Degradation of 4-hydroxybenzoic acid by combined ultrasound irradiation and catalytic wet peroxide oxidation.

The aim of this study is to explore the potential benefits from the combined use of ultrasound irradiation and catalytic wet peroxide oxidation for the degradation of 4-hydroxybenzoic acid (4-HBA). The target compound degradation was studied under direct and indirect sonication, while silent conditions were employed as reference. The catalyst, a mixed (Al-Fe) pillared clay named FAZA, was in the form of powder and of extrudates. In the case of extrudates it was observed that ultrasound improves the catalyst performance due to reduction of diffusion resistance, thereby increasing the conversion after 4 h by 12-15 times. Increasing the initial concentration of 4-HBA was found to lead to lower conversion. The combined ultrasonic/catalytic process appears very promising for environmental applications.