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Publications (3)6.88 Total impact

  • T. Berndt, S. Bräsel
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    ABSTRACT: Epoxidation of ethylene, propylene, 2-methylpropene, trans-2-butene, 2-methyl-2-butene, and 2,3-dimethyl-2-butene were carried out in a flow-through reactor in the homogeneous gas phase at pressures of 0.25–1.0 bar in the temperature range of 250–375 °C. Residence times in the reactor varied from 8.3 to 38 ms. The oxidizing agent needed in the feed gas is ozone. The O3 efficiency (reacted olefin/initial O3) was found to be strongly dependent on the reactivity of the olefin used. For C4–C6 olefins, the O3 efficiency was better than 75 % in each case. For 2-methyl-2-butene and 2,3-dimethyl-2-butene, the O3 efficiency exceeded the theoretical value of 100 % considerably. The selectivity to epoxide was about 90 % independent of the olefin used. Under conditions of nearly total olefin conversion, the high selectivity to the epoxide has been retained as unchanged. There were no indications for consecutive reactions of the epoxides.
    Chemical Engineering & Technology 08/2009; 32(8):1189-1194. · 1.37 Impact Factor
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    ABSTRACT: Mechanistic investigations of atmospheric H<sub>2</sub>SO<sub>4</sub> particle formation have been performed in a laboratory study taking either H<sub>2</sub>SO<sub>4</sub> from a liquid reservoir or using the gas-phase reaction of OH radicals with SO<sub>2</sub>. Applying both approaches for H<sub>2</sub>SO<sub>4</sub> generation simultaneously it was found that H<sub>2</sub>SO<sub>4</sub> evaporated from the liquid reservoir acts considerably less effective for the process of particle formation and growth than the products originating from the reaction of OH radicals with SO<sub>2</sub>. Furthermore, for NO<sub>x</sub> concentrations >5×10<sup>11</sup> molecule cm<sup>−3</sup> the formation of new particles from the reaction of OH radicals with SO<sub>2</sub> is inhibited. This suggests that substances other than H<sub>2</sub>SO<sub>4</sub> (potentially products from sulphur-containing peroxy radicals) trigger lower tropospheric new particle formation and growth. The currently accepted mechanism for SO<sub>2</sub> gas-phase oxidation does not consider the formation of such substances. The analysis of new particle formation for different reaction conditions in our experiment suggests that a contribution of impurities to the nucleation process is unlikely.
    Atmospheric Chemistry and Physics. 01/2008;
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    ABSTRACT: Mechanistic investigations of atmospheric H2SO4 particle formation have been performed in a laboratory study taking either H2SO4 from a liquid reservoir or using the gas-phase reaction of OH radicals with SO2. Applying both approaches for H2SO4 generation simultaneously it was found that H2SO4 evaporated from the liquid reservoir acts considerably less effective for the process of particle formation and growth than the products originating from the reaction of OH radicals with SO2. Furthermore, for NOx concentrations >5×1011 molecule cm-3 the formation of new particles from the reaction of OH radicals with SO2 is inhibited. This suggests that substances other than H2SO4 (potentially products from sulphur-containing peroxy radicals) trigger lower tropospheric new particle formation and growth. The currently accepted mechanism for SO2 gas-phase oxidation does not consider the formation of such substances. The analysis of new particle formation for different reaction conditions in our experiment suggests that a contribution of impurities to the nucleation process is unlikely.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2008; 8(3):6365-6374. · 5.51 Impact Factor