Catalytic combustion of biodiesel wastewater over the Fe2O3 catalyst coupled with a Pt-based catalyst

In this paper, biodiesel wastewater was treated by catalytic combustion in the case of catalyst coupling. The effects of reaction temperature, residence time and air flow on the treatment of biodiesel wastewater were investigated using the Fe₂O₃ catalyst, the Pt/Al₂O₃@cordierite catalyst and the Fe₂O₃ catalyst coupled with the Pt-based catalyst. The effects of high-temperature hydrothermal treatment on the two catalysts were evaluated. The catalytic stability was studied in continuous catalytic combustion. Detailed characterization of the two catalysts was carried out. The X-ray fluorescence (XRF), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) characterization demonstrated that the Fe₂O₃ catalyst contained a significant amount of surface active oxygen and Fe₂O₃ existed in an amorphous form within the catalyst. The Fe₂O₃ catalyst could remove 90.6% of sulfur from wastewater, showing excellent desulfurization performance, but it was not resistant to high temperature. After 500 °C hydrothermal treatment, the chemical oxygen demand (COD) removal rate decreased significantly from 97.98% to 69.04% at the reaction temperature of 280 °C. The COD removal rate of the Pt/Al₂O₃@cordierite catalyst was almost 100% at the reaction temperature of 320 °C, with the activity being basically unchanged after high-temperature hydrothermal treatment, but sulfur poisoning occurred. The Fe₂O₃ catalyst coupled with the Pt/Al₂O₃@cordierite catalyst showed excellent catalytic activity and stability, and the optimal reaction temperature and residence time were 320 °C and 0.3 s, respectively. In the continuous treatment of biodiesel wastewater with the COD of 99 465 mg L⁻¹ for 200 h, the COD and sulfur content of the treated wastewater were less than 400 mg L⁻¹ and 1 mg L⁻¹, with the COD removal rate and sulfur removal rate exceeding 99.62% and 81.38%, respectively. In addition, no organic gas or SO₂ was detected in the exhaust gas generated during the reaction, and the removed organic matter was converted into CO₂ and H₂O.