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

Abstract

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 Fe2O3 catalyst coupled with Pt-based catalyst. The effects of high-temperature hydrothermal on two catalysts were evaluated. The catalytic stability was studied in continuous catalytic combustion. Detailed characterization of the two catalysts were 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 in 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 Pt/Al2O3@cordierite catalyst was almost 100% at the reaction temperature of 320 °C, with the activity been basically unchanged after high-temperature hydrothermal treatment, but sulfur poisoning occurred. The Pt/Al2O3@cordierite catalyst coupled with Fe2O3 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 chemical oxygen demand (COD) of 99465 mg/L for 200 h, the COD and sulfur content of treated wastewater was less than 400 mg/L and 1 mg/L, with the COD removal rate and sulfur removal rate exceeded 99.62% and 81.38%. 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.