Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

PP-II-16In this work, we have increased the concentration of the key reactants in the thiosulfateoxidation reaction by chlorite to achieve the limit of large η. This allowed us, for the firsttime, to achieve experimentally zero value of non-oscillating reaction front propagationvelocity in a wide rage of adverse flow velocities. This corresponds to the observation ofstationary fronts for a range of adverse flow velocities, similar to the observations made forthe BZ reaction in a bed of glass beads. This can be rationalized as follows. The transportmechanism which governs reaction front propagation is diffusion. When flow is turned on,the diffusion in axial direction is essentially quenched, since diffusion along bead wallsimplies a dramatically increased tortuosity factor and possibly a significantly reducedconnectivity for the diffusion path. This quenching of implies that in the adverse flow reactionfront propagates with the velocity V – f ≈ 0, as confirmed by the calculations.We also demonstrate that it is not appropriate to substitute the dispersion coefficient fordiffusivity in the reaction-diffusion-advection equation when describing of the concentrationfronts in autocatalytic reactions in a wide range of flow velocities, in particular if bothsupportive and adverse flows are to be explained. Such substitution completely fails toaccount for the behavior of the reaction front in the case of the adverse flow, at least in thelimiting case described above. Therefore it can be concluded that, an adequate description of areaction front behavior in the presence of advection therefore requires that the flow velocityfield is taken into account explicitly.Conclusions: In this work we studied mechanisms of the formation of stationary reactionfronts in continuous flow packed-bed reactors. It has been demonstrated that stationary frontsin not the exclusive feature of Belousov-Zhabotinsky reaction, but also can be observed innon-oscillating reactions. Corresponding numerical calculations and experimental evidencesshow that such uncommon dynamic behavior of reaction fronts can be explained in term ofspecific influence of the advective flow in a packed-bed.Acknowledgements: Authors are grateful for a support of the presrnt work by the grantsfrom RFBR (05-03-32472 and 07-03-12147), SB RAS (integration grant # 11) and RAS(5.1.1 and 5.2.3).References:1. M. Kaern, M. Menzinger, Propagation of excitation pulses and autocatalytic fronts in packed-bed reactors,J. Phys. Chem. B, 2002, 106, 3751-3758.2. I.V. Koptyug, V.V. Zhivonitko, R.Z. Sagdeev, Advection of chemical reaction fronts in a porous medium,J. Phys. Chem. A, 2008, 112, 1170-1176.301