Effective removal of naproxen from aqueous solutions by CWAO process using noble metals supported on carbon nanospheres catalysts

Abstract

In this research the technical feasibility of catalytic wet air oxidation reactions (CWAO) with a novel ruthenium supported onto carbon nanospheres (CNS-Ru) catalyst for the degradation of a non-steroidal anti-inflammatory drug (NSAID), naproxen (NPR), has been tested. The operating conditions of the reaction, the different loads of ruthenium in the catalyst, the reuse of the material, the reaction kinetics and the degradation mechanism of the pollutant were studied. The complete degradation of the compound was reached in one cycle at the following conditions: 130 °C, 20 bar, [NPR]0 = 20 mg∙L−1, [CNS-Ru] = 0.75 g∙L−1, 2%wt. of ruthenium and an initial pH of 7.0. At these conditions, the efficiency for the pollutant degradation of a platinum-based catalyst (CNS-Pt) as well as its reusability were also tested. In this sense, better results regarding to the NPR degradation were obtained with the CNS-Ru material. Nevertheless, both catalysts could be considered stable after 4 consecutive runs. Furthermore, two potential kinetic models were investigated in order to simulate the degradation of NPR in both WAO and CWAO processes. Thus, the detection of 13 reaction compounds allowed to propose a degradation mechanism for NPR by CWAO. The efficiency of both catalysts was tested in a real hospital wastewater matrix; it was also proved that the NPR degradation decreased in comparison to that one found for the ultrapure water solutions, and that CNS-Ru catalyst achieved a higher pollutant degradation rather than that obtained for CNS-Pt catalyst.