Catalytic oxidation of organic pollutants

The paper presents the results of the measurements of the catalytic activity of V₂O₅/TiO₂ and MoO₃/TiO₂ catalysts (8,10,12 and 15 wt % of V₂O₅ or MoO₃ on TiO₂ - anatase, respectively), prepared in our laboratory, in the complete oxidation (combustion) process of chosen volatile organic pollutants of the air such as methanol and n-butyl acetate. The activity of these catalysts was compared with the activity of industrial catalysts: supported platinum - Pt-p (0.15 wt % of Pt on γ-Al₂O₃) and MCA (15 wt % of CuO and 6 wt % of ZnO on γ-Al₂O₃). The investigations were carried out in the kinetic region (powder of the catalysts with the diameter in the range of 1.02-1.2·10⁻⁴ m) and for the chosen catalysts also in the diffusion region (the grains of the catalysts having the diameter of 2.5·10⁻³ m). On the basis of the obtained results the analysis of the process was performed.It has been stated that reaction rate is well-described by the first order equation in relation to the methanol or n-butyl acetate concentration. On the basis of the obtained results in the kinetic region for all the applied catalysts the parameters of Arrhenius equation were determinated.The comparison of the results for the kinetic region with the results for the diffusion region for the chosen catalysts allowed the calculation of the effective coefficients of diffusion. The parameters of Arrhenius equations as well as the effective coefficients of diffusion show a good correlation with the values obtained for the catalytic combustion of other organic pollutants of the air.The measurements were carried out using a flow tubular reactor. The flow rate of the reaction mixture was kept constant 20 dm³/h (5.56·10⁻⁶ m³/s) in each test, using the space velocity of 20 s⁻¹. It has been stated that the use of the applied catalysts led to the almost total oxidative destruction of both pollutants. Only H₂O and CO₂ were found as the final products of the reaction. The complete oxidation of the methanol process runs at the lower temperature than that of the complete oxidation process of n-butyl acetate. The most active at the combustion of methanol was the Pt-p catalyst. It demonstrates a comparable activity to molybdenum - titanium catalysts and the slightly lower activity than vanadium - titanium catalysts in the combustion of the n- butyl acetate process. The MCA catalyst was less active than the others in the oxidation of both compounds. The structures of the catalysts were tested using the X -ray analysis (XRD), infrared spectroscopy and scanning microscopy (SEM).The results of the investigations show that V₂O₅/TiO₂ and MoO₃/TiO₂ catalysts, especially the most active of them the 8% V₂O₅/TiO₂ catalyst can be used in industrial systems for the purification of the air and industrial waste gases with VOCs, replacing the more expensive noble metals supported catalysts.