Catalytic wet air oxidation of bisphenol A model solution in a trickle-bed reactor over titanate nanotube-based catalysts

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Titanate nanotube-based catalysts were prepared via alkaline hydrothermal synthesis route followed by heat-treatment at different temperatures, ranging from 300 to 700°C. The resulting metal-free solids were then applied as a catalyst in a three-phase trickle-bed reactor, where catalytic wet air oxidation (CWAO) reactions of model aqueous bisphenol A (BPA) solution were performed. Mainly, the CWAO experiments were conducted at 200°C with oxygen partial pressure of 10bar over 300mg of a catalyst. It was observed in the given range of operating conditions that BPA undergoes both non-catalytic as well as catalytic oxidation routes, while the latter is far more pronounced. At 210°C and in the presence of 0.5g of titanate nanotube-based catalyst, which was annealed at 600°C, complete BPA removal was obtained. From TOC point of view, approximately 70% conversion was achieved indicating the persistence of refractory intermediates of lower carboxylic acids. The cross-section of results derived from various analytical techniques, which were used to identify surface, textural and morphological properties, revealed that balanced physicochemical properties are required to achieve meaningful extent of BPA removal. During 2–4 day time on stream, no catalyst deactivation occurred that could be attributed to the dissolution of active powders, or to the carbonaceous deposits accumulated on the catalyst surface. Therefore, these nanotubular materials can be regarded as innocuous and efficient long-term catalysts for oxidation of hazardous organic compounds (such as BPA) in the CWAO process.