Daniela Barba

H2S Removal in Biogas by Direct Catalytic Oxidation to Sulphur on V2O5/CeO2 Catalysts

The direct and selective partial H2S oxidation to elemental sulphur at low temperature may be an interesting alternative to the traditional methods of H2S abatement if an active and selective catalyst is available. In our previous works, a screening of vanadium-based catalysts supported on the metal oxide (V2O5TiO2, V2O5-CeO2, V2O5-CuFe2O4) was performed in the range of temperature 50-250 °C; among all the catalysts investigated, the V2O5/CeO2 catalyst has showed the better catalytic performance in terms of H2S conversion (>95 %) and a low SO2 selectivity (~13 %) at T= 250 °C. Based on these promising results, further investigations on V2O5/CeO2 catalyst were performed to investigate the influence of the inlet concentration of H2S (250-1000 ppm), the gas hourly space velocity (GHSV=15,000-45,000 h -1 ) and the molar feed ratio (O2/H2S=0.4-0.5) in order to minimize the selectivity of the system to SO2. Preliminary results relevant to the effect of the gas hourly space velocity and the inlet concentrations of H2S, showed that they did not contribute to reduce significantly the SO2 selectivity, while interesting result in terms of SO2 selectivity was obtained with a sub-stoichiometric feed ratio (O2/H2S = 0.4), for which it is resulted drastically reduced from 13 % to 4 % without any significant reduction of the H2S and O2 conversions. From these good results, future works will performed to investigate the effect of vanadium load by studying samples in the range 2.55-10 %wt in order to determine the optimal catalyst formulation and operative conditions to obtain a very high H2S conversion and the SO2 selectivity minimization.

Selective Oxidation of H2s to Sulphur from Biogas on V2o5/ceo2 Catalysts

Ceria supported Vanadium-based catalysts were studied for the selective partial oxidation of H2S to sulphur at low temperature. The effect of vanadium content was investigated in the range 2.55 – 20 wt% V2O5 by catalytic activity tests carried out at different temperature. The samples were characterized by XRD and Raman Spectroscopy techniques. The Raman spectroscopy has confirmed highly dispersed vanadium for low V2O5 loading and monovanadate and crystalline forms at V2O5 loads higher > 10 wt%. Results of catalytic activity tests showed that the effect of the vanadium content has affected mainly the selectivity to sulfur, while the catalytic activity is very high for all the tested samples that showed high conversions of H2S (> 90 %) and very close to the thermodynamic values. The most promising catalyst was the sample with the highest Vanadium oxide load (20 wt% V2O5/CeO2) that showed 99 % of sulfur selectivity and equilibrium conversion even at 150 °C.

Honeycomb V2O5-CeO2 Catalysts for H2S Abatement from Biogas by Direct Selective Oxidation to Sulfur at Low Temperature

Honeycomb V2O5/CeO2 structured catalysts were prepared for the H2S abatement from biogas by direct selective catalytic oxidation to sulphur and water at low temperature. Two commercial CeO2-based washcoats (Ecocat, Mel Chemicals) and a CeO2-based washcoat prepared in laboratory, used as a support for the active phase deposition, were deposited on a honeycomb monolith made of cordierite by dip coating procedure; after washcoat deposition and stabilization, the active phase (V2O5) was deposited by wet impregnation. The washcoats were characterized by X-Ray Diffraction, X-Ray Fluorescence (ED-XRF). The adhesion of the different washcoats on cordierite was investigated by ultrasonic vibration, by studying also the effect of the addition of the alumina binder on the catalyst properties. Different washcoats uncatalysed and catalysed with 2 wt% of V2O5 were tested in catalytic activity test at 200°C in order to compare the catalytic performance in terms of H2S abatement efficiency and resistance to the deactivation.

Vanadium-Ceria Structured Catalysts for the Selective Partial Oxidation of H2S from Biogas

The reaction of H2S selective partial oxidation to elemental sulfur in the range of temperature of 150-200 °C was studied on cordierite honeycomb-structured catalysts. The preparation procedure of catalytic cordierite monoliths has been studied, from the washcoating with CeO2 to the deposition of V2O5 by wet impregnation. Two different preparation washcoating procedures deposition were studied: in one case the washcoat had been already added with the salts precursors of the active species (joint impregnation method), in other case the active species were added only after the deposition step of the washcoat on the monolith, by impregnation in a solution of the salt precursor (distinct impregnation method). The catalysts prepared with the two different methods were characterized and the stability was investigated in catalytic activity tests. The catalysts prepared with the “joint impregnation” method have shown a poor catalytic activity and tendency to the deactivation. Very different results were found for the catalysts prepared with the “distinct impregnation” method, for which the effect of the vanadium content (2-19 V2O5 wt %) was also studied at 200 °C. Good catalytic performances were obtained for both samples that have shown a high H2S conversion (~90 %), low SO2 selectivity (2 %) and a high stability.