Cavitation intensifying bags improve ultrasonic advanced oxidation with Pd/Al2O3 catalyst

Maria Pappaterra; Pengyu Xu; Walter van der Meer; Jimmy A Faria; David Fernandez Rivas

doi:10.1016/j.ultsonch.2020.105324

Cavitation intensifying bags improve ultrasonic advanced oxidation with Pd/Al₂O₃ catalyst

Ultrason Sonochem. 2021 Jan:70:105324. doi: 10.1016/j.ultsonch.2020.105324. Epub 2020 Sep 7.

Authors

Maria Pappaterra¹, Pengyu Xu², Walter van der Meer³, Jimmy A Faria⁴, David Fernandez Rivas⁵

Affiliations

¹ Mesoscale Chemical Systems Group, Faculty of Science and Technology, MESA+ Institute for Nanotechnology, and University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands; Delft University of Technology, Delft, The Netherlands.
² Catalytic Processes and Materials Group, Faculty of Science and Technology, MESA+ Institute for Nanotechnology, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands.
³ Oasen Water Company, PO BOX 122, 2800 AC Gouda, The Netherlands; Membranes Science and Technology, Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
⁴ Catalytic Processes and Materials Group, Faculty of Science and Technology, MESA+ Institute for Nanotechnology, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands. Electronic address: j.a.fariaalbanese@utwente.nl.
⁵ Mesoscale Chemical Systems Group, Faculty of Science and Technology, MESA+ Institute for Nanotechnology, and University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands. Electronic address: d.fernandezrivas@utwente.nl.

Abstract

Advanced oxidation processes can potentially eliminate organic contaminants from industrial waste streams as well as persistent pharmaceutical components in drinking water. We explore for the first time the utilization of Cavitation Intensifying Bags (CIB) in combination with Pd/Al₂O₃ catalyst as possible advanced oxidation technology for wastewater streams, oxidizing terephthalic acid (TA) to 2-hydroxyterephthalic acid (HTA). The detailed characterization of this novel reaction system reveals that, during sonication, the presence of surface pits of the CIB improves the reproducibility and thus the control of the sonication process, when compared to oxidation in non-pitted bags. Detailed reaction kinetics shows that in the CIB reactor the reaction order to TA is zero, which is attributed to the large excess of TA in the system. The rate of HTA formation increased ten-fold from ~0.01 μM*min^-1 during sonication in the CIB, to ~0.10 μM*min^-1 for CIB in the presence of the Pd/Al₂O₃ catalyst. This enhancement was ascribed to a combination of improved mass transport, the creation of thermal gradients, and Pd/Al₂O₃ catalyst near the cavitating bubbles. Further analysis of the kinetics of HTA formation on Pd/Al₂O₃ indicated that initially the reaction underwent through an induction period of 20 min, where the HTA concentration was ~0.3 μM. After this, the reaction rate increased reaching HTA concentrations ~6 μM after 40 min. This behavior resembled that observed during oxidation of hydrocarbons on metal catalysts, where the slow rate formation of hydroperoxides on the metal surface is followed by rapid product formation upon reaching a critical concentration. Finally, a global analysis using the Intensification Factor (IF) reveals that CIB in combination with the Pd/Al₂O₃ catalyst is a desirable option for the oxidation of TA when considering increased oxidation rates and costs.

Keywords: Advanced oxidation; Bubble bag; Bubbles; Cavitation; Process intensification.