| Title | SOME GOOD NEWS: INHIBITION OF THE BOUDOUARD REACTION IN REFRACTORY MATERIALS SUBJECTED TO CO AND H2 REDUCING ATMOSPHERE |
| Thematic area | Basic Science |
| Presenter | Prof. Jacques POIRIER |
| Authors | Prof. Jacques POIRIER, CNRS CEMHTI, University of Orleans, ORLEANS - France Dr. Nicolas BOST, CNRS CEMHTI, University of Orleans, ORLEANS - France Dr. Antoine COULON, CNRS CEMHTI, University of Orleans, ORLEANS - France Mrs. Severine BRASSAMIN, CNRS CEMHTI, University of Orleans, ORLEANS - France Dr. Aurélien CANIZARES, CNRS CEMHTI, University of Orleans, ORLEANS - France Dr. Mohamed AMMAR, CNRS CEMHTI, University of Orleans, ORLEANS - France |
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Abstract
The mechanism of carbon monoxide decomposition, called the Boudouard reaction, which results in the deposition of solid carbon (2CO ⟺ CO2 + C(solid)) causes premature degradation of refractory linings. This reaction occurs at temperature ranging between 400 to 900°C with a maximum intensity around 600 °C, and is highly favoured by the presence of catalytic particles such as iron and iron oxides. FexOy particles are present in the refractories as impurities in raw materials and by attrition of the mixing devices while blending the refractory formulation. The CO resistance is usually improved by the selection of raw materials with a low content of iron particles and by raising the refractory sintering temperature. Unfortunately, these solutions are not always very effective for new industrial applications where refractories are subjected to CO and H2 reducing atmospheres (biomass and coal gasification, new generation of blast furnaces with low CO2 emission….). The aim of this study is to understand the mechanisms of carbon formation at a micro- and macro-scale and to find an efficient refractory solution to inhibit the Boudouard reaction. In these extreme conditions, the effect of the iron oxide valence (i.e., oxidation degree: Fe, FeO, Fe3O4 and Fe2O3) and grain size (nanometre to millimetre size) on the carbon deposition amount in different CO + H2 gas mixtures was investigated, using thermogravimetric measurements and in situ Raman spectroscopy. After cooling, the samples were characterised using various methods: X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Transmission Electron Microscopy (TEM). Two different carbons are formed. In pure CO gas, the carbon has a high quality with significantly coherent domains. The addition of H2 (CO + H2 mixture) favored a more disordered sp² carbon and the production of carbon nanofibers. An inhibition mechanism in a CO + H2 gas mixture is proposed and validated. Sulfur inhibits the carbon monoxide dissociation on contact with iron and iron oxides. At 600°C and under CO+ H2 atmosphere, the behavior of iron sulfides was investigated and the inhibiting effect of the sulfur in contact with iron oxides was demonstrated. The conclusions of this study were applied to develop new CO/H2 resistant industrial refractories. The practical solution consists in introducing a very small amount of sulfur compounds (pure S, BaSO4, ...) into refractories.
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