The 10th International Conference on Water Resource and Environment (WRE 2024)

Abstract: In this study, hexavalent iron oxidant was prepared from iron and manganese-containing sludge from water purification plants and was applied to organic sulfur compound under mixing-assisted oxidation desulfurization (MAOD). Dibenzothiophene (DBT)was used as a model fuel oil under high shear force, phase transfer agent or PTA (tetraoctylammonium bromide or TOAB), and oxidant (Fe(VI)) in a phase-transfer reaction to produce low-sulfur oil products. The effects of various ratios in Fe(VI) preparation, FeO42-/S molar ratio, pH regulation, mixing speed, reaction time, and reaction temperature were examined under their desulfurization efficiency.
In the preparation of Fe(VI) oxidant, nitric acid dissolution tests (1M~7M) were conducted. The results indicated that using 2M HNO3 could obtain 17,700 mg/L and 12,500 mg/L of iron and mangaPnese ions, respectively. NaOCl and NaOH ratios, 100 mL/100 g, 100 mL/200 g, 200 mL/100 g, and 200 mL/200 g, were found to synthesize Fe(VI) with the following respective concentrations: 624.8 mg/L, 1476.1 mg/L, 745.98 mg/L, and 597.93 mg/L. It was found that 200 mL NaOCl with 100 g NaOH is the optimal concentration for Fe(VI) production. Moreover, two KOH concentrations (11M and 23M) were examined and confirmed that the better yield of 658.32 mg/L was obtained using 11M KOH.
In the MAOD process, the effect of pH levels (3~12) on desulfurization efficiency was also examined using acetic acid and the optimal level was found at pH 5. Using 50 mL of 500 mg/L DBT solution under the FeO42-/S molar ratio varied from 2:1 to 12:1, the highest oxidative efficiency was observed using the molar ratio of 9:1. Moreover, the test of mixing speed (3400~6000 rpm) indicated that 3,400 rpm produced the highest sulfur oxidation. For the mixing time (5~60 minutes) and temperature (40℃~70℃), the optimal conditions for high desulfurization efficiency were 30 minutes and 40℃, respectively.　Overall, these optimal conditions were applied to reach the highest DBT oxidation efficiency at 81.8%.
By establishing an economical and safe oil desulfurization technology, this study has addressed the support of a circular economy in waste management and promoted the recycling application of wasted products.