Study of the heterogeneous reaction of O3 with CH3SCH3 using the wetted-wall flowtube techniqueReportar como inadecuado

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1 Fraunhofer-Institut für Toxikologie und Experimentelle Medizin 2 University of Bayreuth

Abstract : This work presents the heterogeneous kinetics of the reaction of CH3SCH3 dimethyl sulphide, DMS with O3 ozone in aqueous solutions of different ionic strengths 0, 0.1 and 1.0M NaCl using the wetted-wall flowtube WWFT technique. Henry-s law coefficients of DMS on pure water and on different concentrations of NaCl 0.1M - 4.0M in the WWFT from UV spectrophotometric measurements of DMS in the gas phase, using a numerical transport model of phase exchange, were determined to be H ±s M atm-1 = 2.16±0.5 at 274.4 K, 1.47±0.3 at 283.4 K, 0.72±0.2 at 291 K, 0.57±0.1 at 303.4 K and 0.33±0.1 at 313.4 K on water, on 1.0M NaCl to be H = 1.57±0.4 at 275.7 K, 0.8±0.2 at 291 K and on 4.0M NaCl to be H = 0.44±0.1 at 275.7 K and 0.16±0.04 at 291 K, showing a significant effect of ionic strength, m, on the solubility of DMS according to the equation ln H-M atm-1 = 4061 T-1 - 0.052 m2 - 50.9 m T-1 - 14.0. At concentrations of DMSliq above 50 mM, UV spectrophotometry of both O3gas and DMSgas enables us to observe simultaneously the reactive uptake of O3 on DMS solution and the gas-liquid equilibration of DMS along the WWFT. The uptake coefficient, g gamma, of O3 on aqueous solutions of DMS, varying between 1 and 15·10-6, showed a square root-dependence on the aqueous DMS concentration as expected for diffusive penetration into the surface film, where the reaction takes place in aqueous solution. The uptake coefficient was smaller on NaCl solution in accord with the lower solubility of O3. The heterogeneous reaction of O3gas with DMSliq was evaluated from the observations of the second order rate constant kII for the homogeneous aqueous reaction O3liq + DMSliq using a numerical model of radial diffusion and reactive penetration, leading to kII ± D kII in units of 108 M-1 s-1 = 4.1±1.2 at 291.0 K, 2.15±0.65 at 283.4 K and 1.8±0.5 at 274.4 K. Aside from the expected influence on solubility and aqueous-phase diffusion coefficient of both gases there was no significant effect of ionic strength on kII, that was determined for 0.1M NaCl, leading to kII ± D kII 108 M-1 s-1 = 3.2±1.0 at 288 K, 1.7±0.5 at 282 K and 1.3±0.4 at 276 K, and for 1.0M NaCl, leading to 3.2±1.0 at 288 K, 1.3±0.4 at 282 K and 1.2±0.4 at 276 K, where the error limits are estimated from the output of the model calculations, taking the variability of individual runs at various DMS levels into account.

Autor: M. Barcellos da Rosa - W. Behnke - C. Zetzsch -



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