High-efficiency catalytic wet air oxidation of high salinity phenolic wastewater under atmospheric pressure in molten salt hydrate media

Abstract

An improved catalytic wet air oxidation (CWAO) process for high salinity phenolic wastewater is reported for the first time by using molten salt hydrates (MSHs) as reaction media. One feature of such a process is that it allows the operation to be conducted at atmospheric pressure owing to the temperature-increasing effect of MSHs. Another feature is that the inorganic salts in phenolic wastewater can be separated readily, taking advantage of the common-ion salting-out effect between inorganic salts and MSHs. Continuous catalytic oxidation degradation of the simulated high salinity phenolic wastewater demonstrated that more than 92% of phenol can be removed with chemical oxygen demand (COD) as high as 85% after reacting in CaCl₂·3H₂O medium at 150 °C with air as an oxidant. Meanwhile, the desalination efficiency of NaCl in continuous operation could reach up to 100%. It was found that CeCl₃ was an excellent catalyst for CWAO of phenol. XPS and UV-vis spectral characterization as well as radical scavenger experiments proved that [˙OH/Ce⁴⁺] was responsible for the synergistic catalytic degradation mechanism of phenol. Current work not only paves the way for developing a high-efficiency CWAO technology for concentrated organic wastewaters with high salinity, but also helps to better understand MSHs as reaction media.