Druck- und Termperaturabhängigkeit der Rekombinationreaktionen von Benzylartigen Radikale

In der vorliegenden Arbeit wurden Kombinationsreaktionen p-F-C6H4CH2 + p-F-C6H4CH2 (+M) → C14H12F2 (+M), p-CH3-C6H4CH2 + p-CH3-C6H4CH2 (+M) → C16H18 (+M) und C6H5CH2 + C6H5CH2 (+M) → C14H14 (+M) in den Druck- und Temperaturbereichen von 0,2-800 bar und 255-420 K (p-fluorobenzylradikal), 2-200 bar und 300-515K (p-methylbenzylradikal ), sowie 1-70 bar und 250K-400K (benzylradikal) untersucht. Helium, Argon, CO2, SF6, CF3H und CF4 wurden hierbei als Badgase verwendet. Weiterhin wurden transiente UV-Absorptionsspektren der drei Radikale für eine Wellenlänge bei 300K bestimmt. Die Radikale wurden durch Laserphotolyse von Cl2 bei 308 nm und anschliessender Wasserstoffabstraktion der Vorläufermoleküle durch die Chloratome erzeugt. Die zeitabhängigen Absorptionssignale des p- fluorobenzyl- und des p-methylbenzylradikals wurden bei 253 nm gemessen. Im Fall des Benzylradikals wurden 260 nm vewendet.Es wurden experimentelle Anzeichen für eine schwache Druckabhängigkeit der Absorptionskoeffizienten der p-fluorobenzyl-, p-methylbenzyl- und Benzylradikale in CO2 im Druckbereich von 1-45 bar gefunden. Die Geschwindigkeitskoeffizienten der drei untersuchten Reaktionen erreichten den druckunabhängigen Bereich unterhalb von 1 bar, so daß die Geschwindigkeitskoeffizienten der Hochdruckgrenzwerte des Energietransfermechanismuses (ET) direkt aus den experimentellen Ergebnissen ohne Extrapolation des fall-off -Bereiches bestimmt werden konnten. Weiterhin wurde die Temperaturabhängigkeit der Geschwindigkeitskoeffizienten untersucht.Die Temperatur- sowie Dichteabhängigkeit von k1 im Fall der p-fluorobenzyl- und p-methylbenzylradikale waren vergleichbar mit denen des Benzylradikals. Das Ausmaß der Erhöhung der Geschwindigkeitskonstanten nahm in der Reihenfolge He < Ar < CO2 für alle drei Radikale zu. Die Abnahme der Geschwindigkeitskoeffizienten nach dem Überschreiten des Maximums wurden bei allen drei Radikalrekombinationsreaktionen, die in dieser Arbeit untersucht

On-line in-situ characterization of CO2 RESS processes for benzoic acid, cholesterol and aspirin

Rapid expansions of supercritical solutions (RESS) of benzoic acid, cholesterol and aspirin in supercritical CO2 have been used to investigate the influence of a systematic variation of the pre-expansion temperature and pressure, the distance from the RESS nozzle and the amount of added co-solvent on properties like the average particle diameter D-av and the width of the particle size distribution sigma. The properties of the CO2 expansion have been characterized by a 1-dimensional flow-field model using the Span - Wagner equation of state. Particle detection was performed on-line and in-situ using laser-based three wavelength extinction measurements (3-WEM). For benzoic acid we found a decrease in Dav with increasing pre-expansion pressure, and an increase in Dav with increasing pre-expansion temperature. This is probably due to a lower mass flow rate, which is associated with a lower pre-expansion pressure or higher pre-expansion temperature. This in turn results in a longer residence time in the expansion region and thus a longer particle growth time. Furthermore, a decrease in pre-expansion pressure or an increase in pre-expansion temperature is associated with a decrease in saturation, corresponding to an increase in the critical particle radius and a decrease in the nucleation rate. The size of the benzoic acid particles ranged from about 100 to 500 nm. In addition, we found no obvious correlation between Dav and the distance from the RESS nozzle for benzoic acid and aspirin particles. The particle size was roughly 350 nm and 160 nm for these two solutes, respectively. Obviously, the particle growth processes have already ceased not too far away from the Mach disc. In addition, for cholesterol expansions in CO2 there was no correlation between the amount and type of co-solvent added. Particle sizes of similar to 100 nm were obtained for methanol, ethanol and isopropanol co-solvents. This is most likely due the low solubility of cholesterol in supercritical CO2, compared with molecules such as benzoic acid, which results in a change of D-av which is too small to be detected using 3-WEM

Heterogeneous photocatalytic reduction of ferrate(VI) in UV-irradiated titania suspensions: Role in enhancing destruction of nitrogen-containing pollutants

The results of the heterogeneous photocatalytic reduction of Fe(VI) in UV-irradiated TiO2 suspensions are presented and suggest indirect observation of the formation of Fe(V) by the photoreduction of Fe(VI) with ecb− at TiO2 surfaces. Because Fe(V) selectively and rapidly oxidizes low reactivity pollutants with the production of the non-toxic by-product, Fe(III), the photocatalytic reduction of Fe(VI) has a role in pollution remediation processes. The experiments were conducted as a function of TiO2 suspension concentrations, Fe(VI) concentrations, and pH in basic media. The initial rate of Fe(VI) reduction gave a fractional order with respect to initial Fe(VI) concentrations and adheres to simple Langmuir-Hinshelwood kinetics. Results suggest that the surface reaction (Fe(VI)+ecb−→Fe(V)) is the rate-controlling step. The photocatalytic reduction of Fe(VI) in the presence of less reactive nitrogen-containing species (ammonia, cyanate, and fulvic acid) were also investigated. Enhancement in the rate of Fe(VI) reduction was observed. A reaction scheme involving Fe(V) as an intermediate is presented which explains the faster photocatalytic oxidation of pollutants in the presence of Fe(VI)

Ignition studies of n-heptane/iso-octane/toluene blends

Journal articleIgnition delay times of four ternary blends of n-heptane/iso-octane/toluene, referred to as Toluene Primary Reference Fuels (TPRFs), have been measured in a high-pressure shock tube and in a rapid compression machine. The TPRFs were formulated to match the research octane number (RON) and motor octane number (MON) of two high-octane gasolines and two prospective low-octane naphtha fuels. The experiments were carried out over a wide range of temperatures (650-1250 K), at pressures of 10, 20 and 40 bar, and at equivalence ratios of 0.5 and 1.0. It was observed that the ignition delay times of these TPRFs exhibit negligible octane dependence at high temperatures (T > 1000 K), weak octane dependence at low temperatures (TSaudi Aramco (FUELCOM); King Abdullah University of Science and Technology (KAUST)2018-07-0