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Red mud as an iron-based catalyst for catalytic cracking of naphthalene Madadkhani, Shiva

Abstract

Reducing the tar content in the producer gas of biomass gasification processes remains one of the main challenges in the commercialization of this technology and, hence, the development of clean and economical tar-removing technologies is becoming increasingly important. Catalytic tar removal has the advantage of avoiding expensive gas cleaning systems while maintaining the sensible heat in the producer gas. Commercial catalysts based on noble metals and metal oxides have shown good activity towards tar destruction, but are prone to rapid deactivation. This in addition to the high replacement cost provide the rationale for the development of low-cost alternatives. Red mud, a by-product from bauxite processing, has received considerable attention in this regard due to its high iron content in the form of ferric oxide (Fe₂O₃), high surface area, and its resistance to sintering and poisoning. However, very few studies have been conducted to investigate red mud as a potential catalyst for catalytic tar removal. The aim of this study was to develop a catalyst from red mud for the removal of naphthalene, as a model compound for gasification tar. Red mud catalyst pellets were produced from raw red mud slurry, and their properties were investigated by measuring the chemical composition, surface area, and pore size distribution. Subsequently, the ability for tar decomposition was studied by passing naphthalene-nitrogen and naphthalene-hydrogen mixtures through a bed of the catalyst at five space velocities in the range of 4500-19,000 h-¹, and at reactor temperatures of 500, 600, 700 and 800°C. Catalytic cracking tests confirmed that red mud possesses a very high intrinsic catalytic activity for naphthalene conversion even at temperatures as low as 500°C and space velocities as high as 19,000 h-¹. Kinetic analysis was also performed to determine the apparent reaction order, the kinetic rate constants as well as the activation energy of the reaction. Long term tests of the catalyst showed that the activity of the catalyst diminished over time when no hydrogen was present in the system; however, in the presence of H₂ the activity was found to remain > 90% for 14 h.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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