.

EN

The objective of this research project was to determine the effect of high temperatures and UV irradiation on the dynamics of oxidation of selected cold-pressed oils. The composition of fatty acids in the oil samples and their characteristic numbers were determined. The oil samples were heated to temperatures of: 80, 100 and 110ºC without irradiation, and after UV irradiation. Measurements of the peroxide value during heating were used to determine the oxidation changes. It was determined that that value rose along with the temperature. The processes studied were characterised by varying dynamics, a fact confirmed by the values of rate constants and the ratios of these rate constants for comparable processes. Stability periods were calculated for oil samples heated at the three temperatures, and subjected to UV irradiation prior to heating. The tests demonstrated that both an increase in temperature and irradiation result in the oils having a clearly shorter stability period.